Micro-Doppler Detection and Vibration Sensing Using Silicon-Based THz Radiators

Abstract

In this paper, vibration sensing and micro-Doppler measurements are performed using THz CW and pulse radiator chips in GlobalFoundries 90-nm SiGe BiCMOS process. The pulse source radiates a frequency comb with tones ranging from 10s of GHz up to 1.1 THz, where the spacing between two adjacent tones can be tuned using an external low-frequency source. In THz frequency range, subtle vibrations on the surface of a target results in phase change of the incident beams. Therefore, compared to RF and mm-wave frequency regimes, THz band offers a higher resolution for picking up the signature of subtle sound vibrations. The phase-modulated reflected beams carry the information of the original sound waves resulting in the spectral side tones. The original sound wave is then recovered by down-conversion of THz waves and FM demodulation. In addition, the time-domain phase information is captured by performing I/Q analysis on the down-converted signal allowing us to characterize the vibrations with a high resolution. Moreover, THz interferometry for vibration sensing is demonstrated using THz Continuous Wave (CW) radiator chip enabling the detection of sub- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> vibrations with a sensitivity of 30 nm. In this work, various measurements with different types of audio signals including monotone, chirp, and a music track with the frequency range of 100 Hz up to 1 kHz are performed.