JP2018134578A - Elastic vibration compression apparatus, elastic vibration amplifier, and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve miniaturization of an elastic medium; and to heighten selection flexibility of the kind or the shape of the elastic medium.SOLUTION: An elastic vibration compression-amplification apparatus includes a thin film waveguide (108) which is an elastic medium having a characteristic of desired group velocity dispersion, and vibration application parts (105a, 110) for applying elastic vibration having a modulated frequency to the thin film waveguide (108). The elastic vibration compression-amplification apparatus compresses-amplifies the elastic vibration including vibration having a frequency differentiated by frequency modulation, by an effect of the group velocity dispersion of the thin film waveguide (108).SELECTED DRAWING: Figure 8

Description

  The present invention relates to an elastic vibration compression device that enables compression of elastic vibration and an elastic vibration amplification device that enables amplification of elastic vibration.

  Among elastic vibrations, particularly those having a frequency of several tens of kHz to several tens of MHz are called ultrasonic waves. Ultrasound is the acquisition of biological images represented by ultrasonic echoes, detection and inspection by nondestructive methods in water, in the ground, and in solid materials, and noninvasive destruction of foreign substances in materials such as noninvasive scalpels. Has been used. In order to realize visualization of substances with higher sensitivity and higher resolution and more effective removal of foreign substances, it is necessary to compress and amplify ultrasonic temporal and spatial vibrations. By compressing the ultrasonic pulse, it is possible to shrink the wave packet width and increase the vibration intensity. For example, when compressing the ultrasonic wave, it can be expected to improve the spatial resolution, and when amplifying the ultrasonic wave, the ultrasonic wave Can be expected to increase the destruction energy.

  Several methods and structures have been proposed and demonstrated for ultrasonic compression and amplification. For example, Non-Patent Document 1 discloses a geometric technique for realizing sound wave collection (compression, amplification) by processing a piezoelectric transducer into a concave lens shape. Non-Patent Document 2 discloses a time reversal technique that realizes sound collection by applying an appropriate phase delay to a plurality of sound waves. Non-Patent Document 3 discloses a phased array technique. Non-Patent Documents 4 and 5 disclose a metamaterial-like method using a specific refraction phenomenon of sound waves in an artificial material having a negative refractive index. Non-Patent Document 6 discloses a nonlinear acoustic lens technique using a phase delay effect resulting from a nonlinear elastic effect.

  As described above, in the conventional method, it is possible to compress or amplify ultrasonic waves spatially or temporally by using a specially designed structure. However, since these conventional methods require a two-dimensional or three-dimensional structure, there is a problem that the apparatus becomes large and a precise design of the apparatus is required. Therefore, a compression technique for elastic vibration having a small-scale structure and versatility of the medium and its design freedom has not been proposed so far.

Jun-ichi Kushibiki and Noriyoshi Chubachi, “Material Characterization by Line-Focus-Beam Acoustic Microscope”, IEEE Transactions on Sonics and Ultrasonics, Vol.SU-32, No.2, 1985 Mathias Fink, “Time Reversal of Ultrasonic Fields-Part I: Basic Principles”, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol.39, No.5, 1992 Emad S. Ebbini and Charles A. Cain, “Multiple-Focus Ultrasound Phased-Array Pattern Synthesis: Optimal Driving-Signal Distributions for Hyperthermia”, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol. 36, No. 5, 1989 Xinhua Hu et al., “Superlensing effect in liquid surface waves”, Physical Review E 69, 030201, 2004 Suxia Yang et al., “Focusing of Sound in a 3D Phononic Crystal”, Physical Review Letters, Vol. 93, 024301, 2004 Alessandro Spadoni and Chiara Daraio, “Generation and control of sound bullets with a nonlinear acoustic lens”, Proceedings of the National Academy of Sciences, Vol.107, No.16, p.7230-7234, 2010

  The present invention has been made in order to solve the above-described problems. An elastic vibration compression device, an elastic vibration amplification device, and an elastic vibration compression device that can reduce the size of the elastic medium and increase the degree of freedom in selecting the type and shape of the elastic medium. It aims to provide a method.

An elastic vibration compression device of the present invention includes an elastic medium having desired group velocity dispersion characteristics, and a vibration application unit that applies frequency-modulated elastic vibration to the elastic medium, and generates vibrations having different frequencies by the frequency modulation. The elastic vibration is compressed by the effect of group velocity dispersion of the elastic medium.
Further, in one configuration example of the elastic vibration compressing apparatus according to the present invention, the vibration applying unit generates up-chirp elastic vibration whose frequency increases with time when the elastic medium has anomalous dispersion characteristics. When the elastic medium has a normal dispersion characteristic, down-chirp elastic vibration whose frequency decreases with the passage of time is applied to the elastic medium.
Further, in one configuration example of the elastic vibration compression device of the present invention, the elastic medium includes a first elastic medium to which the elastic vibration is applied by the vibration applying unit, and a propagation distance of the elastic vibration is an effect of the compression. It is characterized by comprising a second elastic medium coupled in series with the first elastic medium at a position where the distance is obtained and having a characteristic that the group velocity dispersion is substantially zero.

The elastic vibration amplifying device of the present invention includes an elastic medium having a desired group velocity dispersion characteristic, and a vibration applying unit that applies frequency-modulated elastic vibration to the elastic medium, and has different frequencies by the frequency modulation. The elastic vibration including vibration is amplified by an effect of group velocity dispersion of the elastic medium.
Further, in one configuration example of the elastic vibration amplifying device of the present invention, the vibration applying unit generates up-chirp elastic vibration whose frequency increases with time when the elastic medium has anomalous dispersion characteristics. When the elastic medium has a normal dispersion characteristic, down-chirp elastic vibration whose frequency decreases with the passage of time is applied to the elastic medium.
Also, in one configuration example of the elastic vibration amplifying device of the present invention, the elastic medium includes a first elastic medium to which the elastic vibration is applied by the vibration applying unit, and a propagation distance of the elastic vibration is an effect of the amplification. It is characterized by comprising a second elastic medium coupled in series with the first elastic medium at a position where the distance is obtained and having a characteristic that the group velocity dispersion is substantially zero.

The elastic vibration compression method of the present invention includes a step of applying an elastic vibration frequency-modulated to an elastic medium having a desired group velocity dispersion characteristic, and the elastic vibration including vibrations of different frequencies by the frequency modulation. The elastic medium is compressed by the effect of group velocity dispersion of the elastic medium.
The elastic vibration amplifying method of the present invention includes a step of applying an elastic vibration frequency-modulated to an elastic medium having a desired group velocity dispersion characteristic, and the elastic vibration including vibrations of different frequencies by the frequency modulation. Amplifying by the effect of group velocity dispersion of the elastic medium.

  According to the present invention, it is not necessary to expand the structure of the elastic medium two-dimensionally or three-dimensionally as in the conventional method, so that the elastic medium can be reduced in size, and the design flexibility of the elastic medium is improved. Can be expected. Further, in the present invention, by adjusting the frequency modulation condition of elastic vibration and the wave bundle width of elastic vibration, it is possible to compress and amplify elastic vibration in an elastic medium with arbitrary group velocity dispersion, and to set the compression ratio and amplification gain. Since it is controllable, the degree of freedom in selecting the type and shape of the elastic medium can be dramatically increased as compared with the conventional method. In the present invention, since an elastic medium can be realized on a semiconductor substrate, it is possible to control a semiconductor electric device or an optical device via an ultrashort / high intensity pulse wave of elastic vibration generated using the present invention. it can. As a result, in the present invention, a dramatic improvement in the usefulness of elastic vibration can be expected.

  Further, according to the present invention, the elastic medium includes a first elastic medium to which elastic vibration is applied by the vibration applying unit, and a first elastic medium coupled in series with the first elastic medium and having a characteristic of substantially zero group velocity dispersion. By constituting with two elastic media, it is possible to transmit elastic vibration while maintaining the shape of the compressed / amplified vibration wave as much as possible.

It is a figure which shows one example of the propagation distance dependence of the wave packet expansion of non-chirp vibration, and one example of the wave packet shape of non-chirp vibration. | K ₂ | is a diagram showing an example of the propagation distance dependency of the wave packet width at each value of / T ₀ ^2. It is a figure which shows one example of the waveform of the up chirp vibration in this invention, and a down chirp vibration. It is a figure which shows an example of the propagation distance dependence of a chirp vibration in case the product of a chirp parameter and group velocity dispersion | distribution is positive, and an example of the wave packet shape of a chirp vibration. It is a figure which shows one example of the propagation distance dependence of a chirp vibration in case the product of a chirp parameter and group velocity dispersion | distribution is negative, and one example of the wave packet shape of a chirp vibration. It is a figure which shows an example of the chirp parameter dependence of the change of the wave packet width of a chirp vibration. It is the top view and sectional drawing of a thin film waveguide which are elastic media concerning the 1st example of the present invention. It is a figure which shows the structure of the elastic vibration compression and amplification apparatus which concerns on 1st Example of this invention. It is a figure which shows one example of the propagation distance dependence of up-chirp vibration when applying up-chirp vibration to the thin film waveguide which concerns on the 1st Example of this invention, and one example of the wave packet shape of up-chirp vibration. It is a figure which shows the other example of the wave packet shape of an up chirp vibration when applying an up chirp vibration to the thin film waveguide which concerns on the 1st Example of this invention. It is a top view which shows the structure of the thin film waveguide of the elastic vibration compression and amplification apparatus which concerns on 2nd Example of this invention. It is a top view which shows the structure of the thin film waveguide of the elastic vibration compression and amplification apparatus which concerns on 3rd Example of this invention, and a figure which shows an example of the waveform of the elastic vibration on a thin film waveguide.

[Principle of the Invention]
As a new method for solving the above problems, in the present invention, compression and amplification of elastic vibration using elastic vibration including frequency-modulated (chirped) ultrasonic waves and group velocity dispersion of an elastic medium in which the elastic vibration propagates are used. We propose a method that enables this. An elastic medium (waveguide) that transmits elastic vibration has a finite group velocity dispersion, and the propagation speed of elastic vibration varies depending on the frequency of the vibration.

  When a non-chirp elastic vibration pulse is applied to such a waveguide, for example, if the waveguide has anomalous dispersion characteristics, the high frequency wave included in the input is compared with the low frequency wave. Therefore, as the propagation distance increases, the wave packet of vibration gradually expands due to the group velocity dispersion effect. On the other hand, when the waveguide has a normal dispersion characteristic, the high-frequency wave included in the input travels slower than the low-frequency wave.

  However, in the present invention, rapid compression of the elastic vibration is realized by applying the group velocity dispersion effect to the frequency-modulated elastic vibration. For example, when the waveguide has anomalous dispersion characteristics, when an up-chirp vibration pulse whose frequency increases with time is input to the waveguide, vibrations of different frequencies distributed temporally and spatially at the input stage, The frequency distribution is gradually eliminated by the difference in vibration velocity due to the group velocity dispersion, and the compression of the pulse (contraction of the wave packet) and the amplification of the pulse intensity are obtained at a specific propagation distance. If the waveguide has normal dispersion characteristics, the same phenomenon occurs when a down-chirp vibration pulse whose frequency decreases with time is input to the waveguide.

  Thus, in the present invention, it is not necessary to make the structure two-dimensional or three-dimensional as in the conventional method, and the wave width, sign, and frequency sweep range of the input chirp pulse are adjusted in the external signal generator. Thus, it is possible to compress and amplify pulses with an arbitrary group velocity dispersion medium. Further, in order to increase the compression ratio and amplification gain of elastic vibration by the conventional method, it is necessary to expand the two-dimensional structure or the three-dimensional structure in addition to the increase of the input signal intensity. On the other hand, in the present invention, this can be solved by adjusting the wavelet width and frequency sweep range (chirp parameter) of the input chirp vibration, and there is no need to change the waveguide structure serving as an elastic medium.

  According to the present invention, since it is not necessary to expand the structure two-dimensionally or three-dimensionally as in the conventional method, an improvement in design flexibility such as downsizing of the elastic medium structure can be expected. In addition, in the present invention, by adjusting the chirp parameter of the frequency modulation wave used for input, vibration compression and amplification can be realized in an elastic medium with arbitrary group velocity dispersion, and the compression ratio and amplification gain of elastic vibration can be controlled. Is possible. These points are also factors that dramatically increase the degree of freedom in selecting the type and shape of the elastic medium as compared with the conventional method.

  Furthermore, since the present invention can realize a waveguide structure on a semiconductor substrate, semiconductor electrical devices and optical devices are controlled through ultrashort and high intensity pulse waves of elastic vibration generated using the present invention. It can be used. As a result, a dramatic improvement in the usefulness of elastic vibration including ultrasonic waves can be expected.

  Hereinafter, the principle of the present invention will be described in more detail. Here, a one-dimensional thin film waveguide that transmits bending vibration is considered as an elastic medium. The wave equation of the bending vibration transmitted through this waveguide can be described as:

Here, A is the vibration amplitude, x is the propagation distance, and η is the propagation loss. Since k is the wave number, ω is the angular frequency, and k _n = ∂ ⁿ k / ∂ω ⁿ , k ₁ is the reciprocal of the group velocity, and k ₂ is the group velocity dispersion. In Equation (1), the nonlinear term of vibration is not considered. This equation (1) is derived from the literature “Daiki Hatanaka, Amaury Dodel, Imran Mahboob, Koji Onomitsu and Hiroshi Yamaguchi,“ Phonon propagation dynamics in band-engineered one-dimensional phononic crystal waveguides ”, New Journal of Physics, 17, 113032, 2015”.
Is disclosed.

The influence of group velocity dispersion on non-chirped and chirped vibration shapes will be described below from the basic wave equation of equation (1). First, a new coordinate system is introduced that travels at the same speed as the vibration of the group velocity v _g (= 1 / k ₁ ). When T = t−x / v _g = t−k ₁ x, the equation (1) can be transformed as the following equation.

Also, using the normalized vibration amplitude intensity U (x, T), A (x, T) = A ₀ e ^−ηx U (x, T), and when introduced into equation (2), the following equation As shown in (3), the wave equation describes the elastic vibration traveling through the one-dimensional thin film waveguide having the group velocity dispersion k ₂ .

  Next, Equation (3) is solved by using Fourier transform. The vibration wave packet function U (x, T) is expressed by the following equation using a Fourier-transformed function tilde U (x, ω). In the following, “˜” similarly attached on the character is called a tilde.

  By substituting equation (4) into equation (3), it can be transformed into the following equation.

  When this equation (5) is solved, the following equation (6) is obtained.

  Then, the equation (4) becomes the following equation (7).

  Here, when a Gaussian function is applied as the wave packet of the input vibration, the input function tilde U (0, ω) in Expression (7) can be described as the following expression.

By substituting equation (8) into equation (7), the following equation (9) is obtained, and a wave packet of vibration having group velocity dispersion k ₂ is obtained.

From the equation (9), the wavelet width T ₁ (the point at which the amplitude becomes 1 / e) of the vibration that has traveled through the thin film waveguide by the distance x is obtained as follows.

FIG. 1A shows a calculation result of the propagation distance (| k ₂ | x / T ₀ ² ) dependency of the wave packet expansion of the group velocity dispersion k ₂ , and FIG. 1B shows | k ₂ | x. It is a figure which shows the calculation result of the wave packet shape in / T ₀ ² = 0,2,4. As shown in FIGS. 1 (A) and 1 (B), the non-chirp vibration applied to the thin film waveguide has a wave packet as the propagation distance x increases because of the group velocity dispersion k ₂ of the thin film waveguide. It can be seen that the wave packet width T ₁ increases, that is, the wave packet width T ₁ increases.

FIG. 2 is a diagram showing a calculation result of the propagation distance dependence of the wave packet width T / T ₀ at | k ₂ | / T ₀ ² = 1, 1.25, 1.67, 2.5, 5. As shown in FIG. 2, the wavelet width T ₁ of the vibration pulse becomes more dependent on the propagation distance x as the absolute value of the group velocity dispersion k ₂ increases. Thus, when non-chirp vibration is used as an input, wave packet expansion is observed regardless of the sign of group velocity dispersion, but wave packet compression / amplification cannot be realized. Therefore, an elastic medium or structure having as little dispersion as possible is preferred for general wave packet transmission.

  However, in the present invention, compression of elastic vibration is attempted by actively utilizing the group velocity dispersion effect on the wave packet. As described above, when frequency-modulated (chirped) vibration is applied to the thin film waveguide, vibration pulses including vibrations of various frequencies distributed in space and time can be compressed by the group velocity dispersion effect. The frequency-modulated vibration pulse used for input can be described as:

  Here, C is a chirp parameter representing the frequency sweep range. If C> 0, as shown in FIG. 3A, up-chirp vibration in which the carrier frequency increases linearly as the vibration pulse moves from the beginning to the rear is obtained. On the other hand, if C <0, as shown in FIG. 3B, down-chirp vibration in which the carrier frequency decreases linearly as it moves from the beginning to the rear of the vibration pulse.

  Substituting equation (11) into equation (8) yields the following equation (12).

  Then, by substituting equation (12) into equation (7), the chirp vibration propagating in the waveguide can be described as the following equation.

Further, the wave packet width T ₁ of the chirp vibration propagating through the waveguide can be described as the following equation (14).

4A shows a calculation result of the propagation distance dependence of the chirp vibration pulse in the case of C = 3 and T ₀ ² / k ₂ = 3, and FIG. 4B shows the calculation result of C = 3, T ₀ ² / in k ₂ = 3, is a graph showing the calculation results of the wave packet shape chirp vibration pulse in each case of x = 0,3,10. FIG. 5A is a diagram showing a calculation result of the propagation distance dependence of the chirp vibration pulse when C = −3 and T ₀ ² / k ₂ = 3, and FIG. 5B is a diagram showing C = −3 and T _0. It is a figure which shows the calculation result of the wave packet shape of the chirp vibration pulse in each case of x = 0, 3, and 10 when ² / k ₂ = 3. FIG. 6 is a diagram showing the calculation result of the chirp parameter dependence of the change in the wavelet width T ₁ / T ₀ of the chirped vibration pulse when T ₀ ² / k ₂ = 3.

As is clear from the equations (13) and (14), when the product of the chirp parameter C and the group velocity dispersion k ₂ is positive (Ck ₂ > 0), the wave packet of the propagation vibration is increased by the propagation distance x. Along with this, it increases monotonously (FIGS. 4A and 4B). On the other hand, when the product of the chirp parameter C and the group velocity dispersion k ₂ is negative (Ck ₂ <0), the compression of the wave packet of the chirp vibration occurs at the propagation distance x _min of the following equation.

Further, the minimum wave packet width T ₁ ^min when the propagation distance is x _min can be expressed by the following equations (FIGS. 5A and 5B).

As is clear from the equation (16), it can be seen that the compression ratio of the chirp vibration can be adjusted by the magnitude of the absolute value | C | of the chirp parameter C, and the chirp vibration can be amplified accordingly. . However, when the pulse further advances after the propagation distance x _min in the equation (15), the wave packet width is expanded by one turn as shown in FIG.

As described above, it is understood that vibration compression and amplification can be obtained by applying frequency swept chirp vibration to a thin film waveguide having a finite group velocity dispersion k ₂ . The effect can be freely controlled by adjusting the value of the chirp parameter C. If the waveguide group velocity dispersion k ₂ is negative (abnormal dispersion), an up-chirp vibration is applied to the waveguide, and if the waveguide group velocity dispersion k ₂ is positive (normal dispersion), down-chirp is applied. What is necessary is just to apply a vibration to a waveguide. In the above principle, the bending vibration propagation wave of the thin film waveguide has been described. However, the present invention is not limited to this, and any elastic vibration, for example, a longitudinal wave or a transverse wave propagating in a solid substance, and the surface of a solid substance (a different substance) The present invention can also be applied to a surface acoustic wave transmitted through an interface between the two.

[First embodiment]
Examples of the present invention will be described below. FIG. 7A is a plan view of a thin film waveguide which is an elastic medium according to the first embodiment of the present invention, FIG. 7B is a cross-sectional view taken along line AA in FIG. 7A, and FIG. ) Is a sectional view taken along line BB in FIG. In this embodiment, a one-dimensional elastic waveguide having a total length of 1 mm is used as the thin film waveguide 108. The thin film waveguide 108 includes a waveguide portion made of a multilayer film disposed with a space between the substrate and a support portion that supports the waveguide portion from a direction perpendicular to the propagation direction of elastic vibration.

In this embodiment, the _{GaAs / Al X Ga 1-X} As multilayer film on a GaAs substrate (not shown), a resist patterning by photolithography or EB lithography, wet etching or reactive ion etching with phosphoric acid The mesa structure which becomes the foundation of the thin film waveguide 108 was formed by the dry etching method using the above. Here, as _{GaAs / Al X Ga 1-X} As multilayer film formed on a GaAs substrate, an Al _0.65 Ga _0.35 As layer 101 having a thickness of 3 [mu] m, a thickness of 100nm formed on Al _0.65 Ga _0.35 As layer 101 The n-GaAs layer 102 and a 100 nm thick Al _0.27 Ga _0.73 As layer 103 formed on the n-GaAs layer 102 were used.

Next, the electrodes 105a and 105b made of Au having a thickness of 80 nm used for induction and detection of chirp vibration are formed on a GaAs / Al _x Ga _{1 having a} mesa structure by photolithography or EB lithography, vacuum deposition, and lift-off. _-X As formed on the As multilayer film (on the Al _0.27 Ga _0.73 As layer 103).

Then, a photolithography method or EB lithography, dry etching method using a wet etching method or reactive ion etching with phosphoric acid, the mesa structure _{GaAs / Al X Ga 1-X} As the multilayer film surface of (Al _0.27 Ga _0.73 As A plurality of holes 106 reaching from the layer 103) to the Al _0.65 Ga _0.35 As layer 101 (sacrificial layer) are formed.

Thereafter, only the Al _0.65 Ga _0.35 As layer 101, which is a sacrificial layer, is isotropically etched with the hole 106 as the center by dilute hydrofluoric acid, whereby the n-GaAs layer 102 and the Al _0.27 Ga _0.73 As layer 103 are formed. The multi-layered film consisting of is in a state of being supported by the remaining Al _0.65 Ga _0.35 As layer 101. That is, the Al _0.65 Ga _0.35 As layer 101 remaining after etching serves as a support portion that supports the multilayer film. When the distance by which the Al _0.65 Ga _0.35 As layer 101 is etched by etching is longer than the distance a between the holes 106, a space 107 having a substantially rectangular shape in plan view is formed in the Al _0.65 Ga _0.35 As layer 101 at the positions of the holes 106. The multilayer film on 107 becomes a thin film waveguide 108 having a substantially rectangular shape in plan view.

  FIG. 8 is a diagram illustrating the configuration of the elastic vibration compression / amplification device according to the present embodiment, and is a diagram illustrating a method for generating chirp vibration. The signal generator 110 and the electrode 105a on the thin film waveguide 108 shown in FIG. 8 constitute a vibration application unit that applies elastically frequency-modulated elastic vibration to the thin film waveguide 108.

  As described above, the thin film waveguide 108 of the present embodiment is composed of a heterostructure of gallium arsenide (GaAs) and aluminum gallium arsenide (AlGaAs), and thus has piezoelectric characteristics. Therefore, as shown in FIG. 8, when an AC voltage is applied from the signal generator 110 between the electrode 105a installed in the thin film waveguide 108 and the n-GaAs layer 102, the electrode 105a and the n-GaAs layer 102 are A strong electric field is generated between them, and distortion is generated via the piezoelectric effect. As a result, bending vibration is induced on the thin film waveguide 108. Since the frequency of this vibration is determined by the frequency of the AC voltage applied to the electrode 105a, vibration having an arbitrary frequency can be induced freely. That is, it is possible to adjust the frequency modulation condition (chirp parameter C and modulation frequency) of the elastic vibration and the wave packet width of the vibration pulse with the AC voltage applied from the signal generator 110.

  The generated vibration propagates at a speed (group speed) according to the frequency along the length direction (left-right direction in FIG. 8) of the thin film waveguide 108. The thin film waveguide 108 is fixed at both ends in the vibration propagation direction. For this reason, when the vibration reaches the end of the thin film waveguide 108, it is reflected, and the vibration proceeds in the direction opposite to that before the reflection. That is, the vibration propagates back and forth in the thin film waveguide 108.

Further, the thin film waveguide 108 of this embodiment includes holes 106 that are periodically formed along the propagation direction of vibration. In addition to the width w of the thin film waveguide 108, the group velocity dispersion of the thin film waveguide 108 can be freely set by changing the interval a of the holes 106 and the diameter of the holes 106. For example, a group velocity dispersion k ₂ ≈−2 × 10 ⁻⁹ s ² / m is obtained at a frequency of 5.7 MHz in the thin film waveguide 108 having a width w = 29 μm and a gap a = 12 μm. The thin film waveguide 108 is in an anomalous dispersion region where the group velocity dispersion k ₂ is negative at the frequency. Therefore, in order to cause vibration compression, an up-chirp vibration pulse may be applied to the thin film waveguide 108.

  In order to apply the up-chirp vibration pulse to the thin film waveguide 108, an AC voltage whose frequency increases linearly with the passage of time may be applied to the electrode 105a. On the other hand, in order to apply the down-chirp vibration pulse to the thin film waveguide 108, an AC voltage whose frequency decreases linearly with the passage of time may be applied to the electrode 105a.

FIG. 9A shows the pulse width T ₁ of the up-chirp vibration pulse when an up-chirp vibration pulse having a Gaussian envelope shape with a chirp parameter C = 3, T ₀ = 3 μm and a Gaussian envelope shape is applied to the thin film waveguide 108. FIG. 9B shows a calculation result of propagation distance dependency. FIG. 9B shows a calculation result of the wave packet shape of the up-chirp vibration pulse when C = 3, T ₀ = 3 μm, and x = ₀ mm, 1.2 mm, and 4 mm. FIG.

In the example of FIGS. 9A and 9B, when the up-chirp vibration pulse propagates through the thin film waveguide 108 by a distance x = 1.2 mm, the wave width of the up-chirp vibration pulse reaches T ₁ = 0.9 μs. As a result, the peak intensity of the up-chirp vibration pulse is amplified 1.7 times.

Since the length of the thin film waveguide 108 of this embodiment is 1 mm and its propagation loss is about 0.4 dB / mm, the compression of vibration can be achieved even under the conditions shown in FIGS. 9A and 9B. It can be confirmed that amplification is sufficiently realizable. The compression ratio and amplification gain of vibration can be increased by increasing the input pulse width T ₀ and increasing the absolute value of the chirp parameter C, as is clear from equation (16).

FIG. 10 is a diagram showing a calculation result of a wave packet shape of an up-chirp vibration pulse in each case of C = 9, T ₀ = 10 μs, and x = ₀ mm, 5.5 mm, and 15 mm. In the example of FIG. 10, it can be seen that strong vibration compression up to the minimum wave packet width T ₁ = 1 μs at a propagation distance x = 5.5 mm and large vibration amplification in which the peak intensity is tripled are obtained.

Of course, the same compression / amplification effect can be realized even if the group velocity dispersion value of the thin film waveguide 108 changes. For example, when the group velocity dispersion of the thin film waveguide 108 is k ₂ ≈−3 × 10 ⁻⁹ s ² / m, the same compression / amplification effect as in the example of FIG. 10 can be obtained at the propagation distance x = 3.6 mm.

  From the above, it has been shown that the method for compressing and amplifying elastic vibrations including ultrasonic waves using the group velocity dispersion of an elastic medium is feasible in an actual device. Compared with the conventional compression / amplification method, this embodiment does not require the expansion of the waveguide structure when improving the compression ratio of vibration, and it is only necessary to adjust the input signal conditions (input wave packet width, chirp parameter). That's it. Further, the present embodiment can be applied to an elastic medium made of various constituent materials or an elastic medium having various group velocity dispersions.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the first embodiment, after the distance x _min where the maximum compression and amplification of the pulse are obtained, there is a problem that the propagation of the wave packet of vibration occurs as propagation proceeds. This problem can be solved by incorporating an elastic medium (zero dispersion medium) having an extremely small group velocity dispersion k ₂ immediately after the propagation distance x _min . As a result, it is possible to spatially extract the elastic vibration compressed and amplified to the maximum via the zero dispersion medium while maintaining the wave packet shape, and transmit the vibration in an arbitrary direction.

In the case of the first embodiment described above, the group velocity dispersion k ₂ can be modulated by changing the width w of the thin film waveguide 108 and the interval a of the holes 106. For example, as shown in FIG. 11, in the thin film waveguide 108a with w = 29 μm and a = 8 μm, the group velocity dispersion becomes k ₂ = −4 × 10 ⁻¹⁰ s ² / m at 6 MHz. For this reason, by applying an up-chirp vibration pulse (C> 0) having a carrier frequency in the vicinity of 6 MHz to the thin film waveguide 108a, the vibration wave packet is compressed and amplified at the propagation distance x _min .

In this embodiment, as shown in FIG. 11, at a position where the propagation distance x of vibration is equal to x _min (x = x _min ), the thin film waveguide 108a is coupled in series along the propagation direction of vibration. A thin film waveguide 108b is provided. The width w of the thin film waveguide 108b is 29 μm, and the distance a between the holes 106 is 12 μm. Thereby, in the thin film waveguide 108b, the group velocity dispersion becomes k ₂ ≈0 (substantially zero) at 6 MHz. In the manufacturing process of the thin film waveguide 108 described in the first embodiment, if the gap a between the holes 106 is changed in the region of the thin film waveguide 108a and the region of the thin film waveguide 108b, the thin film waveguides 108a and 108b It is possible to realize a structure as shown in FIG.

The configuration of the vibration application unit of the elastic vibration compression / amplification apparatus is the same as that of the first embodiment. In this embodiment, since the group velocity dispersion k ₂ of the thin film waveguide 108b is in a zero dispersion state where the group velocity dispersion k ₂ becomes almost zero at 6 MHz, the expansion of the elastic vibration wave packet due to dispersion can be suppressed as much as possible to transmit the elastic vibration. Become.

[Third embodiment]
In the first and second embodiments, the vibration applying unit is realized by the signal generator 110 and the electrode 105a. However, the present invention is not limited to this, and the vibration applying unit may be realized by the structure of the thin film waveguide. FIG. 12A is a plan view showing the configuration of the thin film waveguide of the elastic vibration compression / amplification device according to this embodiment.

In this example, the group velocity dispersion k _{2 has a} positive (normal dispersion) characteristic before the thin film waveguide 108 (the thin film waveguide 108a of the second example) described in the first and second examples. A waveguide 108c having the same is coupled. When elastic vibration that is not frequency-modulated as shown in FIG. 12B is input to the waveguide 108c from the right end of FIG. 12A, frequency modulation is performed due to the normal dispersion characteristic of the waveguide 108c. Non-elastic vibration is converted into frequency-modulated elastic vibration (up-chirp vibration) as shown in FIG. As described above, in general, the elastic vibration traveling through the thin film waveguide causes expansion of the wave width of the elastic vibration and reduction of the vibration intensity in the process.

  However, the elastic vibration input to the thin film waveguide 108 (thin film waveguide 108a of the second embodiment) is compressed and amplified by the effects described in the first and second embodiments. In this way, the expansion and reduction of the wave packet in the thin film waveguide 108c can be compensated for by the waveguides 108 and 108a (FIG. 12D). In this way, it is also possible to realize a vibration applying unit by the structure of the thin film waveguide 108c.

In the first to third embodiments, it is desirable that the frequency f defining the group velocity dispersion k ₂ of the elastic medium is equal to the median value f0 of the frequency of elastic vibration frequency-modulated in a certain frequency range. (F = f0). The median value f0 is, for example, f0 = 1.5 MHz in the case of elastic vibration including frequency components from 1.49 MHz to 1.51 MHz.

Here, if the frequency sweep width is too wide, the value of the group velocity dispersion k ₂ also varies with the respective frequencies, so that it is difficult to determine the position and time at which the elastic vibration is compressed or amplified. Accordingly, it is desirable that the frequency sweep range Δf of the elastic vibration is sufficiently smaller than the median value f0 of the elastic vibration (Δf << f0).

  In the first to third embodiments, the configuration as an elastic vibration compression / amplification device has been described. However, the elastic vibration compression / amplification device (elastic vibration compression / amplification method) of the present invention depends on its application. It can also be used as an elastic vibration compression device (elastic vibration compression method), or as an elastic vibration amplification device (elastic vibration amplification method).

  In the first to third embodiments, the input elastic vibration to the elastic medium has been described by taking a Gaussian pulse whose frequency-modulated vibration pulse has a Gaussian shape as an example, but the present invention is not limited to this. The present invention can also be applied to elastic vibration waves such as rectangular waves and continuous waves.

  In the first to third embodiments, the elastic vibration is converted into a voltage by the piezoelectric effect, and can be electrically detected through the electrode 105b. Further, the electrode 105b is irradiated with laser light from, for example, a helium neon laser, reflected light from the electrode 105b is received by a photodiode, and the output of the photodiode is received by a vector signal analyzer (VSA). Thus, it is also possible to detect elastic vibration by converting it into an electrical signal.

Further, in the first to third embodiments have been excited vibration by using a piezoelectric effect with the _{GaAs / Al X Ga 1-X} As multilayer film, and a chirp signal generated by the signal generator to the intact elastic vibration As long as it can be converted, the excitation method and the type of elastic medium that transmits vibration are not limited.

For example, an elastic medium can be produced using a non-piezoelectric material containing Si or SiO ₂ as well as a laminated structure of piezoelectric materials such as PZT and ZnO. When piezoelectric oxides such as PZT and ZnO are used as the material of the elastic medium, the large piezo constant of these piezoelectric oxides enables efficient excitation and detection of mechanical vibration due to voltage, and driving energy of the elastic medium. Power saving is expected.

On the other hand, when a non-piezoelectric material such as Si or SiO ₂ is used as the material of the elastic medium, it is impossible to induce elastic vibration using only the electrodes as described above. In this case, the first metal film formed on the non-piezoelectric material such as Si or SiO _2, the piezoelectric material formed on the first metal film, and the second metal film formed on the piezoelectric material. Is formed in place of the electrodes 105a and 105b, and an alternating current is formed between the lower first metal film and the upper second metal film formed at the position of the electrode 105a. If a voltage is applied, local excitation of elastic vibration can be realized. Further, the output of the elastic medium can be electrically extracted from between the lower first metal film and the upper second metal film of the laminated structure formed at the position of the electrode 105b.

  The present invention can be applied to a technique for compressing and amplifying elastic vibration.

101 ... Al _0.65 Ga _0.35 As layer, 102 ... n-GaAs layer, 103 ... Al _0.27 Ga _0.73 As layer, 105a, 105b ... electrode, 106 ... hole, 107 ... space, 108, 108a, 108b, 108c ... thin film waveguide 110 ... Signal generator.

Claims (8)

An elastic medium having desired group velocity dispersion characteristics;
A vibration applying unit for applying frequency-modulated elastic vibration to the elastic medium,
An elastic vibration compressing apparatus, wherein the elastic vibration including vibrations of different frequencies by the frequency modulation is compressed by an effect of group velocity dispersion of the elastic medium. The elastic vibration compression apparatus according to claim 1,
When the elastic medium has anomalous dispersion characteristics, the vibration applying unit applies up-chirp elastic vibration whose frequency increases over time to the elastic medium, and the elastic medium has normal dispersion characteristics. In addition, an elastic vibration compression apparatus characterized by applying down-chirp elastic vibration whose frequency decreases with time to the elastic medium. The elastic vibration compression apparatus according to claim 1 or 2,
The elastic medium is
A first elastic medium to which the elastic vibration is applied by the vibration applying unit;
A second elastic medium coupled in series with the first elastic medium at a position where the propagation distance of the elastic vibration is a distance at which the compression effect is obtained, and having a characteristic of substantially zero group velocity dispersion The elastic vibration compression apparatus characterized by the above-mentioned. An elastic medium having desired group velocity dispersion characteristics;
A vibration applying unit for applying frequency-modulated elastic vibration to the elastic medium,
An elastic vibration amplifying apparatus, wherein the elastic vibration including vibrations having different frequencies by the frequency modulation is amplified by an effect of group velocity dispersion of the elastic medium. The elastic vibration amplifying device according to claim 4,
When the elastic medium has anomalous dispersion characteristics, the vibration applying unit applies up-chirp elastic vibration whose frequency increases over time to the elastic medium, and the elastic medium has normal dispersion characteristics. In addition, an elastic vibration amplifying apparatus, wherein down-chirp elastic vibration whose frequency decreases with time is applied to the elastic medium. The elastic vibration amplifying device according to claim 4 or 5,
The elastic medium is
A first elastic medium to which the elastic vibration is applied by the vibration applying unit;
A second elastic medium coupled in series with the first elastic medium at a position where the propagation distance of the elastic vibration is a distance at which the amplification effect is obtained, and having a characteristic of substantially zero group velocity dispersion An elastic vibration amplifying device characterized by that. Applying a frequency-modulated elastic vibration to an elastic medium having a desired group velocity dispersion characteristic;
An elastic vibration compression method comprising compressing the elastic vibration including vibrations having different frequencies by the frequency modulation by an effect of group velocity dispersion of the elastic medium. Applying a frequency-modulated elastic vibration to an elastic medium having a desired group velocity dispersion characteristic;
A method for amplifying elastic vibrations, comprising amplifying the elastic vibrations including vibrations of different frequencies by the frequency modulation by an effect of group velocity dispersion of the elastic medium.