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Description 1 and title of the invention electroacoustic functional device In an electroacoustic
functional device in which a poling piezoelectric polymer membrane having electrodes provided
on both sides is adhered or adhered to an acousto-optic material, the piezoelectric polymer
membrane has a thickness Drive by resonating under stretching vibration
2, the scope of claims
The present invention relates to an electroacoustic functional device. In the field of recent
polymer research, there are various kinds of crucibles which use polymer materials as functional
materials of electronics, and one of them has been successful. The inventors of the present
invention have made a deep study on the piezoelectric phenomenon of a polymer, and found that
the piezoelectric constant and the electromechanical coupling constant sufficient for practical
use as an electroacoustic transducer involving the thickness stretching vibration. Furthermore,
the present inventors have reached the present invention by finding that this conversion element
also operates in the high frequency range. That is, the present invention relates to an
electroacoustic functional device in which a poling piezoelectric polymer film provided with
electrodes on two surfaces is adhered to or adhered to an acousto-optic material, wherein the
piezoelectric polymer film is a tube under thickness stretching vibration. The functional device is
the gist. This piezoelectric polymer film has the advantage of being easy to process, flexible, and
having a large area. It has become clear that it is possible to replace a part of the electro-acoustic
transducer composed of a piezoelectric single crystal or a piezoelectric cellular, which has been
used conventionally, and also to apply to the field which has been intractable with these.
According to a recent study, a kind of synthetic polymer film is stretched and added with a direct
current elevation i and kept at a high temperature for a period of time after which it is cooled to
room temperature while a high electric field is applied. After that, it has been revealed that if the
direct current high electric field is removed (this operation is referred to as Porin EndPage: 1), it
becomes a stable piezoelectric body having symmetry belonging to the fish group of 111111
(applied physics) Mff 1115 (1969) ), Japan, J, Appl. Phys、、8975(1969))。 The
typical polymer is polyvinylidene fluoride (PVDF). According to the study of the present
inventors. In order to obtain the piezoelectric polymer film, the stretching operation is not
necessarily required 2, and the piezoelectric polymer film can also be obtained by poling the nonstretched film. The present inventors have also obtained a piezoelectric polymer film by poling
polyacrylonitrile (PAN). The piezoelectric film can also be obtained by poling a film in which a
powder of a ferroelectric substance, for example, a powder of lead zirconate, is mixed in a
polymer. In the present invention, the piezoelectric film mixed with the inorganic powder in this
way is also called a piezoelectric polymer film. It is expected that the piezoelectric constant 2 of
these piezoelectric polymer films obtained by poling is not zero, for example, the piezoelectric
strain constant is d '51. d 2. , A33. al5. a24. Of these, those interested in practical use are
selected for the first Y-axis (in the case of a -axis stretched film, the stretching axis is lx axis).
D31 = d32. It is a15 = a24. All studies of piezoelectric polymer films obtained by conventional
poling have been conducted for asl, d−s2 <i or corresponding g constants or e constants). Note
that tl−, d33 (e 33. Nothing is known about g33 and the like) and the properties involved. The
present inventors devised a method for measuring d33i quasi-statically in a low frequency region
of a piezoelectric polymer film obtained by poling, and used for measuring the piezoelectric
constant of an inorganic piezoelectric substance at no load. The electrical frequency
characteristics near the resonance frequency of the vibrator are analyzed to obtain piezoelectric
constants. So-called dynamic measurement (Proc. By applying Koura, R, E, 353 (1957) to a
piezoelectric polymer film (a thickness stretchable vibrator) for the first time, we succeeded in
obtaining piezoelectric constants in the high frequency region. The piezoelectric constants at
room temperature obtained by the dynamic measurement method in Table 1 are illustrated for
the poled biaxially stretched PVDF membrane) (value at 24 MHz). Recommendation 1
Piezoelectric acoustical constants of piezoelectric polymer (PVDF) films * * *, g @ = iy 11 k,
electricity *, ... of poling piezoelectric 'electro PVI)' F films polled under good conditions-8, 7 °.
p, s) ÷ Id = -f4 = area (-107 H2) fU normal temperature te 0.10 to 0.14 te. The mechanical Q
value (QM) is about 10 (C 3 is elastic compliance, ε 7 is dielectric constant, el is piezoelectric 5
stress constant). At low temperatures, kt approaches the normal temperature)). Q and M increase.
Thus, it is extremely significant in practice that the coupling constant kt of the thickness
stretching vibration of the piezoelectric polymer film is comparable to that of quartz. QM force
StJ (さ) has an advantage that it can be used as an electro-acoustic transducer 'operating in a
wide frequency band, such as a power ball, which has a large insertion loss and is one of the
drawbacks. In addition, since the dielectric constant is small, it has a high 17) voltage output
coefficient g33i. Therefore, the sensitivity of the longitudinal elastic wave is (1) a receiver.
Further, the thickness of the film can be made very uniform over a wide area, so that it is
possible to generate a directional, totally pure longitudinal acoustic wave i =. Furthermore,
because there is a bend in the town, it has excellent impact resistance in places where it is
lacking in the inorganic electroacoustic transducer with inorganic pressure, and it is noted that H
No O's attention in processing and handling). Not necessary Also, the piezoelectric film can be
easily adhered to an object having a curved surface. A piezoelectric polymer having electrodes on
both sides using the characteristics of such a piezoelectric polymer film is used as an electric
sound 6 for Endwave: 2 sound conversion element for longitudinal wave sound, and this is a
sound to be incident or to be received here The electroacoustic element for longitudinal wave
sound is a piezoelectric film or a piezoelectric plate that uses thickness expansion and
contraction vibration (Th1cknessex 襄 θn-5ionalmode) f, that is, a piezoelectric phenomenon
such as (143 or e33.g33 corresponding thereto is used. Means an electro-acoustic transducer.
In this case, the sound wave propagation medium is preferably two or more types, and it is
preferable that there may be a plurality of electroacoustic transducers used, and may be used
together with elements other than the piezoelectric polymer film. obtain. Hereinafter, an
embodiment of the electroacoustic functional device using the piezoelectric polymer film
according to the present invention will be specifically described. Example A 50 μm thick
biaxially stretched PVDF film having aluminum vapor deposited on both sides is sandwiched
between two aluminum foils, and this aluminum foil is heated to 130 ° C. in an oven while
applying a voltage of 2400 V as an electrode. After 2 hours, it was gradually cooled to room
temperature and the voltage was removed. The piezoelectric strain constant obtained by applying
the alternating force of 110 nz to this film and measuring the amount of alternating charge
generated on the film quasistatically is 12d31 = 6.9 × 10 C / N, d32 == +, 6 × 10 C / N. d6ろ
=22.8x10C/NTあった。 t * This film forms a thickness expansion and contraction
free oscillator, and the piezoelectric acoustic constants in the vicinity of 24 MH 2 measured by
the dynamic measurement method are shown in Table 11. This piezoelectric polymer film was
used as an ultrasonic transducer, and water was used as an acousto-optic material to make an
optical deflector (Figure). That is, metal deposition 6 is performed on one surface 2 of the parallel
square prism type transparent quartz cell 1 This face was cut out from the above-polished
membrane. A 10 mm × 10 mm piezoelectric film 4 on which aluminum was vapor-deposited was
bonded with an epoxy resin. When the cell 1 is filled with water and a high frequency voltage of f
= 1 [1 to 3 [] MH2 is applied to the piezoelectric film 4 through all the electrode linide wires 5
and 6, ultrasonic waves are generated from the piezoelectric film 4 and propagate into water. did.
When the Hθ-Nθ gas laser beam 7 (λ-063 μm) is vertically incident on the traveling direction
of the ultrasonic wave, a part of the incident light is θ-nλf / V (n- ± 1. It was deflected by an
angle given by ± 2. ■ is the speed of sound in water. The polarized light with respect to the
incident light is maximized in intensity when the angle between the wave front of the ultrasonic
wave and the incident light becomes y 2 of θ given by the above equation. If a high frequency
pulse of 8 [] V (pulse width 8 μsec) is applied to the piezoelectric film 4 so as to satisfy this
condition for n = 1, the intensity of polarized light relative to the intensity of incident light
(polarized light of all orders The proportion of the sum of intensities) (deflection efficiency) was
95% at 25 MHz. The deflection efficiencies of iQMH2 and OMH2 were both approximately 50φ.
The undeflected light (n-0) in this case was 95% intensity modulated by an ultrasonic pulse of 25
MH2. In addition to the above-mentioned pVDF, polyvinyl chloride, polyvinyl chloride,
polyvinylidene chloride, nylon 11 ° or a copolymer containing this as a main component is
known as a polymer that becomes piezoelectric by poling.
As a matter of fact, the present inventors have found that polyacrylonitrile-vinylidene chloride
copolymer and the like, which have already been described as polymers containing cyan groups,
also become 9-good piezoelectric materials by poling. The inventors of the present invention
have said that d '53 of these polymeric piezoelectric films has a value of about 1 to 5 times d 1,
and further. It has been observed that these piezoelectric films operate as an electroacoustic
transducer utilizing thickness expansion and contraction of the film. From the viewpoint of the
present inventors, in order for the polymer to have high piezoelectricity by poling, (1) there is no
center of symmetry in the crystal structure, (2) polar group having large dipolarity efficiency (i11
Containing in the lattice, (3) molecules move easily at high temperature, and reorientation under
high electric field. PVDF or PAN or a mixture of polymer and piezoelectric ceramic powder
satisfies these conditions. Polyamides having an even number of carbon atoms in the 1,000-gold
main chain and isotactic-PAN obtained by a special polymerization method Polyamides having an
odd number of carbon atoms in the main chain and PAN obtained by a general polymerization
method Unlike the above, poling does not produce large piezoelectricity. This is because the
former polymer does not satisfy the condition of (1), +2). The crystal structure of polyvinyl
chloride. Since it belongs to 10-EndPage: 3 mm, the piezoelectricity is believed not to be due to
the crystalline part but to the molecular orientation due to the poling electric field of the
amorphous part 2. In this case, the piezoelectricity is expected to disappear at the glass transition
temperature at which the microbrown motion of the amorphous part is initiated, which is
consistent with the experimental facts of the present inventors. It is considered that in the case of
PVDF or PAN obtained by a general polymerization method, crystallites oriented at high
temperature and high electric field mainly give large piezoelectricity. In the future, it is believed
that crystalline piezoelectric polymers having larger electromechanical coupling constants will be
developed, and electroacoustic devices using polymers as functional materials will be actively
used. In one embodiment of the present invention, an example of 33 MH 2 is shown as an
example of the operation of the polymer piezoelectric film and the electroacoustic transducer,
but the present inventors have observed the operation up to 120 MH 2.
4. Brief description of the drawings shows an ultrasonic light deflection or modulator that uses a
piezoelectric polymer film (poled polyvinylidene fluoride) as an ultrasonic transducer and water
as an acousto-optic material. ° Brief description of the drawing 1: Transparent quartz cell 2: One
side of the cell 6: Gold metal lid 4: Piezoelectric film 5.6: Electrode lead wire 7: Laser light Patent
applicant Tohsi Co., Ltd. EndPage: 4