JP2011036049A - Ultrasonic generator and method of generating ultrasonic wave - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic generator capable of efficiently exciting surface acoustic waves having a large oscillation amplitude by a simple and inexpensive structure, and to provide a method of generating ultrasonic waves. <P>SOLUTION: The ultrasonic generator includes a piezoelectric substrate 15, a bamboo blind-like electrode (14a, 14b) provided on the surface of the piezoelectric substrate 15, a switching element 13 for applying a pulsing driving voltage between a first comb-like electrode 14a and a second comb-like electrode 14b that constitute the bamboo blind-like electrode (14a, 14b), and a gate driving circuit 12 for outputting a pulsing voltage to a control electrode of the switching element 13. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ultrasonic generator and an ultrasonic generation method, and more particularly to an ultrasonic generator and an ultrasonic generation method for exciting a surface acoustic wave (SAW) having a large vibration amplitude.

  A surface acoustic wave is a type of ultrasonic wave, and is applied to the field of small signals such as signal processing devices used in communication devices (see Patent Document 1), as well as an ultrasonic motor (see Patent Document 2) and skin sensation. It is also applied as an ultrasonic generator such as a display (see Patent Documents 3 and 4).

These ultrasonic generators, as shown in FIG. 22, are provided with a first comb electrode 14a and a second comb electrode 14b on the surface of a piezoelectric substrate 15 made of a piezoelectric single crystal material, and interdigital electrodes (14a, 14b). ), Which is disposed opposite to the interdigital so as to form a forward-side direction (forward) by applying a high-frequency sine wave voltage between the first comb-shaped electrode 14a and the second comb-shaped electrode 14b. The traveling surface acoustic wave φ _pf and the backward traveling surface acoustic wave φ _pb traveling in the lower left direction (rearward) are excited. The frequencies of the forward traveling surface acoustic wave _φpf and the backward traveling surface acoustic wave _φpb are the frequencies of the sine wave voltages applied to the interdigital electrodes (14a, 14b).

  For surface acoustic waves applied to small signal fields such as signal processing, ultrasonic waves with small vibration amplitude are sufficient, and a low voltage sine wave signal (small signal) from a high frequency transmitter is applied directly to the interdigital electrode. Available at. However, since surface acoustic waves used for ultrasonic motors and skin-sensing displays require larger vibration amplitudes than surface acoustic waves used for signal processing, the power of sine waves input to the interdigital electrodes is also increased. At present, a sine wave signal is amplified at a high frequency by using a high frequency power amplifier. Since one high-frequency power amplifier is required for each interdigital electrode, when a strong surface acoustic wave is excited from a plurality of interdigital electrodes as in a skin sensory display, the circuit configuration becomes enormous.

Japanese Patent Laid-Open No. 2003-244044 Japanese Patent No. 3630949 JP 2001-255993 A Japanese Patent Application No. 2008-146560

  As described above, in a conventional ultrasonic generator for exciting a surface acoustic wave having a large vibration amplitude, a dedicated high-frequency oscillator and high-frequency amplifier are used as one interdigital transducer to excite a surface acoustic wave with a large sine wave power. It is necessary for each electrode. In particular, when multi-channel interdigital electrodes such as a skin sensory display are used at the same time, in order to excite surface acoustic waves having a large vibration amplitude, high-frequency amplifiers corresponding to the number of channels generate sine wave signals. There was a problem in terms of cost.

  In view of the above problems, the present invention provides an ultrasonic generator capable of efficiently exciting a surface acoustic wave having a large vibration amplitude with a simple and inexpensive structure without using a dedicated high-frequency oscillator or high-frequency amplifier, and an ultrasonic wave The purpose is to provide a generation method.

  In order to achieve the above object, an aspect of the present invention includes a piezoelectric substrate, an interdigital electrode provided on the surface of the piezoelectric substrate, and a first comb electrode and a second comb electrode constituting the interdigital electrode. The present invention relates to an ultrasonic generator including a switching element that applies a pulsed driving voltage therebetween and a gate driving circuit that outputs a pulse voltage to a control electrode of the switching element. The ultrasonic generator according to this aspect of the present invention is characterized in that a surface acoustic wave is excited on the surface of the piezoelectric substrate by pulse driving of the interdigital electrode via a switching element.

  According to another aspect of the present invention, the piezoelectric substrate, the interdigital electrode provided on the surface of the piezoelectric substrate, and the pulsed drive between the first comb electrode and the second comb electrode constituting the interdigital electrode. The present invention relates to an ultrasonic generation method using an ultrasonic generator including a switching element that applies a voltage and a gate drive circuit that outputs a pulse voltage to a control electrode of the switching element. In the ultrasonic wave generation method according to another aspect of the present invention, a surface acoustic wave is excited on the surface of the piezoelectric substrate by applying a pulsed drive voltage to the interdigital electrode via the switching element. Features.

  According to the present invention, it is possible to provide an ultrasonic generator and an ultrasonic generation method capable of efficiently exciting a surface acoustic wave having a large vibration amplitude with a simple and inexpensive structure.

It is a block diagram explaining the schematic structure of the ultrasonic generator which concerns on the 1st Embodiment of this invention. It is a block diagram explaining an example of the circuit structure of the switching element used for the ultrasonic generator which concerns on 1st Embodiment. It is sectional drawing explaining the stress which generate | occur | produces in the piezoelectric substrate of the surface acoustic wave excitation propagation part which concerns on 1st Embodiment. FIG. 4A is a cross-sectional view illustrating an initial stress distribution generated in the piezoelectric substrate of the surface acoustic wave excitation propagation unit according to the first embodiment. FIG. 4B is a cross-sectional view for explaining a wave propagating left and right by the initial stress distribution shown in FIG. 4A after a lapse of a certain time from the state shown in FIG. FIG. 4C is a cross-sectional view for explaining the surface acoustic wave generated by the waves propagating left and right shown in FIG. It is a top view explaining arrangement | positioning of the interdigital electrode of the surface acoustic wave excitation propagation part which concerns on 1st Embodiment. Waveform of rising pulse of rectangular wave as control voltage input to gate of upper arm output element of switching element of ultrasonic generator according to first embodiment, waveform of output voltage of switching element, amplitude of elastic wave It is a figure which shows an example of a waveform. The waveform of the falling pulse of the rectangular wave as the control voltage input to the gate of the upper arm output element of the switching element of the ultrasonic generator according to the first embodiment, the waveform of the output voltage of the switching element, It is a figure which shows an example of an amplitude waveform. 8A shows a case where the voltage of the high-voltage power source connected to the first main electrode of the upper arm output element is 10V, and FIG. 8B shows a case where the voltage of the high-voltage power source is 20V. (C) shows the waveform of the control voltage input to the gate of the upper arm output element of the switching element of the ultrasonic generator according to the first embodiment when the voltage of the high-voltage power supply is 30 V, and the output of the switching element. It is a figure which shows an example of the waveform of a voltage, and the amplitude waveform of an elastic wave. FIG. 9D shows an input to the gate of the upper arm output element according to the first embodiment when the voltage of the high voltage power supply is 40 V, and FIG. 9E shows the voltage of the high voltage power supply is 10 V. It is a figure which shows an example of the waveform of the control voltage, the waveform of the output voltage of a switching element, and the amplitude waveform of an elastic wave. FIG. 10A shows the first embodiment when the input impedance connected to the first comb electrode is 0.1Ω, and FIG. 10B shows the first embodiment when the input impedance is 1Ω. It is a figure which shows an example of the waveform of the control voltage input into the gate of an arm output element, the waveform of the output voltage of a switching element, and the amplitude waveform of an elastic wave. 11C shows the upper arm output according to the first embodiment when the input impedance connected to the first comb electrode is 10Ω, and FIG. 11D shows the input impedance when the input impedance is 100Ω. It is a figure which shows an example of the waveform of the control voltage input into the gate of an element, the waveform of the output voltage of a switching element, and the amplitude waveform of an elastic wave. It is an equivalent circuit of the interdigital electrode which concerns on 1st Embodiment. FIG. 13A is a diagram illustrating a rising edge that is input to the gate of the upper arm output element of the switching element of the ultrasonic generator according to the first embodiment, and FIG. It is a figure which shows an example of the amplitude waveform of the elastic wave which the ultrasonic generator which concerns on embodiment excited by the rising edge shown to Fig.13 (a). FIG. 14A is a diagram illustrating a falling edge that is input to the gate of the upper arm output element of the switching element of the ultrasonic generator according to the first embodiment, and FIG. FIG. 15 is a diagram illustrating an example of an amplitude waveform of an elastic wave excited by a falling edge illustrated in FIG. 14A by the ultrasonic generator according to the embodiment. FIG. 15A is a diagram illustrating a waveform of a rectangular wave pulse input to the gate of the upper arm output element of the switching element of the ultrasonic generator according to the first embodiment, and FIG. FIG. 16 is a diagram illustrating an example of an amplitude waveform of an elastic wave continuously excited by a rising edge and a falling edge of the rectangular wave pulse illustrated in FIG. 15A in the ultrasonic generator according to the first embodiment. . It is a top view explaining the schematic structure of the surface acoustic wave excitation propagation part which concerns on the modification of 1st Embodiment. It is a perspective view explaining the schematic structure of the surface acoustic wave excitation propagation part which concerns on the 2nd Embodiment of this invention. It is sectional drawing explaining operation | movement of the surface acoustic wave excitation propagation part which concerns on 2nd Embodiment. It is a top view explaining the schematic structure of the surface acoustic wave excitation propagation part which concerns on the 3rd Embodiment of this invention. It is a top view explaining operation | movement of the surface acoustic wave excitation propagation part which concerns on 3rd Embodiment. It is a schematic diagram explaining the skin sensation display as an application example of the ultrasonic generator which concerns on 3rd Embodiment. It is a perspective view explaining the schematic structure of the conventional surface acoustic wave excitation propagation part.

  Next, first to third embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  The first to third embodiments shown below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is The material, shape, structure, arrangement, etc. are not specified below. The technical idea of the present invention can be variously modified within the technical scope described in the claims.

(First embodiment)
As shown in FIG. 1, the ultrasonic generator according to the first embodiment of the present invention comprises a piezoelectric substrate 15 made of a piezoelectric material and an alternite phase array (interdigital electrode) on the surface of the piezoelectric substrate 15. The surface acoustic wave excitation propagation unit 2 having the first comb electrode 14a and the second comb electrode 14b provided interdigitally so as to face each other, and the first comb electrode of the surface acoustic wave excitation propagation unit 2 A switching element 13 that applies a pulsed driving voltage between 14a and the second comb electrode 14b, a gate driving circuit 12 that outputs a pulse wave that drives a control electrode (gate electrode) of the switching element 13, and a gate And a control circuit 11 that controls driving of the drive circuit 12.

The piezoelectric substrate 15 is a single crystal substrate such as quartz, lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), bismuth germanium oxide (Bi ₁₂ GeO ₂₀ ), or langasite (La ₃ Ga ₅ SiO ₁₄ ). Alternatively, a piezoelectric ceramic such as lead zirconate titanate (PZT) can be used. As the first comb-shaped electrode 14a and the second comb-shaped electrode 14b constituting the alternite phase array, for example, various metal films such as aluminum (Al) and gold (Au) can be employed.

  As shown in FIG. 2, the switching element 13 is preferably a half-bridge driver (half-bridge circuit) made of a power semiconductor element, but is not limited to a half-bridge driver. A pulsed driving voltage may be applied between the comb-shaped electrode 14a and the second comb-shaped electrode 14b.

The power semiconductor element constituting the switching element 13 is preferably a voltage-driven power semiconductor element in which an insulated gate type gate electrode is capacitively coupled. In FIG. 2, a MOS field effect transistor (FET) is used as an upper arm output element. An example is shown in which Q ₁ and the lower arm output element Q ₂ are respectively configured, and the upper arm output element Q ₁ and the lower arm output element Q ₂ are connected in series. One main electrode (first main electrode) of the upper arm output element Q ₁ is connected to the high-voltage power supply, and one main electrode (second main electrode) of the lower arm output element Q ₂ is connected to the ground potential (GND). ing. The other main electrode (second main electrode) of the upper arm output element Q _{1 and} the other main electrode (first main electrode) of the lower arm output element Q ₂ are connected to the neutral point node N _out . is, the neutral point node N _out is connected to the first comb-shaped electrode 14a of the surface acoustic wave excitation propagating portion 2 via the input impedance Z _in of the impedance adjustment. The second comb electrode 14b of the surface acoustic wave excitation propagation unit 2 is connected to the ground potential.

The gate of the upper arm output element Q _1, the upper arm gate diode D _g1 and the upper arm gate resistance R _g1 are connected in parallel, lower arm gate diode D _g2 and lower arm gate resistance to the gate of the lower arm output element Q ₂ R _g2 is connected in parallel. Further, one main electrode of the upper arm output device Q ₁ (first main electrode), via a capacitor C _b is a bypass capacitor is connected to a ground potential. Although not shown, an upper arm recovery diode may be connected to the upper arm output element Q ₁ and a lower arm recovery diode may be connected to the lower arm output element Q ₂ in parallel.

As shown in FIG. 2, the pulse voltage that is the output from the gate drive circuit 12 at the upper arm node N _in1 is output from the upper arm via the upper arm gate diode D _g1 and the upper arm gate resistor R _g1 connected in parallel. A lower arm gate diode in which a pulse voltage which is input to the gate of the element Q ₁ and is output from the gate drive circuit 12 at the lower arm node N _in2 having a potential complementary to the potential of the upper arm node N _in1 is connected in parallel. The signal is input to the gate of the lower arm output element Q ₂ via D _g2 and the lower arm gate resistance R _g2 . That is, complementary pulses are input to the gate of the upper arm output element Q _{1 and} the gate of the lower arm output element Q ₂ , whereby the first comb electrode 14 a of the surface acoustic wave excitation propagation unit 2 and the first A pulsed driving voltage is applied between the two comb-shaped electrodes 14 b, and a surface acoustic wave is excited on the surface of the piezoelectric substrate 15 and propagates on the surface of the piezoelectric substrate 15. The voltage input to the gate of the upper arm output element Q _{1 and} the gate of the lower arm output element Q ₂ may be a step pulse such as a snake side step function, an impulse such as a Dirac delta function, Rising voltage, falling voltage of rectangular break, rectangular break, etc. can be used.

In the ultrasonic generator according to the first embodiment of the present invention, the power semiconductor element constituting the switching element 13 is not limited to the MOSFET illustrated in FIG. 2, and the gate insulating film is a silicon oxide film ( instead of SiO _2), may even single-layer film or a power IGFET having a composite film of SiO ₂ and Si ₃ N ₄ of the silicon nitride film (Si ₃ N _4). Further, in the case of a voltage-driven power semiconductor element, a power insulated gate field effect transistor (power IGFET), a power insulated gate static induction transistor (power IGSIT), a GTO thyristor, an emitter switched thyristor ( EST), a power semiconductor device such as a MOS control thyristor (MCT) can be configured. Even if the junction type static induction transistor (SIT) is a junction type, the junction type static induction transistor (SIT) operates as a voltage driven type power semiconductor element, and is therefore suitable as a power semiconductor element constituting the switching element 13. If the feedback to the gate drive circuit 12 is not a problem, a current drive type power semiconductor element such as a power bipolar transistor (power BJT) can be used as the power semiconductor element constituting the switching element 13. Therefore, in the description of FIG. 2, the “first main electrode” means either the emitter region or the collector region in the IGBT and the power BJT, and either the source region or the drain region in the power IGFET and the power IGSIT, In the thyristor, it means a semiconductor region that is either an anode region or a cathode region. The “second main electrode” refers to either the emitter region or the collector region that does not become the first main electrode in the IGBT, or the source region or the collector region that does not become the first main electrode in the power IGFET and the power IGSIT. In the GTO thyristor, one of the drain regions means a semiconductor region that is either the anode region or the cathode region that is not the first main electrode.

<Excitation mechanism of surface acoustic wave>
In the following, according to the ultrasonic generator according to the first embodiment and the ultrasonic generation method using the ultrasonic generator, a surface acoustic wave having a large vibration amplitude is efficiently excited with a simple and inexpensive structure. First, the mechanism of surface acoustic wave excitation by the ultrasonic generator according to the first embodiment will be described with reference to FIGS. 3 and 4.
(A) First, when a rising voltage (step voltage) is applied between the first comb electrode 14a and the second comb electrode 14b via the switching element 13, an electric field distribution as shown in FIG. Occurs between the first comb electrode 14a and the second comb electrode 14b in the piezoelectric substrate 15. As shown in FIG. 3, when an electric field distribution is generated between the first comb-shaped electrode 14a and the second comb-shaped electrode 14b in the piezoelectric substrate 15, the electrode fingers 14a ₁ , 14a ₂ , .., 14a _n (n is an integer of 2 or more), stresses σ ₁₁ , σ ₁₂ ,..., Σ _1n toward the lower side of the piezoelectric substrate 15 and electrode fingers 14b _{1 of} the second comb electrode 14b , 14b ₂ ,..., 14b _n , stresses σ ₂₁ , σ _{22 ,.}

(B) When spatially periodic stresses σ _{11 to} σ _1n and σ _{21 to} σ _2n are generated at the moment when the staircase voltage is applied, as shown in FIG. 4A, the first comb electrode 14a The waveform of the initial stress distribution S _i is formed in a sine wave shape corresponding to the spatial frequency of the periodic structure formed by the second comb electrode 14b. Waveform of the initial stress distribution S _i shown in FIG. 4 (a) represent the certain instantaneous stress distribution of the instantaneous oscillation mode that bind the initial stress distribution S _i (e.g. Rayleigh wave).

(C) Thereafter, as time elapses, the initial stress distribution S _i is, as shown in FIG. 4B, the forward traveling stress wave S _f traveling in the right direction (forward) in FIG. decomposes backward traveling stress wave S _b which travels in a direction (backward), the forward traveling stress wave S _f and rear travel stress wave S _b propagate in opposite directions. In the present specification, “front” and “rear” are for convenience, and are merely selections of directions, and for example, “front” and “rear” may be reversed.

(D) As time further elapses, the forward traveling stress wave S _f and the backward traveling stress wave S _b propagated in the left and right directions respectively proceed in the right direction (forward) as shown in FIG. The forward traveling surface acoustic wave φ _f propagates left and right as the backward traveling surface acoustic wave φ _b traveling in the left direction (backward). The forward traveling surface acoustic wave φ _f and the backward traveling surface acoustic wave φ _b each have a frequency corresponding to the spatial frequency of the periodic structure formed by the first comb electrode 14a and the second comb electrode 14b. It propagates and radiates to the left and right as a wave having the number of wave fronts equal to the logarithm of the comb electrode 14a and the second comb electrode 14b. For example, when the first comb-shaped electrode 14a and the second comb-shaped electrode 14b are provided on the piezoelectric substrate 15 made of 128 ° Y-cut LiNbO ₃ so as to have a line-and-space with a line width of 100 μm and a space interval of 100 μm. 5, the period length λ of the first comb electrode 14a and the second comb electrode 14b is λ = 400 μm, and the frequencies of the forward traveling stress wave S _f and the backward traveling stress wave S _b are 9.6 MHz, respectively. It becomes.

6 and 7, the waveform of the control voltage V _g which is input to the gate of the arm output device Q ₁ on the switching elements 13 constituting the half-bridge driver of Figure 2, one main electrode of the upper arm output device Q ₁ when the (first main electrode) voltage of the high voltage power supply connected to the 50 V, the output voltage V _sd of the switching device 13 to be measured at the neutral point node N _out of the switching device 13 waveforms, a first comb by the electrodes 14a and the second comb-shaped electrode 14b shows the amplitude of the waveform of the acoustic wave EW is excited (the gate of the lower arm output element Q ₂ is, arm output device Q ₁ upward shown in FIGS. 6 and 7 voltage waveform and complementary waveforms of the control voltage V _g which is input to the gate is input.). The measurement of the elastic wave EW is performed on the surface of the piezoelectric substrate 15 spaced apart from the right end of the 20 pairs of interdigital electrodes (14a, 14b) formed by the first comb electrode 14a and the second comb electrode 14b. The measurement was performed with a laser Doppler vibrometer. In the measurement shown in FIGS. 6 and 7, the input impedance Z _in is connected to the first comb-shaped electrode 14a is 0.1 [Omega.

To the gate of the arm output device Q ₁ on the switching element 13, as the rising pulse of the rectangular wave, the control voltage V _g of the step function as shown in FIG. 6 is input, the forward progress elasticity on the surface of the piezoelectric substrate 15 After a delay of a certain propagation time depending on the propagation speed of the surface wave φ _f , the vibration waveform of the elastic wave EW could be observed at the measurement location. Waveform of the acoustic wave EW, since the logarithm of the first comb-shaped electrode 14a and the second comb-shaped electrode 14b is 20, but can be observed as a wave having a 20 wavefront, backward traveling SAW phi _b reflected at the end portion of the left side of the piezoelectric substrate 15, the reflected wave traveling in the right direction, since it is superimposed on the forward traveling surface acoustic wave phi _f, in succession the waves with a 20 wave front, further Other waves were observed. The waveform of the output voltage V _sd of the switching element 13 measured at the neutral point node N _out of the switching element 13 is basically the control voltage V input to the gate of the upper arm output element Q ₁ of the switching element 13. _Although it is a waveform of a step function of 50V similar to the waveform of _g , a wave having 20 wave fronts is superimposed on the surface of the piezoelectric substrate 15 due to the influence of the elastic wave EW excited, so that it is completely It is not a step function waveform.

When a step voltage control voltage V _g as shown in FIG. 7 is input as a rectangular falling pulse to the gate of the upper arm output element Q ₁ of the switching element 13, it advances forward on the surface of the piezoelectric substrate 15. after delaying certain propagation time worth of relying on the propagation velocity of the surface acoustic wave phi _f, the measuring point, similarly to FIG. 6, the vibration waveform of the acoustic wave EW was observed. Waveform of the acoustic wave EW, since the logarithm of the first comb-shaped electrode 14a and the second comb-shaped electrode 14b is 20, but can be observed as a wave having a 20 wavefront, backward traveling SAW phi _b Since the reflected wave that is reflected at the left end of the piezoelectric substrate 15 and travels in the right direction is superimposed on the forward traveling surface acoustic wave φ _f , the wave is continuously connected to the wave having 20 wave fronts. Similar to 6, other waves were observed. The waveform of the output voltage V _sd of the switching element 13 measured at the neutral point node N _out of the switching element 13 is basically the control voltage V input to the gate of the upper arm output element Q ₁ of the switching element 13. _Although it is a waveform of a step function of 50 V similar to the waveform of _g , a wave having 20 wave fronts is superimposed on the surface of the piezoelectric substrate 15 due to the influence of the elastic wave EW excited. Like 6, it is not a complete step function waveform.

<Depending on drive voltage>
Figure 8 (a) ~ FIG 8 (c), FIG. 9 (d) and FIG. 9 (e) the input impedance Z _in is connected to the first comb-shaped electrode 14a is fixed to 0.1 [Omega, respectively, on The half-bridge driver of FIG. 2 is configured when the voltage of the high-voltage power supply connected to one main electrode (first main electrode) of the arm output element Q ₁ is changed to 10V, 20V, 30V, 40V50V. waveform of the control voltage V _g which is input to the gate of the arm output device Q ₁ on the switching element 13, the waveform of the drain current I _sd of the upper arm output element Q _1, measured at the neutral point node N _out of the switching device 13 4 shows the waveform of the output voltage V _sd of the switching element 13 and the amplitude waveform of the elastic wave EW excited by the first comb electrode 14a and the second comb electrode 14b. As in FIGS. 6 and 7, the measurement of the elastic wave EW is performed by laser Doppler vibration at a measurement location on the surface of the piezoelectric substrate 15 spaced apart from the right ends of the 20 pairs of interdigital electrodes (14a, 14b). Done by total.

When the output voltage V _sd of the switching element 13 is 10 V, a step function control voltage V _g as shown in FIG. 8A is input to the gate of the upper arm output element Q ₁ of the switching element 13 to be constant. After that, the vibration waveform of the elastic wave EW having a very weak amplitude having an amplitude value of about 0.2 nm could be observed at the measurement location. Furthermore, when the output voltage V _sd of the switching element 13 is 20 V, a step function control voltage V _g as shown in FIG. 8B is input to the gate of the upper arm output element Q ₁ of the switching element 13. When the vibration waveform of the weak elastic wave EW having an amplitude value of about 0.6 nm can be observed and the output voltage V _sd of the switching element 13 is 30 V, the gate of the upper arm output element Q ₁ of the switching element 13 is When the control voltage V _g of the step function as shown in 8 (c) is input, the amplitude value is relatively about 1.2 nm, the vibration waveform of strong intensity acoustic wave EW could be observed.

Further, when the output voltage V _sd of the switching element 13 is 40 V, a step function control voltage V _g as shown in FIG. 9D is input to the gate of the upper arm output element Q ₁ of the switching element 13. When the vibration waveform of the strong elastic wave EW having an amplitude value of about 1.4 nm can be observed and the output voltage V _sd of the switching element 13 is 50V, the gate of the upper arm output element Q ₁ of the switching element 13 is When 9 control voltage V _g of the step function as shown in (e) is input, the amplitude value could be observed vibration waveform of a strong acoustic wave EW strength of about 1.8 nm. Incidentally, FIG. 8 (a) ~ FIG 8 (c), in FIG. 9 (d) and FIG. 9 (e), the influence of the superposition of the backward traveling surface acoustic wave phi _b, the wave having a 20 wavefront continuous In addition, other waves have been observed. The waveform of the drain current I _{sd and} the waveform of the output voltage V _sd of the switching element 13 are basically step function waveforms, but are affected by the elastic wave EW excited on the surface of the piezoelectric substrate 15. Because it vibrates, it is not a step function waveform. When comparing FIG. 9D and FIG. 9E, there is a slight tendency to saturate the vibration intensity of the elastic wave EW. Therefore, if the output voltage V _sd of the switching element 13 is about 50 V, the ultrasonic motor It can be seen that almost satisfactory elastic wave EW can be excited for application purposes such as skin sensory display and the like.

<Input impedance dependency>
FIG. 10 (a), the FIG. 10 (b), the FIG. 11 (c) and FIG. 11 (d) of the high voltage power supply connected to one main electrode of the upper arm output device Q ₁ (first main electrode) The gate of the upper arm output element Q ₁ of the switching element 13 when the voltage is fixed at 50 V and the input impedance Z _in connected to the first comb electrode 14 a is changed to 0.1Ω, 1Ω, 10Ω, and 100Ω. , The waveform of the control voltage V _g input to the, the waveform of the drain current I _sd of the upper arm output element Q ₁ , the waveform of the output voltage V _sd of the switching element 13 measured at the neutral point node N _out of the switching element 13, The waveform of the amplitude of the elastic wave EW excited by the first comb-shaped electrode 14a and the second comb-shaped electrode 14b is shown. As in FIGS. 6 to 9, the measurement of the elastic wave EW is performed by laser Doppler vibration at a measurement location on the surface of the piezoelectric substrate 15 spaced apart from the right ends of the 20 pairs of interdigital electrodes (14a, 14b). Done by total.

When the input voltage Z _in is 0.1Ω and a step function control voltage V _g as shown in FIG. 10A is input to the gate of the upper arm output element Q ₁ of the switching element 13, constant propagation is achieved. After being delayed by the time, a vibration waveform of a strong elastic wave EW having an amplitude value of about 1.8 nm could be observed at the measurement location. On the other hand, when the input impedance Z _in is 1Ω, when the step function control voltage V _g as shown in FIG. 10B is input to the gate of the upper arm output element Q ₁ of the switching element 13, the amplitude value is obtained. When the vibration waveform of the strong elastic wave EW of about 1.6 nm can be observed and the input impedance Z _in is 10Ω, the gate of the upper arm output element Q ₁ of the switching element 13 is shown in FIG. When the control voltage V _g of the staircase function is input, the amplitude value is relatively about 1.1 nm, the vibration waveform of strong intensity acoustic wave EW could be observed. However, if the input impedance Z _in is 100Ω, when the step function control voltage V _g as shown in FIG. 11D is input to the gate of the upper arm output element Q ₁ of the switching element 13, the amplitude value is A vibration waveform of an elastic wave EW having an extremely weak intensity of about 0.2 nm was observed. Incidentally, FIG. 10 (a), the FIG. 10 (b), the in FIGS. 11 (c) and 11 (d), under the influence of the superposition of the backward traveling surface acoustic wave phi _b, forward progress elastic having 20 wavefront A wave continuous to the surface wave φ _f is observed. The waveform of the drain current I _{sd and} the waveform of the output voltage V _sd of the switching element 13 are basically step function waveforms, but are affected by the elastic wave EW excited on the surface of the piezoelectric substrate 15. Because it vibrates, it is not a step function waveform. FIG. 10 (a), the FIG. 10 (b), the Comparing FIG. 11 (c) and FIG. 11 (d), the input impedance Z _in is connected to the first comb-shaped electrode 14a, the output impedance of the switching element 13 It can be seen that if the value is as small as 1Ω or less, the elastic wave EW can be excited substantially for application purposes such as an ultrasonic motor and a skin sensory display.

As shown in FIG. 12, an equivalent circuit of the interdigital electrodes (14a, 14b) formed by the first comb electrode 14a and the second comb electrode 14b includes an inductor L, a resistor R, and a capacitor C connected in series. , represented by more the connected capacitance C _d in parallel. The inductor L, the resistor R, and the capacitor C are due to the piezoelectric effect and acoustic characteristics of the piezoelectric substrate 15, and the capacitance _Cd is the capacitance of the first comb electrode 14a and the second comb electrode 14b.

As shown in FIGS. 6 to 11, the waveform of the output voltage V _sd of the switching element 13 has already been vibrated under the influence of the elastic wave EW excited on the surface of the piezoelectric substrate 15. As shown in FIG. 12, the equivalent circuit of the interdigital electrodes (14a, 14b) includes an inductor L, resistor R, capacitor C, because it has a _{C d,} with respect to the control voltage _{V g} of the step function input to the gate, Transmission occurs temporarily due to LC series resonance, but because of the resistance R, it attenuates and eventually stops transmitting.

In the equivalent circuit shown in FIG. 12, since the capacitance C _d at non-resonance is 140 pF, the RC time constant when the input impedance Z _in = 0.1Ω = 14 ps, and the RC when the input impedance Z _in = 1Ω. RC time constant = 140 ns when time constant = 140 ps, input impedance Z _in = 10Ω, RC time constant = 14 ns when input impedance Z _in = 100Ω.

If an interdigital electrode (14a, 14b) having a period length λ = 400 μm as shown in FIG. 5 is used to excite an elastic wave EW of 9.6 MHz, 1 / (2π × 9.6 × 10 ⁶ ) = 16. A step function having a rising voltage sufficiently smaller than 6 ns may be output as the output voltage V _sd of the switching element 13. Specifically, as the output voltage V _sd of the switching element 13, for example, it is preferable to output a pulse voltage having a maximum rise rate dV / dt of 100 V / ns to 10 kV / ns.

<Rectangular wave drive>
As shown in FIG. 1, in order to avoid the influence of the backward traveling SAW phi _b propagating in the opposite direction, the left direction antireflection sound absorbing material of the interdigital electrodes (14a, 14b) shown in FIG. 1 Is preferably provided. For example, the surface acoustic wave excitation propagation unit 2 including the first comb-shaped electrode 14a and the second comb-shaped electrode 14b each having n electrode fingers is connected to the control voltage V having a rising waveform as shown in FIG. If the _g is applied to the gate of the arm output device Q ₁ on the switching element 13 is driven, as shown in FIG. 13 (b), at the rising edge of the control voltage V _g, the influence of the backward traveling SAW phi _b If there is not, a forward traveling surface acoustic wave φ _f having a wave front number n equal to the number n of pairs of electrode fingers is excited and propagates in the right direction of the interdigital electrode (14a, 14b) as an elastic wave EW.

After a lapse of a certain time, the surface acoustic wave excitation propagation unit 2 including the first comb electrode 14a and the second comb electrode 14b each having n electrode fingers, as shown in FIG. 14 (a), the control voltage V _g of the falling waveform is applied to the gate of the arm output device Q ₁ on the switching element 13, is driven, the acoustic wave EW, as shown in FIG. 14 (b), becomes the wave crests number n Propagate in the right direction of the interdigital electrodes (14a, 14b).

When driving the interdigital electrodes (14a, 14b) with a rectangular wave pulse having a duty ratio of 50%, the number of pairs formed by the electrode fingers of the first comb electrode 14a and the second comb electrode 14b is n, and the rectangular electrodes are rectangular. When the repetition period of the wave and (2n-1) T, as the elastic wave EW shown in the control voltage V _g and 15 shown in FIG. 15 (a) (b), excited by the rising edge of the rectangular wave pulse The elastic wave EW having the period T and the elastic wave EW having the period T excited at the falling edge of the rectangular wave pulse are superimposed so as to be continuous, and a continuous elastic wave EW is emitted. For example, when the number n of pairs of electrode fingers of the first comb-shaped electrode 14a and the second comb-shaped electrode 14b is n = 4, 2n-1 = 7, and therefore, a rectangular wave repetition period 7T (= pulse width 3. If an elastic wave EW having a period T of 1/7 of 5T) is excited, continuous elastic wave EW can be excited.

  As described above, according to the ultrasonic generator according to the first embodiment and the ultrasonic generation method using the ultrasonic generator, a surface acoustic wave having a large vibration amplitude is efficiently generated with a simple and inexpensive structure. I can excite well.

(Modification of the first embodiment)
As described with reference to FIG. 1, interdigital electrodes (14a, 14b) from the rear travel traveling forward traveling surface acoustic wave phi _f and the left direction (backward) traveling in the right direction (forward) in FIG. 1 surface acoustic wave phi _b emitted.

For this reason, it is possible to reflect the wave radiated in one direction at the end of the piezoelectric substrate 15 so that the forward traveling surface acoustic wave φ _f and the backward traveling surface acoustic wave φ _b are superimposed on each other. That is, the phases of the front traveling surface acoustic wave φ _f and the reflected wave of the backward traveling surface acoustic wave φ _b are synchronized so that they are superimposed as a continuous wave in one direction. Interdigital transducer (14a, 14b) when the logarithm n formed by the electrode fingers of the period of the acoustic wave EW as T, interdigital rear travel SAW phi _b is reflected at the end of the piezoelectric substrate 15 from being radiated If the time delay until feedback to the electrodes (14a, 14b) is nT, an elastic wave EW having 2n wave fronts can be excited at any one of the rising edge and the falling edge. it can.

  Further, as shown in FIG. 15, the elastic wave EW of the period T excited at the rising edge of the rectangular wave pulse and the elastic wave EW of the period T excited at the falling edge are superimposed so as to be continuous. 16 and the method using the reflected wave from the end of the piezoelectric substrate 15 shown in FIG. 16 are combined so that the elastic wave EW having 2n wave fronts is continuous at the rising edge and the falling edge. It is also possible.

  According to the ultrasonic generator according to the modification of the first embodiment and the ultrasonic generation method using the ultrasonic generator, a surface acoustic wave having a large vibration amplitude is efficiently excited with a simple and inexpensive structure. it can.

(Second Embodiment)
In the surface acoustic wave excitation propagation unit 2 of the ultrasonic generator according to the first embodiment, the first comb electrode 14a and the second comb electrode 14b are formed on the piezoelectric substrate 15, but as shown in FIG. The interdigital electrodes (14a, 14b) comprising the first comb electrode 14a and the second comb electrode 14b are formed on a non-piezoelectric substrate 16 such as glass, and are provided on the interdigital electrodes (14a, 14b). The piezoelectric substrate 15 may be in contact with the interdigital electrodes (14a, 14b).

  Although not shown, like the ultrasonic generator according to the first embodiment, the control circuit and the gate controlled by the control circuit are the same as those of the ultrasonic generator according to the second embodiment. A driving circuit and a switching element to which a control voltage is supplied from the gate driving circuit are provided, and a pulsed voltage output from the switching element is applied between the first comb electrode 14a and the second comb electrode 14b. Is done.

As shown in FIG. 18, the surface acoustic wave excitation propagation unit 2 of the ultrasonic generator according to the second embodiment includes electrode fingers 14a _j , 14a _{j + 1} ,... Provided on the non-piezoelectric substrate 16. , 14b _j−1 , 14b _j ,... (J: integer of 2 to n−1) and electrode fingers 14a _j , 14a _{j + 1} ,..., 14b _j−1 , 14b _j ,. The piezoelectric substrate 15 is provided. The electrode fingers _14a j, 14a _{j + 1,} ...... constitutes a first comb-shaped electrode 14a of FIG. 17, the electrode fingers 14b _j-one, 14b _j, ...... configuration the second comb-shaped electrode 14b of FIG. 17 is doing. As shown in FIG. 18, stresses ^a σ _1j , ^a σ _{1 j + 1} ,... Downward of the piezoelectric substrate 15 generated in the electrode substrates 14 a _j , 14 a _{j + 1 ,. Are} transmitted as stress ^b σ _1j , ^b σ _{1 j + 1} ,... _{Into the} non-piezoelectric substrate 16 through the electrode fingers 14 a _j , 14 a _{j + 1 ,.} Similarly, the stresses ^a σ _{2 j-1} , ^a σ _2j ,... Generated upward in the piezoelectric substrate 15 located in the electrode fingers 14 b _j−1 , 14 b _{j ,.} finger 14b _j-1, 14b _j, via ..., the non-piezoelectric substrate 16, the stress ^{_{b σ 2 j-1, b}} σ 2j, transmitted as .... As shown in FIG. 17, the stresses ^b σ _1j , ^b σ _{1 j + 1} ,..., ^B σ _{2 j−1} , ^b σ _2j,. The forward traveling surface acoustic wave φ _f traveling in the right direction (forward) and the backward traveling surface acoustic wave φ _b traveling in the left direction (rear) are excited and propagated.

  As described above, according to the ultrasonic generator according to the second embodiment and the ultrasonic generation method using the ultrasonic generator, a surface acoustic wave having a large vibration amplitude can be efficiently generated with a simple and inexpensive structure. I can excite.

(Third embodiment)
As shown in FIG. 19, the surface acoustic wave excitation propagation unit used in the ultrasonic generator according to the third embodiment includes a first side, a second side perpendicular to the first side, and a first side. A rectangular flat plate-shaped transparent non-piezoelectric substrate 16 defined by a third side facing the second side and a fourth side facing the second side, and a plurality of the non-piezoelectric substrate 16 arranged side by side on the surface near the first side An electrode array composed of interdigital electrodes T ₁₁ , T ₁₂ ,..., T _1m, and an electrode array composed of a plurality of interdigital electrodes T ₂₁ , T ₂₂ ,..., T _2n arranged side by side on the surface near the second side , A plurality of interdigital electrodes T ₃₁ , T ₃₂ ,..., T _3m arranged side by side on the surface near the third side, and a plurality of interdigital electrodes T arranged side by side on the surface near the fourth side ₄₁ , T ₄₂ ,..., T _4n .

Although the surface acoustic wave excitation propagation unit according to the third embodiment is not shown, the piezoelectric substrate is connected to the interdigital electrodes T ₁₁ , T ₁₂ ,... As shown in FIG. _{..., T 1m, T 21,} T 22, ......, T 2n, T 31, T 32, ......, T 3m, T 41, T 42, ......, provided in contact with an upper portion of each of T _4n Yes. Similar to the surface acoustic wave excitation propagation unit described in the second embodiment, the surface acoustic wave excitation propagation unit according to the third embodiment includes interdigital electrodes T ₁₁ , T _{12 ,.} T ₂₁ , T ₂₂ ,..., T _2n , T ₃₁ , T ₃₂ ,..., T _3m, T ₄₁ , T _{42 ,.} Stress generated in the substrate is interdigital electrodes T ₁₁ , T ₁₂ ,..., T _1m , T ₂₁ , T ₂₂ ,..., T _2n , T ₃₁ , T ₃₂ , ......, T _3m, T ₄₁ , Through T ₄₂ ,..., T _4n , it is transmitted as stress in the non-piezoelectric substrate 16, and a surface acoustic wave is excited near the surface in the non-piezoelectric substrate 16.

When the surface of the non-piezoelectric substrate 16 of the surface acoustic wave excitation propagation portion shown in FIG. 19 is used as the surface side of the tactile sensation member, a skin sensory display 52 can be realized on the display screen 53 as shown in FIG. In the skin sensation display 52, it is necessary to excite surface acoustic waves in the non-piezoelectric substrate 16 that is a tactile sensation member of the skin sensation display 52, so that the non-piezoelectric display 52 is made of a glass substrate larger than the liquid crystal screen forming the display screen 53. The back surface side of the piezoelectric substrate 16 is opposed to the display screen 53 side, and the non-piezoelectric substrate 16 is disposed on the display screen 53. 19, interdigital electrodes T ₁₁ , T ₁₂ ,..., T _1m , T ₂₁ , T ₂₂ ,..., T _2n , T ₃₁ , T ₃₂ are formed around the surface side of the non-piezoelectric substrate 16. ,..., T _3m, T ₄₁ , T ₄₂ ,..., T _4n are arranged, and in the same manner as shown in FIG. Jo electrodes _{T 11, T 12, ......,} T 1m, T 21, T 22, ......, T 2n, T 31, T 32, ......, T 3m, T 41, T 42, ......, the T _4n A piezoelectric substrate is arranged in a frame shape so as to surround the skin sensory display 52. Using the piezoelectric substrate disposed on the non-piezoelectric substrate 16 in the shape of a frame, each interdigital electrode T ₁₁ , T ₁₂ ,..., T _1m , T ₂₁ , T is processed in the same manner as shown in FIG. ₂₂ ,..., T _2n , T ₃₁ , T ₃₂ ,..., T _3m, T ₄₁ , T _{42 ,.} The surface acoustic wave thus excited is excited in the non-piezoelectric substrate 16 serving as a tactile member. For this purpose, interdigital electrodes T ₁₁ , T ₁₂ ,..., T _1m , T ₂₁ , T ₂₂ ,..., T _2n , T ₃₁ , T ₃₂ , ..., T _3m, T ₄₁ , T ₄₂ , ..., each of T _{4n includes} a switching element, and includes a multi-channel gate drive circuit that outputs a control voltage to each switching element, and a control circuit that controls the multi-channel gate drive circuit in an integrated manner. What should I do? Therefore, each interdigital electrode T ₁₁ , T ₁₂ ,..., T _1m , T ₂₁ , T ₂₂ ,..., T _2n , T ₃₁ , T ₃₂ , as in a conventional skin sensory display using surface acoustic waves. ,..., T _3m, T ₄₁ , T ₄₂ ,..., T _4n do not require the use of a dedicated high-frequency oscillator or high-frequency amplifier, and the integration density and configuration become very simple.

For example, interdigital electrodes T _p-1, as shown in FIG. _{20, T p, T p +} 1, T p + 2, T p + 2, using the one-dimensional array of ..., IDT T _{p- 1} , T _p , T _{p + 1} , T _{p + 2} , T _{p + 2} ,..., So that the channels t _{s −1} , t _s , t _{s + 1} ,. When the control voltages V _gp−1 , V _gp , V _{gp + 1} , V _{gp + 2} , V _{gp + 3} ,... _Are applied to the switching elements, the interdigital electrodes T _p−1 , T _p , T _p Surface acoustic waves radiated independently from ₊₁ , T _{p + 2} , T _{p + 2} ,... Interfere with each other so that the surface acoustic waves converge at point P in FIG. can do.

  The skin sensory display 52 using the surface acoustic wave shown in FIG. 21 can be applied to a computer interface having a display screen 53 with a large area. When the skin sensation display 52 is directly traced with a finger 51 or the like as shown in FIG. 21, a tactile sensation according to information displayed on the skin sensation display 52 can be tasted. By applying the skin sensation display 52 to a pen tablet or a touch panel, it is possible to reproduce the writing quality of a pen and to add an auxiliary function for a low vision person.

In cutaneous sensory display 52 shown in FIG. 21, the friction coefficient of the apparent surface of the non-piezoelectric substrate 16 made of the surface side of the touch member, each interdigital transducer _{T 11, T 12, ......,} T 1m, T 21 , T ₂₂ ,..., T _2n , T ₃₁ , T ₃₂ ,..., T _3m, T ₄₁ , T _{42 ,.} It is changing. When the elastic wave is excited in the non-piezoelectric substrate 16, the apparent friction coefficient of the surface of the non-piezoelectric substrate 16 becomes small because the surface of the non-piezoelectric substrate 16 vibrates slightly, and the elastic wave is not excited. Sometimes grows. In this skin sensation display 52, the apparent friction coefficient of the surface of the non-piezoelectric substrate 16 changes with time by switching on / off the elastic wave excitation with respect to the non-piezoelectric substrate 16 in a short cycle. When the surface of the non-piezoelectric substrate 16 is set to the surface side of the tactile sensation member and a finger is placed on the tactile sensation member, a computer interface can be realized in which the skin feels as if the rough solid surface is traced with the finger.

  Thus, according to the ultrasonic generator according to the third embodiment and the ultrasonic generation method using this ultrasonic generator, a surface acoustic wave having a large vibration amplitude can be efficiently generated with a simple and inexpensive structure. Since it can be excited, an inexpensive skin sensation display can be realized.

(Other embodiments)
As described above, the present invention has been described according to the first to third embodiments. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, a stator that propagates a surface acoustic wave to the surface is constituted by the piezoelectric substrate 15 shown in FIG. 1, and the kinetic energy of the surface acoustic wave is obtained from the surface of the stator, and the stator is rotated in the direction opposite to the propagation direction of the surface acoustic wave. It is also possible to constitute a surface acoustic wave actuator such as an ultrasonic motor provided with a mover that moves relative to the actuator. When exciting a surface acoustic wave on the surface of the stator, a surface acoustic wave having a large vibration amplitude can be efficiently excited by simply applying a pulse voltage to the interdigital electrode, as shown in FIG.

  In the surface acoustic wave actuator according to another embodiment, the moving element includes a moving element substrate and an array of moving element segments made of a material having a Young's modulus larger than that of the moving element substrate. The ultrasonic motor may be configured to include a mover segment array in which each upper surface of the mover segment is in contact with the vibrator.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

2 ... SAW excitation propagating portion 11 ... control circuit 12 ... gate drive circuit 13 ... switching elements 14a ... first comb-shaped electrode 14b ... second comb-shaped electrodes _{14a 1 ~14a n, 14b 1 ~14b} n, 14a j, 14a _{j + 1} , 14b _j−1 , 14b _j ... electrode finger 15 ... piezoelectric substrate 16 ... non-piezoelectric substrate 51 ... finger 52 ... skin sensory display 53 ... display screen Nout ... neutral point node Q ₁ ... upper arm output element Q ₂ ... lower arm output element _{T 11, T 12, ...,} T 1m, T 21, T 22, ..., T 2n, T 31, T 32, ..., T 3m, T 41, T 42, ..., T 4n, T _p-1 , T _p , T _{p + 1} , T _{p + 2} , T _{p + 2} ... Interdigital electrode Z _in ... Input impedance

Claims (2)

A piezoelectric substrate;
Interdigital electrodes provided on the surface of the piezoelectric substrate;
A switching element that applies a pulsed drive voltage between the first comb electrode and the second comb electrode constituting the interdigital electrode;
A gate drive circuit for outputting a pulse voltage to the control electrode of the switching element, and exciting a surface acoustic wave on the surface of the piezoelectric substrate by driving the interdigital electrode through the switching element. Ultrasonic generator. Switching element for applying a pulsed driving voltage between the piezoelectric substrate, the interdigital electrode provided on the surface of the piezoelectric substrate, and the first comb electrode and the second comb electrode constituting the interdigital electrode And an ultrasonic generation method using an ultrasonic generator comprising a gate drive circuit that outputs a pulse voltage to the control electrode of the switching element,
A method for generating ultrasonic waves, wherein a surface acoustic wave is excited on the surface of the piezoelectric substrate by applying the pulsed drive voltage to the interdigital electrodes via the switching element.

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