Controlled microwave heating of inhomogeneous materials in medical and space applications

In microwave-induced heating of materials there are two applications for medical and space use that are quite interesting as well as scientifically important. These applications are the treatment of cancer in humans and the melting of thick layers of ice.;In the first application, an improved radio-frequency hyperthermia system for therapeutic tumor heating is investigated. The existing hyperthermia system is a cylindrical phased-array applicator, which operates at 140 MHz and consists of eight dipole antennas connected in parallel pairs, distributed uniformly around the cylinder. The system provides radial power steering by a four channel independent control of power and phase. When used in conjunction with Proton Resonance Frequency Shift (PRFS) Magnetic Resonance Imaging methods (MRI), patient heating within the tumor and surrounding healthy tissue can be monitored and corrected in real time to optimize hyperthermia treatment. To prevent crosstalk between a hyperthermia system and a MRI radio frequency (RF) coil, a bandpass filter which passes frequencies around 140 MHz and rejects frequencies around 64 MHz is designed and added to each channel of the existing system. And due to the complexity of the load, such as the position of the patient and the size of the tumor, etc., an impedance matching network is integrated into the existing applicator. The matching network successfully maximizes power delivered from each channel into a patient. To improve preplanning of treatment, a simulation with HFSS including a realistic human-body model is made. Then the electromagnetic field results from HFSS can be used by ePhysics (Ansoft Corp) to predict temperature distributions as a function of time in the tumor and the surrounding healthy tissue, taking into account blood perfusion and water cooling. Simulation results are compared with results of patient treatments. Meanwhile the results can be used to choose the appropriate settings of each antenna in advance for an individual patient.;In the second application, we explore the feasibility of using microwave energy to bore through thick layers of ice. Microwave energy is capable of achieving a composite depth of penetration of approximately 0.1 m at an operating frequency of 2.45 GHz, a frequency at which waveguide dimensions are practical and high-power sources are more readily available than at higher frequencies. Since ice has a very large depth of penetration and water has a very small depth of penetration at frequencies below 10 GHz, this presents a challenging problem. The problem is compounded because some of the places where this technique could be used may be on Mars or Europa where the ice is hundreds of kilometers thick. We simulated and tested our calculations and assumptions at 2.45 GHz using a 1300-watt microwave oven converted to transmit all output power into a rectangular waveguide terminated in a dome-shaped, open-ended probe pressed against a large block of ice. From multiple tests the melting rate in average is 0.75 inches/minute. Therefore, microwave-induced heating for melting deep layers of ice could be a viable alternative to other methods that have been used such as drilling and electrical resistance heating. In the end, we propose a method to combine the microwave heating and the electrical resistance heating to speed up the melting process. (Abstract shortened by UMI.).