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JPS55156500

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DESCRIPTION JPS55156500
Description 1 and title of the invention Electro-acoustic transducer on the surface opposite to the
surface on the acoustic operation side of the polymeric piezoelectric film Directly or indirectly,
twice the value of the acoustic impedance (zo) of the polymeric piezoelectric film An additional
film with an acoustic impedance (Z) of the above value and a thickness of at least 05 μm and
less than 1λ / 16 (where λ is the wavelength of the sound wave in the additional film at the self
resonance frequency of the piezoelectric film) The electro-acoustic transducer which is provided.
2, the scope of claims
3. Detailed Description of the Invention The present invention relates to an electro-acoustic
transducer using a polymeric piezoelectric film. More specifically, the practicality of the
ultrasonic transducer for generating and receiving ultrasonic waves formed by directly utilizing
the thickness vibration mode of the polymeric piezoelectric film disclosed in Japanese Patent
Publication No. 53-26799 is further enhanced. The invention relates to enhanced and improved
ultrasound transducers. The acoustic impedance of the polymeric piezoelectric material is a
fraction of the acoustic impedance of the inorganic piezoelectric material to 1 AO, which is close
to that of water, biological or organic materials. Therefore, it can be a convenient transmitterreceiver for ultrasound waves propagating to them. However, when using a polymer piezoelectric
film as an ultrasonic transducer, there are the following problems. That is, in an apparatus using
ultrasonic waves such as ultrasonic flaw detection or ultrasonic diagnosis. h−1oM)! The
frequency of z is frequently used. As is well known, in ultrasonic transducers, in order to increase
the ratio (efficiency) of the acoustic output to the electrical input, it is necessary to match the
resonant frequency of the motion to the operating frequency. For this purpose, a piezoelectric
film having a thickness predetermined by the target frequency is required. In the case of
polyvinylidene fluoride, which is a typical example of a polymer piezoelectric substance, 1
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frequency constant foto = 115 KHz * an '(f .: resonant frequency of thickness free oscillator, to 2
thickness) 1 In order to efficiently transmit and receive ultrasonic waves of, for example, 25 M,
which are commonly used, it is necessary to have a thickness of 460 μm for half-wave drive and
250 μm even for 174-wave drive EndPage: 1 motion. However, the poling electric field
necessary for imparting polymer piezoelectricity requires about 10 ′ ′ V / (2), and poling of a
thick film as in the above example causes various difficulties such as gas discharge problems. As
a result, it is difficult to obtain a thick film polymeric piezoelectric film, and 1) an ordinary
production volume and an easy range are 100 μm or less (first defect). Further, it is difficult to
control the thickness of the polymeric piezoelectric film to a thickness suitable for generating
and receiving ultrasonic waves of a frequency according to the purpose. This is because polymer
piezoelectric films are often obtained by stretching and then poling an unstretched film, and
depending on processing conditions such as stretching and heat treatment, the thickness of the
final piezoelectric film obtained from a starting unstretched film is Because they are often
different. Unlike the inorganic piezoelectric material, it is extremely difficult to control the
thickness of the polymeric piezoelectric film uniformly by the usual polishing method, which is
not practical (defects such as 2).
Furthermore, the molecular piezoelectric film does not have a high dielectric constant as does
one ferroelectric inorganic piezoelectric material (eg, PZT). Therefore, when the film thickness
becomes large, the electric capacity decreases, and hence the electric impedance of the vibrator
increases, and the impedance matching with the power supply deteriorates, so that energy from
the power supply can not be injected into the vibrator Occurs (the third drawback). The present
invention uses a thin polymer piezoelectric film without impairing the low acoustic impedance
characteristics of the polymer piezoelectric, and uses longitudinal ultrasonic waves having a
frequency lower than its inherent frequency (free resonance frequency). An object of the present
invention is to provide an ultrasonic transducer that emits and receives efficiently (with a small
loss). The present invention for achieving this object consists of the following gist. On the
opposite side of the acoustically active side of the polymer piezoelectric film. Directly or
indirectly, an additional film having a thickness of not less than 05 μm and less than 1λ / 16
having “a value of acoustic impedance (Z ′) that is twice or more as large as the value of the
acoustic impedance (Zo) of the polymer piezoelectric film (Where λ is an additional film at the
free resonance frequency of the piezoelectric film). The polymeric piezoelectric film according to
the present invention is, for example, one. Piezoelectricity is imparted by poling, and a polymer
film having piezoelectricity in the thickness direction of the film is used,-as a polymer material
for forming such a polymer film. Polyvinylidene fluoride (hereinafter sometimes referred to as
PVDF) or a copolymer thereof, polyvinyl chloride, polyacrylonitrile polymer 9 ferroelectric
ceramic, for example, a polymer material mixed with lead zirconate powder There is. The
acoustically active side of the polymer piezoelectric film means the transmission of a dragon
wave to a desired acoustic propagation medium or the thickness vibration mode of the polymer
piezoelectric film of the two film surfaces of the polymer piezoelectric film. In the reception of
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sound waves from the desired sound propagation medium, this means the side facing the sound
propagation medium. Hereinafter, this surface may be referred to as the front surface of the
polymeric piezoelectric film. That the additional film is provided directly or indirectly on the
surface opposite to the surface on the acoustic operation side of the polymer piezoelectric film
means that the surface on the opposite side to the surface on the acoustic operation side of the
polymer piezoelectric film and the additional film However, the form in which the acoustically
integrated form is in direct contact, or the surface on the opposite side to the surface on the side
of the acoustic operation 5-side of the polymer piezoelectric film and the additional film do not
impair the function and effect of the present invention. In this case, it means a form which is
located indirectly through the intervening layer (for example, the electrode r @) which is
interposed for other purposes, but which is acoustically integrated.
This additional film may be hereinafter referred to as a backside additional film. The additional
film is one of the essential components for achieving the object of the present invention, and its
acoustic impedance, and the value of (2). The value of the acoustic impedance (zo) of the
polymeric piezoelectric film satisfies the condition of Z / Zo ≧ 2 and the thickness (1) is from 05
μm to less than 1λ / 16 (where λ is the free thickness of the piezoelectric film) Sound wave
wavelength in the additional film at the resonance frequency), preferably satisfying the condition
of more than 1 μm and less than 1λ / 16. In addition, conventionally, to form an electrode on
the front surface of the polymeric piezoelectric film (and also on the back surface), AI! And the
like, but this thickness is at most 1000 × (−01 μm), and these have large resistance values. In
addition, in the present invention, by selecting a conductive material more than EndPage: 2 in the
materials described later as an additional film, stable electrical connection with low resistance is
achieved. The advantages that can be formed are also obtained. As a material for forming an
additional film, AI! , C! u、Ag。 Sn, Au, 0 metals such as Sn, Au, Pb, ceramic films, glass thin
films, those in which metal powder or ceramic powder is mixed in polymer, etc. are mentioned,
adhesion of these platings, foils or films, pastes An additional film is formed by directly or
indirectly applying the coating film or the like to the acoustically operating surface of the
polymeric piezoelectric film. Next, before describing the present invention in more detail using
specific embodiments, definitions of various characteristic values used in each embodiment and
measurement methods thereof will be described. When tension T and electric field E work in the
thickness direction of the film-like piezoelectric material, the relationship between strain S2
electric displacement of the thickness oscillator and T and E is given by the following basic
equation. Here, Co and β ′ are mechanical loss, complex elastic modulus (θT / as) n taking
account of dielectric loss and complex electric susceptibility (aE, / aD) s, mechanical loss tangent
φ-tan δm, dielectric loss tangent φ There is the following relationship with −tan δe. C ′ ′ =
C (1 + jφ), β ° = β (1 + jψ), 1ε = D = ε (1−jψ) Further, h is a piezoelectric constant (real
number). Surface of piezoelectric body with thickness t1 area A, density t, speed of sound V, load
(force) of Fl and F2 is added to 1m back surface respectively 1T + speed at IU + IU2 speed
(angular frequency ω), voltage between electrodes ■ When the current flows, there is a gap
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between them. (For example, Takuya Ikeda “Physical Sound Properties of Solids” (Mitsuhisa To
Wada) F 57 (槙, 1 ′ 967)).
ここで。 である。 For non-piezoelectric films, it may be h70 in (1). In general, the general
configuration of the transducer is as shown in FIG. Here, the layers indicated by O 1 ° 2, n, f are
respectively a piezoelectric film, a non-piezoelectric film (1, 2,... N) in front, and a propagation
medium (water, living body, etc.) + 1'12 ' The layer indicated by l... m ′, b is a rear nonpiezoelectric film. These may be an adhesive layer 1 electrode, a protective film, a support plate 1
reflector, or an additional layer according to the present invention, as required. e and e 'are
electrodes (a thickness and a mass are disregarded). The equivalent circuit for driving the system
of FIG. 1 is based on Eq. (1) that the force and displacement at the interface of each layer are
continuous, and the real charge inside the piezoelectric body is zero. The results obtained are
shown in FIG. In FIG. ZA = -jB tanh-9-Zc = -jB cosechrt, and tzAi, ZcLZ'Aj + Z'a, J, etc. also have
similar surface holes .mu.l from Z '% v, Vtt, .phi. . φ-hco is a winding ratio of the secondary coil.
The 4-terminal network in the case of connecting the circuit of FIG. 2 to the impedance of Zs and
connecting it to t 'khfj is represented as shown in FIG. The electrical impedance of the
transformer 1 viewed from the power supply is assumed to be ZL. このとき。 Energy PO from
the power source is distributed and consumed as follows (Fig. 4). Reflection Pr due to the
mismatch between ZEI and Zin: Input energy 'Pr (= Po-Pr) of the transducer, acoustic radiation
energy PAf forward. Acoustic radiation energy PAb to the back, and internal consumption (heat)
energy Pth0 of the transducer here. Pth=Pr−PAf+PAb)である。 ここで
10−EndPage:3である。 Therefore, various losses are defined as follows. Here, it
becomes clear that in order to enhance the practicability of the transducer for nondestructive
ultrasonic inspection, it is necessary to design the TLf to be as wide as possible and to have a
large TIb. . The method of measuring and evaluating the characteristics of the transducer
prepared according to the present invention is as follows. The created transducers CLf, TLf, and
ML were measured by the following method. First of all, as shown in FIG. 5, CLf measurement is
performed by exciting the transducer with a high frequency pulse power supply having a known
impedance (50 Ω). The generated ultrasonic pulse is emitted into water.
This is reflected by the brass block and received by the same transducer. The received signal is
amplified and detected, and the output is displayed on the synchroscope. On the other hand, the
excitation voltage is passed through the attenuator, amplified and detected by the same amplifier,
and displayed on the synchroscope. Determine the attenuation (d) 3 of the attenuator so that the
two displays are the same. Do this at each frequency. Assuming that the amount of attenuation is
Lmes, CLf is as follows. C′Lf=(L+nes−Lref−Lw−6)/2(dB)(61であ
る。 In the above equation, + Lref is the reflection loss of brass. Lw is associated with absorption
by ultrasonic waves by water and loss due to wavefront broadening, 6 dB pulse echo method. It is
a loss due to parallel connection of transmission and reception impedance (Kikuchi, Nakabachi,
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Applied Physics, Vol. 36, No. 11). P927(1969))。 In the conditions of the
embodiment of the present invention, + Lref + Lw is almost 1 dB. In order to determine ML, a
transducer was placed in a water tank where the reflection of ultrasonic waves can be ignored,
and its impedance ZL was determined by measuring the reflected voltage relative to the electrical
input and its phase with the apparatus of FIG. In the example of the present invention, a
piezoelectric film obtained by poling of -axially stretched polyvinylidene fluoride at an electric
field of 10 'v / cm at 120 ° C. for 1 hour was used as a polymeric piezoelectric material. The
piezoelectric constant, the electrical and acoustic properties such as the velocity of sound, etc.
were determined by the resonance method of a polymer piezoelectric film free oscillator reported
by one of the present inventors (large bundle, 'J, Appl, Phys, 47. 949 (1975 )). In the theoretical
evaluation of the transducers in this example, first-order values are used as physical property
values of various substances. The invention will now be described in more detail by way of
specific examples and comparative examples. FIG. 7 is a schematic view of a representative
embodiment of the electro-acoustic transducer according to the present invention; FIG. 7 (in each
of the figures 1 to 4 is the side on which the acoustic propagation medium is located; Therefore,
in FIG. 9, the lower surface of the polymeric piezoelectric film 11 corresponds to the surface on
the side of one acoustic operation of the polymeric piezoelectric film 11. In FIG. 7B) to (1), the
surface of the polymer piezoelectric film 11 opposite to the surface on the acoustic operation
side directly or indirectly has the value of the acoustic impedance (zo) of the polymer
piezoelectric film 11. The additional film 12 having a thickness of 0.58 m or more and less than
1 λA6 having an acoustic impedance (Z) of a value of twice or more is provided. The pair of
electrodes 13.13 is provided on both sides of the polymeric piezoelectric film 11.
When the additional film 12 is made of a conductive material, one of the electrodes 13 can be
omitted, and the additional film 12 can be used concurrently, and an example of the case is
shown in FIG. In FIG. 7 (C), an additional layer 14-EndPage: 414 made of a polymer material is
positioned on the front surface of the conversion element shown in FIG. 7) on the back of the
conversion element shown in FIG. 7). It is of the type in which an additional layer 14 made of a
polymeric material is located, and further, FIG. 7 (e) is obtained by positioning additional layers
14.14 made of a polymer material on the front and back of the conversion element shown in FIG.
7 b). FIG. 7 is of a type in which the additional film 12 is located on the back of the conversion
element through the additional layer 14 of the polymer. This format can also be applied to the
format of FIG. 7 (c), c). In FIG. 7 (to FIG. 7) and in FIG. 7 (e), the acoustic reflection plate 15 is
attached to the back of the conversion element shown. 7 (to), the form of FIG. 7 (e), (i) or (i) is
applied to the case of the conversion element shown in FIG. 7))), (e) There is also a type mounted
on the front surface of the reflection plate 15. FIG. 7 (g) is a type in which the conversion
element shown in FIG. 7 b) is attached to the front surface of the support 16, and the conversion
shown in FIG. 7 (g) 7 (b) to (f) (including the modification of the item b) instead of the elements
may be attached to the front face of the conversion element and the support 16. When the
acoustic impedance of the additional layer 14 is zp + the acoustic impedance of the polymer
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piezoelectric film 11 is zO, the additional layer 14 satisfies 0.2 <Zp / Zo <2, preferably o, 5
<zp7zo <2, yori. Good tL <Ha. 0, 5 (materials 1 satisfying the relationship of Zp / Zo <2 usually 1
polymeric materials 1 such as polyethylene terephthalate. ポリカーボネート、ポリメチルメタア
クリレート。 It is made of polystyrene, ABS, polyethylene / vinyl chloride, polyimide, aromatic
polyamide, polyvinyl fluoride 7 and the like. The nine reflecting plates 15 are made of polymer
piezoelectric films 11. And a material having a sufficiently large acoustic impedance than that of
the support 16, generally metal 1, for example, Au, CutW. Furthermore, the support 16 is formed
of solid materials having various elastic constants, but in order to effectively utilize the effect of
the present invention, it is preferable to use FIG. In the case where the type of (e) is applied, a
substance 1 having a large acoustic impedance, for example, a metal is preferably used, and also,
as shown in FIG.
(Ha), (7) (in the dark). In the type shown in (E) and in the form shown in (B), the support 16 is
preferably formed of a material 1 having a small acoustic impedance, for example, a polymer
material. Methyl methacrylate, polystyrene, AB-8. Bakelite and epoxy resin are suitable. また。
Flexible material 1 such as nylon, polyethylene so as not to impair the flexibility of the polymeric
piezoelectric material. A sheet of rubber or the like can also be used as a support. In order to
further increase the elastic modulus and / or strength, the sheet can also be mixed with carbon
fibers or metal fibers. EXAMPLE 1 FIG. 8 is a schematic structural view of an example of the
electro-acoustic transducer according to the present invention and a graph showing the effect
thereof. That is, FIG. 8 shows that 76 μm thick P 'VD? P, t (thickness 0.1 μm) were vapor
deposited on both sides of the film 11 (uniaxial stretching) to form an electrode 13.13, various
thicknesses of Cu 1.5.20 μm (in this example) The ultrasonic transducer according to the
present invention provided with the additional film 12 of 11540 λ, 1/68 λ, and 1/17 λ
respectively, and the comparative transducer without the back additional film 12 The frequency
dependence of the conversion loss TLf of Usa is shown. FIG. 9 shows the relationship between
the thickness of the Cu film of the back additional film 12 of 76 μm PVDF in FIG. 8 and the
resonance frequency in order to make the effect of the present invention more understandable,
and is defined in the present invention. It is clear that there is an effect of lowering the resonance
frequency with the thickness of the back additional film 12 of a certain degree, and the back
additional film of this thickness is one of the characteristics of the thin film polymer piezoelectric
film. There is no loss of sex. Embodiment 2 FIG. 10 is a schematic structural view of another
transducer device using the electro-acoustic transducer according to the present invention 9 and
a graph showing the effect. The transducer apparatus according to the present invention is a 76
μm thick PVDF film 11 (uniaxially stretched) on both sides KAI! (With a thickness of 0.1 μm)
was deposited to form an electrode 15.13, on the back of which various thicknesses of Ou 5.20
μm (in this example 18-EndPage: 5 1/68 λ, 1 / An additional film 12 corresponding to a
thickness of 17λ), and an additional layer 14.14 made of polyethylene terephthalate having a
thickness of 25 μm positioned on the front surface of the PVDF 11 and on the back surface of
the additional film 12 respectively. It is.
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As a comparative example, a transducer constituted by removing only the back additional film 12
from the above-mentioned type of apparatus was used. The frequency characteristics of the
conversion loss TLf of these transducer devices are as shown in the graph of FIG. FIG. 11 shows
the relationship between the thickness of the back additional film 12 of 76 μm PVDF in FIG. 10
and the resonance frequency in order to make the effect of the present invention more
understandable, and the extent to which the present invention is defined. It is clear that the
thickness of the back additional film 12 has the effect of reducing the resonance frequency, and
the back additional film of this thickness is two of the characteristics of the thin film polymer
piezoelectric film. There is no loss of sex. EXAMPLE 6 FIG. 12 is a schematic structural view of
another transducer device using the electro-acoustic transducer according to the present
invention and a graph showing the effect thereof. The transducer device according to the present
invention is AI on the front face of a 76 μm thick PVDF film 11 (uniaxially stretched)! (Thickness
0.1 μm) was deposited to form one electrode 16. An additional film 12 of various thicknesses of
0.5 ° 5.20 μm (corresponding to 1/680 λ, 1/68 λ, 1/17 λ in this embodiment) of Cu is
provided on the back surface of the film 11 and It is an ultrasonic transducer of the type
attached to the PMMA support 16, and the back additional film 12 is of the type in which one
electrode corresponding to the one electrode 13 is also used. The frequency characteristics of the
conversion loss TLf of this device are as shown in FIG. FIG. 13 shows the relationship between
the thickness of the back additional film 12 of 76 μm PVDF in FIG. 12 and the resonance
frequency in order to make the effects of the present invention 9 easier to understand, and the
extent specified in the present invention 9 It is clear that the thickness of the back additional film
12 has the effect of reducing the resonance frequency, and the back additional film of this
thickness is one of the characteristics of the thin film polymer piezoelectric film, which is flexible.
There is no loss of sex. From Examples 1 to 3 above, according to the various transducers of the
present invention provided with the back surface additional film 12, the polymer piezoelectric
material may be a thin film, and its inherent vibration without impairing the low acoustic
impedance characteristic. Longitudinal ultrasonic waves with frequencies lower than the number
(free resonant frequency) can be efficiently emitted and received, and the flexibility property,
which is one of the characteristics of the polymer piezoelectric film, can also be exploited- You
can
4. Brief description of the drawings. FIG. 1 is a diagram for explaining the general construction of
a transducer, FIG. 2 is an equivalent circuit diagram for driving the system of FIG. 1, and FIG. A 4terminal network circuit diagram in the case of connecting the circuit in the figure to a power
supply having an internal impedance, and FIG. 4 is a diagram for explaining distribution and
consumption of energy PO from the power supply in FIG. Fig. 6 is an explanatory view of a
method apparatus for measuring loss CLf, Fig. 6 is an explanatory view of a method apparatus
for measuring loss ML, and Fig. 7 is a diagram of an electro-acoustic 21-echo conversion element
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according to the present invention. FIG. 5 is a schematic view illustrating various embodiments.
FIG. 8 is a view showing a schematic structure of an ultrasonic transducer device using the
electro-acoustic transducer according to the present invention and the effect thereof. FIGS. 10
and 12 are schematic structural views of an ultrasonic transducer device using another electroacoustic transducer according to the present invention and the effect thereof. FIGS. 9, 11, and 13
show the relationship between the thickness of the additional film and the resonance frequency
in FIGS. 8, 10, and 12, respectively. Brief Description of the Drawings; 11: polymer piezoelectric
film 12: additional film 13: electrode 14: additional layer 15: reflection plate 16: support patent
applicant Toshi Co., Ltd. 22-EndPage: 6 茅 3 (α) (α) b) Harm 4 figure γγP. 5 5 6 寥 7 Figure
(b) (b) (b) (b) (r) to the r> "<((b) End page: 7 Cu's 15 (Fm) pant 13 flash EndPage: 9 Warning: Page
discontinuity
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