Microwave life detector for buried victims using neutrodyning loop based system
Bel Hadj Tahar J.
Graduate School of Communications of Tunis, Sup'Com, Tunisia, Route de raoued, Cité El-Ghazela, Ariana, Tunisia
Received 26 November 2007
Accepted 19 February 2009
Endoscopic and sthetoscopic arrangements
This paper describes a new design of an electromagnetic life detector for the detection of buried victims. The
principle of the microwave life sensor is based on the detection of the modulated part of a scattered wave
which is generated by the breathing activity of the victim. Those movements generate a spectral component
located in the low frequency range, which for most of the cases, is located in a spectrum extending from
0.18 Hz to 0.34 Hz. The detection process requires high sensitivity with respect to breathing movements and,
simultaneously, a relative insensitivity for other non-modulated or modulated parasitic signals. Developed
microwave system, generating a frequency adjustable between 500 MHz and 1 GHz, is based on a
neutrodyning loop required to cancel any non-modulated background and reﬂected signals in order to get
better receiver sensitivity without introducing supplementary distortions on the received signal. Life signal is
considered practically periodic that facilitates the extraction of this spectral component using several
processing techniques, such as adaptive ﬁltering and correlation permitting to ameliorate the detection range
to be more than 15 m in low-loss medium. Detection range is a fundamental parameter for a microwave life
detector. A range around 1 m doesn't have a large interest for this application. To attain a range more than
15 m, while guaranteeing professional performances, the technology has to optimize the system parameters
as well as the involved signal processing for the purpose of overcoming the presence of obstacles,
attenuation, and noise perturbation. This constitutes the main contribution of the present work.
Experimental measurements have conﬁrmed the potentiality of this microwave technique for life detector
with best space covering detection.
© 2009 Elsevier B.V. All rights reserved.
The rescue of earthquake victims, for instance, is based on a
combination of different approaches including the use of dogs, seismic
and acoustic detectors or optical endoscopes. Each of these approaches
has its own limitations. The use of dogs does not necessarily allow
discrimination between living and dead victims. The seismic/acoustic
detection requires quiet environment and cooperative victims. The
range of investigation of the optical endoscopes is evidently limited by
the opacity of the rubble (dust, walls, etc…). As a result, in the case of
intense earthquakes, the number of buried victims saved by these
techniques remains very small as compared to the total number of
victims ranging between several hundreds. Such a situation explains a
true need for new life form detectors, which can be used alone or in
conjunction with existing techniques. In this connexion,it appears that
microwave sensors could bring about speciﬁc advantages for the
detection of living victims. Indeed, microwaves have good penetration
capabilities through ground, rubbles and non-metallic materials.
Accordingly, they do not suffer from sharp screening effects encoun-
tered with optical or infrared sensors. Furthermore they are able to
provide a distinctive life form signal which is related to the breathing
activity of the victims. Focusing on living victims is really essential in
the rescue strategy. Indeed, removing the rubble is a very time
consuming activity, especially in the case of large and modern
buildings made with reinforced concretes. The detection problem is
extremely complicated due the smallness of the movements to be
detected. The selection of the power level and the frequency range
must take into account the propagation losses in the rubble and the
received signal level of the modulation efﬁciency of the breathing
The radio frequency based detection of objects and respiratory
movements as well as heart beat in free space, using the principle of
Doppler frequency measurement, is a well known topic in the
literature (Chen and Chuang, 1988; Chuang and Chen, 1989; Banerjee,
2003; Jianqui et al., 2007; Lopera et al., 2007, Smith et al., 2007). The
development of this detection method was facilitated by the use of the
X-band frequencies (around 10 GHz), with the direct detection over
the free space. Experimental results have showed the feasibility of
Radar system to detect slow vibratory signals created by heart and
respiratory movements. In Jianqui et al. (2007), the person is placed
2 m away from the antenna, and the detection was over free space.
This has a large interest particularly for medical applications. In
another work (Chuang and Chen,1989), a microwave life detector was
Journal of Applied Geophysics 68 (2009) 371–379
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