For long time, radars intended for sounding opaque mediums were developed with the purpose of detection only of motionless objects, as a rule, in soil. It is accepted in the scientific literature to name such radars by ground penetrating radar (GPR). The main fields of GPR's application are:
  • Soil's sounding for inspection of the underground communications (pipes, cables etc.)
  • Detection of unexploded ordnance (UXO)
  • Sounding of building designs for detection of built-in details, defects and latent objects (for example, overhearing devices)
  • Detection of the material evidence in criminalistics.
Traditional ground penetrating radars are usual scientific discipline, and the time-domain impulse radars are being produced in lots in many countries (the USA, Canada, Russia and so on).

      There is now keen interest to use of methods and means of GPR for detection and diagnostics of the live persons, which are taking place under rubble or behind walls of buildings. This task could be solved by radars, which operate in range of wavelengths 3 - 30 см (1 - 10 GHz). In this case, by subtraction of signals reflected from motionless objects, it is possible to achieve high sensitivity at detection of objects, which borders are subject to mechanical fluctuations. According to estimates available in the literature, the sensitivity of the given method can achieve 10-9 м. Let's name the given method by vibro-electromagnetic sounding (VES). Though the objects subject to mechanical fluctuations have a various nature, in the given research we shall be limited only to detection and diagnostics of the live persons.

      Objects in man's body, subjected more or less periodic fluctuations, are the reductions of an cardiac muscle (frequency in range of 0.8 - 2.5 Hz) and breathing (frequency in a range 0.2 - 0.5 Hz). Thus, the values of frequencies are determined by physical loading and physical condition of the examinee. The remote definition of parameters of pulse and breathing rates of the man, which is taking place behind an obstacle or in open space, is the basic task of the present research.

      The main applications of the this research in the field of vibro-electromagnetic sounding are:
  • Detection of alive human persons under rubles of building designs, which are suffered from natural disaster or technical calamity and accident. The urgency of task is defined by necessity for rescuers to begin disassembly of rubles and debris in places, where is a hope to find out the alive people
  • Detection of the people and parameters of their moving inside of building in course of antiterrorist operations
  • Remote diagnostics of the persons during the latent or open checks, for example, at the airports (remote acting lie detector)
  • Contactless measurement of parameters of heartbeat and breath for the patients, for which the contact gauges for whatever reasons can not be used.

      The further researches should show, could this method be used for the definition of parameters of speech.

The Description of Experiments


      In a basis of technology used during experiments, the method of subsurface sounding with continuous signal, which was developed at creation RASCAN type radar, is lying. The method proposed by Russian team has no analogue in current scientific practice. The staff of the Remote Sensing Laboratory of IAMM was awarded the prize of the Russian Federation Government in the field of science and technology in 2000 for the creation of the RASCAN subsurface holographic radar and technology that is being presented.

      In experiments the modified subsurface radar of RASCAN type with the following parameters was used:

Operating frequency 1.6 GHz (wavelength = 19cm)
Gain factor 40 dB
Frequency range of recorded signals 0.03 - 3 Hz
Dynamic range 60 dB
Sampling frequency 20 Hz
Antenna's dimensions:
       Diameter 120 mm
       Height 200 mm

      The thickness of a wall, behind which there was an examinee, equals 10 cm. The examinee settled down on distance about 1 m from a wall. The radar's antenna was fastened directly on a wall. The recording of radar's signals through the interface block was carried out in a PC and then was processed.


Fig. 1. The sketch of the experiment

Experimental results


      The work is at an initial stage, and the experimental results are presented below practically without processing and filtering.

      In Fig. 2 and 4, pulse records of the examinee, which had detained the breath, are presented. In Fig. 2, delay of breath is equal to approximately 30 s. And for Fig. 4, the delay is about one minute. One could see, that at increase of the breath delay time the amplitude and rate of examinee pulse are also increased because of oxygen starvation. The frequency spectrums for signals in Fig. 2 and 4 are shown in Fig. 3 and 5.


Fig. 2. Pulse record of the examinee.
Breath delay is equal to approximately 30 s


Fig. 3. Frequency spectrum of the signal presented in Fig. 2


Fig. 4. Pulse record of the examinee.
Breath delay is equal to about one minute


Fig. 5. Frequency spectrum of the signal presented in Fig. 4


      The results of simultaneous recording of pulse and breath parameters of examinee are presented in Fig. 6. As amplitude of oscillations and volume of lungs considerably surpass similar parameters of heart, the reductions of cardiac muscle are observed as high-frequency modulation on a background of lungs oscillations.


Fig. 6. Breath and pulse record of the examinee without breath delay


Fig. 7. Frequency spectrum of the signal presented in Fig. 6


      Recording of speech of the examinee pronouncing consistently words: one, two, three... one, two, three...(in Russian) is presented in Fig. 8. In this experiment three processes is combined: pulse beating of heart, breathing and speech of the man. Taking into account, that the transmission band of input filter is limited only 3 Hz, we have no basis for the time being to assert that the data of similar measurements could be used for recognition of man's speech.


Fig. 8. Breath and pulse record of the examinee pronouncing
consistently words: one, two, three... (in Russian)


Fig. 9. Frequency spectrum of the signal presented in Fig. 8

Conclusion


      The carried out experiments on radar sounding of parameters of pulse beating of heart and breathing of the man through a barrier (wall separating two adjacent rooms) with the help of the radar of RASCAN type allow to consider technically feasible a task of remote diagnostics of the man parameters. During the further works it is necessary to improve data processing and the equipment with the purpose of definition of distance up to object.


Experimental step-frequency radar intended for remote registration
of biometric parameters of the man



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