US2389935A - Microphonic electron tube - Google Patents

Description

J. ROTHSTEIN MICROPHONIC ELECTRON TUBE Nov. 27, 1945.

Filed June 24, 1945 F Q. 0 a z m 4 F. 6 6 8 8 5 I 4 4 4 M C I ll 1 III I- II a V/// M 1 w G a F 3 8 J 2 e A [Ill A C M 0 J El 2 INVENTOR JEROME ROTHSTEIN Patented Nev. 21, 1945 UNITED STATES (Granted under the act of March 3, 1883, as amended Ap 28; 370 0. G. 757) 2 Claims.

The invention described herein may be manufactored and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to electron emission tubes, and more particularly to such a tube including a diaphragm for controlor measurement purposes.

some objects of this invention are to provide a device sensitive to mechanical vibrations; to provide a microphone to detect faint sounds in which the microphone is its own amplifier tube; to provide a device for measuring changes in barometric pressure, temperature, turbulent pressure, shock pressure, altitude, windpressure, or wind velocity; to provide a device which can measure depth of submergence in a liquid; and to provide a device for measuring the elastic properties of solids.

, invention resides in the microphone and vacuum tube elements, as hereinafter are more particularly described in the specification and sought to be defined in the claims. The specification is accompanied by a drawing in which Figure l is a partially-sectioned elevation through one form of my invention, using a flexible bellowsf Referring now more specifically to Figure 1,

' the tube there shown comprises an envelope [2,

Figure 2 is a section through a modified form anode electrodes C, G, and A respectively, with linkage L mechanically connecting the flexible envelope portion F to one of the electrodes, preferably the grid G, in such a manner that movement of the flexible portion F changes the interelectrode spacing and consequently the amplification iactor of the tube.

having a cathode M, a grid 16, and an anode l8. Cathode I4 and anode l8 are stationary, and are supported by conventional lead-ins 20 and 22. The cathode I4 is indirectly heated by means of a filament 24 having lead-ins 26.

In accordance with the present invention, the grid [6 is movably mounted between the cathode l4 and the anode I8. For this purpose it is supported on wires 3!] which extend to a rigid diaphragm 32. In the present case there are four such wires, and the diaphragm is circular. The latter is carried by a sensitive, flexible, metal bellows 34, the inner end of which is secured to a metal ring 36, which in turn is sealed to the edge of a large aperture in the glass envelope l2.

In other cases, it the tube envelope I2 is made of metal, the bellows 34 or the ring 36 may be welded directly to the metal envelope. In rare cases the bellows may be made of tempered glass, and in such case may be sealed directly toa glass tube envelope.

Electrical connection to the grid it may be made by means of a lead 38 secured to the ring 36. This may be done when there is no need to insulate the diaphragm 32 and the bellows 36 from the grid, but in other cases, when an insulated connection is wanted, the grid connection may be arranged as described hereinafter in connection with Figures 2 and 3.

The arrangement of the electrodes will be clear from Figure 4, which shows how the grid wire formation H is held within a grid frame it, the latter being carried by the support wires 30 (only the left-hand ends of which are shown in Figure 4). Figure 4. also shows how the cathode can it is provided with an oxide or other emissive surface lfi on one side thereof, this being the side which faces the grid l6 and anode M. It will be understood that the cathode can M is an enclosed box-like structure, which may be open at the bottom, or if closed will have apertures for the filament lead-ins 26. The filament 26 may be of any desired shape, and is received and housed within the cathode can it.

When any mechanical vibration, sound, pressure, or other means of producing a displacement is impressed on the diaphragm 32, a change of position results which is applied to the grid it by means of the connections 30. This changes the cathode-to-grid spacing (and also the gridto-anode spacing) and so changes the amplification factor of the tube. The mechanical resonance frequency of the diaphragm system can be varied by varying the mass of the diaphragm 32 and the stifiness of the bellows 33. The tube 'ployed as a barometer or manometer.

should be carefully shielded from all sources of vibration other than those impressed on the diaphragm 32.

Figure 2 differs in eliminating the flexible bellows and instead using a circular flexible diaphragm 40. This is welded at its periphery to a metal ring 42,which in turn is sealed to the edge of a large aperture in glass envelope 44. The grid 46 is supported by wires 48 which are brought together at a glass bead 50, and this is secured to diaphragm 40 at its mid-point 52. Electrical connection to grid 46 is obtained by means of a lead-in 54, which is made very flexible at 56 in order not to interfere with vibration of grid 48.

The arrangement of Figure 3 is the same as that shown in Figure 2 except for the inclusion of two additional grids, there being a "space charge grid" 60, and a suppressor grid 62. These grids may be stationary, like all of the other electrodes except the control grid 64.

The tubes disclosed herein may be used as microphones because pressure variations caused by sound waves cause the diaphragm to vibrate, thereby cyclically changing mu," the amplification factor. In respect to current flowing in the plate circuit of the tube, a voltage e on the grid has the same effect as a voltage 148 on the plate. If 1. now changes to a value of a, and a voltage e is onthe grid, the efiect in the plate circuit will be that of a voltage p'e or a net change of con. where A,u.=[b'#. We will thus have current variations in the plate circuit to correspond to changes in pressure of the sound wave.

If a carrier frequency were impressed on the grid, instead of a constant bias, the sound wave will modulate the carrier frequency.

Inasmuch as the plate current varies with the pressure applied to the sensitive element or diaphragm, the tube may be calibrated and used to indicate static pressure, and thus may be em- Because air pressure varies with the altitude above the surface of the earth, the tube may be calibrated directly as an altimeter. If the structure is reinforced, and made rigid, it may be used as a piezometer, and, inasmuch as water pressure varies directly as the depth at which the pressure is being determined, the tube may be used as a depth meter for submarines or other devices.

An expansible temperature responsive element may be connected to the diaphragm with a heat insulating connection, thus utilizing the invention to measure or record temperature. In some cases, the temperature responsive element may be'a bulb of liquid connected through a pipe to a chamber enclosing the outside of the diaphragm so that expansion of the liquid when increased in temperature will replace the diaphragm.

The. tube may also be used to measure wind velocity because a dynamic pressure is developed in excess of the normal atmospheric pressure. Used as the manometer in connection with a Pitot tube, it may be used as an airspeed meter, or as a flow meter for liquids. Turbulent pressure changes, in a wind tunnel for example, may also be measured. Suitable recording devices enable continuous records to be made over long periods of time in all applications of my improved tube. One such usable recording device makes photographic trace of a light spot reflected from the mirror of a galvanometer energized by the output I to measure the same and so replace devices such as an optical lever. For example, the Young's modulus for a given specimen is determined by finding the strain or fractional elongation produced by a given stress. If the movable part of my tube is connected by a taut wire to a fixed point of the specimen, the application of a stress will cause a small displacement. The plate current indicator can be calibrated in terms of displacement, and thus elastic properties can be de termined.

The tube may also be used to measure forces or weights of objects. The force or weight is caused to act on the movable part of the tube by a taut wire or other suitable connection thereby producing a displacement. The plate current indicator may then be calibrated in terms of force or weight.

It is believed that the construction and operation of my improved microphonic electron tube, as well as the advantages thereof, will be apparent from the foregoing detailed description. The electron tube used may be of the metal or glass envelope type, and may have any number of electrodes, and may be a high vacuum or a gas-filled type. The flexible portion of the envelope may be metal and may be secured to the rigid envelope portion by welding if the latter is also made of metal, or by a metal-to-glass seal if the latter is made of glass. For certain special purposes the bellows may be made of glass so tempered as to fford flexibility, though for most purposes the flcxible part of the envelope is preferably made of metal. If made of glass,-the bellows may be sealed directly to, a glass envelope.

It will be apparent that while I have shown and described my invention in several preferred forms, other changes and modifications may be made in the structures disclosedwithout departing from the spirit of the invention, as sought to be defined in the following claims.

I claim:

1. An electron tube responsive to vibratory wave motion comprising a rigid envelope having a relatively large circular aperture in the side wall thereof, a flexible bellows sensitive to vibratory waves, having one end sealed to the envelope at the aperture and having its outer end. closed by a wave sensitive diaphragm, cathode, grid, and anode electrodes of generally fiat configuration in said envelope, and means mechanically connecting the aforesaid diaphragm to one of said electrodes to vibrate such electrode and move it physically closer to and further from the other electrodes, whereby vibration of the diaphragm correspondingly changes the inter-electrode spacing of the electrodes and thereby changes the amplification factor of the tube.

2. An electron tube responsive to vibratory wave motion comprising a rigid envelope having a relatively large circular aperture in the side wall thereof, a longitudinal flexible bellows sensitive to vibratory waves, having one end sealed to the envelope at the aperture and having its outer end closed by a wave sensitive diaphragm, cathode, grid, and anode electrodes in said envelope, said cathode, grid, and anode electrodes being generally flat and disposed generally parallel to the aforesaid diaphragm, and means mechanically connecting the aforesaid diaphragm to said grid, whereby vibration of the diaphragm correspondingly changes the inter-electrode spacing of the electrodes.

JEROME ROTHSTEIN.

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