Frequency modulated ultrasonic therapeutic apparatus

May 21, 1957 c. _L. calosi 2,792,829

FREQUENCY MODULATED ULTRASONIC THERAPEUTIC APPARATUS

Filed Feb. 6, 1952

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Inventor

Carlo l. Calosi

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United States Patent Office „ 2,792,829

Patented May 21, 1957

2,792,829

FREQUENCY MODULATED ULTRASONIC THERAPEUTIC APPARATUS ⁵

Carlo L. Calosi, Rome, Italy, assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware

Application February 6,1952, Serial No. 270,166 ¹⁰ tor 9 is connected to oscillator 8 to effect frequency modulation thereof.

When the dimensions of a piston vibrator, such as a flat disk which moves to and fro in the direction of the normal to the surface, are comparable with the wave length, the distribution of the intensity of the compressional wave energy is not uniform but there is a maximum on the normal and other maxima in other directions. The compressional wave pressure at various points located on the normal is given by

Iff

Pir=2pcv sin(r'—R) (1) where p is the density of a medium, f is the frequency, v IS is the velocity of the face of the disk, c is the velocity of propagation of compressional wave energy in the medium, R' is the distance from the rim of the disk to the point in question and R is the distance between the center of the disk and point at which the intensity is desired.

From Equation 1 it is evident that the location of maxima and minima in intensity of compressional wave energy along the axis of the disk is dependent upon frequency. There are also other maxima and minima distributed in the space surrounding the disk but there is 25 no simple method of calculating this distribution of the axis of the disk. The compressional wave energy fields in the neighborhood of circular disk type radiators have been observed, however, and it is definitely established toat the compressional wave energy at various points in ^au the region surrounding the transducer disk, as well as the spatial distribution of the diffraction pattern, is dependent upon the frequency of the voltage applied to said transducer disk.

By varying the frequency of oscillator 8 at a given rate, which may be in the order of sixty cycles per second by means of modulator 9, the spatial diffraction pattern of the radiating transducer may be rapidly shifted and the localized intensity spots thereby substantially reduced. Since the energy distribution near the surface of the transducer with a frequency modulated voltage applied thereto is much more uniform, the energy transmitted to the tissue subjected to treatment is also considerably more uniformly distributed throughout the area ₄₅ of the tissue in contact with the applicator portion of therapeutic unit 1.

The amount that the “hot spots” are shifted when the frequency of oscillator 8 is varied by frequency modulator 9 will, of course, depend on the distance away from the 50 face of the transducer radiator; that is, the “hot spots” near the radiator will not shift as much with the application of the frequency modulated voltage as the “hot spots” farther away from the radiator surface. Since the frequency modulation of oscillator 8 is more effective at 55 a distance from the radiator surface, therapeutic unit 1 is preferably constructed so that the radiator is separated from the tissue undergoing treatment by the aqueous medium 6 whose thickness is several wave lengths.

The frequency range of the modulator may be any60 where from a few cycles per second to approximately 10,000 cycles per second. The values given are approximate and are not to be taken as limiting values. The frequency of oscillator 2 is swept over a range approxi65 ^rna7ely equal to ten percent of the mean operating frequency of the oscillator. For example, when operating at a mean frequency of one megacycle, the frequency is varied from about 950 kc. to 1,050 kc. The total swing in frequency is partially dependent upon the Q of the ₇0 transducer, as previously stated.

Numerous other arrangements and modifications can obviously be devised readily by those skilled in the art,

Claims. (Cl. 128—24)

This invention involves a therapeutic apparatus for the treatment of living tissue by compressional wave ; energy.

I . In the therapeutic treatment of living tissue it is desirable to obtain a uniform distribution of energy over the portion of the tissue undergoing treatment.

In previous models of compressional wave diathermy equipments, the transducer or device for converting electrical energy into compressional wave energy has had either unmodulated voltages or C. W. or A. M. modulated voltages applied thereto. This results in an essentially constant frequency of compressional wave energy radiation and consequently in a spatially constant intensity pattern owing to Fresnel diffraction near the transducer. These localized intensity spots create a non-uniform diathermy effect creating “hot spots” that would cause serious discomfort or burning of the tissue unless the latter is placed at a considerable distance from the transducer.

By applying a frequency modulated voltage to the transducer, a rapidly shifting spatial pattern of Fresnel diffraction is obtained, thereby substantially reducing the localized heating or “hot spots” so detrimental to diathermy treatment.

An object of this invention is to provide a therapeutic apparatus for the treatment of living tissue which is productive of more uniform distribution of energy over the area being treated.

Other and further objects and advantages of the invention will become apparent as the description thereof progresses, reference being had to the accompanying drawing wherein the single figure is a schematic diagram of an embodiment of the invention.

Referring to the drawing, a therapeutic unit 1 similar to that described in an application of Luther Davis, Jr., Serial No. 265,278, filed January 7, 1952, but which may be of any electromechanical design permitting a sufiiciently low Q to allow appreciable frequency modulation is shown. Unit 1 comprises a cup-shaped member 2 which is made up of a metallic shell 3 and an applicator 4, preferably made of natural rubber and cemented or otherwise attached to said shell. A transducer 5, which h may be a ceramic disk having a thickness equal to a half wave length at the frequency of operation, is mounted within member 2 in such a manner as to be free to 1 vibrate in the direction of its thickness. An aqueous * medium 6 of thickness equal to several wave lengths at the operating frequency is contained within member 2 and separates transducer 5 from the end portion of rubber applicator 4, as shown in the drawing. Applicator 4 is adapted to contact the tissue 7 undergoing treatment. The aqueous medium and rubber applicator each has a wave impedance substantially equal to that of living tissue to enhance the transfer of compressional wave energy from the radiator to the tissue. The output voltage of a conventional oscillator 8 is applied across the opposite faces of transducer 5. A frequency module2,792,829 within the scope of the invention, as defined in the appended claims.