Date of Award

Spring 1-1-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical, Computer & Energy Engineering

First Advisor

Zoya Popovic

Second Advisor

Edward Kuester

Third Advisor

Dejan Filipovic

Fourth Advisor

Dragan Maksimovic

Fifth Advisor

Joel Libove

Abstract

Microwave thermometry is an attractive non-invasive method for measuring internal body temperature. This approach has the potential of enabling a wearable device that can continuously monitor core body temperature. There are a number of health-related applications in both diagnostics and therapy, which can benefit from the knowledge of core body temperature. However,there are a limited number of device solutions, which are usually not wearable or cannot continuously monitor internal body temperature non-invasively. In this thesis, a possible path toward implementing such a thermometer is presented. The device operates in the "quiet" frequency band of 1.4 GHz which is chosen as a compromise between sensing depth and radio frequency interference(RFI).

A major challenge in microwave thermometry is detecting small temperature variations of deep tissue layers from surface (skin) measurements. The type and thickness of tissue materials significantly affect the design of the probe, which has the function of receiving black-body radiation from tissues beneath it and coupling the power to a sensitive radiometric receiver. High dielectric constant contrast between skin, fat (/bone), and muscle layers suggests structures with dominant tangential component of the electric field, such as a patch or slot. Adding a layer of low-loss,low-dielectric constant superstrate can further reduce the contribution of superficial tissue layers in the received thermal noise. Several probe types are designed using a full-wave electromagnetic simulator, with a goal of maximizing the power reception from deep tissue layers. The designs are validated with a second software tool and various measurements. A stable, narrow-band, and highly sensitive radiometer is developed, enabling the device to operate in a non-shielded RF environment.To use the microwave thermometer in a RF congested environment, not only narrow-band probe and radiometers are used but an additional probe is introduced for observing the environmental interference. By applying an adaptive filter, the effect of RFI is mitigated in long-term measurements. Several solid and liquid tissue phantoms, required for accurate modeling of the probe and human body interaction, are also developed. The concept of human body microwave thermometry is validated through several measurements on the single-layer and multiple-layer tissue phantoms as well as on the surface of the human body, specifically on the cheek where the internal temperature can easily be changed and independently measured with a thermocouple. Measurement results prove the capability of the device in tracking the temperature of buried tissue layer phantoms to within 0.2K, as well as monitoring internal human body temperature.

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