referring to the drawings , and particularly to fig1 generally designates a typical microwave diathermy applicator assembly according to the present invention , for direct application at the 2 . 45 diathermy irradiation band . the main portion of the applicator 11 comprises a rectangular waveguide member 12 provided with a front peripheral securing flange 13 . tightly engaged in the opposite side portions of waveguide member 12 are respective polytetrafluoroethylene ( teflon ) slabs 14 , 14 , whose front ends are substantially flush with the plane of flange 13 . a specified width of slab 14 is necessary to sustain a uniform electromagnetic wave , the transverse electromagnetic mode ( tem ), in the air space between the two slabs as noted below . in a typical small size applicator according to fig1 the waveguide section 12 is 3 inches long and has an inside cross - section 4 . 3 inches wide and 2 . 15 inches high . the teflon slabs 14 , 14 are 3 inches long and 1 . 26 inches wide . for a medium size applicator , the waveguide section 12 is also 3 inches long , and has an inside cross - section 5 . 1 inches wide and 2 . 55 inches high , the teflon slabs 14 , 14 being also 3 inches long and 1 . 26 inches wide . in each case the slabs are of a height sufficient to fit tightly in the opposite side portions of the waveguide cavity . the waveguide section 12 is closely receivable in the rectangular body 15 of a waveguide - coaxial adaptor 16 provided with a connection terminal 17 for connecting the applicator to the end of a coaxial cable 18 ( see fig5 ) leading to the output of a 2 . 45 ghz microwave diathermy machine . the above connection terminal 17 must be placed symmetrically with respect to the vertical walls of the rectangular body 15 to prevent excitation of the first order asymmetric longitudinal section electric ( lse ) mode which would induce a less uniform heating pattern . the front end of body 15 is provided with a peripheral flange 19 . the flanges 13 and 19 have registering apertures for receiving fastening screws or bolts to secure the flanges in abutting relationship . the spaced teflon slabs 14 , 14 serve as loading and absorption elements to modify the heating action of the applicator , applied directly to a tissue area to be treated , so as to provide a desirable heating pattern , for example , a pattern wherein the temperature is substantially uniform at its central portion . the slabs 14 must be spaced sufficiently close to each other , as is this case in this disclosure , to prevent the excitation of the second higher order lse mode in the air space between them which would induce a less uniform heating pattern . fig2 shows a large size direct - contact microwave diathermy applicator according to the present invention , designated generally at 11 &# 39 ;. in this embodiment , the main portion of the applicator comprises a rectangular waveguide member 12 &# 39 ; provided with a front peripheral flange 13 &# 39 ;. tightly fitted in the intermediate portion of member 12 &# 39 ;, coextensive in length therewith , are the spaced longitudinally extending teflon slabs 14 &# 39 ;, 14 &# 39 ; whose front ends are substantially flush with the plane of flange 13 &# 39 ;. a specified width of slabs 14 &# 39 ; is necessary to sustain a tem mode in the air space between the two slabs as noted below . the waveguide section 12 &# 39 ; is closely received in the rectangular body 15 &# 39 ; of a waveguide - coaxial cable adaptor 16 &# 39 ; provided with a terminal 17 &# 39 ; for connecting the applicator to a coaxial feed cable 18 leading from the output of a 2 . 45 ghz microwave diathermy machine . the above connection terminal 17 &# 39 ; must be placed symmetrically with respect to the vertical walls of the rectangular body 15 &# 39 ; to prevent excitation of the first order symmetric lse mode . the front end of body 15 &# 39 ; is provided with a peripheral flange 19 &# 39 ; which is secured to flange 13 &# 39 ; by suitable screws or bolts 20 , as shown in fig2 . in a typical embodiment , following the showing in fig2 the waveguide section 12 &# 39 ; is 3 inches long and has an inside cross - section 6 . 5 inches wide and 3 . 25 inches high . the teflon slabs 14 &# 39 ;, 14 &# 39 ; are 3 inches long and 1 . 26 inches wide . the spacing between the slabs 14 &# 39 ;, 14 &# 39 ; at the midportion of the waveguide cavity is 1 / 2 inch . the slabs 14 &# 39 ;, 14 &# 39 ; are of a height to fit tightly in the intermediate portion of the waveguide cavity . the slabs 14 &# 39 ; must be spaced sufficiently close to each other , as is the case in this disclosure , to prevent the excitation of the second higher order lse mode in the air space between them which would induce a less uniform heating pattern . as in the embodiment of fig1 the teflon slabs 14 &# 39 ;, 14 &# 39 ; serve as loading and absorption elements to modify the heating action of the directly - applied applicator so as to provide a desirable heating pattern , namely , wherein the temperature is substantially uniform over the central portion due to the tem excitation in the air space between the two slabs 14 &# 39 ;. in testing the performance of an applicator 11 or 11 &# 39 ;, a fat - skin planar phantom 21 ( see fig5 ) may be used to stimulate tissue to be treated . the phantom 21 may comprise a pair of symmetrically - mating blocks 22 , 22 , abutting at a vertical midplane , as shown at 23 in fig5 . each block has an outer layer 24 of a material having microwave absorption or dielectric characteristics similar to fat and an inside layer similar to muscle , such as described in a . w . guy , j . f . lehmann , j . a . mcgougal and c . c . sorensen , &# 34 ; studies on therapeutic heating by electromagnetic energy &# 34 ;, page 31 , &# 34 ; thermal problems in biotechnology &# 34 ;, american society of mechanical engineers , n . y ., 1965 ; the fat material consists of 84 . 81 % laminac polyester resin , 0 . 45 % catylist ( methyl ethyl ketone peroxide &# 34 ; 60 %&# 34 ;), 0 . 24 % acetylene black and 14 . 5 % aluminum powder ; the muscle material consists of 15 . 2 % powdered polyethylene , 76 . 4 % saline solution ( 12 gms salt / liter ) and 8 . 4 % silly &# 34 ; stuff &# 34 ; ( silly stuff from whamo co . california .) each block also has an inner matrix 25 simulating muscle . the testing procedure comprises first heating the abutting blocks 22 , 22 , arranged as in fig5 with a direct contact applicator 11 or 11 &# 39 ; placed thereon over the abutment midplane at 23 . the power output of the microwave diathermy machine , operating at 2 . 45 ghz , is about 130 watts , lasting for 5 seconds . the resultant temperature distribution at the center of the heating pattern in the midplane of the phantom is measured by using a thermographic camera 26 ( see fig6 ). the camera scanning line is set parallel to the fatmuscle interface of the planar phantom . for the small direct contact applicator of fig1 in a typical test , the central portion of the heating pattern , about 1 . 6 inches in length , showed an average temperature rise of 2 . 7 ° c , with limits of ± 0 . 2 ° c ; for the medium size direct - contact applicator 11 above described , the central portion , about 2 . 9 inches in length , showed an average temperature rise of 1 . 2 ° c , with limits of ± 0 . 2 ° c , and for the large direct - contact applicator 11 &# 39 ; of fig2 the central portion , about 1 . 85 inches in length , showed an average temperature rise of 0 . 8 ° c , with limits of ± 0 . 2 ° c . a choice of uniform heating patterns of different sizes with different temperature distributions is for example needed in microwave induced hyperthermia treatment of cancer because cancer therapy requires heating of the entire diseased treatment area above a particular elevated temperature to prevent the spread of cancer to other tissue . while certain specific embodiments of improved direct - contact microwave diathermy applicators have been disclosed in the foregoing description , it will be understood that various modifications within the scope of the invention may occur to those skilled in the art . therefore it is intended that adaptions and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments . for example , materials which act in a manner equivalent to polytetrafluoroethylene ( teflon ) in the present environment may be used in its place .
a direct contact microwave diathermy applicator consisting of a rectangular waveguide in which are secured two parallel teflon dielectric loading slabs . this assembly is secured in a waveguide - coaxial cable adaptor , enabling the applicator to be energized from a microwave diathermy machine . the configuration of the applicator causes the tissue under treatment to exhibit approximately uniform heating patterns over a substantial portion of the treated tissue area and minimizes harmful scatter radiation . this uniform heating is particularly useful in effecting microwave induced hyperthermia treatment of cancer .