GB2079056A - Electret device - Google Patents
Electret device Download PDFInfo
- Publication number
- GB2079056A GB2079056A GB8119539A GB8119539A GB2079056A GB 2079056 A GB2079056 A GB 2079056A GB 8119539 A GB8119539 A GB 8119539A GB 8119539 A GB8119539 A GB 8119539A GB 2079056 A GB2079056 A GB 2079056A
- Authority
- GB
- United Kingdom
- Prior art keywords
- cover body
- electret device
- dielectric body
- electret
- dielectric
- 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
- 239000004020 conductor Substances 0.000 claims description 5
- 239000012811 non-conductive material Substances 0.000 claims description 5
- 239000000126 substance Substances 0.000 claims description 3
- 239000011230 binding agent Substances 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 13
- 238000009826 distribution Methods 0.000 description 7
- 230000010287 polarization Effects 0.000 description 6
- -1 polyethylene Polymers 0.000 description 6
- 230000005684 electric field Effects 0.000 description 5
- 239000003989 dielectric material Substances 0.000 description 4
- 230000014759 maintenance of location Effects 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 230000002463 transducing effect Effects 0.000 description 3
- 239000004698 Polyethylene Substances 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- XECAHXYUAAWDEL-UHFFFAOYSA-N acrylonitrile butadiene styrene Chemical compound C=CC=C.C=CC#N.C=CC1=CC=CC=C1 XECAHXYUAAWDEL-UHFFFAOYSA-N 0.000 description 2
- 229920000122 acrylonitrile butadiene styrene Polymers 0.000 description 2
- 239000004676 acrylonitrile butadiene styrene Substances 0.000 description 2
- 239000003990 capacitor Substances 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 229920000573 polyethylene Polymers 0.000 description 2
- 229920001155 polypropylene Polymers 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 1
- 101100400378 Mus musculus Marveld2 gene Proteins 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 229920001577 copolymer Polymers 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 150000002605 large molecules Chemical class 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000015654 memory Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 229920000139 polyethylene terephthalate Polymers 0.000 description 1
- 239000005020 polyethylene terephthalate Substances 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 239000001993 wax Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G7/00—Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture
- H01G7/02—Electrets, i.e. having a permanently-polarised dielectric
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/22—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using ferroelectric elements
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
Abstract
An electret device (16) comprises, a polarized dielectric body (10) secured at one surface to a conductive electrode (12) and attached at its surface opposite to the conductive electrode to a cover body (14). The material of the cover body (14) may be conductive, semi- conductive or non-conductive. <IMAGE>
Description
SPECIFICATION
Electret device
This invention relates to an electret device.
An electret is a dielectric body which is provided with a volume of surface electric charge. The electret dielectric body retains the electric charge for a very long time, often measured in tens of years. The electric charge, or the dielectric polarization, is achieved, for example in one process, by heating a body of dielectric material to a relatively high temperature while the material is exposed to an intense electric field for a substantial time and then cooling the material while maintaining its exposure to the electric field. Upon cooling, the material exhibits characteristics of a permanent charge distribution.
Electrets have many uses as transducers such as microphones, loudspeakers or recorddisc pick-ups. Moreover, electrets are hoped to be used as memories, high potential sources, measuring apparatus and other devices in the near future.
Electrets are dielectrics which produce static electric fields having relatively long lifetimes.
Their long lifetimes are mainly attributable to the development of new materials which are more stable than the earlier employed waxes.
Today, plastics materials such as polyethylene, polypropylene, polyethylene terephthalate are extensively used to form electrets.
Conventionally, electrets are used in the form of electret devices of which an electret body is secured on a conductive electrode.
These electret devices have drawbacks in that the surface charge distribution is less uniform.
According to the present invention, there is provided an electret device, comprising:
a dielectric body provided with electric charges, a conductive electrode on one surface of the dielectric body and a cover body on the opposite surface of the dielectric body.
The present invention will now be described by way of example with reference to the accompanying drawings, in which:~
Figure 1 is a sectional view of an embodiment of an electret device according to the present invention;
Figure 2 shows graphs illustrating charge potential distributions on electret devices;
Figure 3 shows graphs illustrating charge retention properties of embodiments of electret devices according to the present invention;
Figures 4a and 4b are sectional views of modified embodiments of an electret device according to the present invention; and
Figures 5, 6, 7, 8, 9, 10 and 11 are sectional views of other embodiments of electret devices according to the present invention, illustrating various mechanical fixing means for the electret devices.
Throughout the drawings, like reference numerals will be used to designate like or equivalent portions.
Figure 1 shows a sectional view of an embodiment of an electret device 16 according to the present invention. A dielectric body 10 is formed as a plate and provided with a volume of electric charge. A conductive electrode 12 is secured on one flat surface of dielectric body 10. A cover body 14 is attached to the other flat surface of the dielectric body 10, opposite to the conductive electrode 12. The combination of the dielectric body 10 and the conductive electrode 12 is similar to a conventional electret device.
Usually, the polarization is carried out by, for example, imposing an electrical field or applying charged particles like ions before or after conductive electrode 12 is combined with dielectric body 10. The polarity of the dielectric body 10 may be decided by the polarity of the electrical field or charged particles.
Almost all dielectric materials with the nature of an electret may be adopted for the dielectric body 10. High molecular weight compounds like polypropylene, fluorine-containing polyolefins (such as polytetrafluoroethylene) or polyethylene are, however, especially suitable because electric charge in those materials becomes relatively high in potential and is maintained for a long time.
The material of cover body 14 may be a conductive, semi-conductive or non-conductive material or a mixture of such a material with at least one other substance. In the case of non-conductive materials, for example glass or an organic compound with a volume resistivity of more than 10'2Q-cm is particularly suitable. The polarization of the dielectric body 10 is required to be carried out before the cover body 14 has been attached to the dielectric body 10, providing cover body 14 is made of non-conductive or dielectric material.
In the electret device 16 described above, the cover body 14 is polarized dielectrically under the affect of charged dielectric body 10. A positive polarity appears on the cover body 14 at its one surface remote from dielec- tric body 10, providing the polarity of the surface charge of dielectric body 10 is positive, and vice versa. That is, a polarity the same as the polarity of the surface charge of dielectric body 10 appears on the surface of the cover body 14.
Fig. 2 shows graphs comparatively illustrating potential distribution characteristics on the electret device 16 and a conventional electret device, the charge potential in volts (V) being plotted against location on the upper surface, starting at one end and finishing at the opposite end. Graph A is a potential distribution characteristic of the electret device 16 and graph B is a potential distribution characteristic of a conventional electret device similar in its size with that of the device 16. As will be understood from the almost flat characteristic of graph A, the electret device 16 has an exceedingly uniform surface charge at every part of the upper surface of the cover body 14. On the other hand, the conventional electret device does not have a uniform surface charge.
The electret device 16 therefore provides a very good usefulness due to its good uniformity of surface charge distribution. That is, for example, transducers using electret device 16 may provide high-fidelity transducing characteristics because the electrostatic forces arising between electret device 16 as one electrode of a transducing capacitor and an opposite electrode are uniform at every part of the transducing capacitor.
The electret device 16 is provided with exceedingly long-lived charge or polarization retention properties because dielectric body 10 is protected from being exposed to the air by cover body 14, and the charge becomes hard to drain away from dielectric body 10.
Charge retention properties are shown in
Fig. 3 in which charge potential in volts (V) is plotted against time in hours (H). Graph C represents the property of an electret device 16 whose cover body 14 is made from conductive material or metal. On the other hand, graph D represents the property of an electret device 16 whose cover body 14 is made from non-conductive material, for example ABS (acrylonitrile-butadiene-styrene) copolymer. The charge potential of graph C is maintained, for a long time, almost the same as the value at the time of its fabrication. The charge potential of graph D gradually decreases after the time of its fabrication, but the charge potential approaches a steady state about 24 hours afterwards. Then, both of the charge potentials remain at the steady states for a very long time.
Furthermore, an electret device 16 whose cover body 14 is made of conductive material is easily capable of having its decreased surface charge increased by means of supplying a high potential voltage between conductive electrode 12 and conductive cover body 14 because dielectric body 10 is repolarized by the high potential voltage.
The surface area at cover body 14 may be made not only the same as, but also smaller or larger than that of the dielectric body 10 as shown in Figs. 4a and 4b.
In the electret device having a smaller cover body 14 than dielectric body 10 as shown in
Fig. 4a, the charge potential is the same as that of an electret device 16 having the same area cover body 14 as shown in Fig. 1. The charge potential of those electret devices 16 are given by the equation below:
Es = K. Eo where Es represents the charge potential in volts of the electret device 16 as a whole, Eo represents an average charge potential in volts of the dielectric body 10 and K is a polarization constant of the material of cover body 14.
The value of Es is always lower than the value of Eo because the constant K is less than one. The constant K of metal is a numerical value between about 0.6 and 0.99, and the constant K of glass is around 0.83, in our measurements. Therefore, the charge potential of the electret device 16 may be regulated to a desired value by a selection of the material for cover body 14, provided that the desired potential is lower than the average charge potential of the dielectric body 10. In the electret device 16 having a larger cover body 14 as shown in Fig. 4b, the charge potential is a function of the surface area ratio according to the overlapping condition of dielectric body 10 and cover body 14, according to the equation below: S1 Es = K .Eo . - S2 where Es represents the charge potential in volts of the electret device 16 as a whole, Eo represents the average charge potential in volts of dielectric body 10, K represents a polarization constant of the cover body material, S, represents the surface area of cover body 14 and 82 represents the overlapping area of cover body 14 with dielectric body 10. That is, the charge potential of the whole of the electret device 16 becomes lower than that of dielectric body 10, provided that cover body 14 protrudes partly beyond the surface of dielectric body 10. Therefore, the charge potential may also be regulated to a desired value by changing the surface area or the position of cover body 14 for dielectric body 10, provided that the desired potential is lower than that of dielectric body 10.
A lowering of the charge potential is probably due to a repulsion between the dielectric charges on a surface apart from dielectric body 10.
Cover body 14 and dielectric body 10 are required to be fixed with each other because the charge potential Es of the electret device 16 changes in accordance with the position and relationship between cover body 14 and dielectric body 10 as explained above. Figs.
5, 6, 7, 8, 9, 10 and 11 show embodiments of electret devices according to the present invention with various mechanical fixing means. In the electret device 16 of Fig. 5, cover body 14 and dielectric body 10 are fixed with each other by binding agent 18. In the electret device 16 of Figs. 6 and 7, cover body 14 and dielectric body 10 are fixed with each other by screws 19 (Fig. 6) and pins 20 projecting from dielectric body 10 (Fig. 7). In the case of cover body 14 being metal, the material for screws 18 and pins 20 is nonconductive for avoiding an electrical connection of conductive electrode 12 to cover body 14. The top portions of projecting pins 20 are formed into heads 202 after cover body 14 has been applied to dielectric body 10.
In the electret device 16 of Fig. 8, cover body 14, with a smaller surface area than dielectric body 10, is inserted in a recess 22 of dielectric body 10. On the other hand, in the device 16 of Fig. 9, a cover body 14 with larger surface area than dielectric body 10 covers the whole upper surface of dielectric body 10. Figs. 10 and 11 show other embodiments, using clamps. In the electret device 16 of Fig. 10, two clamps 24 hold the combination of cover body 14, dielectric body 10 and conductive electrode 12 at opposite sides, each clamp having parallel legs 242 and 244. In the electret device 16 of Fig. 11, the combination of cover body 14, dielectric body 10 and conductive electrode 12 is inserted into a tube-like clamp piece 26 and is secured against a lip portion 262 of clamp piece 26 by a screwed-in ring-like clamp piece 28.
Claims (15)
1. An electret device, comprising:
a dielectric body provided with electric charges, a conductive electrode on one surface of the dielectric body and a cover body on the opposite surface of the dielectric body.
2. An electret device according to claim 1, wherein said cover body comprises conductive material.
3. An electret device according to claim 1, wherein said cover body comprises non-conductive material.
4. An electret device according to claim 1, wherein said cover body comprises semi-conductive material.
5. An electret device according to claim 3, wherein said cover body is formed by an inorganic substance.
6. An electret device according to claim 3, wherein said cover body is formed by an organic substance.
7. An electret device according to any preceding claim, wherein said cover body has a larger surface than that of said dielectric body.
8. An electret device according to any of claims 1 to 6, wherein said cover body has a smaller surface than that of said dielectric body.
9. An electret device according to any preceding claim, wherein said cover body is mechanically fixed to said dielectric body.
10. An electret device according to claim 9, wherein said dielectric body has a recessed part in its surface adjacent said cover body and said cover body is received in the recessed part of said dielectric body.
11. An electret device according to claim 9, wherein said cover body is fixed to said dielectric body by means of a fastener.
12. An electret device according to claim 11, wherein said fastener is a stud.
13. An electret device according to claim 11, wherein said fastener is a clamp.
14. An electret device according to claim 9, wherein said cover body is fixed to said dielectric body by a binding agent.
15. An electret device, substantially in accordance with any example herein described with reference to the accompanying drawings.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8882080A JPS5714296A (en) | 1980-06-30 | 1980-06-30 | Electret structure |
| JP8877880A JPS6046600B2 (en) | 1980-06-30 | 1980-06-30 | Manufacturing method of electret structure |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2079056A true GB2079056A (en) | 1982-01-13 |
| GB2079056B GB2079056B (en) | 1985-04-17 |
Family
ID=26430119
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8119539A Expired GB2079056B (en) | 1980-06-30 | 1981-06-24 | Electret device |
Country Status (2)
| Country | Link |
|---|---|
| DE (1) | DE3125784A1 (en) |
| GB (1) | GB2079056B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2266792A1 (en) * | 2008-03-27 | 2010-12-29 | Asahi Glass Company, Limited | Electret and electrostatic induction conversion device |
| US8129869B2 (en) | 2008-09-19 | 2012-03-06 | Asahi Glass Company, Limited | Electret and electrostatic induction conversion device |
| US8277927B2 (en) | 2008-04-17 | 2012-10-02 | Asahi Glass Company, Limited | Electret and electrostatic induction conversion device |
| US8763461B2 (en) | 2008-03-31 | 2014-07-01 | Asahi Glass Company, Limited | Acceleration sensor device and sensor network system |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS57188105A (en) * | 1981-05-14 | 1982-11-19 | Toshiba Corp | Electret constituent |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3632443A (en) * | 1968-04-27 | 1972-01-04 | Sony Corp | Method of making polypropylene electrets |
| GB1302590A (en) * | 1969-09-10 | 1973-01-10 | ||
| JPS5220851B1 (en) * | 1969-12-11 | 1977-06-07 | ||
| US3705312A (en) * | 1970-11-02 | 1972-12-05 | Bell Telephone Labor Inc | Preparation of electret transducer elements by application of controlled breakdown electric field |
| US3769096A (en) * | 1971-03-12 | 1973-10-30 | Bell Telephone Labor Inc | Pyroelectric devices |
| US3736436A (en) * | 1971-11-04 | 1973-05-29 | Mc Donnell Douglas Corp | Electret pressure transducer |
| SE362571B (en) * | 1971-12-02 | 1973-12-10 | Ericsson Telefon Ab L M | |
| US3821491A (en) * | 1972-05-15 | 1974-06-28 | Amperex Electronic Corp | Microphone construction |
| JPS6051279B2 (en) * | 1977-10-19 | 1985-11-13 | 呉羽化学工業株式会社 | Method for polarizing thermoplastic resin piezoelectric pyroelectric film |
-
1981
- 1981-06-24 GB GB8119539A patent/GB2079056B/en not_active Expired
- 1981-06-30 DE DE19813125784 patent/DE3125784A1/en not_active Ceased
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2266792A1 (en) * | 2008-03-27 | 2010-12-29 | Asahi Glass Company, Limited | Electret and electrostatic induction conversion device |
| EP2266792A4 (en) * | 2008-03-27 | 2011-08-24 | Asahi Glass Co Ltd | Electret and electrostatic induction conversion device |
| US8212433B2 (en) | 2008-03-27 | 2012-07-03 | Asahi Glass Company, Limited | Electret and electrostatic induction conversion device |
| US8763461B2 (en) | 2008-03-31 | 2014-07-01 | Asahi Glass Company, Limited | Acceleration sensor device and sensor network system |
| US8277927B2 (en) | 2008-04-17 | 2012-10-02 | Asahi Glass Company, Limited | Electret and electrostatic induction conversion device |
| US8129869B2 (en) | 2008-09-19 | 2012-03-06 | Asahi Glass Company, Limited | Electret and electrostatic induction conversion device |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3125784A1 (en) | 1982-05-27 |
| GB2079056B (en) | 1985-04-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |