US2698622A - Phase sensitive control for shortwave therapy devices - Google Patents

Description

Jan. 4, 1955 G. MARTENS 2,698,622

PHASE SENSITIVE CONTROL FOR SHORTWAVE THERAPY DEVICES Filed Dec. 11, 1951 INVENTOR Guntef Martens Agent United States Patent Ofiicc 2,698,622 Patented Jan. 4, 1955 PHASE SENSITIVE CONTROL FOR SHORTWAVE THERAPY DEVICES Gunter Martens, Darmstadt, Germany, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application December 11, 1951, Serial No. 261,036 Claims priority, application Germany January 9, 1951 2 Claims. (Cl. 128-422) capacitor electrodes producing a high-frequency magnetic and electric field respectively. In practice, the difliculty is experienced that the impedance constituted by the treating element and the part of the body to be treated (load impedance) varies during the treatment due to movements of the patient, owing to which the energy given ofi to the patient is reduced.

Due to this the quantity of energy supplied to the patient (dosage) cannot be adjusted with sufiicient accuracy and, moreover, the anode current losses in the output tube of the generator increase. Hence, this output tube cannot be fully loaded if, due to load impedance variations, the anode dissipation increases and exceeds the value permissible at full load.

Devices for treating patients with high-frequency energy are known which comprise a regulating device by means of which the energy supplied to the treating element is automatically maintained substantially constant. These devices employ a control factor for controlling the regulating device, which control factor is taken from the energy consumed by the generator or from the anode current of the output tube. This concerns apparatus Whereing load impedance variations involve adjustment variations of the high-frequency generator. They suflfer from another disadvantage in that the energy fed to the treating element is regulated by greater or lesser detuning of the load circuit relatively to the frequency of the produced oscillations.

The present invention concerns apparatus supplying the resonance frequency. According to the invention provision is made of a regulating device consisting of a comparison network, wherein deviations, due to load impedance variations, from the phase displacement of 90 between the oscillator voltage and the resonance voltage in the circuit of the patient are transformed into a control factor by means of which the variable impedance for tuning the circuit of the patient to the stabilized frequency of the generator is readjusted.

As a phase comparison network a bridge-circuit may be used, one branch of which comprises two resistors and the other branch comprises two discharge tubes, for example nine electrode tubes, functioning as mixing tubes.

In order that the invention may be readily carried into effect it will now be described more fully with reference to the accompanying drawing, wherein one form of a circuit-arrangement for an apparatus according to the invention is represented by way of example, and in which:

A bridge-circuit comprises two nine electrode tubes 1, 2 and two resistors 3, 4, provision being made that in supplying voltages, between which a phase displacement of exists, to grids 5 and 6 the anode currents of the two discharge tubes are equal, for example 250 a. The grids 5 are electrically interconnected and are supplied with alternating voltage obtained by coupling coil 7 inductively to coil 8, the latter forming part of the highfrequency generator whose circuit-arrangement is known per se so that it will not further be described. The voltage produced by coil 7 is in phase with the highfrequency voltage across coil 8. To the grid 6 of the discharge tube 2 is applied an alternating voltage from a tuned circuit including a coil 9 and a capacitor 10, which circuit is resonant with the oscillator frequency. The voltage produced therein has a phase difference of 90 relatively to the voltage across oscillator coil 8.

The grid 6 of the discharge tube 1 is connected to coil 2 2- coupled to the circuit of the patient. The phasedifference between the voltage produced therein and the voltage across the oscillator coil 8 is 90 only if the circuit of the patient is resonant with the oscillatorfrequency. If this circuit is not tuned to resonance the phase-difference is higher or lower than 90 depending on whether the impedance of this circuit behaves inductively or capacitively with respect to the resonance frequency.

The bridge-circuit is in equilibrium if the last-mentioned phase diiference is 90, consequently if the circuit of the patient is tuned to resonance.

In the case of incorrect tuning, a direct voltage is set up between the diagonal junction points 12, 13. Point 12 is connected to control grid 14 of a triode 15 and point 13 is connected to control grid 16 of a triode 17. Both triodes are connected in phase-opposition and the anode currents pass through parts 18 and 19 of the field winding of an electric motor 20. By means of this motor the variable impedance, preferably the rotary capacitor 21 in the patient circuit also including coupling coil 22 and output terminals 23, is readjusted. The anode voltage for the triodes 15 and 17 is supplied to the point connecting parts 18 and 19 of the field winding. Thus when the anode currents of both triodes are equal, that is, when equal voltages are applied to each triode grid, the two parts of the field winding generate equal but oppositeiy directed magnetic fields which balance out.

The anode current of the discharge tube 2 has a constant value, whereas the anode current of the discharge tube It varies in accordance with load impedance variations, since these variations alter the phase difference between the voltages supplied to the grids 5 and 6. Hence, the anode current of tube 1 may become higher or lower than that supplied by tube 2, whereby the direction of rotation of the motor 20 is determined. It may easily be so chosen that the motor moves the capacitor 21 in a direction such that the capacitor variation restores the load impedance to a value at which the condition of resonance is satisfied. Upon reaching the last-mentioned position the bridge is again in equilibrium and the motor comes to a standstill.

What I claim is:

1. A shortwave therapy apparatus for the medical treatment of patients comprising a stabilized high-frequency generator; a resonator inductively coupled to the generator and provided with a treating element to supply high-frequency energy to the patient and a variable impedance to adjust the resonance frequency of said resonator, said patient constituting a variable load on said resonator; and a regulating device to maintain said resonator in tune with said generator despite variations in said load, said device comprising a phase comparison network for comparing the phase of the generator voltage with the resonator voltage and whereby said network yields an output voltage depending on". said load; an electric motor coupled to the variable impedance n s a1d resonator and including a center tapped field w1nd1ng; and a push-pull amplifier for coupling said winding to said phase comparison network and including a pair of electron discharge devices each having a cathode, a control electrode and an anode, means to apply the output voltage of said network in phase opposition to said control electrodes, means connecting said anodes to the ends of 7 said field winding and means to apply a direct anode voltage to said center tap of the winding relative to said cathodes,

2. A shortwave therapy apparatus for the medical treatment of patients comprising a stabilized high-frequency generator; a resonator inductively coupled to the generator and provided with a treating element to supply high-frequency energy to the patient and a variable impedance to adjust the resonance frequency of said resonator, said patient constituting a variable load on said resonator; and a regulating device to maintain said resonator in tune with said generator despite variations in said load, said device comprising a phase comparison network for comparing the phase of the generator voltage with the resonator voltage and including a bridge circuit formed by two branches one of which includes two resistors, the other of which includes two electron discharge tubes each having first and second control grids, means coupled to said generator to apply to corresponding first grids of said tubes an alternating voltage in phase with said generator voltage, means coupled to said resonator to apply to the second grid of one tube an alternating voltage 90 degrees out of phase with said generator 2 voltage, and a tuned circuit coupled to said generator and resonant therewith to supply an alternating voltage to the second grid of the other tube whereby said network yields an output voltage depending on said load; an electric motor coupled to the variable impedance in said resonator and including a center tapped field winding; and a push-pull amplifier for coupling said winding to said phase comparison network and including a pair of electron discharge devices each having a cathode, a control electrode and an anode, means to apply the output voltage of said network in phase opposition to said control electrodes, means connecting said anodes to the ends of said field Winding and means to apply a direct anode voltage to said center tap of the winding relative to said cathodes.

References Cited in the file of this patent UNITED STATES PATENTS 2,396,004 Gilbert Mar. 5, 1946 2,467,285 Young et al Apr. 12, 1949 2,473,188 Albin June 14, 1949

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