A BASIC STUDY ON SIMULTANEOUS HEATING WITH MICROWAVES AND
ULTRASOUND USING COAXIAL, TYPE APPLICATOR
Abstract- A new heating method for hyperthermia using microwave and ultrasound simultaneously is proposed, and temperature distributions are obtained by computer simulations. The results have shown that the simultaneous use of microwave and ultrasound can heat wider and deeper region than the sole use, and can reduce the input power of microwave and ultrasound. This implies that we can reduce the hazards that high power microwave and ultrasound may bring about.
In hyperthermia, tumors are heated with their temperature 41.5-45 degree, but surrounding tissues must remain at normal temperature. So for such treatment, main methods of heating, RF and microwaves are used, while ultrasound is noticed as a new method recently. Microwave heat relatively wide area, but cannot heat so deep because it decays greatly in the medium especially in muscle tissues. On the other hand, ultrasound can be concentrated by beam forming using acoustic lens. And it can heat various region by changing the focal length, but the region is very narrow because the wavelength is very short. Microwave and ultrasound have such merits and defects each other. So if they are applied to the human body simultaneously, it is thought that the defects will be made up and desirable heating pattern will be obtained via a new design of the applicator.
The sectional structure of the applicator consists of two kinds of parts. One is the dielectric to supply microwave. The other is the transducer to supply ultrasound which is a part of inner conductor. With this applicator, electromagnetic (EM) wave at 430 MHz and ultrasound at l MHz are applied simultaneously. Ultrasound is greatly reflected at the boundary surface between different media, because its acoustic impedance is different. So when ultrasound is applied to human tissues, it is necessary to incident on water in advance of the...
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