Study On The Layering Detection Technique Based On UWB Bio-radar

Radar-based life detection technique combines radar technology with many other technologies such as medical science,electrical engineering,computer science,weak signal detection,modern signal processing,etc.It utilizes the fact that the electromagnetic waves transmitted by radar can penetrate non-metallic media(wooden doors,brick walls,ruins,etc.)of a certain thickness to contactlessly detect,identify,and further locate the human target.The radar used for life detection is referred to as bio-radar.The bio-radar accomplishes the human target detection by extracting the body surface micro-motion and the rhythmic vibration of chest wall caused by breathing,heart beating and other physiology activities.It consists of the narrowband bio-radar and the ultra-wideband bio-radar.Owing to its eminent performances on penetration capability,ultra-short-range detection ability and high resolution ability,the UWB bio-radar reserves an enormous untapped application value in rescue operations(earthquakes,landslides,etc.)and anti-terrorist operations(through-wall-surveillance,etc.).Currently,UWB radar-based life detection practice focuses mainly on the detection and identification of the human target.Since the vital echo signals are very weak,many studies raised the center frequency of UWB radar to improve the detection sensitivity.However,the declined penetration capability resulted from the raised center frequency confines the detection practice to the penetration of simple barriers(planks or brick walls),incapable of detecting the human target in complex ruins scenes caused by earthquakes and landslides,etc.Therefore,in order to enhance the penetration capability,many studies proceed the experiments by declining the center frequency.As a result,life detection sensitivity declines.On the other hand,as the trapped survivors buried under the rubbles are in an unnatural state,the SNR of vital echo signs falls sharply due to the weakened life activities,which leads to the declination of the detection accuracy and restricted applications in rescue operations.To solve the above problem,researchers developed a variety of signal processing methods to improve detection performance,but with little effect.In addition to the signals in slow time domain,the 2-D UWB echo signals also contain a wealth of range domain information,but it has not been fully exploited.Time accumulation and layering process are two common information processing techniques in range domain.Due to the nonlinear property of echo signals,our previous studies have demonstrated that time accumulation has limited effect in enhancing detection performance.Whereas,as a common way of linear simplifying,the layering process technique can not only alleviate the problem of mutual interference and overlapping of signals between detection layers,but also effectively increase the contrast and specificity within the detection layers.The purpose of this paper is to introduce the layering process technique to the field of radar-based life detection to realize layering detection,so as to enhance the detection capability of UWB bio-radar in complex ruins scenes.The basic idea of the layering process is to decompose a complex nonlinear problem into several linear approximations.First,segmenting the detection region to form several layers.Then,according to the practical echoes in different layers,adopting the special signal processing methods to enhance the SNR of echo signals and eventually improving target recognition rate.The time window determines the detection range of the UWB bio-radar,therefore,the key of layering detection lies in the division of the time window.In earlier studies,our research group had developed a single-frequency IR-UWB radar with low center frequency of 400 MHz.This paper’s work was based on the former low center frequency IR-UWB radar.Firstly,we established the hardware experimental platform for layering detection study.Secondly,we experimentally analyzed the impact of layering detection on the detection capabilities of the UWB bio-radar,and explored the reason theoretically.Then we developed a control software for layering detection.Finally we compared and confirmed the detection capability of the new IR-UWB layering detection system in different experimental scenarios.The paper completed the following work:(1)A body surface micro-motion simulation system based on precision linear module was set up,serving as a standard detection target for radar-based life detection research.(2)Radar hardware circuit design was modified to achieve the layering detection functionality.The entire detection range was segmented to obtain fine echo signals in different layers,laying a solid foundation for further signal processing and target identification.(3)Compared and analyzed the differences on the target detection capabilities between the newly-built IR-UWB radar layering detection hardware platform and the original radar hardware platform.(4)A joint signal processing algorithm based on wavelet energy and wavelet entropy was proposed.And experimental studies was conducted to evaluate the detection performance of the algorithm in a simulated ruins scene.(5)A software aimed to control the layering detection via UWB bio-radar was developed.And experimental studies in different scenarios were conducted to evaluate the performance of the newly-built IR-UWB bio-radar layering detection system.The main results and conclusions of this paper are as follows:(1)The established human body surface micro-motion simulation systems can realize a precisely controllable periodic motion with an amplitude of 1mm and a frequency of0.1Hz,which meets the amplitude and frequency simulation requirements of body surface micro-motion caused by breathing and heart beating.On this basis,through simulation analysis and experimental studies,we finally determined the material and the size selection of the standard scatter,which had a similar scattering properties with the human target.Regarding it as a standard detection target in our experiments,we can effectively avoid the result errors caused by individual differences or other uncertain factors.(2)An UWB bio-radar hardware platform was developed.By reasonably setting the time window parameters,the refining segmented detection can be achieved in the detection range.(3)Regarding radar echo signal intensity and minimum resolvable displacement to the body surface micro-motion simulation system as two evaluation index,experimental studies was conducted to compare the detection performance of the two radar systems.The experiment results indicate that with the beacon location moving to the distal of detection area,the layering detection performance degrades;the layering detection system’s detecting ability performs better than the original one at any beacon positions.Further analysis shows that the distance attenuation and the equivalent sampling precision attribute to the differences of the detection performance.(4)A joint signal processing method based on wavelet energy and wavelet entropy was proposed to process the UWB echo signals characterized by non-Gaussian,non-stationary and non-linear.Experimental studies in simulated ruins scenes show that the method can improve the detection and identification accuracy in complex scenes.(5)A controlling software was developed based on the Delphi platform.Combining with the newly-built IR-UWB radar layering hardware,it can not only achieve the freely choosing of layering detection,but also continuous detection.This system has advantage over the original one in aspects like detection accuracy and time window selecting flexibility.Therefore it can be applied to rescue operations in complex environments as well as greatly improve the efficiency of post-disaster relief.The main innovations of this paper include:(1)A body surface micro-motion simulation system was set up based on precise control technology and simulation.It can simulate human target from three aspects,body micro-motion amplitude,frequency and echo signal intensity.And it can be applied to the life detection studies of all levels.(2)A new method of detection based piecewise linear approximation was proposed to improve the detection capability in a complex environment,in which the weak detection capability is caused by the echo signals’ nonlinearity.And the layering process method is introduced to improve detection capabilities in complex environments.(3)A new target recognition algorithm was proposed to improve the accuracy of life detection in complex environments.(4)UWB bio-radar layering detection system was established.And experimental studies in different detection scenes show that the newly-built system’s detection capability excels the original system.