JP2012100123A - Electromechanical conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromechanical conversion device capable of improving performance of detection of an acoustic wave generated from a measuring target, by suppressing a wave reflected from a part except a movable area of an electromechanical conversion element.SOLUTION: An electromechanical conversion device such as an electrostatic capacitance type ultrasonic conversion device includes an electromechanical conversion element 10 having a movable area 16 for receiving an acoustic wave emitted from a test object, an electric wiring board 13 electrically connected to the element 10, and a reflection suppression layer 12. The reflection suppression layer 12, which is provided in at least a part, except the movable area, of a surface facing the side of the test object, restrains the acoustic wave, which reaches a part except the movable area, from being reflected to the side of the acoustic wave source.

Description

The present invention relates to an electromechanical transducer such as a capacitive ultrasonic transducer and a device such as a subject diagnostic apparatus using the same.

In general, imaging devices using X-rays, ultrasound, and MRI (nuclear magnetic resonance imaging) are widely used in the medical field. On the other hand, research on an optical imaging apparatus that obtains in-vivo information by propagating light emitted from a light source such as a laser into a subject and detecting the propagating light or the like is also progressing in the medical field. One such optical imaging technique is Photoacoustic Tomography (PAT: Photoacoustic Tomography).

In recent years, a capacitive ultrasonic transducer (CMUT) using micromachining technology has been actively studied. This CMUT transmits and receives ultrasonic waves using a lightweight vibrating membrane, and excellent broadband characteristics can be easily obtained in liquid and gas. Ultrasonic diagnosis with higher accuracy than the conventional medical diagnostic modality using this CMUT is attracting attention as a promising technology. Since a general CMUT element is manufactured on a silicon wafer, a part of the incident acoustic wave is transmitted through the silicon wafer, and the reflected wave reflected at the interface between the back side of the silicon wafer and air is applied to the element. May come back. Since this reflected wave becomes noise, it has been proposed to provide an acoustic backing material to prevent the reflected wave (see Patent Document 1). In addition, in this specification, an acoustic wave includes what is called a sound wave, an ultrasonic wave, and a photoacoustic wave. For example, an acoustic wave generated inside the measurement target by irradiating the measurement target with light (electromagnetic wave) such as visible light or infrared, or a reflected acoustic wave transmitted inside the measurement target and reflected inside the measurement target including.

US Patent No. 6831394

For example, when the direction in which an acoustic wave generated from a subject or the like is transmitted cannot be predicted, if the conventional ultrasonic transducer is used as it is, the acoustic wave is generated in a portion other than the CMUT element (such as the outer circumference of the ultrasonic transducer). Is reflected. The reflected acoustic wave may reach a subject such as a living tissue and distort the desired acoustic wave. In addition, since it is reflected again on the subject side and returns to the CMUT, it becomes noise when a desired acoustic wave is detected. Further, since the intensity of the reflected wave differs depending on the incident angle of the acoustic wave, there is a possibility that the range in which the acoustic wave generated from the subject can be detected at a time becomes narrow.

In view of the above problems, an electromechanical transducer such as a capacitive ultrasonic transducer of the present invention includes an electromechanical transducer element having a movable region for receiving an acoustic wave emitted from a subject, and the electric machine. An electrical wiring board that is electrically connected to the conversion element and a reflection suppression layer are included. The reflection suppressing layer is provided on at least a part of the surface facing the subject other than the movable region, and the acoustic wave reaching the region other than the movable region is reflected to the acoustic wave source side. It is characterized by suppression.

In the present invention, it is possible to improve the detection performance (S / N) of the acoustic wave generated from the measurement target by suppressing the reflected wave from the part other than the movable region of the electromechanical conversion element. In addition, the detection range of the acoustic wave can be expanded, and the detection time can be shortened.

The figure which shows the basic structural example of the electromechanical conversion element of the electromechanical conversion apparatus of this invention. The figure which shows Example 1 of the electromechanical converter of this invention. The figure explaining the comparative example 1. FIG. The figure explaining the deformation | transformation form of Example 1, and the comparative example 2. FIG. The figure which shows Example 2 of the electromechanical converter of this invention. The figure explaining Example 3 and the comparative example 3 of the electromechanical converter of this invention. The figure which shows Example 4 and 5 of the electromechanical converter of this invention. The figure which shows Example 6 which concerns on the subject diagnostic apparatus of this invention.

In the present invention, a reflection suppressing layer is provided on at least a part of the surface of the device facing the acoustic wave source side at the time of use other than the movable region of the cell, so that the acoustic wave reaching the movable region is reflected to the acoustic wave source side. It is characterized by suppressing things to do. What is necessary is just to design where it provides in such a surface according to a case. In the examples described later, an example is shown in which the electric wiring board, the sensor unit, and the case are provided on such a surface. Since the reflection suppressing layer only needs to suppress reflection, it is sufficient to transmit or absorb acoustic waves, and an acoustic wave transmitting layer or an acoustic wave absorbing layer can be used alone or in combination. For example, the transmission layer can be defined as a layer having an acoustic impedance that allows an error of about ± 10% of the value of the acoustic impedance to be completely transmitted, and the acoustic wave attenuation factor is not limited.

That is, Z ₁ : impedance of the first object in contact with the transmission layer, Z ₂ : impedance of the _second object in contact with the transmission layer, Z ₃ = (Z ₁ × Z ₂ ) ^0.5 : transmission through the complete transmission The layer impedance is as follows. 0.9 × Z ₃ <impedance to be regarded as a transmission layer <1.1 × Z ₃ . For example, the absorption layer can be defined as a layer in which the difference in acoustic impedance with an object in contact is within about 20% and the acoustic wave attenuation factor is about 3 [dB / cm] or more. In the examples described later, an example in which an acoustic wave attenuating material is provided on the back side of the electric wiring board or the substrate of the sensor unit is shown, but attenuation and absorption represent the same function. Further, in the electromechanical transducer of the present invention, not only the electrostatic capacitance type electromechanical transducer described in the embodiments described later but also a piezoelectric ultrasonic probe that is a conventional piezoelectric electromechanical transducer is used. You can also do things.

Embodiments of the present invention will be described below with reference to the drawings.
Example 1
A capacitive ultrasonic transducer that is Embodiment 1 of the electromechanical transducer of the present invention will be described. FIG. 1A shows a top view of the basic structure of the ultrasonic conversion element of this conversion device, and FIG. 1B shows a cross-sectional view taken along line AA ′ of FIG.

In the element 10 of the capacitive ultrasonic transducer of this embodiment, the first electrode (lower electrode) 2 and the second electrode (upper electrode) 3 are opposed to each other on the substrate 1 with a cavity 4 serving as a gap. Is provided. An insulating film 5 is disposed between the first electrode 2 and the second electrode 3 facing each other. The second electrode 3 is wired on the membrane 6 and connected to a second electrode pad 7 for applying a voltage. On the other hand, the first electrode 2 has a first electrode pad 8 for applying a voltage. In FIG. 1, four cells 9 which are the minimum unit of the capacitive ultrasonic transducer are connected by the second electrode 3 to constitute one element 10. As the substrate 1, various commercially available substrates such as a silicon wafer and a glass substrate can be used. The first electrode 2 and the second electrode 3 can be formed of at least one material of Al, Cr, Ti, Au, Pt, and Cu, but may be other conductive materials. The cavity 4 may be filled with air or gas, and may be set to a pressure lower than the atmospheric pressure depending on the manufacturing method. The insulating film 5 can be formed of SiN or SiO _2, but other insulating materials may be used. The membrane 6 can use a desired material such as a metal such as Si, SiN, or Al.

When a bias voltage is applied between the first electrode 2 and the second electrode 3 of such an element 10, the distance between the first electrode 2 and the second electrode 3 changes according to the amount of bias voltage applied. In this state, when an acoustic wave enters the membrane 6 from the outside, the movable region 16 of the membrane 6 vibrates as a vibration film. Due to the vibration of the movable region 16, the capacitance between the first electrode 2 and the second electrode 3 changes. By detecting this change in capacitance as a change in voltage, it is possible to detect an incident acoustic wave. Conversely, when an electric signal such as a pulse waveform is applied to the second electrode 3 with a bias voltage applied, an acoustic wave can be transmitted. The element as shown in FIG. 1 can be manufactured by using a known method such as a micromachining process such as surface micromachining or bulk micromachining.

FIG. 2 (a) shows a top view of the ultrasonic transducer of this embodiment including the above-mentioned element which is an electromechanical transducer, and FIG. 2 (b) shows a cross section taken along line BB ′ of FIG. 2 (a). The figure is shown. A plurality of ultrasonic conversion elements 10 as shown in FIG. 1 are gathered to form the sensor unit 11 in FIG. An electric wiring board 13 such as a PCB board is disposed around the sensor unit 11 to make electrical connection with each element 10. The electrical wiring board 13 has electrical wiring, and electrical signals can be transmitted and received through the electrical wiring board 13 by being connected to the electrode pads 7 and 8 of each element 10 by wire bonding or the like.

In the present embodiment, as shown in FIG. 2, the first antireflection layer 12 is provided on the electric wiring board 13. A first acoustic attenuating material 14 that supports the element 10 is provided on the back surface of the sensor unit 11 opposite to the substrate 1. Furthermore, a second acoustic attenuating material 15 is provided on the side opposite to the reflection suppressing layer 12 with respect to the electric wiring board 13 (that is, the back of the electric wiring board 13). In FIG. 2B, the surface of the first antireflection layer 12 protrudes outside the surface of the element 10, but the position where the first antireflection layer 12 is provided is the surface of the element 10. Or the surface of the element 10 may be the forefront. In the present embodiment, it is assumed that the acoustic impedance matching material 25 is provided on the surface side of the element 10 or the first antireflection layer 12 when the acoustic wave is received. The acoustic impedance matching material is a substance for obtaining acoustic matching between the subject and the element 10, or between the holding member that holds the subject and the element, and is generally a gel or water. It is liquid.

Here, consider a case where the first antireflection layer 12 is a transmission layer and is provided between the electrical wiring board 13 and the acoustic impedance matching material 25 as shown in FIG. At this time, the acoustic impedance of the transmission layer is preferably larger than that of the matching material 25 and smaller than that of the electric wiring board 13. For example, the matching material 25 is water, the acoustic impedance of water is Z ₁ = 1.5 [MRayl], the electrical wiring board 13 is a glass epoxy board, and the acoustic impedance of the glass epoxy board is Z ₂ = 5.8 [MRayl]. The case is as follows. In this case, the acoustic impedance Z ₃ of the transmissive layer 12, is preferably in the range of 1.5~5.8 [MRayl]. More preferably, Z ₃ ≈2.95 [MRayl]. Examples of the material having such acoustic impedance include silicone rubber, silicone gel, acrylic resin, acrylic gel, and epoxy resin. In the above case, an epoxy-based adhesive is preferable, but any material can be used as long as a desired acoustic impedance can be obtained. The transmission layer 12 is preferably provided on a surface that reflects incident acoustic waves to the subject side. More preferably, it is provided on the outermost surface of the surface that reflects the incident acoustic wave to the subject side. In the present specification, the fact that the acoustic impedance is matched or the acoustic impedance is equivalent means that the difference between the acoustic impedance values of two different substances is about 20% or less.

Further, consider the case where the first antireflection layer 12 is an absorption layer, as shown in FIG. At this time, the acoustic impedance of the absorption layer is preferably equal to that of the acoustic impedance matching material 25. For example, when the matching material 25 is water and the acoustic impedance of water is Z ₁ = 1.5 [MRayl], the following occurs. Preferable materials include silicone gel, polybutadiene gel, low hardness silicone rubber, urethane rubber, and the like. The absorption layer 12 must have a function of absorbing acoustic waves. When the material contains high-density fine particles, it is possible to adjust acoustic impedance and improve acoustic wave absorption. Examples of the fine particles include tungsten, alumina, copper or a compound thereof, platinum, iron or a compound thereof. In the above case, the acoustic impedance can be adjusted to about 1.8 [MRayl] by mixing and curing about 10 wt% of tungsten fine particles in urethane rubber. The attenuation factor at that time is about 50 [dB / cm] at 1 MHz. In any case, a material that can obtain desired acoustic impedance and desired absorption may be used. The position where the absorption layer 12 is provided is also preferably provided on a surface that reflects incident acoustic waves to the subject side. More preferably, it is preferably provided on the outermost surface of the surface that reflects the incident acoustic wave to the subject side.

The first acoustic attenuating material 14 is preferably matched to the acoustic impedance of the substrate 1. For example, when the substrate 1 is silicon and the acoustic impedance is 19 [MRayl], the first acoustic attenuating material 14 is a material as disclosed in Patent Document 1 (polyvinyl chloride (PVC) with tungsten particles). May be used). The position where the first acoustic attenuation layer 14 is provided is preferably provided on the back surface of the receiving surface that receives the incident acoustic wave. More preferably, it is preferably provided only in the region on the back side of the substrate 1. When exceeding the area | region of the back side of the board | substrate 1, it is necessary to match the acoustic impedance of the exceeding part and parts other than the board | substrate 1. FIG.

The second acoustic damping material 15 is also preferably matched with the electrical wiring board 13 and acoustic impedance. For example, consider the case where the electrical wiring board 13 is a glass epoxy board and the acoustic impedance is Z ₂ = 5.8 [MRayl]. Preferable materials include viscoelastic bodies such as urethane resins and epoxy resins. When these materials contain high-density fine particles, it is possible to realize adjustment of acoustic impedance and improvement of acoustic wave absorption. The fine particles include tungsten, alumina, copper or a compound thereof, platinum, iron or a compound thereof. Specifically, the acoustic impedance is reduced to about 5.8 [MRayl] by mixing and curing about 1 wt% of alumina particles (30 μm to 40 μm) with epoxy resin (for example, LOCTITE # 3036 / trade name made by Henkel). Can be adjusted. The attenuation factor at that time is about 9 [dB / cm] at 1 MHz. In any case, a material that can obtain desired acoustic impedance and desired absorption may be used. The position where the second acoustic attenuating material 15 is provided is preferably provided on the back side of the surface that reflects the incident acoustic wave to the subject side. More preferably, it is preferably provided only in the region on the back side of the electrical wiring board 13. When exceeding the area | region of the back side of the electrical wiring board 13, it is necessary to match the acoustic impedance of the exceeding part and parts other than the electrical wiring board 13. FIG.

Next, Comparative Example 1 will be described with reference to FIG. FIG. 3 illustrates Comparative Example 1 when an acoustic wave generated by the photoacoustic effect is received by a general ultrasonic transducer without using the electromechanical transducer of the present invention.

In the ultrasonic transducer shown in FIG. 3A, an ultrasonic transducer element 10 is formed on a substrate 1, and a first acoustic attenuating material 14 is provided on the back side thereof. An electrical wiring board 13 is disposed around the element 10 to establish electrical connection. For example, it is assumed that light absorbers 18, 19, 20 such as a tumor are present inside the subject 17 to be measured, and irradiation light 24 having a wavelength that is absorbed by the light absorber from outside the subject. Irradiate. Then, the light absorbers 18, 19, 20 absorb the irradiation light 24 and emit the respective acoustic waves 21, 22, 23. Each acoustic wave spreads in the direction of 360 degrees around each light absorber, and an acoustic wave reaching the element 10 of the ultrasonic transducer is detected. Thereby, the position and size of the light absorbers 18, 19, 20 existing inside the subject 17 can be detected. An acoustic impedance matching material 25 such as a liquid or gel may be provided between the ultrasonic transducer and the subject 17 in order to suppress reflection of acoustic waves at the interface with the subject 17.

When an acoustic wave is acquired from the subject 17 with the configuration shown in FIG. 3A, a part of the acoustic wave emitted from the light absorber may become noise. For example, when a part 26 of the acoustic wave emitted from the light absorber 18 is reflected by the surface of the electrical wiring board 13 and returns to the inside of the subject 17, the reflected wave is emitted from the light absorber 19. There is a possibility that a part of the acoustic wave 22 is canceled and distorted. In addition, the reflected wave 27 reflected from the surface of the electrical wiring board 13 may be reflected by the absorber 19 and overlap with a part 28 of the acoustic wave of the absorber 23. This makes it difficult to accurately detect the position and size of each absorber. The intensity of the reflected wave 27 from the electrical wiring board 13 increases as the acoustic impedance difference between the electrical wiring board 13 and the outside (for example, the acoustic impedance matching material 25) increases. Further, the intensity of the reflected wave 27 varies due to the difference in the incident angle to the electrical wiring board 13. In order to accurately acquire an acoustic wave with the configuration as shown in FIG. 3A, the reflected wave 27 is reduced or the light irradiation range 29 is narrowed so that the acoustic wave reaching the electrical wiring board 13 is reflected. It is necessary to make sure that there is no influence.

A reflected wave and a transmitted wave generated at the interface between the electrical wiring board 13 and the outside (for example, the acoustic impedance matching material 25) will be described with reference to FIG. In general, at the interface 30 between two substances, an acoustic wave is incident from the liquid side such as a solution or gel, and the reflection intensity and transmission intensity of the acoustic wave generated at the solid interface such as the electrical wiring board 13 are expressed by the following equations 1 to 3. Can be represented by Where φ _i : incident wave, φ _r : reflected wave, θ _i : incident angle = reflection angle, θ _L : transmission angle (longitudinal wave), θ _T : transmission angle (transverse wave), φ _T : transmitted wave (transverse wave) , Φ _L : transmitted wave (longitudinal wave), R _w : reflection intensity, R _φ : velocity potential of the reflected wave, Z: liquid side acoustic impedance, Z _L : transmitted wave acoustic impedance (longitudinal wave), Z _T : Acoustic impedance of the transmitted wave (transverse wave), T _w ^T : Transmission intensity of the transverse wave transmission wave, T _φ ^T : Velocity potential of the transverse wave transmission wave, T _W ^L : Transmission intensity of the longitudinal wave transmission wave, T _φ ^L : Longitudinal wave transmission Wave velocity potential, ρ: liquid density, ρ ₂ : solid density.

The acoustic impedance at this time can be expressed by Equation 4 below on the liquid side and Equation 5 on the solid side. Also, from the definition of refraction, Equation 6 is derived, and when C _L > C and C _T > C, there are times when the refraction angles θ _L and θ _T = 90 degrees at a certain incident angle. The incident angles at this time are called critical angles θ _icL and θ _icT, and are expressed by equations 7 and 8. The reflection intensity varies greatly at the critical angle. Where C: sound velocity of liquid, C _L : sound velocity of individual (transverse wave), C _T : sound velocity of individual (longitudinal wave).
(Formula 4) Z = Cρ / cos θ _i
(Expression 5) Z _L = C _L ρ ₂ / cos θ _L , Z _T = C _T ρ ₂ / cos θ _T
(Equation _{6) cosθ i / C = cosθ} L / C L = cosθ T / C T
(Expression 7) θ _icL = sin ⁻¹ (C / C _L )
(Formula 8) θ _icT = sin ⁻¹ (C / C _T )

For example, when the electrical wiring board 13 is a board such as FR-4 material for a multilayer printed wiring board and the acoustic impedance matching material 25 is water, reflected waves and transmitted waves generated at the interface are shown in FIG. It becomes like. The vertical axis | shaft of FIG.3 (c) has shown the ratio of intensity | strength. If R _w = 1, complete reflection is indicated. The horizontal axis represents the incident angle of the acoustic wave. C = 1500 [m / s], C _L = 3521 [m / s], C _T = 2240 [m / s], ρ = 1000 [kg / m ³ ], ρ ₂ = 2148 [kg / m ³ ] For this reason, the critical angles are θ _{icL ≈25} ° and θ _{icT ≈42} °, and the intensity of the reflected wave varies greatly around the critical angle. The reflection intensity ratio is as high as 0.34 at the minimum. In order to obtain a desired acoustic wave signal stably, the incident angle must be 25 ° or less, and the range that can be irradiated with light at one time is limited, so it is necessary to inspect a wide range of subjects. It turns out that efficiency falls.

The effects of the present invention including the present embodiment with respect to Comparative Example 1 will be described with reference to FIG. However, in FIG. 4A, an ultrasonic transducer that lacks the second acoustic attenuating material 15 which is a modified form of the present embodiment is used. First, with reference to FIG. 4, a description will be given of how acoustic waves are acquired and the effects thereof using the ultrasonic transducer apparatus according to this modified embodiment. For example, the electric wiring board 13 is a board such as FR-4 material for multilayer printed wiring boards, and an epoxy resin (Young's modulus = 3 [GPa], Poisson's ratio = 0.3) as a matching layer (reflection suppression layer) 12 thereon. ) Is placed. When the acoustic impedance matching material 25 is water, reflected waves and transmitted waves generated at the interface with the matching layer 12 are as shown in FIG. The vertical axis in FIG. 4B also shows the intensity ratio. The horizontal axis represents the incident angle of the acoustic wave. Here, C = 1500 [m / s], C _L = 2010 [m / s], C _T = 1002 [m / s], ρ = 1000 [kg / m ³ ], ρ ₂ = 1150 [kg / m] ³ ], the critical angle is only θ _{icL ≈48} °, and the critical angle is wider than in Comparative Example 1 above. The reflection intensity ratio is less than the critical angle and as low as 0.052. Thereby, until the incident angle is 48 °, the influence of the surface reflected wave is greatly suppressed and a stable reception signal (acoustic wave is received by the element and converted) can be obtained. In addition, since the range in which light can be irradiated at a time is wider than in Comparative Example 1, it is possible to improve the inspection efficiency even when it is desired to inspect a wide range of subjects.

Next, Comparative Example 2 in the case where the reflection suppressing layer 12 and the second acoustic attenuation material 15 are not provided will be described with reference to FIG. In Comparative Example 1 above, the reflection intensity and transmission intensity generated on the outermost surface of the ultrasonic transducer when the matching layer 12 is not provided are shown in FIG. In FIG. 3C, the transmitted acoustic waves T _wt and T _wl pass through the inside of the electric wiring board 13 and are reflected at the interface 33 on the back side, as shown in FIG. 4C. In this case, for example, the back side of the electric wiring substrate 13 of the acoustic impedance Z ₁ is, if the acoustic impedance of Z ₂ air, the reflection intensity R _i, the transmitted intensity T _i The following equation 9, the equation 10.
(Formula 9) R _i = (Z ₂ −Z ₁ ) ² / (Z ₂ + Z ₁ ) ²
(Formula 10) T _i = 4Z ₁ Z ₂ / (Z ₂ + Z ₁ ) ²

Assuming that the acoustic impedance of air is Z ₂ = 0.00041 [MRayl] and the acoustic impedance of the electrical wiring board 13 is Z ₁ = 5.8 [MRayl], the reflection intensity R _i = 0.999 [Watts / m ² ] in the above equation 9 Total reflection. Further, the reflected wave 32 reflected by the back-side interface 33 returns to the subject side while maintaining the intensity from the transmission intensity T _i = 2.83 × 10 ⁻⁴ [Watts / m ² ] in the above equation 10. For this reason, it is necessary to suppress not only the reflected wave 27 from the interface 30 (see FIG. 3A) but also the reflected wave 32 from the interface 33.

As shown in FIGS. 2B and 2C, the reflected wave 32 from the interface 33 returns to the subject side even in the case of the present embodiment in which the matching layer 12 is provided, but this reflected wave 32 is suppressed. What you can do is explained below. In the configuration of FIG. 2C, an acoustic wave transmitted through the transmission layer of the first reflection suppression layer 12 that is a matching layer will be described. The acoustic wave generates a reflected wave 35 with an intensity of about 0.11 [Watts / m ² ] at the interface 34 with the electrical wiring board 13, but transmits the remaining about 0.89 [Watts / m ² ]. The transmitted wave 31 that has passed through the electrical wiring board 13 reaches the interface 33. The second acoustic attenuating material 15 is an object in which the acoustic impedance is substantially matched with the electrical wiring board 13. The materials are as described above. When this is adhered to the back side of the electrical wiring board 13 with an epoxy resin as the second acoustic attenuation member 15 having a thickness of 2 cm, the reflected wave 32 from the interface 33 becomes almost zero. Further, when the back side of the second sound attenuating material 15 is air, complete reflection occurs at the interface 36. The reflection intensity when the reflected wave from the interface 36 returns to the subject side is obtained from the attenuation factor and the above equations 9 and 10, and is about 1.2% of the intensity of the transmitted wave 31. From this, it can be seen that the intensity of the reflected wave can be significantly suppressed as compared with Comparative Example 2 by the ultrasonic transducer of the present embodiment shown in FIGS. 2 (b) and 2 (c).

(Example 2)
FIG. 5 shows a second embodiment of the present invention. In FIG. 5, a third antireflection layer 37 is provided on the electrical wiring substrate 13. The third antireflection layer 37 is an acoustic attenuation material. The acoustic impedance of the acoustic attenuating material is a thing that is substantially matched with the acoustic impedance of the external environment (for example, the acoustic impedance matching material 25).

The material is a material in which high-density fine particles are contained in a viscoelastic body such as urethane resin. The fine particles include tungsten, alumina, copper or a compound thereof, platinum, iron or a compound thereof. Specifically, about 10 wt% of tungsten particles (for example, 2.1 to 2.5 μm / particles manufactured by Allied Material Co., Ltd.) are mixed with special urethane rubber (for example, trade name manufactured by Flexane94L / DEVCON) and cured. . Thereby, the acoustic impedance can be adjusted to about 1.8 [MRayl]. The attenuation factor at that time was about 50 [dB / cm] at 1 MHz. When this is used as a third reflection suppression layer 37 having a thickness of 0.5 cm and adhered to the surface of the electrical wiring board 13 with an epoxy resin, the reflected wave 39 from the liquid-solid interface becomes about 1%.

A commercially available ultrasonic acoustic absorption tile or the like may be used as the third antireflection layer 37 as long as the external environment and the acoustic impedance substantially match. Further, it is also possible to combine the present embodiment with Example 1 (an example in which a matching layer is provided on the outermost surface and an example in which a matching layer is provided on the outermost surface and an acoustic damping material is provided on the back surface of the electric wiring board). .

(Example 3)
A third embodiment of the present invention will be described with reference to FIG. FIG. 6A is an enlarged view of the central portion of the cross section of the ultrasonic transducer according to the present embodiment, and a reflection suppression layer 44 is provided on a part of the sensor unit inside. The space 40 between the ultrasonic transducer elements 10 constituting the sensor unit is made of the same material as that of the substrate 1 or a state in which a thin film such as SiO ₂ or SiN is formed on the substrate 1. Yes. Since the acoustic impedance between the ultrasonic transducer elements 10 and the external environment (for example, the acoustic impedance matching material 25) does not match, a part of the incident acoustic wave 41 is reflected and a reflected wave 42 is generated. A part of the incident acoustic wave 41 is transmitted, passes through the substrate 1 as a transmitted wave 43, reaches the acoustic attenuation material 14, and is absorbed. The reflected wave 42 at this time becomes noise of the received signal when returning to the subject side as in the first comparative example. Therefore, a reflection suppressing layer 44 is provided on the upper portion 40 between the ultrasonic transducer elements 10. That is, the reflection suppression layer 44 is provided on a surface that is outside the movable region and faces the acoustic wave source side when used between the electromechanical conversion elements. Thereby, the same effect as Example 1, 2 can be acquired.

As a comparative example 3 with respect to this, the reflected wave 42 generated in the portion without the reflection suppression layer 44 will be described below. Specifically, FIG. 6B shows reflection and transmission when the distance 40 between the ultrasonic transducer elements 10 is Si (Young's modulus = 169 [Gpa], Poisson's ratio = 0.3). The vertical axis in FIG. 6B also shows the intensity ratio. The horizontal axis represents the incident angle of the acoustic wave. At the interface between the outside world (for example, water) and Si, C = 1500 [m / s], C _L = 9881 [m / s], C _T = 5339 [m / s], ρ = 1000 [kg / m ³ ] , Ρ ₂ = 2330 [kg / m ³ ]. Therefore, the critical angles are θ _{icL ≈8.7} ° and θ _{icT ≈16.3} °. In this way, the intensity of the reflected wave varies greatly around the critical angle. The reflection intensity ratio is as high as 0.7 at the minimum. In order to obtain a stable received signal, it is necessary to make the incident angle 8.7 ° or less, and the range in which light can be irradiated at a time is limited, so that the examination efficiency is lowered when it is desired to examine a wide range of subjects.

On the other hand, in the case of the present embodiment in which the reflection suppressing layer 44 is provided, a reflected wave generated in that portion will be described. For example, when a matching layer is provided as the reflection suppressing layer 44, a material such as glass epoxy can be used. At this time, C = 1500 [m / s], C _L = 3521 [m / s], C _T = 2240 [m / s], ρ = 1000 [kg / m ³ ], ρ ₂ = 2148 [kg / m] ³ ]. Accordingly, the critical angles are θ _{icL ≈25} ° and θ _{icT ≈42} °, and the critical angles can be widened as compared with the state without the reflection suppression layer 44. That is, almost the same result as in FIG. 3C can be obtained. Furthermore, by providing an epoxy resin (Young's modulus = 3 [GPa], Poisson's ratio = 0.3) as a separate matching layer on the matching layer of glass epoxy, the critical angle is further expanded as shown in FIG. 4B. I can do things. In this way, a more stable received signal can be obtained than in the state without the reflection suppression layer 44.

The transmitted wave 43 is transmitted and absorbed by the first acoustic attenuation material 14 present on the back side of the substrate 1. The first acoustic absorber 14 may be a material as described above. The acoustic absorbing material 14 and the reflection suppressing layer 44 can be provided using a known method such as micromachining or transfer. Further, even if the reflection suppressing layer 44 is provided in a portion (see FIG. 1) other than the movable region 16 of the minimum unit cell 9 constituting the ultrasonic conversion element 10, the same effect can be exhibited. Furthermore, it is possible to combine the first to third embodiments with the present embodiment.

In the above configuration, the reflection suppressing layer 44 may be an acoustic attenuation material. In that case, the same effect as that of the second embodiment can be obtained by providing the same material as that of the second embodiment between the ultrasonic conversion elements 10. Further, even when the reflection suppressing layer 44 is made of an acoustic attenuation material, the same effect can be exhibited if it is provided in a portion other than the movable region 16 of the minimum unit cell 9 constituting the element 10. Furthermore, it is possible to combine the first to third embodiments with this modification.

Example 4
FIG. 7A shows a fourth embodiment of the present invention. In FIG. 7A, the electrical wiring board 13 is arranged at a certain angle with respect to the acoustic wave receiving surface of the ultrasonic transducer 10. Typically, the element 10 is installed in a direction perpendicular to the receiving surface that receives the acoustic wave and at an angle greater than 90 degrees. A reflection suppressing layer 12 is disposed on the electrical wiring board 13, and a second acoustic attenuation material 15 is disposed on the back side of the electrical wiring board 13. A first sound attenuating material 14 is disposed on the back side of the ultrasonic conversion element 10. The element 10 and the electric wiring board 13 are connected via a flexible wiring 45. The flexible wiring 45 is covered with the reflection suppressing layer 12. In such a configuration, the reflected wave 47 of a part 46 of the incident acoustic wave can be reflected in a direction other than the subject. Thereby, reflection to the subject side can be suppressed. By adjusting the angle α between the electrical wiring board 13 and the receiving surface of the element 10, a desired irradiation range can be obtained and a desired inspection efficiency can be achieved.

In FIG. 7A, the reflection suppression layer 12 and the second acoustic attenuation material 15 are provided, but the effect of suppressing reflection to the subject side can be obtained by providing either one. It is also possible to combine the first to third embodiments with the present embodiment.

(Example 5)
FIG. 7B shows a fifth embodiment of the present invention. In FIG. 7B, the ultrasonic transducer is housed in the case 48. The case 48 may be a hollow or a molded product integrated with a resin or the like. In this case, a reflected wave may be generated at the interface between the case surface and the outside. Therefore, the reflection wave to the subject side can be suppressed by providing the reflection suppression layer 49 on the surface of the case or combining with the configuration described in the first to fourth embodiments. In addition, it is also possible to suppress the reflected wave by using a material on the case surface on which the acoustic wave is incident that does not generate a reflected wave at the interface with the outside world.

(Example 6)
FIG. 8 shows a subject diagnosis apparatus or photoacoustic measurement apparatus that is Embodiment 6 of the present invention. The light source 50 is, for example, a light source that generates laser light, and the light 24 is, for example, pulsed laser light.

In this apparatus, when the irradiation light 24 emitted from the light source 50 toward the subject 17 strikes the light absorber 51 inside the subject, an acoustic wave 52 called a photoacoustic wave is emitted by the photoacoustic effect. The frequency of the acoustic wave 52 is about 300 kHz to 10 MHz, although it varies depending on the substance constituting the light absorber 51 and the size of the individual. The acoustic wave 52 passes through the acoustic impedance matching material 25 with good propagation, and is detected by the ultrasonic transducer 53. The signal subjected to the current voltage amplification is sent to the signal processing unit 55 via the signal line 54. The detected signal is signal-processed by the signal processing unit 55, and the physical information of the subject is extracted. The signal processing unit 55 is mainly a computer, but part of the signal processing unit 55 may be an integrated circuit and can reconstruct a two-dimensional or three-dimensional image. As the ultrasonic transducer 53, the ones of Examples 1 to 5 described above can be used.

The electromechanical transducer of the present invention can be applied to an optical imaging apparatus that obtains information in a measurement target such as a living body, a conventional ultrasonic diagnostic apparatus, and the like. Furthermore, it can be applied to other uses such as an ultrasonic flaw detector.

DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 9 ... Cell, 10 ... Electromechanical conversion element, 12, 37, 44, 49 ... Antireflection layer, 13 ... Electric wiring board, 14, 15, 37 ... Acoustic damping material, 16 ... Movable area, 25 ... Acoustic impedance matching material, 48 ... Case

Claims (10)

An electromechanical transducer element having a movable region for receiving an acoustic wave emitted from a subject;
An electrical wiring board that is electrically connected to the electromechanical transducer element;
A reflection suppressing layer that is provided on at least a part of the surface facing the subject side other than the movable region and suppresses reflection of the acoustic wave reaching the non-movable region to the acoustic wave source side;
The electromechanical converter characterized by having. The electrical wiring board is disposed around the electromechanical conversion element,
The electromechanical transducer according to claim 1, wherein the reflection suppression layer is provided on a surface of the electric wiring board facing the subject. The electromechanical transducer according to claim 2, wherein an acoustic attenuating material is provided on a side opposite to the reflection suppressing layer with the electric wiring board interposed therebetween. Comprising a plurality of the electromechanical transducer elements;
4. The electromechanical transducer according to claim 1, wherein the reflection suppression layer is provided on a surface other than the movable region and facing the subject. 5. The electromechanical transducer according to claim 3, wherein an acoustic impedance of the acoustic damping material is equal to an acoustic impedance of the electrical wiring board or the board. 6. The electromechanical transducer according to claim 1, wherein the reflection suppression layer includes at least one of an acoustic wave transmission layer and an acoustic wave absorption layer. The acoustic impedance of the transmissive layer is greater than the acoustic impedance of the subject side of the two interfaces contacting the transmissive layer and smaller than the acoustic impedance of the opposite side, and the acoustic impedance of the absorbent layer is in contact with the absorbent layer The electromechanical transducer according to claim 6, characterized in that, of the two interfaces, the acoustic impedance of the subject side is equivalent. 8. The electrical wiring board according to claim 1, wherein the electromechanical conversion element is installed at an angle greater than 90 degrees with respect to a direction perpendicular to a receiving surface that receives an acoustic wave. 9. The electromechanical transducer according to item 1. The electromechanical conversion element and the electrical wiring board are housed in a case,
The electromechanical transducer according to any one of claims 1 to 8, wherein the reflection suppression layer is provided on a surface of the case facing the subject side. The electromechanical transducer according to any one of claims 1 to 9,
A light source that generates light in pulses;
A signal processing unit for processing a signal output from the electromechanical transducer;
Have
A photoacoustic wave generated by the light emitted from the light source and applied to the subject is detected by the electromechanical conversion device, and the converted signal is processed by the signal processing unit to acquire information inside the subject. A diagnostic apparatus for a subject characterized in that

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