US2565996A - Cold cathode gas-filled transducer device - Google Patents

Description

Aug. 28, 1951 P. F. STILL 2,565,996

COLD CATHODE GAS FILLED TRANSDUCER DEVICE Filed Feb. 10, 1948 Patented Aug. 28, 1951 COLD CATHODELGAS-FILLEDTRANSDUGER DEVICE Paul-F. Still, Los Angeles, Califi assignorr to John Steere-Paul. Still; Incorporated, Hollywood; Calif., awcorporation of California" Application February 10, 1948;; SerialaNo:..7;500.-ff*

7 Claims. (Cl. "Bu-100L411.

This invention relatesito electrical apparatus, and' particularlyto an improvedform of. electri-- cal transducer for the conversionof mechanicalenergy, intoelectrical: impulses; ortinto variationsin an electrical current.

It :is a principal object: of the I invention to provide a transducer of: extremely simple and economical construction;.,yetwhich willbecapable of. providing a. relatively large electrical output onvariation in responseto mechanical movements of a veryismall order. As-such, the device is particularly well adapted for-'use'-:as-- a phonograph pick-up or. microphone element, as the driving power required iswery small indeed, so' that operation: ati acoustical frequencieswithout undesirable damping: of" thew-higher frequencies is r f acilitatei:

Another." obj ect; of r the: invention is to j provide aw. transducer offtliistypeembodying a sealed container: of: a? suitable gaseous medium; for-ex, ample one? ofthe: noble'gasesor a: mixture there-- OflWiUbZ' othergasesrand'which does not-depend for its operation upon the existence of thermion'swithin the envelope: In. other words,v as: comparedr-withthotecathodeatypes.of transducers; the present invention requires" no? power supply r for the production" of thermionsywhich' not only increases its power efficiency; but greatly simplifies the construction of apparatus, for example, sound reproducers; whichr-are driven by the transducer. Thus, the invention-provides a transducer which" incapable of replacing;- ex-isting-ztypes; for exam-- ple. ofathe magneticorzpiezo electricetypes, with azminimum'; of" redesign 'orreconstruction.- of the auxiliary apparatus.

Still-another object of the invention is to pro-- vide such a-- transducer-which is very. small andc,ompact,- andwhich may; readily take a the. form: ofra capsule-or cartridge thatrmayeasily bacon! nectedtwith and disconnectedufrom. its. auxiliary apparatus, so that replacement:isfacilitated-andmade more.economicalthan.ispossiblewithexist ingtypes ofltransducer. cartridges.

A further object of. the inventionistoprovide a: transducer. ofthe above type which will. be imperviousto climaticconditions such as high ,or. low. temperaturesorhumidities, .as compared with existing. typesbmanyr of. which are permanently injured by exposure toconditions-whichoare commn.:-in-many partsof the world. The unit of the present inventionis capableoi operation independently, ofjhumidity and altitude, for ex.-. ample, and insofaras temperature is .concerned, requires merely the. existence of.,a temperature. greater than a. certain minimum which may.

2; beextended: downward almost indefinitely? by the ,proper seleetiom or the gaseous .medium; and. the: other components-0f..the='device.. v

Still;- afurther obiectof; the: invention is ta provide a devicezof this type whoseoutput char!- acteristic, in terms: of,--amp1-itude1 at various fre-- quencies- --of-. energization, may. be. varied almost without; limit: inv order; to provide a frequency response :best suitedtovar particular application; or for use with. given auxiliary equipmentnsuch as reproduceraamplifiers-landthelike;-

Anadditional: object of. therinvention is .to pro.- vide a: transducermhaving-.1 the movable, or. me-- chanically: drivenyportionz of'itamassso'lightand small thatthe: inertiaof this portion doesnot op,- erateatorlim-it therspeedmofr response=to an-rappre ciableextent, within? audio: frequency ranges.

Moreover; the-:device; does; not require for its op,- eration: any -permanenirmagnetsaor the like such asrarezusediini certaineotherr types: of transducers;

whereby the: total mass :oflthewhole element or cartridge iszmaintainedu as small .-.-as-possible.

The: above: and: ctherrobjeots and advantages ofz-the inventiomzare obtained byaa construction WhiCh1;.iS:- extremely rugged and: immunerto; me-' chanical shocks such as often occur in service conditions. and; yet which-i is? well adapted? to large-scale production: upon existingemachinery; so thatthe cost per unit-may be-made-to compare favorably: with': known devices: intended for the same". purposes; but-which: are incapable of. the performance: obtained a with: the present. unit.

'Iheiinventionrwlll best be understood by! ref.- erence'to. 1 thecfollow-ing detailed specification: of azpreferredt'embcrdiment thereof; taken in ZCOIlIlGC? tion :witlr.ithetaccompanyingr drawings. in: which Fig. 1 is a side elevation: of .-one form: of: the inventi'ong as embodiedzxinrra phonograph pick-up. cartridge Fig: ZZis'a perspective :view. oiithearrangement of the electrodes iwithin .theaenveloper of Figz: 1;.

Fig: 3* is a fragment'ary sectional; view." of? a-por-z V tion-cf Fig-a' l"; illustrating the manner of sealing producer cartridge, but it is to be understood that the principles of the invention are in no way limited to such application, and may be utilized as well in microphones, vibrations or pressure and motion pick-ups, stethophones or similar devices, by the application of means Well known to the skilled worker in this general field. Also, the disclosure of certain preferred circuits for utilizing the output of the transducer is not to be taken .as a limitation on the circuits which can b employed, since these also are capable of Wide variation without departing from the spirit of the invention. All such changes and modifications as come within the scope of the claims appended hereto, are deemed to be covered by this application.

In general, the invention depends for its operation upon the fact that there exists a potential gradient along any electrically ionized column of as, and hence that the potential of an electrode lying in such a column may be varied by moving the electrode along the column. It is, of course, known that the conversion of mechanical variations into electrical can be accomplished by the movement of one or the other of the electrodes of a hot-cathode type of vacuum tube. most often the control grid of such a tube, but all such proposals have been rendered impractical either by the complexity or instability of the necessary electrode assembly, or by the ex cessive cost of manufacture, or other factors. In accordance with the present invention, the number of component parts of the transducer has been reduced to a minimum, without sacrificing any of the inherent sensitivity of such a device.

Moreover, prior art hot-cathode types of transducers have always depended for their operation upon the control of the number of thermions which reach a collector plate from a heated cathode, which number is very far from being a simple function of the position of the control grid. The result has always been non-linearity of response, and the output of such devices has therefore been rich in harmonics and distortion of various kinds, even with simple forms of mechanical motions.

Referring now to the device shown in Figs. 1 to 3 of the drawings, numeral Ill designates generally a transducer element in the form of a phonograph pick-up cartridge, by way of example, which may be mounted at the free end of any well-known form of pick-up arm; said element comprising an envelope l2 preferably formed of glass within which is provided an atmosphere of a suitable ionizable gas, neon being preferred, although many other gases or mixtures thereof could be used. The pressure of the gas, within envelope I2, may be varied within wide limits in accordance with the electrode construct on and the applied voltage, but a pressure within the range of to 30 millimeters of mercury has been found to produce good results. At one end of the envelope 12 its walls are sealed together in a typical form of press l4 through which pass three conductors l6, l8 and (see Fig. 2) whose outer ends may serve as contactpins for the connectionof the device to the external circuit, and whose inner ends constitute, or are electrically connected with, the electrodes of the unit.

The material of which the conductors l3, l8 and 20 are formed is subject to wide variation, the principal requirement being that it form a gas-tight and structurally rugged seal to the glass of the envelope. Where the envelope is formed of asoft glass of the composition of Corning G-l or G-12, the conductors may desirably be formed '4 of a special alloy known to the trade as Sylvania #4, a stainless steel alloy which may be sealed hermetically to glass either by flame, radio-frequency heating or by other methods. Alternatively, such metals as Kovar, Fernico or the like may be employed.

In the construction shown in Figs. 1 to 3, the three conductors l6, I8 and 20 lie in substantially the same horizontal plane throughout most of their length, and are supported within envelope i2 by a supporting plate 22 of mica or other suitable insulating material, beyond which the conductors diverge in a manner to be described below. That end of envelope l2 opposite to the press 14 may be provided with a sealed-01f tip 24 resulting from the evacuation and filling of the envelope in a manner so well known in the vacuum tube art that it need not be here described. As best shown in Fig. 3, the under surface of envelope I2, adjacent the electrode end thereof, is provided with an aperture 26 surrounded by an external lip or ring 28 to which is secured a cup 30 which may be of the same material as conductors I6 to Z0 and sealed to the envelope by the application of heat. The bottom surface of cup 30, which is designated by numeral 32, is preferably annularly corrugated to increase its flexibility, and constitutes a diaphragm through which is passed a metallic movable-electrode control rod 34, the latter being welded or soldered to the diaphragm 32 in any desired gas-tight manner. Rod 34 is here shown for simplicity as terminating in a stylus point 36, but it may equally well be provided with a socket to receive a separate needle or stylus as is well known in the pick-up art. In order to provide a controlled degree of damping of the motion of rod 34 in response to mechanical motions or vibrations of its stylus end 36, a layer 38 of vinyl plastic or similar resilient material having a suitable damping coefficient is secured as by cementing to the under side of diaphragm 32, and apertured so as to pass around the rod 34.

Support plate 22, as best shown in Fig. 2, may have peripheral cut-outs 22', and the holes which pass the conductors 16 to 20 may be intersected by slots 23 to provide free passage of ionized (luminous) gas throughout the length of the envelope l2.

The thickness of the material constituting cup 30, and particularly the thickness of that portion thereof forming the diaphragm 32, is made as small as possible consistent with adequate mechanical strength, and may be of the order of .001 to .003 inch, in order to provide a minimum of inertia and hence an extended upper frequency-response characteristic. Such a thickness has been found suitable for a device intended as a phonograph pick-up, but obviously the figures given may be varied to suit other requirements or applications.

Referring now particularly to Fig. 2, the conductor I6 is shown as terminating at its inner end in a portion turned to approach the center-line of the central conductor l3, and has secured to such in-turned portion an electrode plate 40 con-.

stituting the cathode of the electrode system. Conductor 20 terminates at its inner end in a portion 42 also deflected toward the center-line of conductor I8, and a terminal portion 44 lying parallel to the diagonal of plate 40 but spaced therefrom by a distance which may be of the order of .030 to .060 inch, this terminal portion 44 constituting the anode of the device. Between these terminal portions of conductors l6 and 20 extends the upper end of therod34, substantially midway therebetween when the deviceis at rest. Central conductor i8 is deflected down ward from its-center-lineas at 461 and is soldered, welded, orotherwise secured 'to an edge portion of diaphragm 32 or to the inner wall of cup below ring 28. Thus, conductor I8 is in electrioal connection with the movable-or control electrode constituted by the-upper end of rod 34 which rod also constitutes means for varying the position of the movable electrode along the path between electrodes-4'0 311C144.

It will be observed that the point on rod 34' at which it is connected to the flexible diaphragm 32 is only about one third or one fourth of the distance along rod 34 from its lower end. In this way, a mechanical amplification of the order of three or four times is obtained as regards the relative movements'of theelectrode end of'the rod and the movements of its stylus end 36 Compared to the flexibility of the corrugated d-iaphragm 32, rod 34 is of course relatively rigid, so that its upper or electrode end faithfully executes movements proportional to the extent to which its lower end 38 is driven, as by the-sound groove of a phonograph record or the like.

The actual operation of the device wil-l'b made clear by an inspection of Fig. 4, which illustrates a typical operating circuit connected to the device. In this figure, numeral 48 designates a battery or other suitable source-of director highfrequency alternating current of sufiicient'vol'tage to produce ionization,.and preferably, a glow discharge, between the anode 44 and cathode 40. I

Suitable D. C. voltages may range from 100' to 250 Volts for a unit of dimensions such as earlier described, "and alternating voltages of '70 to 250 volts may be used, depending upon the particular gaseous medium being employed. One side of this current source, herein the negative side, is also connected to the cathode of any suitable form of amplifier tube 50. The movable electrode (rod 34) is connected through a blocking condenser 52 to the grid of the tube 50. Hence, as the electrode 34 moves back and forth along the potential path represented by the discharge between the outer electrodes and 44, the potential of electrode 34 and of the vacuum tube grid will be varied accordingly, and the output of the amplifier will be varied in accordance with the mechanical motion of the stylus end 36. A grid resistor 54 may connect the grid of tube 50 with the cathode in a known manner, but it is to be understood that the variations in the potential of the movable electrode may be utilized in any desired manner without departing from the spirit of the invention.

It will be clear from the above that the output of the device is primarily sensitive only to movement of the electrode 34 in a direction to and from the fixed electrodes, and only to an insignificant degree to motions thereof in a vertical direction, or in a direction perpendicular to thedischarge path. This is a desirable feature, since in reproducing a laterally cut phonograph record, for example, it is undesirable that the pick-up device be affected by merely incidental vertical modulation of the groove depth. On the other hand, the transducer of this design can readily be made sensitive to movements in any desired direction, merely by supplying a suitable mechanical linkage to the outer end of the rod 34.

As shown by way of further example in Fig. 5, the output of the transducer may also be utilized directly, without amplification, where the power output required isnot excessive." Asthere shown, the fixed electrodes "40 and'44' are connected-to the opposite ends of the coil of any desi'redtype of sound reproduc'er, or to an impedance-matching transformer connected thereto, and themow able electrode 34 may be connected through battery '48 or other source of potential to the midpoint of the coil or transformer primary. In Fig; 6 a balanced bridge type of circuit is shown the transducer l fl, battery 48 and a center-tapped resistorbei-hg connected in parallel, and the movable electrode 34 and the center-tap being con.- nected respectively to the cathode and control grid of the amplifiertube 50. Many" otherpossibilitiesuin the way of circuits will suggest themselves to those skilled in electronics.

It will have been. noticed :that the. envelope 1.2 has'been referred to above as formed of glass; whileit could equally well. be made of a metal, as by the utilization of known techniques for the fabrication of vacuum tubes, there is a considerabl'e advantage in the use of a transparent material. When the device is in operation,,and usinga gaseous atmosphere such as neon or the mixture 01 gases known commercially as 3-10, theglowdischarge is, of course, visible, and provides a visual'indication that the. device is in o.p erative condition. Thus, the unit isinameasure self-testing, since the presence .or absence of the glow whenthe device is energizedto some extent indicates whether the envelope has been damaged or has developed leaks, and whether energizing potential is being received at the device. Moreover, the glow discharge serves. the function of a pilot or indicator light for the energization circuit, andgreatly contributes to the aesthetic appearance of the'unit and its :associated equipment.

The current flow through the transducer under the conditions of operation stated above as exemplary only, may range from 0.5 to as much as 15 milliamperes, and of course much larger current flows could be obtained by suitable design of the electrode areas and spacing. Useful output voltages ranging from 0.1 to 1.0 volt have been obtained under actualoperating conditions,

which compares favorably with existing types of transducers operating on dynamic or piezo-electric principles.

It will be seen from the above description that there has been provided a transducer element of perfectly general application, in that any sort of motion-transmitting connection can be coupled to the movable electrode exteriorly of the envelope I2, so that the device can be used not only for microphones, phono pick-ups and similar audio frequency appliances, but can be operated by much slower impulses, such as might be produced by gauges, indicators or the like. In this connection,-it is to be noted that the potential output of the device depends upon the position of the movable electrode with respect to the fixed electrodes, and not upon the existence of a certain velocity of travel of the movable element. Moreover, since the potential drop across the ionized column of gas is substantially independent of the supply voltage, the output is relatively stable with reference to minor variations in the supply.

While there have been disclosed herein certain preferred details of an exemplary embodiment of the invention, and the best method known for practicing the same, it is to be understood that departing from the spirit of the invention as defined in the following claims.

I claim:

1. A transducer for converting mechanical movements into electrical variations, comprising a sealed envelope, an ionizable gas in said envelope, electrodes in said envelope for establishing a potential gradient therebetween sufficient to ionize said gas, a potential sensing electrode mounted in said envelope for movement along the path of said gradient, and a single electrically conductive support element mounting said last named electrode and extendin through said envelope for conducting the potential of said electrode to an external circuit.

2. In combination, a transducer for converting mechanical movements into electrical variations, comprising a sealed envelope containing an ionizable gas, a pair of fixed electrodes in said envelope, a movable electrode located between said fixed electrodes, an electrically conductive connecting element extending outside said envelope for moving said movable electrode with respect to said fixed electrodes, a source of ionizing potential connected across said fixed electrodes, and an output utilization circuit connected to said movable electrodes and at least one of said fixed electrodes.

3. A transducer for converting mechanical energy to electrical energy, comprising an elongated sealed envelope containing an ionizable gas, conductors passing lengthwise of said envelope and having their inner ends deflected towards one another to provide fixed electrodes for ionizing a column of gas therebetween, an aperture in a lateral wall of said envelope opposite to the inner ends of said conductors, a

flexible diaphragm sealed to said envelope about the said aperture, and a rigid conducting element passing through said diaphragm and sealed thereto, said element extending to a point between the deflected ends of said conductors.

4. The invention in accordance with claim 3, and a support member fitted within the profile of said envelope and supporting said conductors in spaced relationship.

5. The invention in accordance with claim 4, in which said support member has cut-out portions to provide free passage along said envelope for said ionizable gas.

6. The invention in accordance with claim 3, in which said diaphragm is of metal, and a conductor secured to the inner surface of a eripheral portion thereof and passing out of said envelope.

7. A transducer for converting mechanical energy to electrical energy, comprising an envelope containing an ionizable gas, means for maintaining an arc in said ionizable gas, a movable electrode in the path of said are, and means extending outside said envelope and connected to said movable electrode for receiving mechanical energy to vary the position of said movable electrode.

PAUL F. STILL.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 2,157,719 Pulaski May 9, 1939 2,440,565 Antalek Apr. 2'7, 1948

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