Noninvasive Internal Body Thermometry With On-Chip GaAs Dicke Radiometer

In this letter, we present an on-chip radiometer for noninvasive internal body temperature measurements. The switch and low-noise, high-gain amplifier parts of the Dicke radiometer are designed as a single monolithic microwave integrated circuit (MMIC) using enhancement-mode 0.1 \mu m GaAs pseudomorphic high electron mobility transistor (pHEMT) technology. The radiometer shows 45 dB of gain and 0.88 dB noise figure (NF) at 1.4 GHz. When connected to a near-field antenna probe, measurements are obtained on a skin-muscle phantom to track the muscle temperature. The near-field antenna is designed to receive blackbody radiation from the 15 mm thick muscle phantom under the 2 mm thick skin phantom. To retrieve the subcutaneous temperature of the muscle, a radiometer calibration is performed with a reference noise source by switching at 10 Hz. The integration time of the measurements is 2 s. A 27-MHz bandwidth results in an average measurement error of 0.77 K compared to a thermocouple measurement of the muscle phantom performed 30 s before the radiometric measurement.