US 1833640 A
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Nov. 24, 1931. FRUTH 1,833,640
MIGROPHONIC MATERIAL AND METHOD OF PRODUCING THE SAME Filed Dec. 51. 1928 //7 yen/0r 7 H0/ f/h/f/z Patented Nov. 24, 1931 UNITED STATES PATENT OFFICE HAL FBEDERIGK PRU TH, OF CHICAGO, ILLINOIS, ASSIGNOR 'IO WESTERN ELEUIRIG COMPANY, INCORPORATED, 015 NEW YORK, N. Y., A. CORPORATION OF NEW YORK This inventibn relates to microphonic material and methods of producing the same,
and more particularly to a coated, variable resistance material for use in microphone or telephone transmitters.
Objects of the invention are to provide an improved microphonic material and meth' d of producing the same to provide a microphonic material of superior elasticity and sensitivity; to provide a microphonic material having a high melting point and good wearing properties; and to provide a relatively light microphonic material which shall be capable of carrying a heavy electric current.
In general terms, the present invention contemplates the use as a microphonic material of particles of an elastic substance such as glass or other vitreous substance, each particle being coated with a thin layer of metal or other conducting substance, such as platinum or iridium. The invention further contemplates an improved method for "producing the microphonic material wherein a very thin layer of metal is applied to particles of glass or other elastic substance by a cathodic sputtering method. In a microphonic material composed of such particles, the layers of metal or other conducting material are in contact with each other to permit electrical current to pass therethrough, and when pressure is applied to the material, as by a transmitter diaphragm, the particles of glass or other elastic material are distorted in such a manner that the electrical resistance of the material is decreased, but when the pressure is released the particles resume their normal positions quickly because of the high'elasticity of the material. The particles are preferably of spherical, spheroidal, or hollow spherical shape, although granular material may also be used.
The invention will bemore fully understood from the following description, taken in connection with the appended drawings, in which Fig. 1 diagrammatically illustrates an apparatus for coating the particles, and
Fig. 2 is a greatly enlarged sectional view of one form of particle which may be used to make up the microphonic material.
MICROPHONIG MATERIAL AND METHOD OF PRODUCING- THE SAME Application filed December 31, 1928. Serial No. 329,645.
In the drawings, which are to be construed her by means of a rod 17 of insulating material and is connected to anode 14 by means of an electrical circuit 18 which includes the secondary of a transformer 19; The cathode is preferably provided with a cover or shield 20 Within the vacuum chamber is positioned a frame 22 which supports a bin 23 containing a supply 24 of the particles to be coated.
vBy means of a gate 25 the particles are allowed to roll by gravity over an inclined platform 26 which is paralled to and immediate- 1y below the cathode 16, the particles forming a continuous layer 27 which is preferably not more than one particle deep at any point. In order to provide for slow but continuous movement of the particles over the inclined platform, a cylinder 28 is mounted at the lower edge of the platform and is driven at a slow speed by a coiled spring 30 connected thereto by suitable gears 31, 32 and 33. A governor 35 is connected to the train of gears by spiral gearing 36 and 37. A receptacle 38 is positioned to receive the particles passing over cylinder 28.
A vacuum of .1 of mercury or thereabouts is maintained in the vacuum chamber by means of the vacuum pump connected to tube 12, the degree of evacuation being regulated by means of a manually operated bleeder valve 40, the pressure being indicated by a gauge 41.
It will be understood that when a suitable vacuum is produced in the chamber and transformer 19 is energized, current will flow therefrom to cathode 16 and thence through the exhausted atmosphere to anode 14 in the known manner, carrying with it particles of the metal forming the cathode 16 and depositing such particles upon any objects which may lie in .their path, thus coating the layer of particles 27 by the process commonly known as cathodic sputtering. In order to prevent reversal of this action, the surface area of cathode 16 is made several times greatously during their passage, thereby presentspheroidal ing their entire surfaces to the stream of metallic particles and acquiring a thin uniform coating. I
Fig. 2 shows a spherical bead 43 of glass or other vitreous substance having a coating 44: of metal thereon. Such beads without the coating) may be readily made by a process of liquid comminuting and solidifying. The beads may vary considerably in size, and since both the larger and the smaller sizes are undesirable in microphonic material they should be graded by sifting. A satisfactory material may be obtained by thus selecting only those beads which pass a 50-mesh screen and are rejected by a 100-mesh screen, althou h the size of the beads may be varied wide y depending upon the particular nature of the instrument in which the material is to be used and upon other factors.
Hollow beads of the sizes and shapes above specified may be used in place of the solid beads illustrated in Fig. 2. It is also within the scope of the present invention to use as the basis of the microphonic material beads formed of metallic oxides, also granular particles such as may be obtained by crushing and sifting quartz, glass, or other crystalline or vitreous material, the essential qualities of such material being hardness, elasticity, and lightness.
Microphonic material formed in accordance with this invention has a high elasticity and sensitivity, a high melting point and good wearing properties.
It is obvious that the method and apparatus shown and described herein may be widely varied without departing from the spirit of the invention as defined in the following claims.
What is claimed is:
1. Microphonic material consisting of metal-coated glass beads.
2. Microphonic material consisting of hollow, metal-coated glass beads.
3. Microphonic material consisting of particles of glassTcoated with platinum.
4. Microphonic material consisting of particles of glass coated with a noble metal.
5. Microphonic material consisting of partlcles of insulating material having a coating of metal deposited thereon by cathodic sputtering.
6. Microphonic material consisting of particles of a non-carbonaceous material having a coating of metal deposited thereon by cathodic sputterin 7. Microphonic material consisting of particles of an elastic material having a coating of conducting material deposited thereon by cathodic sputtering.
8. Microphonic material consisting of particles-of glass coated with a noble metal by a cathodic sputtering process.
9. A method of producing microphonic material which consists in coating particles .of an elastic substance with metal by cathodic sputtering.
10. A method of producing microphonic material which consists in cathodically sputtering on glass-particles a coating of noble metal.
.11. A method of producing microphonic material which consists in successively moving vitreous particles adjacent a metallic cathode, and depositing on said particles a coating of metal by sputtering from said cathode.
12. A method of producing microphonic material which consists in successively rolling glass particles adjacent a metallic cathode, and activating the cathode to cause metal to be transferred therefrom to the particles.
13. A method of producing microphonic material which consists in positioning particles of insulating materialv adjacent a metallic cathode for a predetermined period, and activating the cathode to cause metal to be transferred therefrom to the particles.
14. Microphonic material comprising particles of glass coated with conducting material.
In witness whereof, I hereunto subscribe my name this 19th dayof December, A. D.,
HAL FREDERICK FRUTH.