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JP2012100123

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2012100123
The present invention provides an electromechanical transducer capable of improving detection
performance of an acoustic wave generated from an object to be measured by suppressing a
reflected wave from a portion other than a movable region of an electromechanical transducer
element. An electromechanical transducer such as a capacitive ultrasonic transducer includes an
electromechanical transducer (10) having a movable area (16) for receiving an acoustic wave
emitted from a subject, and the element (10) electrically It has the electric wiring board 13 which
makes a connection, and the reflection suppression layer 12. The reflection suppression layer 12
is provided on at least a part of the surface facing the subject side other than the movable region,
and suppresses the reflection of the acoustic wave reaching the region other than the movable
region to the acoustic wave source side. [Selected figure] Figure 2
Electromechanical converter
[0001]
The present invention relates to an electromechanical transducer such as a capacitive ultrasonic
transducer, and a device such as an object diagnostic device using the same.
[0002]
In general, imaging devices using X-rays, ultrasound, MRI (nuclear magnetic resonance imaging)
are widely used in the medical field.
04-05-2019
1
On the other hand, research on an optical imaging apparatus for obtaining information in a living
body by propagating light irradiated from a light source such as a laser into a subject and
detecting propagation light and the like is also advanced in the medical field. One such optical
imaging technology is Photoacoustic Tomography (PAT).
[0003]
In recent years, capacitive ultrasonic transducers (CMUTs) using micromachining technology
have 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 conventional medical diagnostic
modalities using this CMUT is attracting attention as a promising technology. Since a typical
CMUT element is fabricated on a silicon wafer, part of the incident acoustic wave is transmitted
through the silicon wafer, and the reflected wave reflected at the interface between the back of
the silicon wafer and air is transmitted to the element. It 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 the present specification, the acoustic wave includes
what are called sound waves, ultrasonic waves, and photoacoustic waves. For example, an
acoustic wave generated inside the measurement object by irradiating the inside of the
measurement object with light (electromagnetic wave) such as visible light or infrared light, or a
reflected acoustic wave that transmits the acoustic wave inside the measurement object and is
reflected inside the measurement object including.
[0004]
U.S. Patent No. 683 1394
[0005]
For example, when the direction of propagation of the acoustic wave generated from the subject
etc. can not be predicted, if the conventional ultrasonic transducer is used as it is, the acoustic
wave is generated in parts other than the elements of the CMUT (such as the outer periphery of
the ultrasonic transducer). Is reflected.
The reflected acoustic wave may reach an object side such as a living tissue and distort the
desired acoustic wave. Further, since the light is reflected again on the object side and returned
04-05-2019
2
to the CMUT, it becomes noise when detecting a desired acoustic wave. In addition, since the
intensity of the reflected wave varies depending on the incident angle of the acoustic wave, the
range in which the acoustic wave generated from the subject can be detected at one time may be
narrowed.
[0006]
In view of the above problems, an electromechanical transducer such as a capacitive ultrasonic
transducer according to the present invention comprises an electromechanical transducer having
a movable region for receiving an acoustic wave emitted from a subject, and the
electromechanical transducer It has an electrical wiring board which makes an electrical
connection with the conversion element, and a reflection suppression layer. The reflection
suppression layer is provided on at least a part of the surface facing the subject side other than
the movable region, and an acoustic wave reaching other than the movable region is reflected to
the acoustic wave source side. It is characterized by suppressing.
[0007]
In the present invention, the detection performance (S / N) of the acoustic wave generated from
the measurement target can be improved by suppressing the reflected wave from the part other
than the movable region of the electromechanical conversion element. Further, the detection
range of the acoustic wave can be expanded, and the detection time can be shortened.
[0008]
The figure which shows the example of a basic structure of the electro-mechanical transducer
element of the electro-mechanical transducer of this invention. BRIEF DESCRIPTION OF THE
DRAWINGS The figure which shows Example 1 of the electro-mechanical transducer of this
invention. FIG. 7 is a diagram for explaining a comparative example 1; FIG. 6 is a view for
explaining a modified embodiment of Example 1 and Comparative Example 2; The figure which
shows Example 2 of the electro-mechanical transducer of this invention. The figure explaining
Example 3 and the comparative example 3 of the electro-mechanical transducer of this invention.
The figure which shows Example 4 and 5 of the electro-mechanical transducer of this invention.
The figure which shows Example 6 which concerns on the object diagnostic apparatus of this
invention.
04-05-2019
3
[0009]
The present invention provides a reflection suppression layer on at least a part of the surface of
the device facing the acoustic wave source side in use other than the movable area of the cell,
and the acoustic wave reaching other than the movable area is reflected to the acoustic wave
source side It is characterized by suppressing what it does. Of these planes, it may be designed
according to the situation. In the later-described embodiment, an example provided on such a
surface of an electric wiring board, a sensor unit or a case is shown. The reflection suppression
layer only needs to suppress reflection, and thus it may transmit or absorb the acoustic wave,
and the acoustic wave transmission layer or the acoustic wave absorption layer can be used
alone or in combination. The transmission layer can be defined, for example, as a layer having an
acoustic impedance that allows an error of about ± 10% of the value of the completely
transmitted acoustic impedance as an allowable value, and the acoustic wave attenuation factor
does not matter.
[0010]
That is, Z1: the impedance of the first object in contact with the transmission layer, Z2: the
impedance of the second object in contact with the transmission layer, Z3 = (Z1 × Z2) <0.5>: the
impedance of the transmission layer which is completely transmitted As follows. 0.9× Z3
<impedance considered as transmission layer <1.1 × Z3. The absorption layer can be defined as,
for example, a layer having a difference in acoustic impedance with an object in contact of about
20% or less and an acoustic wave attenuation factor of about 3 [dB / cm] or more. Although an
example in which the acoustic wave attenuation material is provided on the back side of the
electric wiring substrate or the substrate of the sensor unit is shown in the embodiment
described later, the attenuation and the absorption represent the same function. Further, in the
electromechanical transducer of the present invention, not only the capacitive electromechanical
transducer described in the following embodiment but also a piezoelectric ultrasonic probe or the
like which is a conventional piezoelectric electromechanical transducer is used. You can also do
things.
[0011]
An embodiment of the present invention will be described below with reference to the drawings.
04-05-2019
4
Embodiment 1 A capacitive ultrasonic transducer which is Embodiment 1 of the
electromechanical transducer according to the present invention will be described. The top view
of the basic structure of the ultrasonic transducer element of this converter is shown in FIG. 1 (a),
and the A-A 'sectional view of FIG. 1 (a) is shown in FIG. 1 (b).
[0012]
In the element 10 of the capacitive ultrasonic transducer of the present embodiment, the first
electrode (lower electrode) 2 and the second electrode (upper electrode) 3 are opposed to each
other on the substrate 1 with the cavity 4 as a gap therebetween. Is provided. Further, 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 form one element 10. The
substrate 1 may be any of various commercially available substrates such as silicon wafers and
glass substrates. The first electrode 2 and the second electrode 3 may be formed of at least one
material of Al, Cr, Ti, Au, Pt, and Cu, but may be another conductive material. The cavity 4 may be
filled with air or gas, and may be at a pressure lower than atmospheric pressure depending on
the manufacturing method. The insulating film 5 may be formed of SiN or SiO2, but may be
another insulating material. The membrane 6 can be made of a desired material such as Si, SiN,
or a metal such as Al.
[0013]
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 application of the bias voltage. In this state, when an acoustic wave is
incident on the membrane 6 from the outside, the movable region 16 of the membrane 6 vibrates
as a vibrating membrane. The vibration between the movable area 16 changes the capacitance
between the first electrode 2 and the second electrode 3. 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 in a state where a
bias voltage is applied, an acoustic wave can be transmitted. Elements such as FIG. 1 can be made
using known methods such as micromachining processes such as surface micromachining and
bulk micromachining.
04-05-2019
5
[0014]
FIG. 2 (a) shows a top view of the ultrasonic transducer of the present embodiment including the
element as described above which is an electromechanical transducer element, and FIG. 2 (b) is a
cross-sectional view taken along the line B-B 'of FIG. Figure shows. A plurality of ultrasonic
transducer elements 10 as shown in FIG. 1 are gathered to form the sensor unit 11 of FIG. 2 (a).
An electrical wiring board 13 such as a PCB board is disposed around the sensor unit 11 in order
to make an electrical connection with each element 10. The electric wiring board 13 has electric
wiring, and by connecting the electrode pads 7 and 8 of each element 10 by wire bonding or the
like, transmission and reception of electric signals can be performed via the electric wiring board
13.
[0015]
In the present embodiment, as shown in FIG. 2, the first reflection suppressing layer 12 is
provided on the electric wiring board 13. Further, on the back surface of the sensor unit 11 on
the opposite side of the substrate 1, a first sound attenuating material 14 for supporting the
element 10 is provided. Furthermore, a second acoustic attenuation material 15 is provided on
the opposite side to the reflection suppression layer 12 (that is, the back of the electric wiring
board 13) with the electric wiring board 13 interposed therebetween. In FIG. 2 (b), the surface of
the first reflection suppressing layer 12 protrudes outside the surface of the element 10, but the
position where the first reflection suppressing layer 12 is provided is the surface of the element
10. Alternatively, the surface of the element 10 may be brought to the front. Further, in the
present embodiment, it is assumed that the acoustic impedance matching material 25 is provided
on the surface side of the element 10 and the first reflection suppressing layer 12 at the time of
receiving the acoustic wave. The acoustic impedance matching material is a substance for
obtaining acoustic matching such as between the subject and the element 10, and between the
holding member for holding the subject and the element, and is generally a gel or water. It is a
liquid.
[0016]
Here, the case where the first reflection suppression layer 12 is a transmission layer and is
provided between the electric wiring board 13 and the acoustic impedance matching material 25
as shown in FIG. 2B will be considered. At this time, it is preferable that the acoustic impedance
04-05-2019
6
of the transmission layer is larger than the matching material 25 and smaller than the electric
wiring board 13. For example, in the case where the matching material 25 is water, the acoustic
impedance of water is Z1 = 1.5 [MRayl], the electric wiring substrate 13 is a glass epoxy
substrate, and the acoustic impedance of the glass epoxy substrate is Z2 = 5.8 [MRayl] It
becomes as follows. In this case, the acoustic impedance Z3 of the transmission layer 12 is
preferably in the range of 1.5 to 5.8 [MRayl]. More preferably, Z3 Z 2.95 [MRayl]. As materials
having such acoustic impedance, silicone rubber, silicone gel, acrylic resin, acrylic gel, epoxy
resin, etc. may be mentioned. 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 position
where the transmission layer 12 is provided is preferably provided on the surface that reflects
the incident acoustic wave to the object side. More preferably, the incident acoustic wave is
provided on the outermost surface of the surfaces reflecting to the object side. In the present
specification, that the acoustic impedances are matched or equal to each other means that the
difference between the acoustic impedance values of two different substances is about 20% or
less.
[0017]
Also, consider the case where the first reflection suppressing layer 12 is an absorbing layer, as
shown in FIG. 2 (b). At this time, it is preferable that the acoustic impedance of the absorption
layer be equal to that of the acoustic impedance matching material 25. For example, in the case
where the matching material 25 is water and the acoustic impedance of water is Z1 = 1.5
[MRayl], the following occurs. As preferable materials, silicone gel, polybutadiene gel, low
hardness silicone rubber, urethane rubber and the like can be mentioned. The absorbing layer 12
must have the function of absorbing acoustic waves. When the above-described material contains
fine particles of high density, it is possible to adjust the acoustic impedance and to improve the
absorption of the acoustic wave. 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 the urethane rubber. The attenuation factor at that time is about 50 [dB / cm] at
1 MHz. In any case, a material that can obtain a desired acoustic impedance and a desired
absorption may be used. Also for the position where the absorption layer 12 is provided, it is
preferable to provide the incident acoustic wave on the surface that reflects the object side. More
preferably, it is preferable to provide on the outermost surface of the surface that reflects the
incident acoustic wave to the object side.
[0018]
04-05-2019
7
It is preferable that the first acoustic attenuation material 14 be matched with the substrate 1 in
acoustic impedance. For example, when the substrate 1 is silicon and the acoustic impedance is
19 [MRayl], the first acoustic attenuation material 14 is a tungsten particle made of polyvinyl
chloride (PVC) as disclosed in Patent Document 1 And the like) may be used. The position where
the first acoustic attenuation layer 14 is provided is preferably provided on the rear side of the
receiving surface that receives the incident acoustic wave. More preferably, it is provided only in
the region on the back side of the substrate 1. When the region on the back side of the substrate
1 is exceeded, it is necessary to match the acoustic impedances of the portion beyond the
substrate 1 and the portion other than the substrate 1.
[0019]
Also for the second acoustic attenuation material 15, it is preferable that the electrical wiring
board 13 and the acoustic impedance be matched. For example, consider the case where the
electrical wiring substrate 13 is a glass epoxy substrate and the acoustic impedance is Z2 = 5.8
[MRayl]. Preferred materials include viscoelastic bodies such as urethane resins and epoxy resins.
When these materials contain high-density fine particles, adjustment of acoustic impedance and
improvement of absorption of acoustic waves can be realized. The fine particles include tungsten,
alumina, copper or its compound, platinum, iron or its compound. Specifically, by mixing about 1
wt% of alumina particles (30 μm to 40 μm) with an epoxy resin (for example, LOCTITE # 3036
/ product name of Henkel) and curing it, the acoustic impedance is about 5.8 [MRayl]. It 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 a desired acoustic impedance and a desired absorption may be used. The
position where the second acoustic attenuation material 15 is provided is preferably provided on
the back side of the surface that reflects the incident acoustic wave to the object side. More
preferably, it is provided only in the region on the back side of the electric wiring board 13.
When the area on the back side of the electric wiring board 13 is exceeded, it is necessary to
match the acoustic impedance between the part that is exceeded and the part other than the
electric wiring board 13.
[0020]
Next, Comparative Example 1 will be described with reference to FIG. FIG. 3 illustrates
Comparative Example 1 when an acoustic wave generated by a photoacoustic effect is received
by a general ultrasonic transducer without using the electromechanical transducer of the present
invention.
04-05-2019
8
[0021]
In the ultrasonic transducer shown in FIG. 3A, an ultrasonic transducer element 10 is formed on
a substrate 1, and a first acoustic attenuation material 14 is provided on the back side thereof.
An electrical wiring board 13 is disposed around the element 10 for electrical connection. For
example, it is assumed that light absorbers 18, 19 and 20 such as a tumor are present inside a
subject 17 to be measured, and the irradiation light 24 of a wavelength which the light absorber
absorbs from the outside of this 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 the acoustic wave
reaching the element 10 of the ultrasonic transducer is detected. Thereby, the position and the
size of the light absorbers 18, 19 and 20 present inside the subject 17 can be detected. An
acoustic impedance matching material 25 such as 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.
[0022]
When an acoustic wave is acquired from the subject 17 with the configuration as 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 on the
surface of the electric 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 the acoustic wave 22 may
be canceled and distorted. In addition, the reflected wave 27 reflected on the surface of the
electric wiring board 13 may be reflected by the absorber 19 and may overlap with a portion 28
of the acoustic wave of the absorber 23. This makes it difficult to accurately detect the position
and size of each absorber. The strength 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 world (for example, the acoustic impedance matching material 25) increases. In
addition, the intensity of the reflected wave 27 fluctuates due to the difference in the incident
angle to the electrical wiring board 13. In order to accurately acquire the acoustic wave with the
configuration as shown in FIG. 3A, the reflected wave 27 is reduced or the light irradiation range
29 is narrowed, and the acoustic wave reaching the electric wiring board 13 is reflected and
There is also a need to ensure that there is no impact.
04-05-2019
9
[0023]
The reflected wave and the transmitted wave generated at the interface between the electrical
wiring substrate 13 and the outside world (for example, the acoustic impedance matching
material 25) will be described with reference to FIG. Generally, at the interface 30 of two
substances, an acoustic wave is incident from the liquid side such as solution or gel, and the
reflection intensity and the transmission intensity of the acoustic wave generated at the solid
interface such as the electrical wiring substrate 13 Can be represented by Where: φi: incident
wave, φr: reflected wave, θi: incident angle = reflection angle, θL: transmission angle
(longitudinal wave), θT: transmission angle (transverse wave), φT: transmitted wave (transverse
wave), φL: transmitted wave ( Longitudinal wave), Rw: reflection intensity, Rφ: velocity potential
of reflected wave, Z: acoustic impedance of liquid side, ZL: acoustic impedance of transmitted
wave (longitudinal wave), ZT: acoustic impedance of transmitted wave (transverse wave), Tw <
T>: transmission strength of shear wave transmission wave, Tφ <T>: velocity potential of shear
wave transmission wave, TW <L>: transmission strength of longitudinal wave transmission wave,
Tφ <L>: speed potential of longitudinal wave transmission wave, ρ: Liquid density, ρ2:
individual density.
[0024]
[0025]
[0026]
[0027]
The acoustic impedance at this time can be expressed by Equation 4 below for the liquid side and
Equation 5 below for the solid side.
Further, from the definition of refraction, equation 6 is derived, and in the case of CL> C and CT>
C, there are times when the refraction angle θL and θT = 90 degrees at a certain incident angle.
04-05-2019
10
The incident angles at this time are referred to as critical angles θicL and θicT, and are
represented by Equations 7 and 8.
The reflection intensity greatly fluctuates at the critical angle. However, C: speed of sound of
liquid, CL: speed of sound of individual (transverse wave), CT: speed of sound of individual
(longitudinal wave). (Equation 4) Z = Ccos / cos θi (Equation 5) ZL = CLρ2 / cos θL, ZT =
CTρ2 / cos θT (Equation 6) cosθi / C = cosθL / CL = cosθT / CT (Equation 7) θicL = sin
<−1> (C / CL) (Expression 8) θicT = sin <−1> (C / CT)
[0028]
For example, when the electric wiring substrate 13 is a substrate such as FR-4 material for a
multilayer printed wiring board and the acoustic impedance matching material 25 is water, the
reflected wave and the transmitted wave generated at the interface are shown in FIG. It becomes
like. The vertical axis in FIG. 3C indicates the ratio of intensities. If Rw = 1, it indicates complete
reflection. The horizontal axis indicates the incident angle of the acoustic wave. C = 1500 [m / s],
CL = 3521 [m / s], CT = 2240 [m / s], ρ = 1000 [kg / m <3>], ρ2 = 2148 [kg / m <3>]
Therefore, the critical angle becomes θicL2525 °, θicT ≒ 42 °, and the intensity of the
reflected wave largely varies around the critical angle. The reflection intensity ratio is as high as
0.34 at the minimum. In order to stably obtain a desired acoustic wave signal, it is necessary to
set the incident angle to 25 ° or less, and since the range in which light can be irradiated at one
time is limited, the inspection is performed when testing a wide range of subjects It can be seen
that the efficiency is reduced.
[0029]
The effect of the present invention including the present embodiment and the like to the
comparative example 1 will be described with reference to FIG. However, in FIG. 4 (a), the
ultrasonic transducer which lacked the 2nd sound attenuating material 15 which is a
modification form of a present Example is used. First, how acoustic waves are acquired using the
ultrasonic transducer of this modification and the effects thereof will be described with reference
to FIG. For example, the electric wiring substrate 13 is a substrate such as FR-4 material for a
multilayer printed wiring board, and an epoxy resin (Young's modulus = 3 [GPa], Poisson's ratio =
0.3 as the matching layer (reflection suppressing layer) 12 thereon. ) Is placed. When the
acoustic impedance matching material 25 is water, the reflected wave and the transmitted wave
generated at the interface with the matching layer 12 are as shown in FIG. 4 (b). The vertical axis
04-05-2019
11
in FIG. 4 (b) also shows the intensity ratio. The horizontal axis indicates the incident angle of the
acoustic wave. Here, C = 1500 [m / s], CL = 2010 [m / s], CT = 1002 [m / s], ρ = 1000 [kg / m
<3>], 22 = 1150 [kg / m < 3>], the critical angle is only θic L 48 48 °, and the critical angle is
wider than in Comparative Example 1 above. Further, the reflection intensity ratio is as low as
0.052 at the maximum at a critical angle or less. By this, the influence of the surface reflection
wave is largely suppressed up to the incident angle of 48 °, and a stable reception signal (the
acoustic wave is received by the element and the converted electric signal) can be obtained.
Further, by expanding the range in which light can be irradiated at one time as compared with
Comparative Example 1, the examination efficiency can be improved even when it is desired to
examine a wide range of subjects.
[0030]
Next, Comparative Example 2 in the case where the reflection suppressing layer 12 and the
second sound attenuating material 15 are not provided will be described with reference to FIG.
The reflection intensity and the transmission intensity generated on the outermost surface of the
ultrasonic transducer in the case where the matching layer 12 is not provided in the comparative
example 1 are shown in FIG. In FIG. 3C, the transmitted acoustic waves Twt and Twl pass through
the inside of the electrical wiring board 13 as shown in FIG. 4C, and are reflected at the interface
33 on the back side. At this time, for example, when the back side of the electric wiring substrate
13 having an acoustic impedance of Z1 is air having an acoustic impedance of Z2, the reflection
intensity Ri and the transmission intensity Ti are expressed by the following equations 9 and 10.
(Equation 9) Ri = (Z2-Z1) <2> / (Z2 + Z1) <2> (Equation 10) Ti = 4Z1Z2 / (Z2 + Z1) <2>
[0031]
Assuming that the acoustic impedance of air is Z2 = 0.00041 [MRayl] and the acoustic
impedance of the electric wiring board 13 is Z1 = 5.8 [MRayl], almost all of the reflection
intensity Ri = 0.999 [Watts / m <2>] It becomes reflection. In addition, the reflected wave 32
reflected by the interface 33 on the back side returns to the subject side while maintaining the
intensity according to the transmission intensity Ti = 2.83 × 10 <-4> [Watts / m <2>] of the
above equation 10 Go. From this, 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.
[0032]
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12
Also in the case of the present embodiment in which the matching layer 12 is provided as shown
in FIGS. 2B and 2C, the reflected wave 32 from the interface 33 returns to the subject side, but
this reflected wave 32 is suppressed. What can be done is explained below. In the configuration
of FIG. 2C, an acoustic wave transmitted through the transmission layer of the first reflection
suppressing layer 12 which 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 the remaining about 0.89 [Watts / m <2>] is transmitted. The
transmitted wave 31 transmitted through the electric wiring board 13 reaches the interface 33.
The second sound attenuating material 15 is one in which the acoustic impedance is
substantially matched to the electrical wiring board 13. The materials are as described above.
When this is adhered to the back side of the electric wiring board 13 with an epoxy resin as a
second acoustic damping material 15 of 2 cm thickness, the reflected wave 32 from the interface
33 becomes almost zero. Also, when the back side of the second sound attenuating material 15 is
air, perfect reflection occurs at the interface 36. The reflection intensity when the reflection wave
from the interface 36 returns to the object side is obtained from the attenuation factor and the
above equations 9 and 10, and becomes about 1.2% of the intensity of the transmission wave 31.
From this fact, it can be understood that the intensity of the reflected wave can be largely
suppressed as compared with Comparative Example 2 by the ultrasonic transducer of this
embodiment shown in FIGS. 2 (b) and 2 (c).
[0033]
Second Embodiment FIG. 5 shows a second embodiment of the present invention. In FIG. 5, the
third reflection suppressing layer 37 is provided on the top of the electric wiring board 13. The
third reflection suppression layer 37 is an acoustic attenuation material. The acoustic impedance
of the acoustic attenuation material is substantially matched with the acoustic impedance of the
outside world (for example, the acoustic impedance matching material 25).
[0034]
The material is a material in which fine particles of high density are contained in a viscoelastic
body such as urethane resin. The fine particles include tungsten, alumina, copper or its
compound, platinum, iron or its compound. Specifically, about 10 wt% of tungsten particles (for
example, particles of 2.1 to 2.5 μm / particles manufactured by Allied Materials, Inc.) are mixed
and cured with special urethane rubber (for example, a trade name manufactured by Flexane 94L
/ DEVCON) . Thereby, the acoustic impedance can be adjusted to about 1.8 [MRayl]. The
04-05-2019
13
attenuation factor at that time was about 50 [dB / cm] at 1 MHz. When this is adhered to the
surface of the electrical wiring board 13 with an epoxy resin as a third reflection suppressing
layer 37 with a thickness of 0.5 cm, the reflected wave 39 from the liquid-solid interface
becomes about 1%.
[0035]
A commercially available ultrasonic sound absorbing tile or the like may be used as the third
reflection suppressing layer 37 as long as the external environment and the acoustic impedance
substantially match. Furthermore, it is possible to combine the present embodiment with the
above-described first embodiment (an example in which the matching layer is provided on the
outermost surface, and an example in which the matching layer is provided on the outermost
surface and an acoustic damping material is provided on the back surface of the electric wiring
substrate). .
[0036]
Third Embodiment 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 of this embodiment, in which a reflection suppressing layer 44 is provided on a part
inside the sensor unit. Between the ultrasound conversion elements 10 constituting the sensor
unit 40, the same material as the substrate 1 is used, or a thin film such as SiO 2 or SiN is formed
on the substrate 1 or the like. . Since the acoustic impedance between the ultrasonic transducer
elements 10 is not matched with the external world (for example, the acoustic impedance
matching material 25), a part of the incident acoustic wave 41 is reflected to generate a reflected
wave 42. Further, a part of the incident acoustic wave 41 is transmitted, passes through the
substrate 1 as the transmission 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 it
returns to the object side as in the first comparative example. Therefore, the reflection
suppressing layer 44 is provided on the upper portion 40 between the ultrasonic conversion
elements 10. That is, the reflection suppressing layer 44 is provided on the surface other than
the movable region, which faces the acoustic wave source side during use between the
electromechanical conversion elements. As a result, the same effects as in the first and second
embodiments can be obtained.
[0037]
04-05-2019
14
As a comparative example 3 to this, the reflected wave 42 which arises in the part without the
reflection suppression layer 44 is described below. Specifically, FIG. 6B shows reflection and
transmission when the interval 40 between the ultrasonic conversion elements 10 is Si (Young's
modulus = 169 [Gpa], Poisson's ratio = 0.3). The vertical axis in FIG. 6 (b) also indicates the
intensity ratio. The horizontal axis indicates the incident angle of the acoustic wave. C = 1500 [m
/ s], CL = 9881 [m / s], CT = 5339 [m / s], ρ = 1000 [kg / m <3>] at the interface between the
external world (for example, water) and Si , 22 = 2330 [kg / m <3>]. From this, the critical angle
becomes θicL ≒ 8.7 ° and θicT ≒ 16.3 °. In this way, the intensity of the reflected wave
greatly varies near the critical angle. The reflection intensity ratio is as high as at least 0.7. In
order to obtain a stable reception signal, it is necessary to set the incident angle to 8.7 ° or less,
and the range in which light can be irradiated at one time is limited.
[0038]
On the other hand, in the case of a present Example which provided the reflection suppression
layer 44, the reflected wave which arises in the part is described. For example, when providing a
matching layer as the reflection suppressing layer 44, a material such as glass epoxy can be used.
At this time, C = 1500 [m / s], CL = 3521 [m / s], CT = 2240 [m / s], ρ = 1000 [kg / m <3>], 22 =
2148 [kg / m < 3>]. From this, the critical angle becomes θicL ≒ 25 ° and θicT ≒ 42 °, and
the critical angle can be broadened as compared with the state without the reflection suppression
layer 44. That is, almost the same result as that shown in FIG. 3 (c) 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 top of the matching layer of glass epoxy, the critical angle is further
broadened as shown in Fig. 4 (b). I can do things. Thus, it is possible to obtain a received signal
that is more stable than the state without the reflection suppression layer 44.
[0039]
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 sound absorbing material 14 may be the
one described above. The sound absorbing material 14 and the reflection suppressing layer 44
can be provided by using a known method such as micromachining and transfer. The same effect
can be exhibited even when the reflection suppressing layer 44 is provided in a portion (see FIG.
1) other than the movable region 16 of the cell 9 of the minimum unit constituting the
ultrasound conversion element 10. Furthermore, it is also possible to combine the first to third
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15
embodiments with the present embodiment.
[0040]
In the above-described configuration, the reflection suppression layer 44 may be used as an
acoustic attenuation material. In that case, by providing the same material as that of the second
embodiment between the ultrasonic conversion elements 10, the same effect as that of the
second embodiment can be obtained. Further, even when the reflection suppressing layer 44 is
made of an acoustic attenuation material, the same effect can be exhibited even if it is provided
in a portion other than the movable region 16 of the cell 9 of the minimum unit constituting the
element 10. Furthermore, it is also possible to combine the first to third embodiments with the
present modification.
[0041]
Fourth Embodiment FIG. 7A shows a fourth embodiment of the present invention. In FIG. 7A, the
electrical wiring board 13 is disposed at an angle to the acoustic wave receiving surface of the
ultrasonic conversion element 10. Typically, the element 10 is placed in a direction
perpendicular to the receiving surface where the acoustic wave is received and at an angle
greater than 90 degrees. A reflection suppressing layer 12 is disposed on the top of the electrical
wiring board 13, and a second acoustic attenuation material 15 is disposed on the back side of
the electrical wiring board 13. On the back side of the ultrasonic transducer element 10, a first
acoustic attenuation material 14 is disposed. The element 10 and the electric wiring board 13
are connected via the flexible wiring 45. The flexible wiring 45 is covered with the reflection
suppressing layer 12. In the case of such a configuration, the reflected wave 47 of the part 46 of
the incident acoustic wave can be reflected in a direction other than the object. This makes it
possible to suppress reflection on the subject side. By adjusting the angle α between the electric
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.
[0042]
Although the reflection suppressing layer 12 and the second sound attenuating material 15 are
provided in FIG. 7A, the effect of suppressing the reflection toward the object side can be
obtained by providing only one of them. Moreover, it is also possible to combine the said
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16
Examples 1-3 and a present Example.
[0043]
Example 5 FIG. 7 (b) shows Example 5 of the present invention. In FIG. 7 (b), the ultrasonic
transducer is housed in the case 48. The inside of the case 48 may be hollow or may be a
molding integrated with a resin or the like. In this case, a reflected wave may occur at the
interface between the case surface and the outside world. Therefore, by providing the reflection
suppressing layer 49 on the surface of the case or combining it with the configuration described
in the first to fourth embodiments, it is possible to suppress the reflected wave to the object side.
Moreover, it is also possible to suppress a reflected wave by using the material of the case
surface into which an acoustic wave injects, and a thing which a reflected wave does not produce
in the interface with the external world.
[0044]
Sixth Embodiment FIG. 8 shows an object diagnostic apparatus to a photoacoustic measurement
apparatus according to a sixth embodiment of the present invention. The light source 50 is, for
example, a light source that generates a laser beam, and the light 24 is, for example, a pulsed
laser beam.
[0045]
In this apparatus, when the irradiation light 24 emitted from the light source 50 is directed to the
light absorber 51 inside the subject toward the subject 17, an acoustic wave 52 called a
photoacoustic wave is emitted by the photoacoustic effect. The frequency of the acoustic wave
52 varies depending on the size of the substance or individual constituting the light absorber 51,
but is about 300 kHz to 10 MHz. The acoustic wave 52 passes through the acoustic impedance
matching material 25 whose propagation is good, 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 subjected to signal processing by the signal
processing unit 55 to extract physical information of the subject. Although the signal processing
unit 55 is mainly a computer, a part of the signal processing unit 55 may be an integrated circuit,
and can reconstruct a two-dimensional or three-dimensional image. The ultrasonic transducer 53
can use the one in the first to fifth embodiments.
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17
[0046]
The electro-mechanical transducer according to the present invention can be applied to an
optical imaging apparatus for obtaining information in an object to be measured such as a living
body, a conventional ultrasonic diagnostic apparatus, and the like. Furthermore, it can be applied
to other applications such as an ultrasonic flaw detector.
[0047]
DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 9 ... Cell, 10 ... Electromechanical conversion
element, 12, 37, 44, 49 ... Reflection suppression layer, 13 ... Electric wiring board, 14, 15, 37 ...
Sound attenuating material, 16 ... Movable area, 25 ... Acoustic impedance matching material, 48
... case
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