The study of ferrite sleeve for realizing electrically short choke is reported in this work for coaxial antennas used in intracavitary microwave hyperthermia treatment. Electromagnetic simulations of ...intracavitary applicators with the optimized ferrite sleeve operating at 700, 915, and 2450 MHz demonstrated stable resonance and targeted power deposition independent of the insertion depth when compared to their unbalanced counterparts. Thermal simulations indicated spherical heating volume for the applicators with the ferrite sleeve. Intracavitary applicator prototypes of <inline-formula> <tex-math notation="LaTeX">\boldsymbol {\lambda }/\mathbf {4} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">\mathbf {3\lambda }/\mathbf {8} </tex-math></inline-formula> coaxial monopoles with the optimized ferrite choke indicated return loss more than 22, 27, and 22 dB at 700, 915, and 2450 MHz, respectively, for varying insertion depths (70-130 mm) in agreement with the simulations. Local electric field measurements at 915 MHz in phantom indicated 51% and 58% reduction in 25% field contour along the antenna axis for the <inline-formula> <tex-math notation="LaTeX">\boldsymbol {\lambda }/\mathbf {4} </tex-math></inline-formula> monopole with <inline-formula> <tex-math notation="LaTeX">\mathbf {0}.\mathbf {24\lambda } </tex-math></inline-formula> ferrite sleeve and <inline-formula> <tex-math notation="LaTeX">\mathbf {3\lambda }/\mathbf {8} </tex-math></inline-formula> monopole with <inline-formula> <tex-math notation="LaTeX">\mathbf {0}.\mathbf {12\lambda } </tex-math></inline-formula> ferrite sleeve, respectively. Specific absorption rate and thermal measurements in phantoms confirm that ferrite sleeve <inline-formula> <tex-math notation="LaTeX"> < \boldsymbol {\lambda }/\mathbf {4} </tex-math></inline-formula> is sufficient to choke the secondary current on coaxial monopole antennas for delivering targeted power deposition at varying tissue insertion depths.
Ferrite chokes are often applied to suppress electromagnetic interference (EMI) in power converters. In this paper, an improved ferrite choke RLC model and its parameters determination method are ...proposed. The improved ferrite choke RLC model can overcome the limitation of the existing RLC model in the low frequency band, and the proposed parameters determination method can calculate the values of RLC parameters more accurate according to curve fitting of the ferrite choke datasheet. The effectiveness of the improved ferrite choke RLC model is verified by simulation based on a PWM rectifier, and the accuracy of the parameters determination method is verified by the impedance fitting results. The proposed ferrite choke RLC model and parameters determination method in this paper can provide ferrite choke choosing guidance for power converters in engineering application.
