Terahertz Radar Signal for Heart and Breath Rate Detection Based on Time-Frequency Analysis
The method of human heartbeat and breath detection in terahertz band is studied in this chapter which uses frequency information extraction with twice T-F (time-frequency) analysis towards echo signal. Firstly, the echo model of human target is built and
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Terahertz Radar Signal for Heart and Breath Rate Detection Based on Time-Frequency Analysis Yuanjie Wu, Zhengwu Xu, and Jin Li
Abstract The method of human heartbeat and breath detection in terahertz band is studied in this chapter which uses frequency information extraction with twice T-F (time-frequency) analysis towards echo signal. Firstly, the echo model of human target is built and accurate speed information, containing the micro features of human target ,is got by the combination of WVD (Wigner-Ville distribution) T-F analysis and centroid curve. Then, frequency of heartbeat and breath is extracted accurately by the second T-F analysis. According to the comparative analysis, SPWVD (smoothed pseudo Wigner-Ville distribution) based on the windowed WVD can effectively reduce the disturbance of cross-terms which can favor the detection of heartbeat and breath. Keywords Terahertz • Heartbeat • Breath • Centroid • SPWVD
53.1
Introdution
Terahertz radar has a very narrow radar beam and huge bandwidth of signal which can be used to precise target imaging [1]. Compared to other band, features of micro Doppler are more obvious [2]. Terahertz signal can penetrate certain material clothes and be reflected back by the skin. Therefore, a Doppler modulation on the radar echo is generated by even the short-term micro movement when human target is in the radar beam [3]. Relative to the movement of human body, breath and heartbeat which are generated by the movement of lungs and heart are micro motions [4].
Y. Wu (*) • Z. Xu • J. Li School of Electronic Engineering, University of Electronic Science and Technology of China, Chengdu, China e-mail: [email protected] Q. Liang et al. (eds.), Communications, Signal Processing, and Systems, Lecture Notes in Electrical Engineering 202, DOI 10.1007/978-1-4614-5803-6_53, # Springer Science+Business Media New York 2012
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Currently, the methods of heart and breath rate detection are divided into contact and non-contact ways [5]. The former one has a lot of detection methods in the clinic, such as: ECG (electrocardiogram), respiration belt. However, these detection methods mainly rely on sensors, electrodes and some other devices attached to the body. As the condition restricts its scope of application, those methods are not suitable for security check and battlefield environment. Micro pulse radar [5] and microwave technology [6] are the non-contact ways which all use the echo signal to detect objects. But these techniques are limited for distance, frequency detection accuracy and capability of weak signal detection in the complex environments such as avalanches, earthquakes and debris flow.
53.2
Target Modeling
For Terahertz continuous wave radar, assuming that the transmitter and receiver are located at the same location away from the radar, the signal transmitted at time t can be defined as ST ðtÞ ¼ ej2pf c t
(53.1)
Here, f c is the frequency of the transmitted signal. In fact, f c is 240 GHz. The signal received at time t is SR ðtÞ ¼ ej2pf c ðt
2R
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