Tunable dielectric resonator with circumferentially magnetized ferrite disks
Electronically tunable dielectric resonator containing circumferentially magnetized ferrite elements has been investigated. The structure of the resonator has been analysed to obtain the optimal parameters. The resonator was constructed whose resonant frequencies can be switched by short current pulses between two stable values that differ in frequency up to 25 MHz with Q-factor value about 4200.
Magnetic tuning of cylindrical H/sub 01 delta /-mode dielectric resonators
The theory of magnetic tuning of cylindrical H/sub 01 delta / dielectric resonators is developed. It is based on rigorous solutions to the dielectric resonator systems containing microwave ferrites. It is shown that the most effective magnetic tuning of H/sub 01 delta / dielectric resonators can be accomplished by inserting a thin ferrite rod through an axial hole in the resonator. This kind of tuning utilizes the dependence of the parallel permeability tensor component mu /sub z/ on the magnetic field applied. Experiments have been performed which show that a 4% tuning range can be attained with a Q-factor of the resonant system of the order of 2000 at X-band. Using an appropriate DC magnetic field circuit, a 120 MHz tuning bandwidth has been obtained with a consumption of tuning power of about 75 mW. >
New Low-Profile Applicators for Local Heating of Tissues
A new type of low-profile applicator is described giving efficient power transfer to tissue with low leakage. It consists of a resonant element spaced from a ground plane by low-loss material having high relative permittivity and some relative permeability. This combination is covered by similar material which can be placed in direct contact with the tissue to be heated, or separated from it by a water bolus as required. Laboratory measurements using phantom materials show that these applicators are well matched and produce well defined and relatively uniform heating profiles. Applicators having maximum dimensions of 3-15 cm covering the frequency range 1000-100 MHz, respectively, are described. Penetration depths of at least 4 cm at 100-200 MHz are achieved. Tests on anesthetised pigs and some clinical assessment have confirmed the usefulness of this compact low-frequency type of applicator and have shown that performance compares favorably with that of other recently reported types. The design can be optimized for treatment of specific sites, and suitable choice of dimensions and electrical characteristics of the layer material allow the low-profile concept to be extended over a wide range of operating frequencies.