FR2573603A1 - OPTO-ACOUSTIC TRANSDUCER IN PARTICULAR FOR ITS USE IN A SPEAKER - Google Patents

Abstract

OPTO-ACOUSTIC TRANSDUCER CHARACTERIZED IN THAT IT INCLUDES A FLAT PHOTO-ELECTRIC CELL 7 OF WHICH ONE SIDE IS MOUNTED NEARBY AND PARALLEL TO A METALLIC DIAPHRAGM 6, THE ARRANGEMENT BEING SUCH AS WHEN A LIGHT BEAM, INCLUDING L 'AMPLITUDE IS MODULATED ACCORDING TO AN ACOUSTIC SIGNAL, STRIKES THE PHOTO-ELECTRIC CELL, THE VOLTAGE PRODUCED BY THE PHOTO-ELECTRIC CELL ACTS ON THE DIAPHRAGM SO THAT THE LAST VIBRATES DEPENDING ON THE INSTANT AMPLITUDE OF THE LIGHT, AND THEREFORE THE ACOUSTIC SIGNAL.

Description

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  The present invention relates to an optoacoustic transducer.

  that, usable, for example, as a speaker.

  Sometimes it is necessary to be able to use a transducer.

  in hazardous environments, such as when the presence of electricity is undesirable.

  One of the aims of the present invention is to provide a trans-

  conductor that can be used in such circumstances.

  To this end, the invention provides an opto-acoustic transducer, which comprises a flat photoelectric cell, one of the faces of which is

  mounted near and parallel to a metallized diaphragm, the agency-

  by being such that when a light beam, the amplitude of which is

  modulated according to an acoustic signal, hits the photocell

  the voltage produced by the photocell acts on the

  diaphragm so that it vibrates according to the amplitude ins-

  of light, and therefore of the acoustic signal.

  The various objects and characteristics of the invention will be

  now detailed in the description which follows, made under

  non-limiting example, referring to the appended figure which represents

  te a sectional view, very simplified, of the effective part of a built-in

  speaker incorporating the present invention.

  There is shown in the figure a glass substrate 1, on the upper face of which is a layer of silicon 2 covered with a

  silicon wafer 3. This silicon wafer has a truncated hole

  fuck. The underside of the silicon wafer and the inclined wall of the hole are covered with a metallized layer 5. The metallized layer 5 forms a single piece with a thin diaphragm 6, obtained by etching,

  whose upper surface is flush with the surface of the silicon wafer

  cium 3 and forms the hole 5; if desired, this upper face can also be curved outwards. The hole is cut by attacking the silicon wafer (3) to obtain the frustoconical wall

the hole.

  A large-area photoelectric cell 7 is placed on the silicon layer 2 and arranged inside the hole. When using the device, a light beam modulated by a signal

  acoustic is "guided" to the underside of the photocell

  electric, through the substrate 1, then the silicon layer 2 which is also transparent. The lasers and optical fibers available on the market transmit sufficient power to allow the guiding of the light beam towards the device using such an optical fiber.

(not shown).

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  The light which strikes the photocell 7 is converted into a voltage which causes a certain level of repulsion of the diaphragm, the latter being thus obliged to oscillate according to the modulation of the

light bleam.

  Thus the photoelectric cell converts optical power into electric power, and the voltage created between the surface of the photoelectric cell and the metallized diaphragm causes repulsion. This repulsion drives the diaphragm causing the air to move. The diaphragm can be arranged at the small end of an acoustic horn, which converts the relatively low output level of the diaphragm into a

audible signal.

  The resonant frequency of the diaphragm must be higher than the highest sound frequency which must be transmitted. The diaphragm can be produced in quartz by plasma attack. It is also possible to use a thin membrane of insulating material, coated with a

  metal layer, for example Mylar.

  The air layer between the photocell and the rear face of the diaphragm should be reduced, as the voltage produced by the photocell is usually less than 1 volt. However, in the case where the modulated incident light is scattered and the charge on the photocell is low, it is possible to use

  several photocells in series.

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Claims (5)

  1. Opto-acoustic transducer characterized in that it comprises a flat photoelectric cell (7) one of the faces of which is mounted close to and parallel to a metallized diaphragm (6), the arrangement being such that when a light beam, the amplitude of which is modulated as a function of an acoustic signal, strikes the photoelectric cell, the voltage produced by the photoelectric cell acts on the diaphragm so that the latter vibrates as a function of the instantaneous amplitude of the   light, and therefore of the acoustic signal.   2. Transducer according to claim 1 characterized in that the photoelectric cell (7) is arranged on a silicon layer (2)   located on one side of a glass substrate (2), the light beam   neux being guided towards the photocell through said substrate then the silicon layer (2).   3. Transducer according to claim 2 characterized in that   that it includes a silicon wafer (3), covering the silicon layer   cium '(2), the underside of which is coated with a metallized layer (5), and in which a hole (4), surrounding the photocell, is   cut, said diaphragm closing said hole (4).   4. A transducer according to claim 3, characterized in that the diaphragm is a layer of insulating material, coated with metal, said metal forming a single piece with said metallized layer (5) to which   it is connected by the wall of said hole (4).   5. Loudspeaker characterized in that it comprises a transducer   according to any one of claims 1 to 4, disposed at the small end mite of an acoustic horn.