US2774068A - Diathermy applicators - Google Patents

Description

Dec. 11, 1956 D. B. HAAGENSEN DIATHERMY APPLICATORS Filed Feb. 16,V 1955 /NVENTOR DLMNE B. NAA GENseN BVM TTORNE V United States Patent@ DiArHEnMY APPLICATORS Duane B. Haagensen, Wayland, Mass., assignorto Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application February 16, 1953, Serial No. 336,981

Claims. (Cl. 343-770) This invention pertains to a diathermy applicator and, more particularly, pertains to a coaxial line antenna which is easy to fabricate and which is Acapable of producing a relatively uniform near field necessaryr'for proper diathermy treatment of living tissue.

In the eld of microwave diathermy it is desirable to produce uniform heating of the'tissue placed Ain the vicinity of the energy radiating means. Uniformity of heating becomes increasingly dimc'ult to achieve asthe area of the tissue increases. Previous diathermy directors have been of limited effectiveness in treatingetissue of large area such as the lumbar region or Ientire portions of the arm or leg because of this dicultyin obtaining a near field radiation pattern uniform'over a widev area.

in accordance with this invention, a coaxialline slotted antenna is employed having asquareouter conductor to which is connected a reflector element. -A reilector jelement is used in order that the radiation from lthe antenna will not be omuidirectional but will be directed over a limited area. lt has been found that the combineduse of a slotted coaxial line with a square outerconductoraud a reilector element for limiting the angle of radiation produces a relatively uniform near iield radiation-pattern over a substantial area with consequently uniform fabsorption of microwave energy and heating of the tissue.

Fihe inner conductor of the coaxial line should be capable of being machined and assembled readily. The characteristic impedance of a coaxial line is inversely proportional to the square root of the capacitance of theL line. By making the outer conductor of a coaxial line of square cross section having a width equal to the diameterofthe circularouter conductor of a conventional coaxial line, the total capacitance between inner and outerconductor is decreased. in other words, for a given size line and a given characteristic impedance the'V inner conductor of a coaxial line having an outer conductor of rectangular cross section is greater than the inner conductor ofthe usual circular coaxial line; the machining of the inner conductor and the assembly of the inner conductor within the outer conductor is thereby facilitated.

Referring to the drawings:

Fig. l is an isometric view of an embodiment of the subject invention;

Fig. 2 is a diagrammatic representation, partly in section, of the embodiment shown in Fig. l;

Fig. 3 is a fragmentary plan view of a portion of the antenna shown in Figs. 1 and 2;

Fig. 4 is a view illustrating certain details of mounting the inner conductor of the coaxial line antenna; and

Fig. 5 is a detail view showing the manner of securing a cover plate over the slotted face of the antenna.

The antenna lil comprises a coaxial line 11 whose outer conductor l2 is of square cross section and whose inner conductor 14 is a cylindrical rod which, although shown as a solid rod, may be tubular. A substantially V-shaped reector l5 is bent in the manner shown in Fig. l so as to surround three faces of outer conductor 12. The edges of the rellector in contact with conductor 12 are fastened Patented Dec.V 1 1,.1956

. 2 thereto, ,as .by Awelding. The entire antenna, including reectonis. preferably made of a material of low density andhigh.electrical conductivity, such as aluminum. yThe remaining faceof conductor V12 contains a `plurality of spaced narrowresonant slots 16 whose length, width and spacing will depend upon the microwave operating frequency and the type of radiation pattern desired. In one application, in which `the operating frequency was approximately 2450 megacycles, each of the four slots was approximately 8.5 centimeters long and one millimeter wide and the spacing `between centers of adjacent slots was approximately 12.6 centimeters or approximately one wavelength. [The Aslots arev arranged with their longitudinal axes .collinear and parallel to the longitudinal axis of the coaxial line. I As shown in Fig. 3, the slots are displaced slightly rom the center line of line 11; this displacement isa mechanical expedient to permit a good mechanical 'spacing ofthe inner and outer conductors.

`A descriptionof ,themanner of mounting inner conductor 14 within outer conductor 12'will now be given. A square plug 18 is mounted at one endof line 11 by means of a'taper pin 19whioh passes through a taper bore in4 conductor 14. `This plug is of substantially the same dimensions as theinner dimensions of conductor 12 and serves ynot only as asupport for inner conductor 14, but also to prevent the access of foreign matter Vinto the line.

At inter/als along the inner conductor equal to the spacing betweentransverse center lines of adjacent slots and arrangedito line up with the :center Aof each slot, a plurality of-holesvis bored and tapped to receive threaded pins 20. Between the vinner surface of conductor 12 and the periphery ofvinner conductor Mat each location of a tapped hole in conductor 14, a tubular collar or spacer 22 is inserted. As shown in Fig. 4, the bottom edge of spacer 22 is so shaped as to conform to the circular periphery ofthe inner conductor. A plurality of holes 24 is -cutin the slotted face of the outer conductor 12 in alignment with the holes in conductor 14; holes 24'are locatedion the longitudinal center line of the slotted face 12 of line 11 and opposite the center of the corresponding slot, vasshown in Fig. 3. Pins 20 are inserted through corresponding holes 24 Vand spacers 22 and screwed into the. threaded holes of conductor 14 until the spacer'22 is iirmly maintained in position. The head portion of each pin 2i) isCentere'd 'about the longitudinal center line of the slotted face of conductor 12 and opposite the center of the. corresponding slot. Pins 20, in addition to supporting inner conductor 14 in proper spatial relationship with respect toouter conductor 12, also servexas probes for coupling energy'from the lines to the corresponding slot.. y

At the endof coaxiallinell remote fromplug-lv an impedance ymatching; Ysection of Vgradually -f decreasing cross sectionis Iemployedjto match the coaxial-line antenna, to apower` supply line. The sectionincludes a choke 26 in the form of a tubular sleeve surrounding the main portion of inner conductor 14 and secured thereto by a taper pin 27. As shown in Fig. 2, an extension 14' of inner conductor 14 is inserted in a recess 29 in one end of conductor 14 and held firmly in contact with the latter by one or more taper pins 39. An extension 14" of the inner conductor is formed by machining `down the end of conductor 14 as shown in Fig. 2 and is of proper size for engagement with a standard coaxial line connector. Alternately, the extension 14 could be connected to extension 14 in the same manner that extension 14" is connected to conductor 14.

Similarly, the internal periphery of outer conductor 12 is tapered in steps having a rst reduced portion 12 and a second reduced inserted portion 12". As previously stated, the coaxial line 11 is preferably made of aluminum which is a soft material. ln order to provide a good bearing surface when the end 32 of coaxial line is connected to a coaxial connector, the inserted portion 12 comprises a cyindrical sleeve of a hard metal, such as brass, which is inserted in the end of the coaxial line as shown in Fig. 2. The end portion 32 of the coaxial line is machined round as shown in Fig. l, so that connection maybe made to a standard coaxial connector (not shown). Diametrically opposed guide pins 33 mounted on the periphery of the round end portion 32 of the outer conductor are adapted to lit into corresponding slots in the aforesaid coaxial connector. 4

Although theoretically unnecessary for proper and cicient operation, a thin cover strip 35 (see Fig. 5) of a ma-v terial transparent to microwave energy, such as polystyrene, is mounted over the slotted face'of the coaxial line. This cover strip prevents the entrance of dust and other foreign matter by way of the slots which would not only alter the dielectric constant of the coaxial line but alter the effective dimensions of the radiating slots and, consequently, aiect the beam pattern'. Cover strip 35 also protects the operator or patient from severe burns which would be received if contact were acidentally made with the high voltage existing across opposite edges of the slots. The cover strip is fastened to both sides of reector 15 by means of screws 36 inserted in holes 38 in the reector. The only restriction on the dimensions of the plastic cover strip is that it not be so thick as to alter the dielectric constant of the antenna. ln practice, cover strip 3S is as long as the reector and approximately one-sixteenth inch thick.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A microwave antenna comprising a coaxial line having a circular inner conductor and a rectangular outer porting said inner conductor in fixed spatial relationship with respect to saidouter conductor means included within said means for supporting for coupling energy from said line to said radiating slots, and reector means attached to opposite edges of the slotted face of said outer conductor for restricting the angle of radiation from said antenna.

2. A microwave antenna comprising a coaxial line having a circular inner conductor and a rectangular outer conductor, one face of said outer conductor containing a single collinear array of spaced energy radiating slots resonant at the operating frequency and having their longitudinal axes parallel to and displaced from the central longitudinalaxis of said line, means for supporting said inner conductor in xed spatial relationship with respect to said outer conductor, means included within said means for supporting for coupling energy from said line to said radiating slots, and reector means attached to oppostie edges of the slotted face of said outer conductor.

3. A microwave antenna comprising a coaxial Vline having a circular inner conductor and a rectangular outer conductor, one face of said outer conductor containing a single collinear array of slots spaced along the longitudinal axis of said line, Vmeans including a plurality of spaced pins securely attached to said inner and outer conductors for maintaining a xed spatial relationship between said inner and outer conductors, said pins being positioned in energy-coupling relationship with said slots, and a reector having a pair of angularly disposed plates attached to opposite longitudinal edges of the slotted face of said outer conductor.

4. A microwave antenna comprising a coaxial line having a circular inner conductor and a rectangular outer conductor, one face of said outer conductor containing a collinear array of slots spaced along the longitudinal axis of said line, a plurality of spaced pins having a head portion resting against the outer surface of said outer Yconductor and a threaded portion extending through fsaid outer conductor into said inner conductor, said pins being positioned in energy-coupling relationship with said slots, and a reector having a pairof angularly disposed plates attached to opposite edges of the slotted face of said outer conductor. i

5. A microwave antenna comprising a coaxial line having a circular inner conductor and a rectangular outer conductor, one face of said outer conductor containing a collinear arrayofy narrow slots resonant at the operating frequency and having their longitudinal axes parallel to and displaced from the central longitudinal axis of said line, a plurality of tubular spacers positioned between said inner and outer conductors, a plurality of spaced pins having a head portion resting against the outer surface of said outer conductor and a threaded portion extending through saidouter conductor and said spacers into said inner conductor, said pins being positioned in energy-coupling relationship with said slots, and a reflector having a pair of angularly disposed plates attached to opposite edges ofthe sloted faces of said outer conductor.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Jordan et al.: Slotted-Cylinder Antenna, Electrics, February 1947. f

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