JPS59174098A - Device for burying piezoelectric diaphragm, method of manufacturing same and electromechahical converter using same device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to transducer or sensor devices that utilize embedded polymeric diaphragms to perform mechanical or acoustic transmission functions. For more details, please see
The present invention relates to electromechanical transducers and accelerometers.

Recent developments in piezoelectric polymers have made it possible to apply them in devices that often use them in the form of embedded diaphragms.

This embedding is generally done by fixing it between metal plates. Metal composites have the advantage over those made from other materials that they provide implants with superior mechanical properties and can withstand the flow stresses that occur when fixing the diaphragm. Metal noyo also meets the requirements of accuracy and mass production. If the piece used for implantation needs to be pressed to make electrical contact with the electrodes supported by the diaphragm, metal is a perfectly natural choice.

This type of structure, which combines different materials such as metals and polymers, has the disadvantage of large differences in the coefficients of thermal expansion of these materials. In fact, typical values for the coefficient of thermal expansion range from 0.5·1o-5 to 210 k for metals, and from 0.5·10-' to 5-1 for commonly used polymers.
0-' k-1te6tle. Compared to metals, polymers deform more greatly due to temperature. Changes in temperature can change the mechanical conditions of the diaphragm by causing differences in the expansion of the diaphragm and by changing the shape of the diaphragm, thereby changing its stress state. Mechanical changes in the diaphragm are reversible if temperature fluctuations are small. For large temperature fluctuations, for example on the order of those imposed by military standards, this is not the case.

In this case, the diaphragm undergoes irreversible mechanical changes and its magneto-mechanical properties also change.

In order to overcome the above-mentioned difficulties, the invention proposes the use of means to prevent relative movement of the diaphragm to the embedded part due to temperature changes. This measure works in such a way as to increase the friction between the different parts or to anchor the diaphragm to the show.

The invention also provides a device in which a piezoelectric diaphragm is embedded during a show and the jaws exert a fixing force on this diaphragm in one or more peripheral zones, the device being exposed to temperatures that can cause contraction of the diaphragm with respect to the show. The present invention relates to an implantable device in which the membrane and diaphragm define an implantation profile having one or more surfaces that counteract said contraction, subject to the potential for mouth fluctuations.

The present invention also provides a method of making such an implantable device.

The present invention also provides an electromechanical transducer in which the implanted device uses a piezoelectric diaphragm having a profile that counteracts contraction of the diaphragm against show.

The invention will be better understood, and other advantages will become apparent, from the following description and accompanying drawings.

FIG. 1 shows the basic structure of a microphone insert with a vibrating element in the form of an embedded grate. Is the insertion part 4? The case is made up of two parts: Day 1 and Color 2. A grate 3 made of a pressure 4 injection polymer and used as a diaphragm (diaphragm) is sandwiched between If- of the case and the collar. The insertion section has been partially cut away to better show the various parts.

Elements l and 2 are generally made from aluminum and are recessed? - plays the role of 2 Figure 2 a to 2
Figure d shows the deformation that occurs in the embedded diaphragm due to differential expansion.

FIG. 2a schematically shows the diaphragm 4 and its embedded pieces 5 and 6. This figure is a cross-sectional view of a microphone insert of the type shown in FIG. 1, shown undeformed at ambient temperature. Fluctuations in the temperature of the insert cause expansion or contraction of its component elements. For example, at temperatures below ambient temperature, the element experiences a radial stress, Xr, which reduces the outer dimensions of the insert, as shown in FIG. metal part 5
Since polymers have a larger dimensional change due to drift than No. 6 and No. 6, polymers tend to deform and pull the metal.

This change is reversible as long as the temperature change is small. The effect on the function of the diaphragm ip is often tolerably low or can be compensated for by other actors. This is simply not the case if the temperature difference with respect to the ambient temperature is large. Depending on the amount of snow, the insertion part as described above may be 40 degrees.
It may be necessary to withstand temperature differences on the order of C for hundreds or even thousands of hours. Under these conditions, the diaphragm exerts significant radial tensile stress on the jaws by contracting! ! However, the stress may be so strong that the force exerted on the diaphragm may be such that a permanent fixing force may not be sufficient to prevent the diaphragm from slipping within the implant. This is shown in Figure 2.7c, where it can be seen that diaphragm 4 has contracted more than pieces 5 and 6. Returning to ambient conditions will result in thermal expansion, but this will not result in a return to the condition shown in FIG. 2.

In fact, the stress caused by the expansion of the diaphragm causes the diaphragm to puncture (buckling) rather than reinserting the diaphragm into its original implanted position. As shown in Figure 2d, the diaphragm remains in the extended position within the jaws and the puncture ring is greatest in its central portion.

As a result of such extensive temperature cycling, irreversible changes in the properties of the insert occur. In particular, the values of parameters such as co/f and the resonance mode frequency change. This may result in degraded operation, damage, or reduced reproducibility of received or transmitted signals.

As an illustration, let us examine in detail the effect of temperature changes on an insert of the type shown in FIG.

The properties of the materials used are as follows: The piezoelectric diaphragm 3 is made of polyvinylidene fluoride (PPVDF).
) is made from. Its thickness is 200 microns, the embedded diameter is 14 mm, and the linear expansion coefficient α of PVDFO is 100.10.
It is k.

*Shows 1 and 2 are linear expansion coefficient α'=22・10-
Made from 6-1 aluminum.

At a temperature difference ΔT, the radial stress Xr is expressed by the relational expression Xr='E
(α−α′)·ΔT, where E is the Young's modulus of PVDF (31ONm). Moving from ambient temperature to a temperature of -40°0 results in a radial stress corresponding to a force of approximately 14 ON distributed radially across the periphery of the implant.

It has been found that the shape given to the diaphragm influences its behavior with respect to temperature differences.

In particular, a slightly convex dome-shaped diaphragm whose embedded part is shaped like a truncated cone exhibits a relatively good response to the effects of temperature differences. The principle of this type of insert is explained in the French patent application no. 81.15506, filed August 11, 1981. FIG. 3 is a vertical sectional view of this type of microphone insert having a pressure relief grate. The case includes an upper part 16 made of metal, which includes an insulated coupling terminal 1
4 fits into the case bottom 11. Piezoelectric grate 1
7 is provided with a metal coating 15, 18 and is embedded between the edge of the upper part 16 of the case and the metal ring 8 of trapezoidal cross section. The plate 8 is pressed against the grate 17 by means of an insulating washer 9 which rests on a resilient locking piece 10 which passes through a circular slit in the upper part 16 of the case. A cushion 12 of sound absorbing material is housed in a central recess in the upper part 16 of the case. This tunnel is packed between the electron 9 and the printed circuit grate 13 in which the electrical components of the impedance matching electrical circuit are arranged. The materials used for the grates 17 and the embedded pieces are assumed to be the same as in the previous case. The dimensions of the plate 17 are also similar. In this figure, you can see the slightly convex dome shape of the plate 17 and its embedded part in the shape of a truncated cone, but the apex angle of the truncated cone is very open (74 in this example).
166).

This geometry is very favorable in terms of cold behavior, with the diaphragm collapsing, essentially collapsing the dome, and exhibiting almost no radial stress. This structure starts from the chamber 1' crystal and up to a temperature of -10°C,
It is considered that no radial stress is applied to the embedded piece. At -40°C, the radial stress exerted by the grate is 70
This is Newton's order. The effect of the shrinkage of the embedded diaphragm then appears and has a substantial effect on the frequency f of the first resonant mode of the diaphragm and on the sensitivity S of this microphone insert at 1 kHz. These effects are shown in the table below: =40° After several hours at 0 and returning to ambient temperature, it can be seen that the frequency fo and the sensitivity S change substantially in value.

The geometry given to the piezoelectric grating in this case does not compensate for the effects of large temperature changes.

The method chosen is uniaxially drawn and its expansion coefficient α
1. It will be necessary to take into account the fact that PVDF grades with a ratio of α22 of approximately 4 are sometimes used. Generally, as in the field of the present invention, there may be cases where there is a large difference in coefficient of thermal expansion between the diaphragm and the potted piece, whether or not that piece is metal.

The purpose of the means used in the invention is to respond to stress Xr in such a way as to prevent slippage.

For polymeric diaphragms, the solution of increasing the fixing force is not chosen. This is because, since polymers have fluidity, the compressive force applied to them will be relaxed after a certain amount of time. This effect is particularly pronounced when the insert undergoes a heating cycle before a cooling cycle.

If the shape of the diaphragm is obtained by molding, an annular bead can be provided around the rim so that it abuts the outer side of the potting piece as shown in FIG. This method can prevent shrinkage of the implanted part.

To be effective, there must be no play at this end. For that, diaphragm 2° bead 2
It is a prerequisite that the inner diameter of 1 matches the outer diameter of the implant pieces 22 and 23 very precisely. This method is
This is not applicable when the diaphragm is simply stamped out of a sheet of large dimensions, as is the case with most devices having piezoelectric polymer diaphragms.

To counter the tensile stress Xr, it is more effective to fix the diaphragm between rough surfaces. In that case, the surface of the implanted piece in contact with the diaphragm serves to prevent contraction of the diaphragm. Actually, the embedded PV
In order to effectively affect the movement of the DF diaphragm, the amplitude of this roughness must be on the order of the size of the diaphragm thickness.

An effective method of combating shrinkage is to create a corrugation over the entire surface of the diaphragm that contacts the potting piece, with the amplitude of the corrugation and its average pitch being on the order of a fraction of the thickness of the diaphragm. .

This method has the disadvantage that the diaphragm does not have a positioning part, which affects the speed at which the implantation process is performed. Another difficulty arises in the inner contact zone of the different yarns, shown at 25 in Figure 2a. Indeed, depending on the corrugation profile, the condition at the boundary (and specifically the original slope) may depend on the assembly accuracy.

The best solution is to use an embedding profile consisting of two concentric regions that serve separate roles: one region adjacent to the inner edge of the embedding piece and another region adjacent to the outer edge. Adjacent. FIG. 5 shows an example of an embedding profile made in accordance with the present invention. Polymer plate 31 is fixed between pieces 32 and 33. The area 34 adjacent to the inner edge has a profile suitable for optimal implantation conditions: the planes of the jaws 32 and 33 are very parallel and the surface is smooth and fine. This is in the form of a ring, the width of which is much greater than the thickness of the diaphragm to prevent hinge action. This profile sill is also very suitable for forming electrical contacts on photoelectrodes attached to the show and diaphragms.

The area 35 adjacent the outer edge of the potting piece provides excellent resistance to stress due to shrinkage of the grain. The L-shaped groove provided on the pieces 32 and 33 acts as an anchor at the periphery and resists sliding force more strongly than a completely flat grate.

Anchor functions can be provided by a variety of norofeels. Their profile shapes, in order of increasing complexity and effectiveness, are L, S.

U, or, more generally, has n bent cycarbs. The greater the number of bends, the greater the resistance to sliding of the fire part. In all cases, the two main geometrical parameters that determine the effectiveness of this anchoring function are the depth p defined with respect to the average plane of the polymeric grating and the radius r of the rounded portion of the bend. The radius r is always
It must be selected to a value that is at least comparable to the thickness of the diaphragm, and preferably on the order of a fraction thereof. The most favorable situation is when the flexural tab of the diaphragm is determined by the acute profile of the jaws, which is possible when made with undercanting. Other methods of making these guns (stamping, extrusion, casting) do not easily produce such profiles.

In such a case, the depth p must be increased or the number of bends must be increased to compensate for the weakening of the frictional resistance of the bends. depth pfd, at least 10 diaphragm thickness
It is best to reduce the amount by two to three times.

6 to 8 show implantable variants according to the invention. In FIG. 6(d) plate 40 is gripped between shows 41 and 42 in an S-shaped profile. In FIG.
A U-shaped embedded profile is imposed on the user. In FIG. 8, the shape of jaws 51 and 52 defines a three-curved groove for embedding grating 5o.

The waveform profile of one jaw is substantially parallel to the waveform profile of the other show.

Its dimensions must be such that, after fixing, the distance between the two corrugations perpendicular to the diamond slum is slightly greater than its thickness (approximately 5 centimeters). With dimensions with this tolerance width, it is avoided that material gets stuck inside the corrugation, and more particularly the fixing force is placed where it is needed, ie on the embedding ring.

Regarding the method of incorporating the diaphragm during the show (two possibilities are conceivable), the corrugated show can be used as a means of forming the diaphragm. In this case, the diaphragm is assembled in the form of a flat disc. inserted into
Tightening the show gives it a wavy profile. In that case, it is preferable to complete the molding by subjecting the diaphragm to a heat treatment at a sufficient temperature after the assembly process to soften the polymer and bring the diaphragm into contact with the curved edges of the norofeel. This method may not be usable if the required clamping force is too great to be applied to the jaws or if the entire device cannot withstand heat treatment. In such cases, the diaphragm should be
Or it can be pre-thermoformed according to a similar profile.

A hybrid method is to tighten the show with a high width, in which case the show acts as a mold for thermoforming.

Regardless of the method of assembly, another advantage of this recessed diaphragm construction is that the jaws can be automatically aligned by fitting the corrugated grooves together. In typical device construction, this function is usually performed by a separate guide piece or by an assembly tool that provides precise alignment. With embedded glofiles according to the present invention, the importance of this function is reduced;
One piece of the assembly may even be omitted.

As a practical example, extensive tests have been carried out on a microphone entry where the recess has an acute S-shaped profile and whose depth p is equal to the thickness of the diaphragm. Tightening was done without prior thermoforming of the diaphragm and then reheated at 90°C for 1 hour. After several thousand hours of storage at -40°C, the relative change in microphone sensitivity after returning to 1 degree ambient packing did not exceed 10 or -0.5 dB. This test was performed on approximately 20 microphones.

[Brief explanation of drawings]

FIG. 1 shows the basic structure of a microphone insert having a vibrating element in the form of an embedded grate; FIGS. ° Figure 3 is a vertical sectional view of the microphone insertion part,
The figures show annular bead-embedded norofils according to the invention, and FIGS. 5 to 8 show variations of the embedding profile according to the invention. 3... Great, 4... Diaphragm, 5.6...
Embedded piece, 17...Diaphragm, 22, 23゜32.33, 41, 42, 46, 47, 51゜52...
・Noyo, 21, 31, 40, 45.50 Guyafram, 20... circular beads. Hajime Imamura, more than agent

Claims (1)

Claims: (1) A device in which a diaphragm is embedded between the jaws and the show exerts a fixing force on the diaphragm in one or more zones of its periphery, the device having a diaphragm that causes contraction of the diaphragm relative to the jaws. An implantable device that is subject to temperature fluctuations and wherein said jaws and said diaphragm define an implantable groin having at least one surface that resists said contraction. (2) The implantable device of claim 1, wherein the diaphragm has piezoelectric properties. (3) The implantable device of claim 1, wherein the diaphragm is made of a polymeric material. (4) The implantable device of claim 1, wherein the diaphragm is made from a polymeric alloy. (5) The implantable device according to claim 1, wherein the main surface of the diaphragm is covered with an electrode. (6) The implantable device according to claim 3, wherein the polymeric material is made from polyvinylisofluoride/or a copolymer thereof. (7) The implantable device of claim 1, wherein the show is a conductive jaw. (8) The implantation device of claim 7, wherein the jaws are made from aluminum. 9. The implantable device of claim 1, wherein the active portion of the diaphragm is convex in shape. (to) The embedded part is of the diaphragm! Implantation device according to claim 1, which is carried out along an eight-edge ring. σ force. Implantation device according to claim 1, wherein said contraction is countered by an annular bead that hooks on the outer surface of the jaw on the periphery of the diaphragm. The implantation device of claim 1, wherein the implantation profile is L-shaped. U→ Implantation device according to claim 1, wherein the implantation profile is S-shaped. Q→ Implantation device according to claim 1, wherein the implantation profile is U-shaped. (1υ An implantation device according to claim 1, wherein the implantation profile is corrugated. uQ An implantation device according to claim 1, in which the depth p of the implantation profile is at least equal to two-tenths to three-tenths of the thickness of the diaphragm. Implant device according to claim 1. Cl force according to claim 1, wherein the value of the radius r of the rounded part of the curve giving the diaphragm the profile is at most equal to the thickness of the diaphragm. Implantation device. C1l The implantation device of claim 1, wherein the implantation profile has an acute angle. (6) the spacing of the jaws in the contraction opposing portion is about 5% greater than the thickness of the diaphragm. An implantation device according to claim 1. An implantation device according to claim 1, wherein the diaphragm is initially flat and the implantation Zorofil is applied by pressing the jaws. How to mold. I2! 21. The method of forming an implantable device according to claim 20, wherein the pressing is performed at a high temperature. 21. The method of molding an implanted device according to claim 20, further comprising: performing a heat treatment after said pressing to complete the molding. ) the diaphragm is thermoformed before pressing;
A method of forming an implantable device according to claim 20. (c) An electromechanical transducer that holds a piezoelectric diaphragm between the nozzles and includes an implanted device according to claim 1. (c) The electric machine four precepts converter according to claim 24, which is used as a microphone insertion section.