Automatic Clutter-Canceler for Microwave Life

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I EEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 40, NO.4. AUGUST 1991

747

Automatic Clutter-Canceler for Microwave
Life-Detection Systems
Huey-Ru Chuang, Member, IEEE, Y.-F. Chen, and Kun-Mu Chen, Fellow, IEEE

Abstract-A microprocessor-controlled automatic cluttercancellation subsystem, consisting of a programmable microwave attenuator and a programmable microwave phase-shifter controlled by a microprocessor-based control unit, has been developed for a microwave life-detection system (L-band 2 GHz or X-band 10 GHz) which can remotely sense breathing and

heartbeat movements of living subjects. This automatic cluttercancellation subsystem has drastically improved a very slow p~ocess .of manual clutter-cancellation adjustment in our preVIOU.S mlcro~av.e sys~em. ~his is very important for some potential applications mcludmg location of earthquake or avalanche-trapped victims through rubble. A series of experiments have been conducted to demonstrate the applicability of this microwave life-detection system for rescue purposes. The automatic clutter-canceler may also have a potential application in some CW radar systems.

I. INTRODUCTION

ECENTLY a microwave life-detection system
(L-band 2 GHz or X-band 10 GHz) has been developed [1]-[2] to remotely detect the breathing and heartbeat signals of human subjects lying on the ground at a 100-ft distance, or located behind a barrier wall. The basic principle of the system is to illuminate the human subject

with a low-intensity microwave beam so that the small
amplitude body-vibrations due to the breathing and heartbeat of the human subject will modulate the backscattered microwave signal. The breathing and heartbeat signals can
be extracted from this backscattered signal by phase-detection in the microwave receiving system. A potential application of this system is to locate living
human subjects buried in rubble after an earthquake or
avalanche by remotely detecting breath and heartbeat
movements through the barrier (Fig, 1). In order to maintain a high sensitivity for this application, the clutter wave reflected from the rubble or the surface of the ground has
to be cancelled as thoroughly as possible before it reaches
and saturates the receiving microwave amplifier. In our
previous system, the clutter cancellation was performed
by a very slow manual-adjustment process. This is not
practical for a real-world emergency rescue operation
which demands a fast process. In this paper, we present
a newly developed automatic clutter-cancellation subsys-

R

Manuscript received June 6. 1990: revised March 6. 1991.
Y.-F. Chen and K.-M. Chen are with the Department of Electrical Engineering and Systems Science. Michigan State University. East Lansing. MI48824.
H.-R. Chuang is with the Department of Electrical Engineering. National Cheng Kung University. Tainan , Taiwan. Republic of China. IEEE Log Number 9100365.

RESCUE

Fig. I. Rescue application of the microwave life-detection system.

tem using a microprocessor-based control unit designed
to control a programmable microwave attenuator and a
programmable microwave phase-shifter for performing the
real-time automatic clutter-cancellation. The basic principle of this subsystem is to use the microprocessor-based control unit to scan the attenuator and phase-shifter to
minimize the input signal to the microwave amplifier and
hence cancel the clutter component.
A series of experiments has been conducted to measure
the breathing and heart signals of a human subject through
a layered pile of bricks simulating rubble. It was found
that the performance of the X-band (10 GHz) system became marginal when the brick structure exceeded about 1.5 ft in thickness (about 5 layers of bricks), while for the L-band (2 GHz) system it was possible to penetrate a pile

of dry rubble of up to about 3 ft in thickness (about 10
layers of bricks). This suggests that a lower frequency
will be more...
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