radial stiffeners instead of a conventional honeycomb internal struc- ture. Moreover, the improved design is quite easy to manufacture. This is an interesting and clever idea.-GLA

prised of a mobile plate in the form of a conductively coated nylon membrane. The amplifier shows an "impedance inverting network" which utilizes an "operational amplifier." There may be several original factors in this patent which close study would reveal.-RWC

4A68,725

43.88.Bs ELECTRET MICROPHONE

S. Nakagawa and M. Shinohara, assignors to Hosiden Electronics Company

19 May 1981 (Class 179/111 E); fred in Japan 21 August 1978

This patent describes the layout for an electret combining most of the prior art features, including a polarized dielectric fdm depo- sited on a metal foil; a generally thin layout; an impedance-reducing element comprised of a field-effect transistor and damping members front and rear to approximate a cardioid field pattern. Murphy Re. 28, 4 20 is cited, presumably for polarization.-RWC

4,281,222

43.88.Bs MINIATURIZED UNIDIRECTIONAL ELECTRET MICROPHONE

S. Nakagawa and M. Shinohara, assignors to Hosiden Electronics Company

28 July 1981 (Class 179/111 E); fred in Japan 30 September 1978

This patent follows up 4,268,725 (reviewed above) to the same inventors and assignee with a •ing date one month later. It encom-

4A86,122

43.88.Bs ACOUSTIC ELECTRICAL CONVERSION

DEVICE WITH AT LEAST ONE CAPACITOR ELECTRET

ELEMENT CONNECTED TO AN ELECTRONIC CIRCUIT

Wilhelmus H. Iding, assignor to U.S. Philips Corporation 25 August 1981 (Class 179/111 E); fred in the Netherlands

13 March 1978

There is an extraordinary structure described in minute detail in this patent. Every dimension, every detail of the electret foil, every part of the supporting structure is presented. It is as if several years of engineering work were encompassed in one patent applica- tion. The patent describes a head-on attack on the neutralization of ambient vibration pickup by constructing a microphone with back-

9 $ 2 $ /,/3

/ Ill t 8 635 2 8

to-back diaphragm portions. Such neutralization has been shown in many patents, but few have survived to see the light of success when duplication is attempted. Specifically a honeycomb back plate has alternate portions which form a checkerboard with one side facing one way and the other side facing the opposite way. A cross section of the device is shown.-RWC

24 20 23 16 14

,•15

41

37-'

45-

38 •

29 •'48

passes various improvements by which better cardioid pattern is ob- tained without increased axial dimension.-RWC

4,281,221

43.88.Bs CONDENSER MICROPHONE

Vincenzo DelBello, assignor to Societa Italiana Telecomunicazioni Siemens S.p.A.

28 July 1981 (Class 179/111 R); fred in Italy 12 July 1978

This patent describes an ingenious amplifying system coupled to a "condenser" microphone. This is described as a transducer com-

4,302,633

43.88.Bs ELECTRODE PLATE ELECTRET OF

ELECTRO-ACOUSTIC TRANSDUCER AND ITS

MANUFACTURING METHOD

J. Tamamura, Y. Murakami, and A. Terada, assignors to Hosiden Electronics Company

24 November 1981 (Class 179/111 E); fried 28 March 1980

A relatively new class of polarizable fdm is 4 ethylene fluoride-6 propylene fluoride copolymer. New polarization methods are re- quited. The patent describes the forming of a tripleqayer film with the outer layers being capable of withstanding higher temperatures than the middle layer. This tripleqayer f'fim is then polarized at temperatures greater than would have been possible without the outer protective layers. The polarization system is described in ex- traordinary detail.-RWC

4,302,634

43.88.Bs SPRING FORCE BIASING MEANS FOR A

CAPACITANCE-TYPE ELECTROSTATIC TRANSDUCER

Richard Paglia, assignor to Polaroid Corporation 24 November 1981 (Class 179/111 R); f'ded 5 May 1980

There is a problem in small capacitance-type transducers main- raining even tension in the diaphragm. It is stated that this is especially difficult when a given transducer is used alternatively as microphone and reproducer. The solution described is a leaf spring interposed between the backphte and the diaphragm, having alter- nate strips bent oppositely to engage both parts and press them a- part with controlled force.-RWC

1314 J. Acoust. Soc. Am. 71 (5), May 1982' 0001-4966/82/051314431500.80; ¸ 1982 Acoust. Soc. Am ß Patent Reviews 1314

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