Noninvasive Microwave Radiometer and Near-field Probe Design for Internal Body Temperature Measurement

Autor: Mao-Sheng Cheng, 鄭茂盛
Rok vydání: 2018
Druh dokumentu: 學位論文 ; thesis
Popis: 106
The thesis implemented a radiometric thermometer to noninvasively measure the temperature of internal body. The radiometric thermometer consists of a near-field probe and a Dicke radiometer device. The temperature of in-body heat sources under subcutaneous about three or four centimeters is measured by the Dicke radiometry designed to transfer RF signal to DC voltage. The goal of the thesis is to design and optimize the near-field probe antennas that can be attached to the skin and connected to the microwave radiometers. The probe integrated with the microwave radiometer was constructed to non-invasively measure the temperature of the subcutaneous tissue. The probe and the radiometer are designed to meet the requirements of the technology in the frequency bands, 1.575 GHz and 3.8 GHz. First, the thesis is to research and develop a near-field circular patch antenna probe and then study how to reduce the volume by using short-pin grounded post for the temperature monitoring device which is used to detect the temperature of internal human tissues. A FR4 superstrate was added between the skin and the designed probe because of considering material change at the boundary of the simulation model to easily collect the black body radiation under the superficial tissue. Adding the superstrate achieves the normal component electric field matching so as to make the power loss density into the internal body the best since the tissues and the skin have high dielectric constant contrast. The absorbed power in the layer of interest finally increases, from 8.5 % to 43 %, for the probe with superstrate. The probe antennas were constructed and the phantom based on Agar material was fabricated to emulate the real tissue of skin and muscle for experiments. We set up the human body phantom to conduct experiment in order to verify the accuracy of the EM simulation. The radiometer prototype is composed of a Dicke switch at the input port of the radiometer for calibration, two low noise amplifiers to achieve the required gain, two cascaded custom-built BPFs for filtering the outside of the interest band, a square-law diode power detector with high sensitivity, and a DC gain amplifier. All of them are off-the-shell components, except the power detector. We employed a Schottky diode, SMS7630-079LF of Skywords to design the power detector and used a RF choke to block the harmonic frequencies feeding through the load to influence the RF performance. The measured sensitivity of the square-law diode detector is about 0.1 mV/0.01W. The Dicke radiometers were designed and fabricated to collect the power of the black body radiation under the superficial tissue. The radiometer has a system gain of 53.45 dB and total noise figure of 1.33 dB at 1.575 GHz. The radiometer has a system gain of 48.3 dB and total noise figure of 1.85 dB at 3.8 GHz. Finally, the microwave radiometer intergrated with the antenna probe was fabricated and tested. The measured voltage by the 1.575 GHz microwave radiometer is 187 mV as attaching the cold saline water, while the voltage of the hot saline water is 203 mV. The temperature difference is 30 mV between attaching the hot and cold saline water. The measured voltage by the 3.8 GHz microwave radiometer is 1.36 V as attaching the cold saline water, while the voltage of the hot saline water is 1.4 V. The temperature difference is 40 mV between attaching the hot and cold saline water. The hardware system can meet the requirement of a radiometric device for detecting blackbody radiation. The measured results depict the temperature difference in the internal body can be accurately predicted by the difference of the output voltage from the radiometer connected with the near-field probe.
Databáze: Networked Digital Library of Theses & Dissertations
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