ULTRASONIC TOUCH SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The present invention relates to an ultrasonic touch system, having a

substrate and an ultrasonic transducing system on one end surface thereof, for

sensing a touch on the end surface of the substrate with a finger or other

things, the ultrasonic transducing system comprising ultrasonic input and

output devices, composed of at least one interdigital transducer, respectively.

2. Description of the Prior Art.

Conventional touch panels are classified into two types, resistance

film— type and ultrasonic type. The resistance film— type touch panel has an

electrically conductive transparent film, the magnitude of the resistance of the

transparent film changing when touching on the transparent film. The

resistance film -type touch panel operating under low power consumption has

some problems on response time, sensitivity, durability and others. The

ultrasonic type touch panel has a nonpiezoelectric plate under acoustic

vibration, which is decreased when touching on the nonpiezoelectric plate.

Conventional means for generating the acoustic vibration on a nonpiezoelectric

plate include a means for vibrating a nonpiezoelectric plate indirectly by a

wedge-shaped transducer with a bulk wave vibrator, a means for vibrating a

nonpiezoelectric plate directly by a piezoelectric thin film transducer and other

means. The wedge-shaped transducer is used for a non -destruction

evaluation by ultrasound and for others under only a comparative low frequency

operation because of the difficulty on manufacturing accuracy of the wedge

angle and so on. The piezoelectric thin film transducer, in which a

piezoelectric thin film made from ZnO and others is mounted on a

nonpiezoelectric plate with interdigital transducers generating acoustic

vibration thereon, is used as a high frequency device for the reason that the

interdigital transducer shows various transmission characteristics according to

the structure thereof. However, the piezoelectric thin film transducer has

operation frequencies limited to the UHF and VHF bands, and has some

problems on manufacturing and mass-producing. Thus, there are some

problems on response time, sensitivity, durability, manufacturing,

mass-producing and others in conventional touch panels having limited

operation frequencies.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a touch system capable

of generating an acoustic vibration on a substrate with a high efficiency.

Another object of the present invention is to provide a touch system

capable of sensing a touch on the substrate with a finger or other things with a

high sensitivity and a quick response time.

Another object of the present invention is to provide a touch system

excellent in durability, manufacturing, mass— producing and others.

A still other object of the present invention is to provide a touch

system operating under low power consumption with low voltage.

A still further object of the present invention is to provide a touch

system with a small size which is very light in weight and has a simple

structure.

According to one aspect of the present invention there is provided a

touch system comprising a substrate and at least an ultrasonic transducing

system on one end surface Zl of the substrate, the ultrasonic transducing

system comprising at least one interdigital transducer P and at least one

interdigital transducer Q corresponding to the interdigital transducer P.

According to another aspect of the present invention there is provided

a means for applying the interdigital transducer P with an electric signal having

a frequency approximately corresponding to the interdigital periodicity of the

interdigital transducer P, and then generating the acoustic wave, having a

wavelength approximately equal to the interdigital periodicity, on the end

surface Zl.

According to another aspect of the present invention there is provided

a means for delivering an electric signal, having a frequency approximately

corresponding to the wavelength of the acoustic wave on the end surface Zl,

from the interdigital transducer Q, the interdigital transducers P and Q being

arranged face to face each other to make a pair such that the transmitting

direction of the acoustic wave by the interdigital transducer P is the same as

the receiving direction of the acoustic wave by the interdigital transducer Q.

According to another aspect of the present invention there is provided

a means for sensing a touch with a finger or other things on a part of the

propagation medium of the acoustic wave on the end surface Zl by the

magnitude of the electric signal detected at the interdigital transducer Q.

According to another aspect of the present invention there is provided

a substrate made from an almost transparent piezoelectric ceramic, the

direction of the polarization axis thereof being parallel to the direction of

thickness thereof, the interdigital transducers P and Q being mounted on the

end surface Zl directly.

According to another aspect of the present invention there is provided

a substrate made from a nonpiezoelectric body, the ultrasonic transducing

system comprising an input device A, consisting of a piezoelectric thin plate TA

and the interdigital transducer P mounted thereon, and an output device B

consisting of a piezoelectric thin plate TB and the interdigital transducer Q

mounted thereon, the piezoelectric thin plates TA and TB being mounted on the

end surface Zl.

According to another aspect of the present invention there is provided

an ultrasonic transducing system comprising N interdigital transducers P i (i =

1, 2, ^{• • •} \', N) and N interdigital transducer groups Q i (i = 1, 2, ^{• • •} \', N)

consisting of at least two interdigital transducers, Q i - 1 and Q i -2.

According to another aspect of the present invention there is provided

a connection point M 1 , each output terminal of the interdigital transducers Q i -

1 being connected with each other thereat.

According to another aspect of the present invention there is provided

a connection point M2, each output terminal of the interdigital transducers Q i -

2 being connected with each other thereat, a touch with a finger or other

things on a part of the propagation medium of the acoustic wave on the end

surface Zl being detected by the magnitudes of the electric signals delivered

from the connection points M i and M2, respectively.

According to another aspect of the present invention there are

provided N switches S i (i = 1, 2, ^{• •} \', N), output terminal thereof being

connected with each input terminal of the interdigital transducers P i .

According to another aspect of the present invention there is provided

a means for controlling turn on and off of the switches S i with a fixed period in

turn.

According to another aspect of the present invention there is provided

a connection point MS, each input terminal of the switches S i being connected

with each other thereat.

According to other aspect of the present invention there is provided an

amplifier, the connection point Mi being connected with the connection point

MS through the amplifier.

According to a further aspect of the present invention there are

provided N oscillators H i (i = 1, 2, ^{■ •} , N) including N corresponding

propagation paths D i (i = 1, 2, ^• \' ^• , N) as delay elements, the propagation

paths D i comprising the substrate between the interdigital transducers P i and

the interdigital transducers Q i - 1 , the respective signal loops of the oscillators

H i comprising the interdigital transducers P i , the propagation paths D i , the

interdigital transducers Q , - 1 and the amplifier.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be clarified from

the following description with reference to the attached drawings.

FIGURE 1 shows a sectional view of the ultrasonic touch system

according to a first embodiment of the present invention.

FIGURE 2 shows the relationship between the phase velocity of the

acoustic wave of each mode in the piezoelectric thin plate 2 and the kd value or

the d/ λ value.

FIGURE 3 shows the relationship between the phase velocity of the

acoustic wave of each mode in the piezoelectric thin plate 2 and the kd value or

the d/ λ. value.

FIGURE 4 shows the relationship between the kd value or the d/ λ

value, and the electromechanical coupling constant k ² .

FIGURE 5 shows the relationship between the k ² value and the kd

value or the d/ λ value.

FIGURE 6 shows the relationship between the k ² value and the kd

value or the d/ λ value.

FIGURE 7 shows the relationship between the k ² value and the kd

value or the d/ λ value.

FIGURE 8 shows the relationship between the displacement and the

depth under the fd value of 1.0 MHz-mm, corresponding to the nearly maximum

k ² value in the first mode acoustic wave.

FIGURE 9 shows the relationship between the displacement and the

depth under the fd value of 2.0 MHz-mm, corresponding to the nearly maximum

k ² value in the second mode acoustic wave.

FIGURE 10 shows the relationship between the displacement and the

depth under the fd value of 3.0 MHz-mm, corresponding to the nearly maximum

k ² value in the third mode acoustic wave.

FIGURE 11 shows the relationship between the displacement and the

depth under the fd value of 0.7 MHz-mm in the 0— th mode acoustic wave.

FIGURE 12 shows a plan view of the ultrasonic touch system

according to a second embodiment of the present invention.

FIGURE 13 shows a perspective view of the input device DTI seen in

FIGURE 12.

FIGURE 14 shows a schematic illustration of the ultrasonic touch

system, shown in FIGURE 12, under an rf pulse operation.

FIGURE 15 shows a schematic illustration of the ultrasonic touch

system, shown in FIGURE 12, under an operation with a delay line oscillator.

FIGURE 16 shows a plan view of the ultrasonic touch system

according to a third embodiment of the present invention.

FIGURE 17 shows a plan view of the input device DTX and the output

device DRX in the ultrasonic touch system shown in FIGURE 16.

FIGURE 18 (a) shows a plan view of an interdigital transducer taking

the place of that seen in FIGURE 16.

FIGURE 18 (b) shows a plan view of an interdigital transducer taking

the place of that seen in FIGURE 16.

FIGURE 19 shows a schematic illustration of the ultrasonic touch

system, shown in FIGURE 16, under an rf pulse operation.

FIGURE 20 shows the waveforms corresponding to the respective

parts, ®~(D, seen in FIGURE 19.

FIGURE 21 shows a schematic illustration of the ultrasonic touch

system, shown in FIGURE 16, under an operation with a delay line oscillator.

FIGURE 22 shows the frequency dependence of the insertion loss

between the interdigital transducers Tl and Rl l in case of untouching on the

substrate 5.

FIGURE 23 shows the frequency dependence of the insertion loss

between the interdigital transducers Tl and Rl l in case of touching on the

substrate 5.

FIGURE 24 shows the response between the interdigital transducers

Tl and Rl l under operation with 3.96 MHz rf pulse in case of untouching on

the substrate 5.

FIGURE 25 shows the response between the interdigital transducers

Tl and Rl l under operation with 3.96 MHz rf pulse in case of touching on the

substrate 5.

FIGURE 26 shows the relationship between the relative amplitude and

the frequency in the delay line oscillator shown in FIGURE 21.

FIGURE 27 shows a plan view of the ultrasonic touch system

according to a fourth embodiment of the present invention.

FIGURE 28 shows a plan view of the interdigital transducers Tl, T2,

Rl l, R12, R13, R14, R21, R22, R23 and R24 in the ultrasonic touch system

shown in FIGURE 27.

FIGURE 29 shows a circuit diagram of the amplifier A or B under

operation with the delay line oscillator in FIGURE 27.

FIGURE 30 shows the frequency dependencies of the insertion loss

and the phase of the delay line oscillator employed in the ultrasonic touch

system shown in FIGURE 27.

FIGURE 31 shows the relationship between the relative amplitude and

the frequency in the delay line oscillator employed in the ultrasonic touch

system shown in FIGURE 27.

DETAILED DESCRIPTION OF THE PRESENTLY

PREFERRED EXEMPLARY EMBODIMENTS

FIGURE 1 shows a sectional view of an ultrasonic touch system

according to a first embodiment of the present invention. The ultrasonic touch

system comprises an input device DT, an output device DR and a substrate 1

made from a borosilicate glass with a dimension of 1.9 mm in thickness. The

input device DT has a piezoelectric thin plate 2, of which material is TDK-91A

(Brand name), having a dimension of 220 m in thickness, and an interdigital

transducer T made from aluminium thin film. The output device DR has a

piezoelectric thin plate 2 and an interdigital transducer R having the same

material and dimensions of the interdigital transducer T. The interdigital

transducers T and R, whose types are normal, are mounted on each

piezoelectric thin plate 2 which is cemented on the substrate 1 through an

epoxy resin with thickness of about 20 m. Both the interdigital transducers

T and R, consisting of ten finger pairs, respectively, have an interdigital

periodicity of 640 βm and a center frequency of 5.1 MHz. If an electric signal

with a frequency approximately equal to the center frequency of the interdigital

transducer T is applied to the input device DT through the interdigital

transducer T, the electric signal is converted to the acoustic wave, which is

transmitted to the piezoelectric thin plate 2 on the substrate 1. At this time, it

is possible to generate the acoustic wave of the first mode or the higher modes

on the substrate 1 effectively under low power consumption with low voltage.

Furthermore, the phase velocity of the acoustic wave in the piezoelectric thin

plate 2 is approximately equal to the propagation velocity of the surface

acoustic wave on the substrate 1 in case which exists as a mono— layer

medium. Therefore, it is possible not only to increase the transducer efficiency

from the input electric signal to the acoustic wave, but also to remove the

reflection and others generated by the miss -matching and others on the

acoustic impedance at the boundary surface between the piezoelectric thin

plate 2 and the substrate 1. The acoustic wave, having a frequency

approximately equal to the center frequency of the interdigital transducer R is

converted to an electric signal, which is detected at the interdigital transducer

R. Thus, the input device DT and the output device DR make an ultrasonic

transducing system with a simple structure, where the interdigital transducers

T and R are arranged face to face each other to make a pair such that the

transmitting direction of the acoustic wave from the interdigital transducer T is

the same as the receiving direction thereof by the interdigital transducer R.

When operating the ultrasonic touch system shown in FIGURE 1, the acoustic

wave generated on the substrate 1 between the interdigital transducer T and

the interdigital transducer R is decreased in response to a touch with a finger

or other things on the substrate 1 between the interdigital transducer T and the

interdigital transducer R. Thereby, the electric signal detected at the

interdigital transducer R is decreased. Accordingly, it is possible to sensing a

touch with a finger or other things on the substrate 1 with a high sensitivity

and a quick response time.

FIGURE 2 shows the relationship between the phase velocity of the

acoustic wave of each mode in the piezoelectric thin plate 2 and the kd value or

the d/ λ value, the kd value being the product of the wave number k of the

acoustic wave in the piezoelectric thin plate 2 and the thickness d of the

piezoelectric thin plate 2, the d/ λ value being the thickness d per the

wavelength λ of the acoustic wave in the piezoelectric thin plate 2. The

numbers in FIGURE 2 correspond to the mode order, and the mark O shows

the observed value. There are two types of the piezoelectric thin plate 2. One

type of the piezoelectric thin plate 2 has one surface, being in contact with the

substrate 1 and under an electrically opened condition, and the other surface

coated with a metal thin layer, coating with a metal thin layer making an

electrically shorted condition. The other type of the piezoelectric thin plate 2

has both surfaces coated with metal thin layers, respectively, causing the both

surfaces electrically shorted conditions. The acoustic wave in the piezoelectric

thin plate 2 in the ultrasonic touch system shown in FIGURE 1 has various

modes. When the kd value is zero, the velocity of the 0— th mode acoustic

wave in the piezoelectric thin plate 2 is coincident with the velocity of the

acoustic wave on the substrate 1 in case which exists as a mono— layer

medium. As the kd value becomes larger, the velocity of the 0-th mode

acoustic wave in the piezoelectric thin plate 2 comes near the velocity of the

acoustic wave in the piezoelectric thin plate 2 in case which exists as a

mono-layer medium. There are the cut-off frequencies in the modes higher

than the 0-th mode. Thus, when the kd value is lowest, the velocity of the

acoustic wave of the higher mode in the piezoelectric thin plate 2 comes near

the velocity of the side wave on the substrate 1 in case which exists as a

mono— layer medium.

FIGURE 3 shows the relationship between the phase velocity of the

acoustic wave of each mode in the piezoelectric thin plate 2 and the kd value or

the d/ λ value. The numbers in FIGURE 3 correspond to the mode order, and

the mark O shows the observed value. There are two types of the

piezoelectric thin plate 2. One type of the piezoelectric thin plate 2 has each

surface under an electrically opened condition. The other type of the

piezoelectric thin plate 2 has one surface, being in contact with the substrate 2

and under an electrically shorted condition, and the other surface, exposed to

the air and under an electrically opened condition. When the kd value is zero,

the velocity of the 0— th mode acoustic wave in the piezoelectric thin plate 2 is

coincident with the velocity of the acoustic wave on the substrate 1 in case

which exists as a mono-layer medium. As the kd value becomes larger, the

velocity of the 0— th mode acoustic wave in the piezoelectric thin plate 2 comes

near the velocity of the acoustic wave in the piezoelectric thin plate 2 in case

which exists as a mono— layer medium. There are the cut— off frequencies in

the modes higher than the 0— th mode. Thus, when the kd value is lowest, the

velocity of the acoustic wave of the higher mode in the piezoelectric thin plate

2 comes near the velocity of the shear wave on the substrate 1 in case which

exists as a mono— layer medium.

FIGURE 4 shows the relationship between the kd value or the d/ λ

value, and the electromechanical coupling constant k ² calculated from the

difference between the phase velocities for electrically opened and shorted

conditions, respectively. The numbers in FIGURE 4 correspond to the mode

order. The piezoelectric thin plate 2 has one surface, being in contact with the

substrate 1 and having the interdigital transducer (IDT) T, and the other

surface under an electrically shorted condition. The k ² value of the higher

mode acoustic wave is larger than that of the 0-th mode acoustic wave.

Particularly, when the kd value of the first mode acoustic wave is 1.8, the k ²

value is 17.7 %, showing the maximum value.

FIGURE 5 shows the relationship between the k ² value and the kd

value or the d/ λ value. The numbers in FIGURE 5 correspond to the mode

order. The piezoelectric thin plate 2 has one surface, being in contact with the

substrate 1 and having the interdigital transducer T, and the other surface,

exposed to the air and under electrically opened condition. The k ² value of the

higher mode acoustic wave is larger than that of the 0— th mode acoustic wave.

FIGURE 6 shows the relationship between the k ² value and the kd

value or the d/ λ value. The numbers in FIGURE 6 correspond to the mode

order. The piezoelectric thin plate 2 has one surface, being in contact with the

substrate 1 and under an electrically shorted condition, and the other surface

having the interdigital transducer T.

FIGURE 7 shows the relationship between the k ² value and the kd

value or the d/ λ value. The numbers in FIGURE 7 correspond to the mode

order. The piezoelectric thin plate 2 has one surface, being in contact with the

substrate 1 and under an electrically opened condition, and the other surface

having the interdigital transducer T.

It is clear from FIGURE 2 to FIGURE 7 that the k ² value is maximum

when the phase velocity of the acoustic wave of the first mode or the higher

modes in the piezoelectric thin plate 2 is coincident with the velocity of the

acoustic wave on the substrate 1 in case which exists as a mono -layer

medium.

It is also clear from FIGURE 4 to FIGURE 7 that the transducer

efficiency of the electric energy, applied to the interdigital transducer T, to the

acoustic wave is increased, when the piezoelectric thin plate 2 has one surface,

being in contact with the substrate 1 and having the interdigital transducer T,

and the other surface under an electrically shorted condition.

When generating the acoustic wave on the substrate 1 in the

ultrasonic touch system shown in FIGURE 1, it is necessary to consider the

reflection and others generated by the miss— matching and others on the

acoustic impedance at the boundary surface between the piezoelectric thin

plate 2 and the substrate 1. In order to make the reflection coefficient

minimum, it is necessary to design the ultrasonic touch system such that the

phase velocity of the acoustic wave in the piezoelectric thin plate 2 is

coincident with the velocity of the surface acoustic wave on the substrate 1 in

case which exists as a mono -layer medium, or such that the d/ value

becomes small, and so forth. If the d value is constant, the acoustic wave of

the first mode is available in comparison with the second mode, the second

mode being available in comparison with the third mode. After all, when the d

value is less than the interdigital periodicity of the interdigital transducer and

the interdigital periodicity is approximately equal to the wavelength of the

acoustic wave of the first mode or the higher modes, it is possible not only to

increase the transducer efficiency of the electric energy, applied to the

interdigital transducer T, to the acoustic wave, but also to remove the reflection

and others generated by the miss— matching and others on the acoustic

impedance at the boundary surface between the piezoelectric thin plate 2 and

the substrate 1.

When the piezoelectric thin plate 2 comprises a piezoelectric ceramic,

where the directions of the polarization axis and the thickness run parallel with

each other, the acoustic wave of the first mode or the higher modes can be

generated on the substrate 1 effectively.

When the piezoelectric thin plate 2 comprises a piezoelectric thin film

made from highly polymerized compound such as PVDF and so on, the acoustic

wave of the first mode or the higher modes can be generated on the substrate 1

effectively.

When the substrate 1 comprises an acrylate plate or other highly

polymerized compound having transparency, the acoustic wave can be

generated on the substrate 1 effectively. When the piezoelectric thin plate 2

comprises a single crystal, such as LiNbOβ or LiTaOβ, the acoustic wave can

be generated on the substrate 1 effectively.

FIGURE 8 shows the relationship between the displacement and the

depth under the fd value of 1.0 MHz-mm, corresponding to the nearly maximum

k ² value in the first mode acoustic wave. The fd value is the product of the

frequency of the acoustic wave in the piezoelectric thin plate 2 and the d value.

The piezoelectric thin plate 2 has both .solaces under electrically opened

conditions. U i and Uβ in FIGURE 8 show a parallel component and a

perpendicular component of the displacement, respectively. The displacement

is normalized by the maximum value. The depth of zero shows the boundary

face between the piezoelectric thin plate 2 and the substrate 1. Both the

displacement U i and J~ are normalized by the maximum value, (U i ² +U3 ² ) ^L

² . The ratio of the displacement component of the first mode acoustic wave on

the substrate 1 is 58 %.

FIGURE 9 shows the relationship between the displacement and the

depth under the fd value of 2.0 MHz-mm, corresponding to the nearly maximum

k ² value in the second mode acoustic wave. The piezoelectric thin plate 2 has

both surfaces under electrically opened conditions. The ratio of the

displacement component of the second mode acoustic wave on the substrate 1

is 52 %.

FIGURE 10 shows the relationship between the displacement and the

depth under the fd value of 3.0 MHz-mm, corresponding to the nearly maximum

k ² value in the third mode acoustic wave. The piezoelectric thin plate 2 has

both surfaces under electrically opened conditions. The ratio of the

displacement component of the third mode acoustic wave on the substrate 1 is

47 %.

FIGURE 11 shows the relationship between the displacement and the

depth under the fd value of 0.7 MHz-mm in the 0-th mode acoustic wave. The

piezoelectric thin plate 2 has one surface, being in contact with the substrate 1

and under an electrically opened condition, and the other surface, having the

interdigital transducer and under an electrically shorted condition. The 0-th

mode acoustic wave, concentrated near the surface of the piezoelectric thin

plate 2, comes near the acoustic wave in the piezoelectric thin plate 2 in case

which exists as a mono -layer medium.

It is clear from FIGURE 8 to FIGURE 11 that the acoustic wave of the

first mode or the higher modes is available in order to generate the acoustic

wave on the substrate 1, because the acoustic wave of the mode, where the

ratio of the displacement component of the acoustic wave on the substrate 1 is

large, is available

FIGURE 12 shows a plan view of an ultrasonic touch system according

to a second embodiment of the present invention. The ultrasonic touch system

comprises seven input devices, DTI, DT2, DT3, DT4, DT5, DT6 and DT7, seven

output devices DRl, DR2, DR3, DR4, DR5, DR6 and DR7, and a substrate 3

made from a pyrex glass with dimensions of 70 mm in length, 55 mm in width

and 1.9 mm in thickness. Both the seven input devices and the seven output

devices are made from the same piezoelectric materials, and have the same

functions as well as the same construction. If an electric signal is applied to

each input device, the electric signal is converted to the acoustic wave, which is

transmitted to the substrate 3. The acoustic wave on the substrate 3 is

converted to an electric signal again, the electric signal being detected at each

output device corresponding to each input device. For example, an electric

signal applied to the input device DTI is converted to the acoustic wave, which

is detected at the output device DRl as an electric signal. Thus the seven

input devices and the seven output devices make seven ultrasonic transducing

systems classified into two groups, one group including the input devices, DTI,

DT2 and DT3, and the output devices, DRl, DR2 and DR3, the other group

including the input devices, DT4, DT5, DT6 and DT7, and the output devices,

DR4, DR5, DR6 and DR7. Moreover, the propagation direction of the acoustic

wave on the substrate 3 in the one group is perpendicular to that in the other

group.

FIGURE 13 shows a perspective view of the input device DTI seen in

FIGURE 12. The input device DTI has a piezoelectric thin plate 4, of which

material is TDK— 91A (Brand name), having dimensions of 10 mm in length, 10

mm in width and 220 /tcm in thickness, and an interdigital transducer T made

from aluminium thin film. The interdigital transducer T, whose type is normal,

is mounted on the piezoelectric thin plate 4 which is cemented on the substrate

3 through an epoxy resin with thickness of about 20 βm. The interdigital

transducer T consisting of ten finger pairs has an interdigital periodicity of 640

βm and an overlap length of 5 mm. Another input devices and the output

devices have the same constructions as the input device DTI.

If an electric signal with a frequency approximately equal to the

center frequency of each input interdigital transducer in the ultrasonic touch

system shown in FIGURE 12 is applied to each input device through each input

interdigital transducer, the electric signal is converted to the acoustic wave,

which is transmitted to the piezoelectric thin plate 4 on the substrate 3. The

acoustic wave, having a frequency approximately equal to the center frequency

of each output interdigital transducer is converted to an electric signal, which is

detected at the output interdigital transducer. When the thickness of the

piezoelectric thin plate 4 is less than the interdigital periodicity of each

interdigital transducer, and the interdigital periodicity of each interdigital

transducer is approximately equal to the wavelength of the acoustic wave of the

first mode or the higher modes, the acoustic wave of the first mode or the

higher modes is generated on the substrate 3. At this time, if the phase

velocity of the acoustic wave in the piezoelectric thin plate 4 is approximately

equal to the propagation velocity of the surface acoustic wave on the substrate

3 in case which exists as a mono— layer medium, it is possible not only to

increase the transducer efficiency of the electric energy, applied to the input

interdigital transducers, to the acoustic wave, but also to remove the reflection

and others generated by the miss -matching and others on the acoustic

impedance at the boundary surface between the piezoelectric thin plate 4 and

the substrate 3. Thus, it is possible to generate the acoustic wave on the

substrate 3 effectively under low power consumption with low voltage.

When the piezoelectric thin plate 4 comprises a piezoelectric ceramic,

where the directions of the polarization axis and the thickness run parallel with

each other, the acoustic wave of the first mode or the higher modes can be

generated on the substrate 3 effectively.

When the piezoelectric thin plate 4 comprises a piezoelectric thin film

made from highly polymerized compound such as PVDF and so on, the acoustic

wave of the first mode or the higher modes can be generated on the substrate 3

effectively.

When the substrate 3 comprises an acrylate plate or other highly

polymerized compound having transparency, the acoustic wave can be

generated on the substrate 3 effectively. When the piezoelectric thin plate 4

comprises a single crystal, such as LiNbOβ or LiTaOβ, the acoustic wave can

be generated on the substrate 3 effectively.

When operating the ultrasonic touch system shown in FIGURE 12, the

acoustic wave propagating the substrate 3 is decreased in response to a touch

with a finger or other things thereon. The acoustic wave on the junction of two

propagation directions, of which, for example, one is the area between the input

device DTI and the output device DRl and the other is the area between the

input device DT4 and the output device DR4, is decreased in response to a

touch with a finger or other things thereon. Therefore, the electric signals

detected at the corresponding output interdigital transducers are also

decreased. Accordingly, it is possible to sense a touch with a finger or other

things on the substrate 3 with a high sensitivity and a quick response time. In

addition, the touched position can be specified from the output interdigital

transducers, where the electric signal is decreased. At this time, if there are

more ultrasonic transducing systems, of which each comprises a pair of input

and output devices such as the input device DTI and the output device DRl,

the touched position can be sp cified more clearly.

FIGURE 14 shows a schemati illustration of the ultrasonic touch

system, shown in FIGURE 12, under an rf pulse operation. If an rf pulse (D is

applied to the input device through the interdigital transducer, an electric

signal is detected at the output interdigital transducer, and the electric

signal (2) is amplified via an amplifier. An electric signal (1) detected at the

amplifier is converted to a direct current voltage © via a voltage doubling

rectifier. At this time, the direct current voltage © in case of touching on the

substrate 3 is different from that in case of untouching thereon. In short, there

are two kinds of the direct current voltages @. By means of setting the

threshold voltage at a proper level, it is possible to set the two direct current

voltages © at the two fixed values © in a comparator, respectively. Thus, the

voltage (5) in case of touching on the substrate 3 is 0 V, and the voltage © in

case of untouching thereon is 5 V.

FIGURE 15 shows a schematic illustration of the ultrasonic touch

system, shown in FIGURE 12, under an operation with a delay line oscillator. If

an electric signal is applied to the input device through the interdigital

transducer, an electric signal is detected at the output interdigital transducer

and is amplified via an amplifier. An electric signal CD detected at the

amplifier is converted to a direct current voltage φ via a voltage doubling

rectifier. At this time, the direct current voltage φ in case of touching on the

substrate 3 is different from that in case of untouching thereon. In short, there

are two kinds of the direct current voltages φ. By means of setting the

threshold voltage at a proper level, it is possible to set the two kinds of the

direct current voltages Φ at the fixed values, respectively. The operation with

the delay line oscillator does not require pulse generator. Therefore, it is

possible to provide the ultrasonic touch system with a smaller size which is

very light in weight and has a simple structure.

FIGURE 16 shows a plan view of an ultrasonic touch system according

to a third embodiment of the present invention. The ultrasonic touch system

comprises two input devices DTX and DTY, two output devices DRX and DRY,

a substrate 5 made from a pyrex glass with dimensions of 70 mm in length, 55

mm in width and 1.9 mm in thickness, and a display face 6 included in a display

device, the display face 6 being not drawn in FIGURE 16. The input device

DTX has a piezoelectric thin plate 7, of which material is TDK- 101A (Brand

name), having a dimension of 230 βm in thickness, and two interdigital

transducers Tl and T2 made from aluminium thin film, respectively. The input

device DTY has a piezoelectric thin plate 7 and two interdigital transducers T3

and T4 made from aluminium thin film, respectively. The output device DRX

has a piezoelectric thin plate and eight ink igital transducers, Rll, R12,

R13, R14, R21, R22, R23 and R24, made from aluminium thin film, respectively.

The output device DRY has a piezoelectric thin plate 7 and eight interdigital

transducers, R31, R32, R33, R34, R41, R42, R43 and R44, made from aluminium

thin film, respectively. Each interdigital transducer, whose type is normal, is

mounted on each piezoelectric thin plate 7 which is cemented on one surface of

the substrate 5 through a. ^poxy resin with thickness of ut 20 βm. The

display face 6 is mounted on the other surface, without the input and output

devices, of the substrate 5. Each inte-digital tr . iducer consisting of 7.5 finger

pairs has an interdigital periodicity of 640 βm.

FIGURE 17 shows a plan view of the input device DTX and the output

device DRX in the ultrasonic touch stem shown in FIGURE 16. The input

device DTX and the output device DRX are placed at the opposite ends. In the

same way, the input device DTY and the output device DRY are placed at the

opposite ends. The interdigital transducers, Tl, T2, T3 and T4, have an overlap

length of 18 mm, respectively. The interdigital transducers, Rl l, R12, R13,

R14, R21, R22, R23, R24, R31, R32, R33, R34, R41, R42, R43 and R44, have an

overlap length of 2.7 mm, respectively. The interdigital transducers, Rl l, R12,

R13 and R14, are corresponding to the interdigital transducer Tl. The

interdigital transducers, R21, R22, R23 and R24, are corresponding to the

interdigital transducer T2. The interdigital transducers, R31, R32, R33 and

R34, are corresponding to the interdigital transducer T3. The interdigital

transducers, R41, R42, R43 and R44, are corresponding to the interdigital

transducer T4.

If an electric signal is applied to the input devices DTX and DTY of the

ultrasonic touch system shown in FIGURE 16, the acoustic wave is generated

on the substrate 5. The acoustic wave is converted to an electric signal which

is detected at the output devices DRX and DRY. Thus, the two input devices

and the two output devices make sixteen ultrasonic transducing systems

classified into two groups, one group including the input device DTX and the

output device DRX, the other group including the input device DTY and the

output device DRY. Moreover, the propagation direction of the acoustic wave

on the substrate 5 in the one group is perpendicular to that in the other group.

When the thickness of the piezoelectric thin plate 7 seen in FIGURE

16 is less than the interdigital periodicity of each interdigital transducer, and

the interdigital periodicity of each interdigital transducer is approximately equal

to the wavelength of the acoustic wave of the first mode or the higher modes,

the acoustic wave of the first mode or the higher modes is generated on the

substrate 5. At this time, if the phase velocity of the acoustic wave in the

piezoelectric thin plate 7 is approximately equal to the propagation velocity of

the surface acoustic wave on the substrate 5 in case which exists as a

mono— layer medium, it is possible not only to increase the transducer

efficiency of the electric energy, applied to the input interdigital transducers, to

the acoustic wave, but also to remove the reflection and others generated by

the miss— matching and others on the acoustic impedance at the boundary

surface between the piezoelectric thin plate 7 and the substrate 5. Thus, it is

possible to generate the acoustic wave on the substrate 5 effectively under low

power consumption and low voltage.

When the piezoelectric thin plate 7 comprises a piezoelectric ceramic,

where the directions of the polarization axis and the thickness run parallel with

each other, the acoustic wave of the first mode or the higher modes can be

generated on the substrate 5 effectively.

When the piezoelectric thin plate 7 comprises a piezoelectric thin film

made from highly polymerized compound such as PVDF and so on, the acoustic

wave of the first mode or the higher modes can be generated on the substrate 5

effectively.

When the substrate 5 comprises an acrylate plate or other highly

polymerized compound having transparency, the acoustic wave can be

generated on the substrate 5 effectively. When the piezoelectric thin plate 7

comprises a single crystal, such as LiNbOβ or LiTaOβ, the acoustic wave can

be generated on the substrate 5 effectively.

When inserting the ultrasonic touch system according to the present

invention into a display in a computer and so on, the substrate of the ultrasonic

touch system is set up such that the surface having the input and output

devices is faced outside, moreover such that only the area surrounded with the

input and output devices on the surface is exposed to outside.

FIGURE 18 (a) shows a plan view of an interdigital transducer taking

the place of that seen in FIGURE 16. There are two interdigital periodicities

shown in FIGURE 18 (a), the overlap length of the first being different from

that of the second. One consists of five finger pairs with an interdigital

periodicity of 620 βm, the other consists of five finger pairs with an interdigital

periodicity of 295 βm. When the interdigital transducers are employed, they

are placed such that the part consisting of five finger pairs with the interdigital

periodicity of 295 βm is opposed inside to each other, because the acoustic

wave with a higher frequency generated on the substrate 5 in case of the

interdigital periodicity smaller is highly decreased on the substrate 5. Thus,

the interdigital transducers are placed such that the part with a smaller

interdigital periodicity has a smaller propagation distance of the acoustic wave.

The arrangement such that the finger pairs with a smaller interdigital

periodicity is placed inside to each other restrains the decrease of the acoustic

wave on the substrate 5.

FIGURE 18 (b) shows a plan view of an interdigital transducer taking

the place of that seen in FIGURE 16. The interdigital transducer has

interdigital periodicities with hyperbolical variation along the direction of the

electrode finger located at the central part of the interdigital transducer. The

interdigital transducer consists of 26.5 finger pairs with interdigital periodicities

of 260 βm ~ 390 βm, the overlap length being 23.4 mm. When the

interdigital transducers are employed, they take the symmetrical positions each

other against the center line between the two interdigital transducers. In the

above device configuration, the operation frequency is in the range from 5.4

MHz to 8.2 MHz.

FIGURE 19 shows a schematic illustration of the ultrasonic touch

system, shown in FIGURE 16, under an rf pulse operation. FIGURE 20 shows

the waveforms corresponding to the respective parts, φ~®, seen in FIGURE

19. When operating the ultrasonic touch system shown in FIGURE 16, a

continuous wave CD generated by a function generator is modulated to rf pulses

φ- 1 and φ- 2 in the corresponding double balanced mixers (DBMs) 1 and 2 by

the corresponding clock pulses φ- l and φ-2 from a computer. The DBM 1

and the DBM 2 play a role of switching to apply with an rf pulse to the

interdigital transducers Tl and T3 (Tl group of IDTs) or the interdigital

transducers T2 and T4 (T2 group of IDTs). If an rf pulse is applied to each of

the Tl group of IDTs, the rf pulse with a frequency approximately

corresponding to the interdigital periodicity of the Tl group of IDTs is

converted to the acoustic wave which is transmitted to the respective

piezoelectric thin plate 7 in the input devices DTX and DTY and then

transmitted to the substrate 5. The acoustic wave having a wavelength

approximately corresponding to each interdigital periodicity of the interdigital

transducers, Rl l, R12, R13, R14, R31, R32, R33 and R34 (Rl group of IDTs), is

converted to a delay electric signal, which is detected at the Rl group of IDTs.

If an rf pulse is applied to each of the T2 group of IDTs, the rf pulse with a

frequency approximately corresponding to the interdigital periodicity of the T2

group of IDTs is converted to the acoustic wave which is transmitted to the

respective piezoelectric thin plate 7 in the input devices DTX and DTY and

then transmitted to the substrate 5. The acoustic wave having a wavelength

approximately corresponding to each interdigital periodicity of the interdigital

transducers, R21, R22, R23, R24, R41, R42, R43 and R44 (R2 group of IDTs), is

converted to a delayed electric signal, which is detected at the R2 group of

IDTs. If an rf pulse is applied to the Tl and T2 groups of IDTs alternately, a

delayed electric signal is detected at the Rl and R2 groups of IDTs alternately.

The connections between the interdigital transducers Rl l and R21, R12 and

R22, R13 and R23, R14 and R24, R31 and R41, R32 and R42, R33 and R43, and

R34 and R44, make the circuit construction simple. In addition, the delayed

electric signal CD detected at each pair of the interdigital transducers, for

example the pair of the interdigital transducers Rl l and R21, is received so

that they overlap each other. Therefore, when touching with a material, softer

than the substrate 5 and easy to absorb the acoustic wave, on the propagation

way, made from the Tl and Rl groups of IDTs, of the acoustic wave on the

substrate 5, the acous - wave on the touched position is decreased © only in

case that an electric signal is applied to each of the Tl group of IDTs. In the

same way, touching with the material on the propagation way, made from the

T2 and R2 groups of IDTs, of the acoustic wave on the substrate 5, the acoustic

wave on the touched position is decreased © only in case that an electric

signal is applied to each of the T2 group of IDTs. Such the delayed electric

signals ©, © and © are amplified via an amplifier and rectified via a voltage

doubling rectifier, and then become a direct current signals φ, © and ©,

respectively. By means of setting the threshold voltage at the proper value

between the direct current signals φ and ©, or φ and ©, the digital signals

corresponding to the direct current signals φ, © and ©, respectively, are

obtained in a comparator. The digital signals are taken in the computer as the

parallel signals with a proper timing by the computer. Thus, the ultrasonic

touch system shown in FIGURE 16 has a short response time, and therefore

has a high sensitivity. Accordingly, the touched position on the substrate 5 can

be appointed clearly and quickly. If there are more ultrasonic transducing

systems consisting of an input interdigital transducer and an output interdigital

transducer, respectively, the touched position on the substrate 5 can be more

strictly appointed.

FIGURE 21 shows a schematic illustration of the ultrasonic touch

system, shown in FIGURE 16, under an operation with a delay line oscillator.

The waveforms corresponding to the respective parts, ®~©, seen in FIGURE

21 are the same as the FIGURE 20. The delay line oscillator has an 8-shaped

signal loop which makes the area between the interdigital transducers Tl and

Rl l, or T2 and R21 on the substrate 5 a first delay element, and the area

between the interdigital transducers T3 and R31, or T4 and R41 thereon a

second delay element. When operating the ultrasonic touch system shown in

FIGURE 21, switches, SI, S2, S3 and S4, are opened and closed by order of a

computer. While the switches SI and S3 ( SI group of switches) are closed,

the switches S2 and S4 ( S2 group of switches) are opened. Thus, an electric

signal is applied to the Tl and T2 groups of IDTs, alternately, by opening and

closing of the SI and S2 groups of switches alternately. An electric signal ©

applied to the Tl or T2 groups of IDTs is modulated to rf pulses ©- 1 or ®-2,

respectively, by the corresponding clock pulses ©- 1 or φ—2 from a computer.

If the rf pulse ©— 1 is applied to the Tl group of IDTs, then when the SI

group of switches are closed, the rf pulse ©— 1 with a frequency approximately

corresponding to the interdigital periodicity of the Tl group of IDTs is

converted to the acoustic wave which is transmitted to the respective

piezoelectric thin plate 7 in the input devices DTX and DTY and then

transmitted to the substrate 5. The acoustic wave having a wavelength

approximately corresponding to each interdigital periodicity of the interdigital

transducers, Rl l, R12, R13, R14, R31, R32, R33 and R34 (Rl group of IDTs), is

converted to a delayed electric signal, which is detected at the Rl group of

IDTs. If the rf pulse ©-2 is applied to the T2 group of IDTs, then when the

S2 group of switches are closed, the rf pulse ©-2 with a frequency

approximately corresponding to the interdigital periodicity of the T2 group of

IDTs is converted to the acoustic wave which is transmitted to the respective

piezoelectric thin plate 7 in the input devices DTX and DTY and then

transmitted to the substrate 5. The acoustic wave having a wavelength

approximately corresponding to each interdigital periodicity of the interdigital

transducers, R21, R22, R23, R24, R41, R42, R43 and R44 (R2 group of IDTs), is

converted to a delayed electric signal, which is detected at the R2 group of

IDTs. Thus, if an electric signal is applied to the Tl and T2 groups of IDTs

alternately, a delayed electric signal is detected at the Rl and R2 groups of

IDTs alternately. The connections between the interdigital transducers Rl l

and R21, R12 and R22, R13 and R23, R14 and R24, R31 and R41, R32 and R42,

R33 and R43, and R34 and R44, make the circuit construction simple. In

addition, the delayed electric signal © detected at each pair of the interdigital

transducers, for example the pair of the interdigital transducers Rl l and R21, is

received so that they overlap each other. A part of the delayed electric signal

© detected at the pair of the interdigital transducers Rl l and R21 and a part

of the delayed electric signal © detected at the pair of the interdigital

transducers R31 and R41 are amplified via the amplifiers A and B, respectively,

and each phase thereof is shifted to the fixed value via each phase shifter, the

two electric signals with each shifted phase are applied to the Tl and T2 groups

of IDTs again, respectively, through the S i and S2 groups of switches. In

short, the electric signals applied to the interdigital transducers Tl and T2

through the switches SI and S2 are applied to the interdigital transducers T3

and T4 through the switches S3 and S4, and the electric signals applied to the

interdigital transducers T3 and T4 through the switches S3 and S4 are applied

to the interdigital transducers Tl and T2 through the switches Si and S2.

Thus, the delay line oscillator having the 8 -shaped signal loop is constructed.

The delayed electric signal © detected at each pair of the interdigital

transducers is decreased (© or ©) in response to a touch on the substrate 5.

When touching with a material, softer than the substrate 5 and easy to absorb

the acoustic wave, on the propagation way, made from the Tl and Rl groups of

IDTs, of the acoustic wave on the substrate 5, the acoustic wave on the touched

position is decreased © only in case that an electric signal is applied to each of

the Tl group of IDTs. In the same way, touching with the material on the

propagation way, made from the T2 and R2 groups of IDTs, of the acoustic

wave on the substrate 5, the acoustic wave on the touched position is decreased

© only in case that an electric signal is applied to each of the T2 group of

IDTs. Such the delayed electric signals ©, © and © are amplified via an

amplifier and rectified via a voltage doubling rectifier, and then become a direct

current signals φ, © and ©, respectively. By means of setting the threshold

voltage at the proper value between the direct current signals φ and ®, or φ

and ©, the digital signals corresponding to the direct current signals φ, © and

©, respectively, are obtained via a comparator. The digital signals are taken

into the computer in the form of the parallel signals with a proper timing by the

computer. The operation with the delay line oscillator has no need for a

function generator. Therefore, it is possible to provide the ultrasonic touch

system, with a smaller size which is very light in weight and has a simple

structure, capable of an operation under low power consumption with low

voltage as compared with the case of the rf pulse operation shown in FIGURE

19.

When operating the ultrasonic touch system shown in FIGURE 16, an

information given in a color is appeared on the display face 6 in response to the

touched position by order of the computer. At this time, the frequency of the

electric signal applied to the Tl or T2 group of IDTs is corresponding to the

color. It is possible to look the information on the display face 6 through the

substrate 5. When touching on the propagation medium of the acoustic wave

on the substrate 5, the acoustic wave decreases and the information given in

the color corresponding to the touched position is appeared on the display face

6. It is possible by means of changing the frequency of the input electric signal

to indicate each information given in the color corresponding to the frequency

of the input electric signal on the identical position of the display face 6.

Therefore, when using two kinds of frequencies of the input electric signals,

two kinds of the information given in each color on the identical position of the

display face 6 are obtained. In addition, the information can be indicated for a

fixed period. Thus, when writing, for example, a character with a material,

softer than the substrate 5 and easy to absorb the acoustic wave, on the

substrate 5, the character is appeared on the display face 6. If the ultrasonic

touch system shown in FIGURE 16 has the interdigital transducers as shown in

FIGURE 18 (a), two kinds of input electric signals having the respective

frequencies, which are corresponding to the respective interdigital periodicities

and different from each other, can be applied to the interdigital transducer.

Moreover, it is possible to more increase the number of the input electric

signal, because there are many kinds of the frequencies approximately

corresponding to each interdigital periodicity. As a result, many kinds of

information given in each color can be appeared on the display face 6 by

changing the frequency of the input electric signal.

FIGURE 22 shows the frequency dependence of the insertion loss

between the interdigital transducers Tl and Rll in case of untouching on the

substrate 5. FIGURE 23 shows the frequency dependence of the insertion loss

between the interdigital transducers Tl and Rl l in case of touching on the

substrate 5. The peak around 3.96 MHz corresponds to the first mode acoustic

wave. The difference between the insertion loss in case of untouching on the

substrate 5 and that in case of touching on the substrate 5 is about 10 dB with

regard to the first mode acoustic wave. The difference on the insertion loss is

enough to treat the electric signals in the ultrasonic touch system shown in

FIGURE 16.

FIGURE 24 shows the response between the interdigital transducers

Tl and Rl l under operation with 3.96 MHz rf pulse in case of untouching on

the substrate 5. FIGURE 25 shows the response between the interdigital

transducers Tl and Rl l under operation with 3.96 MHz rf pulse in case of

touching on the substrate 5. Since there is the substrate 5 between the

interdigital transducers Tl and Rl l, the waveforms without spurious signals

are observed with a good response to touch on the substrate 5. Therefore, it is

easy to treat the electric signals in the ultrasonic touch system shown in

FIGURE 16.

FIGURE 26 shows the relationship between the relative amplitude and

the frequency in the delay line oscillator shown in FIGURE 21. Fo in FIGURE

26 corresponds to the fundamental mode wave with the frequency of 3.951

MHz. Because the ultrasonic touch system shown in FIGURE 16 is designed

with the first mode, the stable oscillation without the influence of other modes

is obtained. In addition, the acoustic wave is transmitted on the substrate 5

almost without extension of the acoustic wave, causing easy oscillation without

the influence of other modes.

FIGURE 27 shows a plan view of an ultrasonic touch system according

to a fourth embodiment of the present invention. The ultrasonic touch system

comprises 14 interdigital transducers, having each overlap length of 5 mm, 56

interdigital transducers, made from aluminium thin film, having each overlap

length of 0.8 mm, a piezoelectric substrate 8 being 128 rotated Y cut X

propagation LiNbO3 with dimensions of 50 mm in length, 40 mm in width and

0.5 mm in thickness, and a display face 9 being not drawn in FIGURE 27. Only

the interdigital transducers, Tl, T2, T3 and T4, having each overlap length of 5

mm and the interdigital transducers, Rl l, R12, R13, R14, R21, R22, R23, R24,

R31, R32, R33, R34, R41, R42, R43 and R44, having each overlap length of 0.8

mm are drawn in FIGURE 27. The display face 9 included in a display device is

mounted on the other surface, without the input and output devices, of the

piezoelectric substrate 8. Each interdigital transducer, whose type is normal,

consisting of 7.5 finger pairs, has an interdigital periodicity of 640 βm.

FIGURE 28 shows a plan view of the interdigital transducers, Tl, T2,

Rl l, R12, R13, R14, R21, R22, R23 and R24, in the ultrasonic touch system

shown in FIGURE 27. The interdigital transducers Tl and T2 are placed

opposite to the interdigital transducers, Rl l, R12, R13, R14, R21, R22, R23 and

R24. In the same way, the interdigital transducers T3 and T4 are placed

opposite to the interdigital transducers, R31, R32, R33, R34, R41, R42, R43 and

R44. The interdigital transducers, Tl, T2, T3 and T4, are used for input. The

interdigital transducers, Rl l, R12, R13, R14, R21, R22, R23, R24, R31, R32,

R33, R34, R41, R42, R43 and R44, are used for output. The interdigital

transducers, Rl l, R12, R13 and R14, correspond to the interdigital transducer

Tl. The interdigital transducers, R21, R22, R23 and R24, correspond to the

interdigital transducer T2. The interdigital transducers, R31, R32, R33 and

R34, correspond to the interdigital transducer T3. The interdigital transducers,

R41, R42, R43 and R44, correspond to the interdigital transducer T4.

If an electric signal is applied to the input interdigital transducer in

the ultrasonic touch system shown in FIGURE 27, respectively, the acoustic

wave is generated on the piezoelectric substrate 8. The acoustic wave is

converted to each electric signal which is detected at the output interdigital

transducer. Thus, the 14 input interdigital transducers and the 56 output

interdigital transducers make 56 ultrasonic transducing systems classified into

two groups, the propagation direction of the acoustic wave on the piezoelectric

substrate 8 in the one group being perpendicular to that in the other group.

Accordingly, the ultrasonic touch system shown in FIGURE 27 has a simple

structure with a small size which is very light in weight, and is operated under

a low power consumption with a low voltage.

It is possible to employ interdigital transducers, having at least two

kinds of interdigital periodicities as show in FIGURE 18, in the ultrasonic touch

system shown in FIGURE 27. For example, the interdigital transducers

composed of two parts, respectively, are used, one consisting of five finger pairs

with an interdigital periodicity of 178 βm, the other consisting of five finger

pairs with an interdigital periodicity of 160 βm. When the interdigital

transducers are employed, they are placed such that each part consisting of five

finger pairs with an interdigital periodicity of 160 βm is opposed inside to each

other, because the acoustic wave with a higher frequency is generated on the

piezoelectric substrate 8 in case of the interdigital periodicity smaller, and is

easier to be decreased on the piezoelectric substrate 8. Thus, the interdigital

transducers are placed such that the part with a smaller interdigital periodicity

has a smaller propagation distance of the acoustic wave. The arrangement

such that the finger pairs with a smaller interdigital periodicity is placed inside

to each other restrains the decrease of the acoustic wave on the piezoelectric

substrate 8.

In the ultrasonic touch system shown in FIGURE 27 an rf pulse

operation seen in FIGURE 19 can be employed. In this case, the respective

parts, ®~©, corresponds to the waveforms shown in FIGURE 20. When

operating the ultrasonic touch system shown in FIGURE 27, a continuous wave

® generated by a function generator is modulated to rf pulses ©- 1 and ©-2

in the corresponding double balanced mixers (DBMs) 1 and 2 by the

corresponding clock pulses φ- 1 and φ-2 from a computer. The DBM 1 and

the DBM 2 play a role of switching to apply with an rf pulse to the interdigital

transducers Tl and T3 (Tl group of IDTs) or the interdigital transducers T2 and

T4 (T2 group of IDTs). If an rf pulse is applied to each of the Tl group of IDTs,

the rf pulse with a frequency approximately corresponding to the interdigital

periodicity of the Tl group of IDTs is converted to the acoustic wave which is

transmitted to the piezoelectric substrate 8. The acoustic wave having a

wavelength approximately corresponding to each interdigital periodicity of the

interdigital transducers, Rl l, R12, R13, R14, R31, R32, R33 and R34 (Rl group

of IDTs), is converted to a delayed electric signal, which is detected at the Rl

group of IDTs. If an rf pulse is applied to each of the T2 group of IDTs, the rf

pulse with a frequency approximately corresponding to the interdigital

periodicity of the T2 group of IDTs is converted to the acoustic wave which is

transmitted to the piezoelectric substrate 8. The acoustic wave having a

wavelength approximately corresponding to each interdigital periodicity of the

interdigital transducers, R21, R22, R23, R24, R41, R42, R43 and R44 (R2 group

of IDTs), is converted to a delayed electric signal, which is detected at the R2

group of IDTs. If an rf pulse is applied to the Tl and T2 groups of IDTs

alternately, a delayed electric signal is detected at the Rl and R2 groups of

IDTs alternately. The connections between the interdigital transducers Rl l and

R21, R12 and R22, R13 and R23, R14 and R24, R31 and R41, R32 and R42, R33

and R43, and R34 and R44, make a circuit construction simple. In addition, the

delayed electric signal ® detected at each pair of the interdigital transducers,

for example the pair of the interdigital transducers Rl l and R21, is received so

that they overlap each oth <»°. Therefore, when touching with a material, softer

than the piezoelectric substrate 8 and easy to absorb the acoustic wave, on the

propagation way, made from the Tl and Rl groups of IDTs, of the acoustic

wave on the piezoelectric substrate 8, the acoustic wave on the touched

position is decreased © only in case that an electric signal is applied to each of

the Tl group of IDTs. In the same way, touching with the material on the

propagation way, made from the T2 and R2 groups of IDTs, of the acoustic

wave on the piezoelectric substrate 8, the acoustic wave on the touched

position is decreased © only in case that an electric signal is applied to each of

the T2 group of IDTs. Such the delayed electric signals ©, © and © are

amplified via an amplifier and rectified via a voltage doubling rectifier, and then

become a direct current signals Φ, © and ©, respectively. By means of

setting the threshold voltage at the proper value between the direct current

signals Φ and ©, or Φ and ©, the digital signals corresponding to the direct

current signals Φ, © and ©, respectively, are obtained via a comparator. The

digital signals are taken into the computer in the form of the parallel signals

with a proper timing by the computer. Thus, the ultrasonic touch system

shown in FIGURE 27 has a short response time, and therefore has a high

sensitivity. Accordingly, the touched position on the piezoelectric substrate 8

can be appointed clearly and quickly. If there are more ultrasonic transducing

systems consisting of an input interdigital transducer and an output interdigital

transducer, respectively, the touched position on the piezoelectric substrate 8

can be more strictly appointed.

In the ultrasonic touch system shown in FIGURE 27 an operation as a

delay line oscillator seen in FIGURE 21 can be employed. In this case, the

respective parts, ® ©, corresponds to the waveforms shown in FIGURE 20.

FIGURE 29 shows a circuit diagram of the amplifier A or B under operation

with the delay line oscillator in FIGURE 27. When operating the ultrasonic

touch system shown in FIGURE 27, switches, SI, S2, S3 and S4, are opened

and closed by order of a computer. While the switches SI and S3 ( SI group of

switches) are closed, the switches S2 and S4 ( S2 group of switches) are

opened. Thus, an electric signal is applied to the Tl and T2 groups of IDTs,

alternately, by opening and closing of the SI and S2 groups of switches

alternately. An electric signal ® applied to the Tl or T2 group of IDTs is

modulated to rf pulses ©- 1 or ©-2, respectively, by the corresponding clock

pulses ©- 1 or φ-2 from a computer. If the rf pulse ©- 1 is applied to the Tl

group of IDTs, then when the SI group of switches are closed, the rf pulse ©

- 1 with a frequency approximately corresponding to the interdigital periodicity

of the Tl group of IDTs is converted to the acoustic wave which is transmitted

to the piezoelectric substrate 8. The acoustic wave having a wavelength

approximately corresponding to each interdigital periodicity of the interdigital

transducers, Rl l, R12, R13, R14, R31, R32, R33 and R34 (Rl group of IDTs), is

converted to a delayed electric signal, which is detected at the Rl group of

IDTs. If the rf pulse ©-2 is applied to the T2 group of IDTs, then when the

S2 group of switches are closed, the rf pulse ©-2 with a frequency

approximately corresponding to the interdigital periodicity of the T2 group of

IDTs is converted to the acoustic wave which is transmitted to the piezoelectric

substrate 8. The acoustic wave having a wavelength approximately

corresponding to each interdigital periodicity of the interdigital transducers,

R21, R22, R23, R24, R41, R42, R43 and R44 (R2 group of IDTs), is converted to

a delayed electric signal, which is detected at the R2 group of IDTs. Thus, if

an electric signal is applied to the Tl and T2 groups of IDTs alternately, a

delayed electric signal is detected at the Rl and R2 groups of IDTs alternately.

The connections between the interdigital transducers Rl l and R21, R12 and

R22, R13 and R23, R14 and R24, R31 and R41, R32 and R42, R33 and R43, and

R34 and R44, make a circuit construction simple. In addition, the delayed

electric signal © detected at each pair of the interdigital transducers, for

example the pair of the interdigital transducers Rl l and R21, is received so

that they overlap each other. A part of the delayed electric signal © detected

at the pair of the interdigital transducers Rl l and R21 and a part of the delayed

electric signal © detected at the pair of the interdigital transducers R31 and

R41 are amplified via the amplifiers A and B, respectively, and each phase

thereof is shifted to the fixed value via each phase shifter, the two electric

signals with each shifted phase are applied to the Tl and T2 groups of IDTs

again, respectively, through the SI and S2 groups of switches. In short, the

electric signals applied to the interdigital transducers Tl and T2 through the

switches SI and S2 are applied to the interdigital transducers T3 and T4

through the switches S3 and S4, and the electric signals applied to the

interdigital transducers T3 and T4 through the switches S3 and S4 are applied

to the interdigital transducers Tl and T2 through the switches SI and S2.

Thus, the delay line oscillator having the 8— shaped signal loop is constructed.

The delayed electric signal © detected at each pair of the interdigital

transducers is decreased (© or ©) in response to a touch on the piezoelectric

substrate 8. When touching with a material, softer than the piezoelectric

substrate 8 and easy to absorb the acoustic wave, on the propagation way,

made from the Tl and Rl groups of IDTs, of the acoustic wave on the

piezoelectric substrate 8, the acoustic wave on the touched position is

decreased © only in case that an electric signal is applied to each of the Tl

group of IDTs. In the same way, touching with the material on the propagation

way, made from the T2 and R2 groups of IDTs, of the acoustic wave on the

piezoelectric substrate 8, the acoustic wave on the touched position is

decreased © only in case that an electric signal is applied to each of the T2

group of IDTs. Such the delayed electric signals @, © and © are amplified

via an amplifier and rectified via a voltage doubling rectifier, and then become a

direct current signals φ, © and ©, respectively. By means of setting the

threshold voltage at the proper value between the direct current signals φ and

©, or φ and ©, the digital signals corresponding to the direct current signals

φ, © and ©, respectively, are obtained via a comparator. The digital signals

are taken into the computer in the form of the parallel signals with a proper

timing by the computer. The operation with the delay line oscillator has no

need for a function generator. Therefore, it is possible to provide the ultrasonic

touch system, with a smaller size which is very light in weight and has a simple

structure, capable of an operation under low power consumption with low

voltage as compared with the case of the rf pulse operation.

When operating the ultrasonic touch system shown in FIGURE 27, an

information given in a color is appeared on the display face 9 in response to the

touched position. At this time, the frequency of the electric signal applied to

the Tl or T2 group of IDTs corresponds to the color. It is possible to look the

information on the display face 9 through the piezoelectric substrate 8. When

touching on the propagation medium of the acoustic wave on the piezoelectric

substrate 8, the acoustic wave decreases and the information given in the color

corresponding to the touched position appears on the display face 9. It is

possible by means of changing the frequency of the input electric signal to

indicate each information given in the color corresponding to the frequency of

the input electric signal on the identical position of the display face 9.

Therefore, when using two kinds of frequencies of the input electric signals,

two kinds of the information given in each color on the identical position of the

display face 9 are superposed. In addition, the information can be indicated for

a fixed period. Thus, when writing, for example, a character with a material,

softer than the piezoelectric substrate 8 and easy to absorb the acoustic wave,

on the piezoelectric substrate 8, the character appears on the display face 9. If

the ultrasonic touch system shown in FIGURE 27 has the interdigital

transducers as shown in FIGURE 18 (a), two kinds of input electric signals

having different frequencies, which correspond to the respective interdigital

periodicities, can be applied to the interdigital transducers. Moreover, it is

possible to more increase the number of the input electric signal, because there

are many kinds of frequencies approximately corresponding to each interdigital

periodicity. As a result, many kinds of information given in each color can be

appeared on the display face 9 by changing the frequency of the input electric

signal.

FIGURE 30 shows the frequency dependencies of the insertion loss

and the phase of the delay line oscillator employed in the ultrasonic touch

system shown in FIGURE 27.

FIGURE 31 shows the relationship between the relative amplitude and

the frequency in the delay line oscillator employed in the ultrasonic touch

system shown in FIGURE 27, where fo corresponds to the fundamental mode

wave with the frequency of 24.3 MHz. The stable oscillation is obtained.

When the piezoelectric substrate 8 comprises a transparent

piezoelectric ceramic such as (Pb-La)(Zr-Ti)O3, what is called the PLZT, the

directions of the polarization axis and the thickness of the transparent

piezoelectric ceramic running parallel with each other, the acoustic wave can

be generated on the piezoelectric substrate 8 effectively. Moreover, it is

possible to look many kinds of information on the display face 9 through the

piezoelectric substrate 8 by using the transparent piezoelectric ceramic as the

piezoelectric substrate 8. In order to transmit the acoustic wave to the

piezoelectric substrate 8, the thickness of the piezoelectric substrate 8 is

requested to be over three times as much as the interdigital periodicity of the

input interdigital transducer. In case that the thickness of the piezoelectric

substrate 8 is smaller than the interdigital periodicity, the Lamb wave is

transmitted to the piezoelectric substrate 8. However, it is possible to use the

Lamb wave mode, if it has the modes capable of fulfilling the sensing function in

the ultrasonic touch system shown in FIGURE 27. In place of the transparent

piezoelectric ceramic, the single crystal, having transparency and

piezoelectricity, such as LiNbOβ, LiTaOβ and so on, can be used as the

piezoelectric substrate 8. When using the single crystal as the piezoelectric

substrate 8, it is necessary to design the ultrasonic touch system in

consideration of the electromechanical coupling constant k ² because of the

anisotropy of the single crystal. Furthermore, there is the possibility to be in

need of an extra complicated circuit. However, the single crystal is promising

as the piezoelectric substrate. The PLZT is promising as the piezoelectric

ceramic substrate among other things, because of the transparency,

manufacturing and durability thereof being excellent. By making use of the

transverse isotropy of the piezoelectric substrate 8 made from the PLZT, the

electric signal levels of the two groups of the output interdigital transducers

become equal, the propagation directions of the acoustic wave on the

piezoelectric substrate 8 in the two groups of the output interdigital

transducers being perpendicular to each other. Accordingly, the circuit

construction becomes so simple that it is possible to provide the ultrasonic

touch system not only with a smaller size which is very light in weight and has

a simple structure. In addition, because of the output signals being always

unified, the signal treatment becomes accuracy and the sensitivity becomes

high. Furthermore, since th--, resolution of the electric signal is increased, the

quantity of the information can be increased.