GB2219129A - Piezoelectric composites - Google Patents
Piezoelectric composites Download PDFInfo
- Publication number
- GB2219129A GB2219129A GB8812508A GB8812508A GB2219129A GB 2219129 A GB2219129 A GB 2219129A GB 8812508 A GB8812508 A GB 8812508A GB 8812508 A GB8812508 A GB 8812508A GB 2219129 A GB2219129 A GB 2219129A
- Authority
- GB
- United Kingdom
- Prior art keywords
- composite
- manufacturing
- polymer
- ceramic
- piezoelectric
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000002131 composite material Substances 0.000 title claims abstract description 91
- 229920000642 polymer Polymers 0.000 claims abstract description 59
- 239000000919 ceramic Substances 0.000 claims abstract description 53
- 239000011159 matrix material Substances 0.000 claims abstract description 26
- 238000004519 manufacturing process Methods 0.000 claims abstract description 24
- 238000000034 method Methods 0.000 claims abstract description 18
- 239000007772 electrode material Substances 0.000 claims abstract description 10
- 230000009257 reactivity Effects 0.000 claims abstract description 6
- 239000000203 mixture Substances 0.000 claims description 9
- 150000002118 epoxides Chemical class 0.000 claims description 6
- 229910052751 metal Inorganic materials 0.000 claims description 6
- 239000002184 metal Substances 0.000 claims description 6
- 239000000758 substrate Substances 0.000 claims description 4
- 239000011231 conductive filler Substances 0.000 claims description 2
- 229920001577 copolymer Polymers 0.000 claims description 2
- 229920001971 elastomer Polymers 0.000 claims description 2
- 229920002959 polymer blend Polymers 0.000 claims description 2
- 239000011342 resin composition Substances 0.000 claims 1
- 239000000843 powder Substances 0.000 abstract description 5
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 5
- 229920005989 resin Polymers 0.000 description 5
- 239000011347 resin Substances 0.000 description 5
- 229910052709 silver Inorganic materials 0.000 description 5
- 239000004332 silver Substances 0.000 description 5
- 239000002245 particle Substances 0.000 description 4
- 239000006185 dispersion Substances 0.000 description 3
- 239000003822 epoxy resin Substances 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229920003986 novolac Polymers 0.000 description 3
- 229920000647 polyepoxide Polymers 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 238000000748 compression moulding Methods 0.000 description 2
- 239000004020 conductor Substances 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- IIZPXYDJLKNOIY-JXPKJXOSSA-N 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine Chemical compound CCCCCCCCCCCCCCCC(=O)OC[C@H](COP([O-])(=O)OCC[N+](C)(C)C)OC(=O)CCC\C=C/C\C=C/C\C=C/C\C=C/CCCCC IIZPXYDJLKNOIY-JXPKJXOSSA-N 0.000 description 1
- 244000068988 Glycine max Species 0.000 description 1
- 235000010469 Glycine max Nutrition 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 238000004026 adhesive bonding Methods 0.000 description 1
- 238000003491 array Methods 0.000 description 1
- 238000004814 ceramic processing Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000009734 composite fabrication Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- NKZSPGSOXYXWQA-UHFFFAOYSA-N dioxido(oxo)titanium;lead(2+) Chemical class [Pb+2].[O-][Ti]([O-])=O NKZSPGSOXYXWQA-UHFFFAOYSA-N 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 229910052732 germanium Inorganic materials 0.000 description 1
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 1
- 238000007731 hot pressing Methods 0.000 description 1
- 230000002706 hydrostatic effect Effects 0.000 description 1
- 238000001746 injection moulding Methods 0.000 description 1
- 229940067606 lecithin Drugs 0.000 description 1
- 235000010445 lecithin Nutrition 0.000 description 1
- 239000000787 lecithin Substances 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 238000003801 milling Methods 0.000 description 1
- 238000010422 painting Methods 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 229920001296 polysiloxane Polymers 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 150000003512 tertiary amines Chemical class 0.000 description 1
- 238000001721 transfer moulding Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/01—Manufacture or treatment
- H10N30/09—Forming piezoelectric or electrostrictive materials
- H10N30/092—Forming composite materials
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Composite Materials (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
- Compositions Of Oxide Ceramics (AREA)
Abstract
The invention relates to piezoelectric composites and more particularly, but not exclusively, to a method of manufacturing a composite material in which a piezoelectric ceramic is dispersed as a powder within a polymer matrix. The method comprises forming a composite including a ceramic dispersed within a polymer matrix, partially curing the polymer matrix to a desired resistivity relative to the resistivity of the ceramic, applying a poling field to the composite to render the ceramic piezoelectric and increasing the resistivity of the polymer matrix by further curing. In one embodiment electrodes are bonded to the ceramic polymer composite by utilising the residual reactivity in the partially cured composite material to bond chemically the composite to the electrode material.
Description
IMPROVEMENTS IN AND RELATING TO PIEZOELECTRIC COMPOSITES
The present invention relates to piezoelectric composites and more particularly, but not exclusively, to a method of manufacturing a composite material wherein a piezoelectric ceramic is dispersed uniformly as a powder through a polymer matrix.
It is known that piezoelectric ceramics are widely used in transducer applications ranging from simple piezoelectric buzzers to complex multilayer actuators. They are also extensively utilised in underwater transducer applications such as hydrophones despite a number of distinct disadvantages. Although they have large d33 piezoelectric coefficients, these materials often have poor hydrostatic piezoelectric coefficients because the d31 coefficients are negative and serve to cancel out the contribution made by the d33 coefficient since dh = d33 + 2d31. In some applications their high permittivities are undesirable because this leads to a low voltage coefficient (gh = dh/e). Their high densities also prevent good impedance matching to water.Finally, being brittle ceramics they require sintering or hot pressing and subsequent machining to achieve the required shapes and in many cases a more compliant material with greater shock resistance is preferred.
One possible way of obviating these undesirable properties is to produce a composite material in which the ceramic powder is dispersed in a polymeric phase. This so called 0-3 composite approach offers distinct advantages for many uses since the polymer phase lowers the permittivity and density making the composites more suitable for underwater applications. The polymer phase also increases the compliance of the composite and offers the possibility of processing by more economical plastics processing technology such as compression, transfer and injection moulding. Using this approach the fabrication of complex shapes is much easier than by conventional ceramic processing and in particular the manufacture of large area tiles for underwater flank array application is considerably simplified.
The dispersion of the ceramic powder into a polymeric matrix is such that the individual particles of ceramic are effectively isolated from each other in all three dimensions by a continuously connected polymer. Because the ceramic particles are small compared with the thickness of typical composites, it is difficult to achieve satisfactory poling of the composite at the fields typically used for the ceramic.
This is because the field is disproportionately applied across the polymer rather than the ceramic as can be seen from the following equation which defines the field acting across an isolated ceramic particle in a low permittivity matrix:
E1, the field appearing across the ceramic particle is determined by the permittivities of the ceramic kl and the polymer k2. For typical values of 2000 for a piezoelectric ceramic and an epoxide matrix of 4.3, the field appearing across the ceramic could be less than 1% of the applied field Eo, and consequently very high fields would be required to achieve acceptable poled activity from the ceramic.
However, where the poling field can be applied to the composite for periods well in excess of the sample relaxation time, as in typical DC poling, the relationship between the electric fields appearing across the ceramic and polymer matrix can be defined by the Maxwell Wagner model as: E1/E2 = P1/P2 where E1 and E2 are the fields across the ceramic and polymer respectively and P1 and P2 are the resistivities of the ceramic and polymer. Consequently, if the resistivity of the ceramic and polymer matrix can be balanced it is possible to achieve reasonable poling of the ceramic. Most polymers have resistivities several orders of magnitude higher than the ceramic.The resistivity of a typical modified lead titanate ceramic at room temperature would be ~ 5 x 1010cm, whereas a suitable silicone or high purity epoxide might be 1 x 1015cm.
Various methods have been proposed to reduce the resistivity of the resin systems used, typical examples include loading the polymer with conducting or semiconducting materials such as carbon, germanium and silicon. Alternatively, lower purity resins can be used to closely match the resistivity to the ceramic. In many transducer applications however, it is desirable to maintain the highest resistivity possible in the polymer matrix in order to minimise the contribution to the dielectric loss of the composite and hence reduce the electrical noise generated. Also, the higher the resistivity of the polymer the higher the loading of conductive phase that is required to achieve a resistivity balance. At levels above 1.5 vol% loading the dielectric loss increases rapidly, and the application of large fields becomes increasingly difficult.
According to the present invention there is provided a method of manufacturing a piezoelectric composite, the method comprising forming a composite including a ceramic dispersed within a polymer matrix, partially curing the polymer matrix to a desired resistivity relative to the resistivity of the ceramic, applying a poling field to the composite to render the ceramic piezoelectric and increasing the resisflvity of the polymer matrix by further curing.
In one embodiment electrodes are bonded to the ceramic polymer composite by utilising the residual reactivity in the partially cured composite material to bond chemically the composite to the electrode material.
In one embodiment the poling field is maintained during at least part of the further curing process.
Multilayer composite electrode structures may be fabricated by applying the poling field to alternating layers of part cured polymericeramic and electrode material, and then by applying the further curing process to provide the final composite multilayer structure.
In one embodiment the ceramic polymer composite and the electrode material have identical or similar part cured compositions.
In another embodiment they have dissimilar part cured compositions. For example in the latter embodiment the ceramic polymer composite may be an epoxide resin whilst the electrode material may be a rubber based polymer. In yet a further embodiment co-polymer or polymer blends are utilised for both the composition of the ceramic polymer composite and the electrode polymer.
In a preferred embodiment the polymer matrix of the composite exhibits a large resistivity change during curing, the resistivity of the polymer matrix being similar to the ceramic in the partially cured state but being significantly higher after the full cure.
The electrode may in one form be screen printed on to the partially cured composite, the poling field being applied via the screen printed electrode and the electroded composite being fully cured with the poling field applied.
In one embodiment the desired resistivity of the polymer matrix is achieved partly by loading the composite with a conductive filler and partly by exploiting the resistivity change on curing of the composite polymer mix.
Other aspects of the invention include the provision of a piezoelectric/polymer '0-3' composite manufactured by embodiments of the invention described above; and the manufacture of a transducer incorporating piezoelectric composites manufactured in accordance with the present invention. In one embodiment the method of manufacturing the transducer includes bonding of the partially cured, poled composite to a metal substrate by utilising the residual reactivity of a partially cured resin component of the composite. In another embodiment the partially cured composite is attached to a metal substrate during the final curing process whilst simultaneously applying the poling field.
This invention is based on the fact that the resistivity of most polymers changes between the cured and uncured states, and is particularly relevant when the changes are several orders of magnitude. With the correct choice of polymer matrix, its resistivity can be made to balance the ceramic resistivity. By partially curing the polymer to the required resistivity, poling can be achieved before final cure of the resin is completed. In this way high purity, high resistivity polymers can be utilised in composite fabrication and these can provide both the resistivity balance required for poling to suitable activity and the high resistivities required to produce low loss composites for low noise transducers.
The concept of utilising a partially cured polymer matrix also offers the advantage of allowing chemical bonding of electrode structures to the piezoelectric ceramic polymer composite. In order to pole a typical composite structure, and also to allow the electrical connection required for any conceivable transducer application, electrodes have to be applied. Simple electroding can be achieved by painting on conductive silver electrodes such as silver DAG but for enhanced ruggedness robust conductive polymeric electrodes are preferred. There is often difficulty in bonding these electrodes to the fully cured polymer ceramic composites resulting in poor interfacial integrity between the composite and the electrode. By utilising only a partial cure, the composite polymer matrix can have sufficient reactivity remaining to allow chemical bonding of the polymeric electrode system.Various alternatives exist with this method, for example, the partially cured composite could have the polymeric electrode attached by further partial curing. The composite would then be poled and full cure completed after poling or even towards the end of poling, with the temperature being increased whilst the field was still applied. Alternatively poling could be achieved by the attachment of temporary electrodes, such as silver DAG, to the composite which would then be removed prior to attachment of the robust electrodes and final cure.
Further possibilities exist for utilising the partial cure concept, since advanced device structures could be configured in such a way as to allow direct bonding of the transducers to their host vehicle, plane or vessel. An example would be in the bonding of hydrophone tiles directly to submarine hulls in flank arrays. This method would be particularly suitable for attaching larger area transducers to any metal surface such as aircraft fuselage or perhaps underground piping systems. Poling during transducer attachment, by the use of suitable corona poling equipment would also be possible. A combined poling/curing apparatus might also be feasible for certain applications.
As an example of a composite utilising this partial cure route, a piezoelectric ceramic and an epoxide resin system could be formulated as follows.
The selected ceramic powder is roll milled with the epoxide resin system to facilitate dispersion and this may (optionally) be assisted by the use of a chosen dispersion agent, such a soya bean lecithin. A suitable epoxide system would be an epoxidised novolac cured by the tertiary amine accelerated reaction with a novolac resin.
This type of system has the advantage that it could be partially cured (B staged) at temperatures below 1000C and this could be easily achieved during the milling of the ceramic and polymeric components. This system would also conveniently produce a B stage material which was solid at room temperature, thereby facilitating relatively easy processing. For example, if removed from the roll mill as solid sheets subsequent processing into suitably shaped tiles could be achieved at modest temperatures and pressures by, for example, compression moulding. The temperatures and times of this process would be determined in order to maintain or to adjust the resistivity balance to the desired value. Electrodes would then be temporarily attached and poling performed.After electrode removal, permanent robust electrodes could then be attached to the partially reacted composite. A suitable electrode system would again be a B stage epoxide novolac as used for the composite but this time being filled with a conductive material such as carbon, silver or copper. In addition, a metal mesh could be incorporated to facilitate ease of connection. Alternatively a conductive ink such as a copper or silver filled epoxide system could be screen printed on to the partially cured composite. In all of these examples the composite could be poled after the attachment of the final robust electrode system but prior to final curing. If the chosen resin system requires an elevated temperature cure this could be performed with the poling field still applied in order to prevent depoling although for some ceramics this would not be a problem. If both the partially cured composite and the electrode polymer are identical or are chosen to be chemically compatible in terms of adhesive bonding the two will react during the final cure, effectively eliminating the electrodelcomposite interface.
Claims (17)
1. A method of manufacturing a piezoelectric composite, the method comprises forming a composite including a ceramic dispersed within a polymer matrix, partially curing the polymer matrix to a desired resistivity relative to the resistivity of the ceramic, applying a poling field to the composite to render the ceramic piezoelectric and increasing the resistivity of the polymer matrix by further curing.
2. A method of manufacturing a piezoelectric composite according to claim 1 wherein electrodes are bonded to the ceramic polymer composite by utilising the residual reactivity in the partially cured composite material to bond chemically the composite to the electrode material.
3. A method of manufacturing a piezoelectric composite according to claim 1 or claim 2 wherein the poling field is maintained during at least part of the further curing process.
4. A method of manufacturing a piezoelectric composite according to any one of claims 1 to 3 wherein multilayer composite structures are fabricated by applying the poling field to a plurality of layers of part cured polymer/ceramic via interleaved electrode material, and then applying the further curing process to provide the final composite multilayer structure.
5. A method of manufacturing a piezoelectric composite according to claim 2 wherein the ceramic polymer composite and the electrode material have identical or similar part cured polymer compositions.
6. A method of manufacturing a piezoelectric composite according to claim 2 wherein the ceramic polymer composite and the electrode material have dissimilar part cured polymer compositions.
7. A method of manufacturing a piezoelectric composite as claimed in claim 6 wherein the ceramic polymer composite is an epoxide based composition and the electrode material is a rubber based polymer.
8. A method of manufacturing a piezoelectric composite as claimed in claim 2 wherein copolymer or polymer blends are utilised for both the composition of the ceramic polymer composite and the electrode polymer.
9. A method of manufacturing a piezoelectric composite as claimed in any one of claims 1 to 8 wherein the polymer matrix of the composite exhibits a large resistivity change during curing, the resistivity of the polymer matrix being similar to the ceramic in the partially cured state but being significantly higher after the full cure.
10. A method of manufacturing a piezoelectric composite as claimed in claim 1 wherein an electrode is screen printed on to the partially cured composite.
11. A method of manufacturing a piezoelectric composite as claimed in claim 10 wherein the poling field is applied via the screen printed electrode and the electroded composite is fully cured with the poling field applied.
12. A method of manufacturing a piezoelectric composite as claimed in any one of claims 1 to 11 wherein the desired resistivity of the polymer matrix is achieved partly by loading the composite with a conductive filler and partly by exploiting the resistivity change on curing of the composite polymer mix.
13. A method of manufacturing a transducer, the method comprising manufacturing a piezoelectric composite according to any one of claims 1 to 12, wherein bonding of the partially cured, poled composite to a metal substrate takes place by utilising the residual reactivity of a partially cured resin composition of the composite.
14. A method of manufacturing a transducer, the method comprising manufacturing a piezoelectric composite according to any one of claims 1 to 12, wherein attaching the partially cured composite to a metal substrate takes place during the final curing process whilst simultaneously applying the poling field.
15. A method of manufacturing a piezoelectric composite substantially according to the method as hereinbefore described in the description.
16. A piezoelectricipolymer '0-3' composite manufactured by a method as claimed in any of claims 1 to 13.
17. A transducer incorporating a piezoelectric composite manufactured by a method as claimed in any one of claims 1 to 13.
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8812508A GB2219129B (en) | 1988-05-26 | 1988-05-26 | Improvements in and relating to piezoelectric composites |
| EP89906386A EP0368986A1 (en) | 1988-05-26 | 1989-05-22 | Improvements in and relating to piezoelectric composites |
| PCT/GB1989/000561 WO1989011738A1 (en) | 1988-05-26 | 1989-05-22 | Improvements in and relating to piezoelectric composites |
| AU36976/89A AU613773B2 (en) | 1988-05-26 | 1989-05-22 | Improvements in and relating to piezoelectric composites |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8812508A GB2219129B (en) | 1988-05-26 | 1988-05-26 | Improvements in and relating to piezoelectric composites |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8812508D0 GB8812508D0 (en) | 1988-06-29 |
| GB2219129A true GB2219129A (en) | 1989-11-29 |
| GB2219129B GB2219129B (en) | 1992-06-03 |
Family
ID=10637591
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8812508A Expired GB2219129B (en) | 1988-05-26 | 1988-05-26 | Improvements in and relating to piezoelectric composites |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0368986A1 (en) |
| AU (1) | AU613773B2 (en) |
| GB (1) | GB2219129B (en) |
| WO (1) | WO1989011738A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2243946A (en) * | 1990-05-09 | 1991-11-13 | Plessey Res Caswell | A method of poling an electroactive composite material |
| US7213339B2 (en) * | 2000-12-12 | 2007-05-08 | Gyros Ab | Method of manufacturing a microscale nozzle |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2235576B (en) * | 1989-08-30 | 1993-05-12 | Plessey Co Plc | Improved electro-active composite poling efficiency |
| CN108846191B (en) * | 2018-06-07 | 2022-04-15 | 哈尔滨工业大学 | Distributed parameter saturated capacitance model modeling method for piezoelectric ceramic actuator |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB455186A (en) * | 1936-01-10 | 1936-10-15 | Solomon Marcus Sager | Improvements in a fountain pen |
| US2434143A (en) * | 1943-04-17 | 1948-01-06 | Chilowsky Constantin | Supersonic signal transmitter and receiver |
| GB665452A (en) * | 1944-04-08 | 1952-01-23 | Technical Assets Inc | Method and apparatus for making artificial piezoelectric elements |
| FR2501916A1 (en) * | 1981-03-13 | 1982-09-17 | Commissariat Energie Atomique | PIEZOELECTRIC COMPOSITE MATERIAL AND METHOD FOR MANUFACTURING THE SAME |
| DE3138249C2 (en) * | 1981-09-25 | 1983-10-27 | Siemens AG, 1000 Berlin und 8000 München | Synthetic resin-impregnated piezoceramic body |
-
1988
- 1988-05-26 GB GB8812508A patent/GB2219129B/en not_active Expired
-
1989
- 1989-05-22 AU AU36976/89A patent/AU613773B2/en not_active Ceased
- 1989-05-22 WO PCT/GB1989/000561 patent/WO1989011738A1/en not_active Application Discontinuation
- 1989-05-22 EP EP89906386A patent/EP0368986A1/en not_active Withdrawn
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2243946A (en) * | 1990-05-09 | 1991-11-13 | Plessey Res Caswell | A method of poling an electroactive composite material |
| US7213339B2 (en) * | 2000-12-12 | 2007-05-08 | Gyros Ab | Method of manufacturing a microscale nozzle |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8812508D0 (en) | 1988-06-29 |
| GB2219129B (en) | 1992-06-03 |
| AU613773B2 (en) | 1991-08-08 |
| WO1989011738A1 (en) | 1989-11-30 |
| EP0368986A1 (en) | 1990-05-23 |
| AU3697689A (en) | 1989-12-12 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19920903 |