US2171670A - Electrotherapeutic device - Google Patents

Description

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i -lil H, W. PARKER ELECTROTHERAPEUTIC DEVICE Flled July 30 1937 OINOOOOQO Sept. 5, 1939.

Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE ELECTROTIHERAI'EUTIC DEVICE Canada Application July 30, 1937, Serial No. 156,515

1 Claim.

My invention relates in general to electrotherapeutic devices and more particularly to those of such devices which employ high frequency alternating current to raise the temperature of the human body.

In such devices as now made, it is the custom to employ some type of oscillation generator, usualy thermionic, to convert the available low voltage commercial power to high voltage, high frequency alternating current. Such devices are very expensive, as due to the high voltage employed the condensers used to achieve resonance for the circuits and for by-passing purposes are costly andthe meter necessary to indicate the strength of current applied to the patient is likewise very expensive, in fact constitutes one of the largest items of expense in such devices.

It has been determined that the frequency most suitable for the purposes for which such devices are used is of the order of 50 megacycles and I have discovered and successfully demonstrated that for frequencies of this order all of the expensive condensers may be omitted and a simple, cheap indicating device substituted for the meter to provide a novel circuit and arrangement of apparatus which is simple, safe, cheap and fully effective and efficient for the purpose intended.

One of the principal objects of my invention comprises producing an inexpensive Oscillation generator which is fully effective and efficient for electrotherapeutic purposes.

Another object comprises producing an oscillation generator which, while simple and inexpensive, is ruged, reliable and especially adapted for electrotherapeutical uses.

I accomplish all of the above noted desirable objects and results and others which will hereinafter be apparent by means of the construction, combination and arrangement of circuits and apparatus which will be hereinafter more specifically described with reference to the accompanying drawing forming a part of this specification and which is a diagrammatic representation of a preferred embodiment of my device.

Referring now to the drawing which illustrates diagrammatically a preferred embodiment of my device, the thermionic tubes l, 2, 3, and 4, each provided with a cathode, a grid, and an anode, are connected as shown in parallel in pairs. The cathodes of tubes l and 2 are connected in parallel and are energized by the winding It] on transformer 9, the primary l2 of which is connected as usual through fuses and a switch with any suitable source of commercial alternating current. Similarly, the cathodes of tubes 3 and 4 are connected in parallel and are energized by transformer winding I l of transformer 9. The grids of tubes l and 2 are connected together through an inductor or inductance 5 which is designed to, in cooperation with the interelectrode capacity of m the tubes, form an input circuit for the tubes which is resonant to the frequency of the current generated by the generator. This is of the order of 50 megacycles. Similarly, the grids of tubes 3 and 4 are connected together through the inductor 6 which is likewise designed to, in cooperation with the internal capacity of tubes 3 and 4, form an input circuit resonant to a frequency of 50 megacycles. The grid bias resistors I and 8 connected to the midpoints of inductors 5 and 6, respectively, serve as means for properly biasing the grids with which they are associated for proper operation of the generator.

The anodes of tubes l and 2 are connected together through an output inductor or inductance 15, as are the anodes of tubes 3 and 4. The anode operating potential and current are supplied from winding E3 on transformer fi, one extremity of which is connected as shown to the input circuit of tubes l and 2, and the other to the input circuit of tubes 3 and 4, while the midpoint is connected through an electric lamp l4 to ground. The common return path for the anode current is effected through ground, lamp M, inductor l5, conductors I8 and I9, and high frequency choke coils l6 and II, which are connected to ground as shown. It will be observed that no tuning condensers are utilized in either the resonant grid input circuits or the anode output circuits. The anode circuits are made reso nant to the frequency desired, megacycles, by properly proportioning inductor iii to, in. cooperation with the internal capacity of the tubes 1 and 2, and 3 and 4, provide anode output circuits which are resonant to the desired frequency. 45

It will be further noted that no by-passing condensers are utilized with the grid bias resistors 1 and 8, as it has been found for the frequency used that'there is sufficient capacitance in the coils 5;and 6 to effect the necessary by-passing for proper functioning of the oscillator. The radio frequency choke coils l6 and H in the common return of the anode supply circuit prevent the passage of the high frequency current therethrough and confine such current to the load circuit comprising the output impedance l5, conductors I8 and I9 and the variable coupler connected between the applicator pads 26 and 21 and the output impedance I5, the applicator pads and the patient to whom they are applied. The variable coupler shown comprises a pair of metallic plates 22 and 23 mounted in fixed relation with their plane surfaces coplanar by means of the insulating member 24 and a pair of similar plates 20 and 2| mounted with their plane surfaces coplanar and for rotation in a plane parallel to the plane of the plates 22 and 23 and maintained in such relative position to each other and with plates 22 and 23 by means of the insulating knob 25. As the knob 25 is rotated plates 20 and 2| are rotated relatively to plates 22 and 23.

As shown in the drawing, the variable coupler is adjusted for maximum transfer of energy between the output inductor |5 and the applicator pads 26 and 21. When the plates 20 and 2| are rotated by the knob 25 the transfer of energy to the load is gradually reduced until a minimum or zero transfer of energy is reached, when the plates 20 and 2| have been turned through an angle of degrees with respect to that shown in the drawing. This variable coupler serves as an effective means for varying the load current without disturbing the symmetry of the connection between the generator and load and with minimum frequency change, as fully disclosed in my copending application Serial No. 99,221, filed September 3, 1936, Patent No. 2,116,080 dated May 3, 1938.

The applicator pads 26 and.2| are the usual metal back fabric pads employed in applying electricity to the human body, and no further explanation of such electrodes is deemed necessary. In the operation of the device the pads are applied to the desired portions of the patients body and the portion of the body included between the pads constitutes a resistance completing the load circuit of the device.

It will be noted that the generator circuit is of the push-pull type and therefore symmetrical and that tubes and 2 are in one symmetrical half and tubes 3 and 4 in the other symmetrical half of the generator. It will be further noted that the lamp l 4 is included in the common return connection of the anode current supply circuit or, that is, the circuit supplying. alternating current from the source to the generator through the transformer 9.

I have discovered and successfully demonstrated that for such a generator having the desired output of about 500 milliamperes, the lamp l4 may preferably be an ordinary volt 60 watt lamp to serve as the sole inexpensive means for correctly indicating the strength of current supplied to the generator as determined by the current drawn from the output of the load circuit of the generator and thus to eliminate an expensive meter for thesame purpose. Such a lamp shows no illumination at all when no current is drawnfrom the load circuit, as the no load current of the generator is of the order of 200 milliamperes and this is not sufiicient to heat the filament of the lamp to a visible degree.

At 275 milliamperes load the lamp glows at a dull orange color, and at 500 milliamperes, or full load, the lamp glows with a dazzling bright white light. The scale of color of the lamp indicating the current in the load circuit is as follows: 1

Illumination Current in load Milliamperes The scale of a meter for indicating the current strength in the load circuit is linear, while the light scale is approximately a fourth power relation of the temperature of the filament. The temperature of the filament is in accordance with they half power of the current. It is, therefore, apparent that the lamp is more sensitive in indication than a meter. The lamp is further of advantage as it has been found that, if the patient moves his body relative to the electrode pads, the lamp changes in color, indicating more or less heat transfer and as such color changes can be seen across the operating room, the lamp indicator is preferable to a meter because such electrical treatments are generally applied to several patients in the same room and the condition of each patient can be noted by one operator. The overload characteristic of the lamp in flashing as the patient moves and the fact that the lamp burns out without noise or smoke in case of exreme overload is important in that it saves the oscillator tubes from overload and does not startle the patient. I prefer to employ a lamp of the incandescent filament type rather than a gaseous discharge type such as a neon lamp because the filament lamp shows no illumination for the no load current of the generator.

It will be noted that the oscillation generator circuit is of the type generally referred to as selfrectifying in that each symmetrical part oscillates alternately, that is, as the cathodes of one pair of tubes are energized by a negative half wave of alternating current and consequently the anodes of the same tubes have impressed on them a positive half wave that particular pair of tubes oscillate while the remaining pair do not oscillate; thus, each pair of tubes oscillate alternately to produce in the output inductor l5 a substan-' tially continuous high frequency current. It will be further noted that the tubes in each symmetrical half of the oscillator are provided with independent cathode energizing circuits; that is, transformer windings l0 and M, respectively. This allows the cathodes of the tubes to have a potential different from ground potential-and permits the grounding of the anode circuit as shown for the sake of safety and to protect the patient from shocks.

It Will be observed from the foregoing that my improved device comprises a minimum number of inexpensive parts and is consequently simple, inexpensive, rugged and reliable. It will be 0-bservedthat there are no expensive condensers or meters employed and that, as the cathodes are independently energized, the output and anode supply circuit maybe grounded and the device thus be made safe to operate. I

While I have illustrated and completely described by way of example, only one embodiment of my device, it will be apparent that numerous changes in details may be made therein without departing from the spirit or intended scope of the invention. 1 do not, therefore, desire to limit myself to the foregoing except as may be pointed out in the appended claim in which I claim:

An oscillation generator for electro-therapeutic use comprising, two pairs of two thermionic tubes each, input and output circuits connecting the tubes in said pairs symmetrically with respect to each other, a load circuit common to said two pairs of tubes, a source of alternating current for energizing said tubes, a transformer one winding of which is connected to said source, separate windings on said transformer for separately energizing the cathodes of each symmetrical pair of said tubes whereby the cathodes of said tubes may have a potential different from ground potential to permit of the grounding of the anode circuits of said tubes for the sake of safety and to protect the patient from shocks, an additional winding on said transformer connected to the anodes of said tubes and including a connection common to said anodes, said common connection including a tuned impedance connected between the anodes of the tubes in each pair of said tubes whereby each pair of tubes operates alternately to generate oscillations during positive half cycles of the alternating current from said source and said common connection being grounded and including an indicating device for indicating the strength of current supplied to said oscillation generator as determined by the current in said load circuit.

HENRY W. PARKER.

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