Body Conformal Antennas for Superficial Hyperthermia: The Impact of Bending Contact Flexible Microstrip Applicators on Their Electromagnetic Behavior

Hyperthermia is a powerful radiosensitizer for treatment of superficial tumors. This requires body conformal antennas with a power distribution as homogeneous as possible over the skin area. The contact flexible microstrip applicators (CFMA) operating at 434 MHz exist in several sizes, including the large size 3H and 5H. This paper investigates the behavior of the electromagnetic fields for the 3H and 5H CFMA in both flat and curved configurations, and the impact on performance parameters like the penetration depth (PD) and the effective heating depth (EHD). The underlying theory behind the electromagnetic behavior in curved situations is presented as well as numerical simulations of both flat and curved configurations. The results are compared to measurements of the electromagnetic field distributions in a cylindrical patient model. Due to their large size multimode solutions may exist, and our results confirm their existence. These multimode solutions affect both the power distribution and PD/EHD, with a dependence on applicator curvature. Therefore, the performance parameters like PD and EHD need to be carefully assessed when bending large size CFMA applicators to conform to the patient body. This conclusion also holds for other types of large size surface current applicators.      

Transient Behavior of the ${hbox{a}}{hbox{-}}{hbox{Si}}:{hbox{H/Si}}_{3}{hbox{N}}_{4}$ MIS Capacitor and Its Impact on Image Quality of AMLCDs Addressed by a-Si:H Thin-Film Transistors

Transient behavior of the a-Si:H/Si₃N₄ metal-insulator-semiconductor (MIS) capacitor and its relationship to the performance of a-Si:H based active-matrix liquid crystal displays (AMLCDs) have been analyzed in detail. A relatively slow voltage decay whose time constant is comparable to the frame period of the LCD is observed after applying a voltage pulse that drives the MIS capacitor into the electron accumulation. The voltage decay is due to electron emission from the localized states at the a-Si:H/Si₃N₄ interface. It is also found that this voltage transient results in a shift in the optimum common voltage for the liquid crystal pixel by changing the temperature and light exposure when an MIS-type capacitor is inserted between the pixel electrode and the adjacent gate bus-line as the storage capacitor. This shift in the optimum common voltage affects the image quality of AMLCDs through image sticking or flicker. A similar effect can occur even without an MIS-type storage capacitor in high resolution AMLCDs, where the gate-source parasitic capacitance of the thin-film transistor is comparable to the net capacitance of the pixel. It is important to take such transient effects of MIS capacitors into consideration in pixel designing