Design and assessment of low frequency synchronous demodulator in Dicke radiometer for passive tissue thermometry

• Published in: 2024 IEEE Microwaves, Antennas, and Propagation Conference (MAPCON) pp. 1 - 5
• Main Authors: Arjun, A K, Arunachalam, Kavitha
• Format: Conference Proceeding
• Language: English
• Published: IEEE 09.12.2024
• Subjects: core body temperature; Demodulation; Frequency synchronization; microwave; Microwave amplifiers; Microwave circuits; Microwave measurement; Microwave radiometry; Microwave theory and techniques; Noise; radiometry synchronous demodulator; Signal resolution; Temperature measurement
• DOI: 10.1109/MAPCON61407.2024.10923045

In this paper we present the design and assessment of a low frequency synchronous demodulator circuit in a single reference Dicke microwave radiometer meant for tissue thermometry. In medical applications, microwave radiometry is used as a non-invasive method to estimate the core-bodytemperature (CBT) of a subject by integrating the total noise power emitted by the sub-cutaneous heat source. However, since the method is sensitive to ambient conditions and external noise, a bias cancellation system configuration known as Dicke radiometer is needed. This system configuration requires a synchronous demodulator which allows us to subtract the system bias signal from the noise signal of interest. Towards this goal, we have designed, simulated, fabricated, and tested a low frequency synchronous demodulator circuit. This circuit uses an analog SPDT switch to separate the source and reference signals from the modulated signal, integrates them and then uses a switched capacitor circuit to obtain the differential signal. Preliminary results show the ability to resolve signals with differences in amplitude of few millivolts over the narrow clinical temperature range of 35 to 42^{\circ} \mathrm{C}.