US2373273A - Signal recording and reproducing method - Google Patents

Description

April 10, 1945. G. c. szlKLAl i SIGNAL RECORDING AND REPRODUCING METHOD Filed Oct. 28, 1942 HMPZ /F/EE HUD/O S/G/HL. SOURCE Snventor IKLHI 1 MREMZ Gttorneg Patented Apr. 10,1945

l 'am .George C. Sziklai, Bloomington, Ind., asslgnor to Radio Corporation of America, a corporation of Delaware Application october 2s, 1942, senat No. 463,610

(ci. 11s-100.1) p

8 Claims.

' This invention relates to a Signal recording and.: reproducing method. and hasfor lts principal object the provisionof a novel method of recording and reproducing sound electrically.

More particularly, it is an object of the present invention to provide an improved method of recording and reproducing sound electrically by means of which high fidelity recording and reproduction may beobtained.

, Another object ofthe present invention is to provide a novel sound record which is durable and permanent in character.

Still another object of the present invention is to provide an improved sound record as aforesaid which will vhave a long playing time. yet will require small storage space.

A further object of the present invention is to provide an improved method of sound recording which will yield a plurality of identical sound records in only one recording operation.

It is also an object of the present invention to provide an improved methed as afoesaid which 1s inexpensive to practice and is highly efficient. as well as to provide an improved record which will-be comparatively lowin cost.

In accordance with this invention, a strip of conductive tape orwire isconnected to one of the terminals of an audio voltage source. the other terminal therecf being connected tn a film forming solution. The stfip is advanced along a path such that it is brought either into contact with or in veryclose proximity to the film forming electrolyte over a very small area of the strip. As the potential changesa dielectric film of varying thickness forms on the conductive strip. 'I'he strip is preferably biased beyond the audio peak voltage, so that the thickness of dielectric lm which forms onv the stripwill be a replicaof the frequency and amplitude of the sound. To reproduce this sound record, the coated strip may be passed through a conductive bath, `again with only a small area thereof in contact with the bath, so that this small portion or area acts as a condenser. The variations in thickness of the dielectric lm will cause the capacity to change corresponding to the audio -yoltage which was used in forming the lilm. This change in capacity may be utilized to change 'the-frequencyfof an associated reproducing cir- 'cuit to produce frequency, amplitude, o: phase modulation,depending upon the typeof reproducing circuit employed. or it may -be utilized .similarly to a condenser microphone, for example, to vary. a suitable voltage to produce A.signal voltages representative of the sound origoperation simultaneously,

inally recorded.' If a relatively wide strip o tape is used on^which to record, the strip may be split longitudinally after recording to provide a plurality of individual, identical records. each of which may be reproduced separately. A plurality of identical records may also be produced by subjecting a number of strips to the recording the strips being arranged in side-by-side relation.

The novel features that I consider charactegistie of my invention are set forth with particularity in the appended claims. -The inven tion itself, however. both as to its organization and method of operation, as well as additional objects and advantages thereof, will best -be understood from the following description of one embodiment thereof. when read in connection with the accompanyingr drawing in which Figure l is a diagrammatic view of a recording system employing the method of my present invention.

Figure 2 is a similar view of a reproducing system by means of which the novel record of my invention may be reproduced, and

Figure 3 is a fragmentary sectional view of one form of my improved record.

Refering more particularly to the drawing.

wherein similar reference characters designate corresponding parts throughout. there is shown. in Flg. l, a source -I of audio signals coupled to an amplifier 3, in turn coupled to an output transformer 5. One terminal of the secondary winding of the tansformer 5 is connected through a polarizing battery l to a conductive receptacle 9 which contains an electrolyte il. The other terminal of the secondary winding'of the transformer has electrical connection with a conductive roller i3 through a resilient brush or the like l5.

A conductive strip, such as a tape or wire il, is fed from a supply reel i9 around the conductive roller i3, then down around a small dielectric vroller 2l where the strip Il is given a sharp.

substantially reverse bendof small radius,zthence around a. roller 23 and on to a takeup reel 25.

The strip ll andthe electrolyte Il are of such I1 is of aluminum. and the electrolyte I| is approxlmately a two percent aqueous solution of borax or Vammonium borate.

so that contact therebetween will be obtainedthrough capillary attraction and the required electrolytic action will take place instantaneously over only a very narrow, line-like area transversely of the strip i1.

It will be obvious, from the foregoing, that, as the signal potential changes, a dielectric iilm layer or coating 21 of varying thickness will be formed along the length of the strip I1. The polarizing battery 1 serves to appliY a bias beyond the peak audio voltage, so that regardless of the direction in which the audio voltage swings, a dielectric film of varying thickness will be formed on the conductive strip I1. In this way, variations in signal voltage will produce a dielectric coating of varying' thickness representative of the frequency and amplitude of the sound or other signals being recorded. Obviously, a number of parallel strips may be fed past the electrolyte Il simultaneously to provide a plurality of identical records which can be reproduced'or played back separately, or, if a wide strip is used, it can be split longitudinally after recording across its entire width to provide a plurality of identical records.

A record formed as above may be utilized in a reproducing system such as that illustrated in Figure 2, for example. In this system there is shown a grounded conductive receptacle 3| containing a conductive body 33, such as mercury. 'Ihe receptacle 3| is connected to one terminal o! a timed circuit 35 which constitutes the tank circuit of a suitable oscillator 31. The other terminal of the tuned circuit is connected through a resilient brush 39 to a large conductive roller I8. The coated strip l1, 21 may be fed from a supply reel 43 around a roller 45, and thence down around a small roller 41 similar to the roller 2| and around which the record strip takes a sharp. substantially reverse bend of small radius. From there, the strip i1, 21 passes around a roller I8 and then is guided by a pair of rollers 49 around and in contact with a large portion of the circumference of the conductive roller l0, and from there, the strip 1, 21 passes around a roller B0 toatakeupreel 4|.

As the successive, small areas of the record strip |1, 21 come into contact with the conductive body 33, the varying thicknesses of the dielectric coating 21 will produce changes in capacity to vary the tuning of the tuned circuit 35 and thereby vary correspondingly the frequency of the voltage supplied by the oscillator 3T. .In this way. there are set up signal voltages representative of the sound originally recorded. The conductive roller l0, in cooperation with that portion ci' the conductive `strip |1 between the rollers I3 and the dielectric coating 21 therebetween i'orms a large -capacitor in series with the small. constantly varying, timing capacitor under the roller I1 and it should be made so large that it will not appreciably alter the tuning provided by the small capacitor under the roller 41. A coupling coil may couple the oscillator circuit to suitable reproducing apparatus such as a limiter, frequency dlscrlminator, amplifier and loudspeaker, to reproduce the sound.

The speed with which the strip I1 is advanced either during recording or reproducing, and the area of contact between the advancing strip and the electrolyte I |-or the conductive body 33, as the case may be, will vary in accordance with the highest frequency which it is desired to record. For example, with an area of exposure of approximately .003 inch along the length of the strip, the strip may be advanced at a rate of 100 inches per minute to record up to -5000 cycles per second. With the same exposure area, if it is desired to .record -up to 10,000 cycles per second, the strip should be advanced at a speed of about 200 inches per minute. However, if the slower speed is preferred, the exposed area should be only 0.0015 inch along the length of the strip. In general, exposure areas oi' from about .01 inch to about .001 inch will be found satisfactory for most practical purposes.

Although I have shown and described certain forms of my invention in considerable detail, it will be obvious to those skilled in the art that many other forms of the invention, as well as variations in the ones described, are possible. For example, in the reproducing system of Fig. 2, a second and relatively long conductive receptacle vsimilar to the receptacle 3| but very much longer than the latter and also containing mercury or any other suitable conductive body may be substituted for the large conductive roller and the strip l1, 21 caused to pass therethrough in advance of the takeup reel. Thus, there will also be provided a large capacitor in series with the small, constantly varying tuning capacitor under the roller 41. Iny an alternative reproducing arrangement, the roller 40 or other conductive member which aids in forming the large capacitor may be entirely dispensed with and the reels 4| and I3 made of conductive material with which both ends of the conductive strip |1 would have electrical contact. One brush corresponding to the brush 39 would then engage one of the reels to connect it to one terminal of the tuned circuit 35 and` another, similar brush would have electrical contact with the other of the reels and would also be connected to the same terminal of the tuned circuit 35. I f the tuned circuit 35 were connected to only one of the reels (for example, the takeup reel 4| then the gradually increasing inductance i'ormedV by the portion of the strip wound thereon would choke off the higher signal frequencies. However, by connecting the tuned circuit 35 to both of the reels 4| and |13, then, as the inductance increases on one wheel it would correspondingly decrease on the other, but the effective inductance would remain constant. Many other changes will, no doubt, readily suggest themselves to those skilled in the art. I therefore desire that my invention shall not be limited except insofar as is made necessary by. the prior art and by the spirit of the appended claims.

I claim as my invention:

1. The method of recording signals which comprises subjecting successive portions of an electro-conductive material to the action of a second material which is adapted to react therewith chemically under the iniiuence of an electrical potential to form adielectric coating thereon while applying thereto avarying potential representative of said signals whereby to form on said chemically under the iniiuence of an electrical tical signal records which comprises passing a astraavs 3 ilrst named material a dielectric coating of varytiguous, small areas oi said strip to contact said ing thickness representative oi said signals. electrolyte as said strip advances in said path, 2. The method of recordingsignals which comand simultaneously applying to said strip varying prises bringing successive, small areas of an elec potentials representative of said signals whereby tro-conductive material into reactive relation to form on said strip a continuous dielectric coatwith a second material which is adapted to react' .ing ci varying thickness representative of said therewith chemically under the influence of an` signals. electrical potential to form a dielectric coating 6. Thev invention set forth in claim 5 .characthereon, and simultaneously applying thereto terized in that said path has a substantially revarylng potentials representative cf said signals l0 verse bend therein of small radius, and characwhereby to form on said irst named material a terized further in that said strip is brought into dielectric coating of varying thickness represencontact with said electrolyte at said bend. tative of said signals. 7.= The invention set forth in claim 5 charac- 3. The method of recording signals which comterized in that said strip is of aluminum, and prises bringing successive, small areas of an elecl5 characterized further in that said electrolyte is tro-conductive material into contact with a secconstituted by an aqueous solution cf a berate. ond material which is adapted to react therewith 8. The method of forming a plurality of idenpotential to form a dielectric coating thereon, strip of electro-conductive material continuously and simultaneously applying thereto varying po- 20 along a path in the neighborhood of an electrotentials representative of said signals whereby lyte which is adapted to react chemically with to i'orm on said rst named material a dielectric said material under the influence of an electrical coating of varying thickness representative of potential to form a dielectric coating on said strip, said signals. causing successive, contiguous, small areas oi' said 4. The invention set iorth in claim 3 charac- 25 strip to contact said electrolyte as said strip adterized in that said areas are contiguous whereby vances in said path, said areas extending all the said coating is continuous on said rst named way across said strip, simultaneously applying to material. said strip varying potentials representative of the 5. The method of recording signals which comsignals whereby to form on said strip a continuous prises passing a strip of electro-conductive maso dielectric coating oi varying thickness representerial continuously along a path in the neighbortative of said signals, and ilnally dividing said hood of an electrolyte which is adapted to react strip longitudinally to thereby provide a plurality chemically with said material under the inuoi' identical, individual records of said signals. ence oi an electrical potential to form a dielectric coating on said strip, causing successive, conas GEQRGE C. SZIKLAI.

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