Ultrawideband and Ultrashort Impulse Signals, 15-19 September, 2008, Sevastopol, Ukraine pp. 34-38

978-1-4244-2738-3/08/$25.00 ©2008 IEEE

REMOTE MONITORING OF HUMAN CARDIO-RESPIRATORY SYSTEM PARAMETERS

BY RADAR AND ITS APPLICATIONS 1 Immoreev I. and 2 Ivashov S.

1 Moscow Aviation Institute (State Technical University), Moscow, Russia E-mail: immoreev@aha.ru

2 Bauman Moscow State Technical University, Moscow, Russia E-mail: sivashov@rslab.ru

Abstract The diagnostic monitoring of humans (as well as their detection behind of the

opaque obstacles), by means of radar have called bio-radiolocation. As an illustration ultra-wideband (UWB) radar in medicine and in psychophysiology for remote measuring of patient's heart activity and respiration is shown. The measuring method is described and practical results of tests are cited. New technical decisions on hardware and software which allow obtaining reliable physiological data at the monitoring of back-and-forth motion of objects are considered. This paper considers various applications of the bio-radiolocation.

Keywords: radar, breathing, heartbeat, back-and-forth motion, bio-radiolocation.

1. INTRODUCTION The analysis of fields of application for UWB radars demonstrates that radars of that type can be used practically in all cases where we need highly precise re-mote observation of moving objects at short distances. UWB radars can be used in automobile traffic control systems to prevent collisions while driving and parking. They can be also used in security systems as security signalling sensors, which provide detection of unsanctioned intrusion into the guarded area. This type of radars can be applied in a rescue service to detect people buried under building obstructions or snow slips by their movement; if a person is motionless, the detection can be performed using person’s heart and thorax beats. UWB radars criminals concealed themselves under various covers. UWB radars are useful in hospitals and at home where they can provide remote measuring heart and respiratory beats and other parameters of patient’s vital activity. UWB radar can perform non-destructive control over building constructions, detect hidden communications in old buildings and so on.

Below is shown radars of such a type, also demonstrated are their possibilities to solve medicine problems.

2. THE MEASURING METHOD While constructing UWB radars, as with constructing conventional narrow-band radars, we use the property of electromagnetic waves to be scattered from a boundary of two media with different parameters, which is well-known from the general theory. The

electromagnetic wave pulses radiated by radar are scattered by a moving object. In this case, the oscillation frequency f within the pulse is changed owing to Doppler effect. As frequency variation leads to variations of the oscillation period T and the number of these periods in the pulse remains the same, the duration of a scattered pulse τ also changes. The repetition frequency of pulses scattered by an object Fr and correspondingly the pulse repetition period Tr also change simultaneously thanks to the same effect. The sign of these variations depends on the direction of target movement relative to the radar and the variation value depends on the object’s radial velocity. According to this direction, the signal spectrum is going wider or narrower and moves towards high or low frequency area.

The transmitter with controlled pulse repetition frequency produces pulses with frequency about 6.75 GHz and with frequency of repetition from 0.05 to 30 MHz. The example of this pulse with duration about 2 nanosecond are shown in Fig. 1

The radar works in conditions of high level of passive noise – the signals, reflected from walls and stationary objects, which will have large amplitude and will disguise useful signal. Time slots, opening the receiver at the moment of input of signal reflected from object at distance defined are formed in receiving path to eliminate interfering pulses. This task in radar design is executed by time discriminator, being gated. It consists of fast-acting electronic switches. The switching time is in order of 200-300 picoseconds. The switches connect receiving antenna to UWB amplifier at the moments of signals’ input.

Remote Monitoring of Human Cardio-Respiratory System Parameters by Radar and Its Applications

Ultrawideband and Ultrashort Impulse Signals, 15-19 September, 2008, Sevastopol, Ukraine 35

These moments are defined by delay magnitude of control signal at software-controlled delay line. All the rest time the receiver is shut. The signals received at time slots are detected and amplified in integrating amplifier and the signal, carrying data of target motion is selected at its output.

Time constant of integration of integrating amplifier is chosen in dependence of the bandwidth of desired signal. For example under measuring of parameters of person vital activity the bandwidth of desired signal is near 40-50 Hz, that corresponds to accumulation of 10~30 thousands of pulses

approximately. The accumulation permits to decrease average radiated power of transmitter and increase signal-to-noise ratio at the input of amplifier.

The selected and amplified low-frequency signal enters to analog-digital converter (ADC). The microprocessor-controlled unit directs the work of radar on given algorithms, monitors the state of major units and modules and provides data output for further digital processing in computer. The selection of moving targets, fast Fourier transform and digital filtration are software-programmable at the computer.

3. RADAR OBSERVATION OF OBJECTS, WHICH FULFILL BACK-AND-FORTH MOTION

In medical radars the main objects - the thorax and heart - have back-and-forth motion. In result, radar observation of such objects becomes unusual. Let's consider model shown in Fig. 2. The object makes back-and-forth motion under the harmonious law with frequency Ω: ( )( ) sinR t R R t θ= +Δ Ω + .

The radar radiates a signal: ( )0 0 0sinu t E tω= . The signal, reflected from object, is equal:

( )

( )1 1 0

1 0

sin 2 ( ) /

sinsin 2 .

u t E t R t c

R R tE t

c

ω

θω

⎡ ⎤= − =⎣ ⎦⎡ ⎤⎛ ⎞⎛ ⎞+Δ Ω + ⎟⎜ ⎟⎜⎢ ⎥⎟⎟⎜ ⎜ ⎟⎟= −⎢ ⎥⎜ ⎜ ⎟⎟⎜ ⎟⎜ ⎝ ⎠⎝ ⎠⎢ ⎥⎣ ⎦

The receiver is the correlator with an output signal cz (Fig. 3).

We believe object is motionless during time of integration. Then the output signal of the correlator:

0 10 0

0 10

0 0

0 10

0 0

sin( )( ) cos 2

24 4

cos cos sin( )2

4 4sin sin sin( )

2

c

E E R R tz t nT

cE E R R

nT t

E E R RnT t

θω

π πθ

λ λ

π πθ

λ λ

⎡ ⎤⎛ ⎞+Δ Ω + ⎟⎜⎢ ⎥⎟= =⎜ ⎟⎟⎜⎢ ⎥⎝ ⎠⎣ ⎦⎛ ⎞ ⎡ ⎤Δ⎟⎜ ⎢ ⎥⎟⎜= Ω + −⎟⎜ ⎢ ⎥⎟⎟⎜⎝ ⎠ ⎢ ⎥⎣ ⎦⎛ ⎞ ⎡ ⎤Δ⎟⎜ ⎢ ⎥⎟⎜− Ω +⎟⎜ ⎢ ⎥⎟⎟⎜⎝ ⎠ ⎢ ⎥⎣ ⎦

At 0

R λΔ , function ( )cz t is close to harmonious function. When the amplitude of movement of object RΔ increases and approaches to length of wave 0λ ,

the function ( )cz t appreciably changes and gets the complex form (see example in Fig. 4) and a complex spectrum.

In this case is necessary restoration the form of the signal corresponding to true movement of object. For this purpose the receiver has two quadrature channel ( )sz t and ( )cz t . The true trajectory of movement of

object is described by the formula:

[ ]0( ) arg ( ) ( ) .4 c sR t z t jz tλπ

= +

To find argument we should calculate function of arc tangent:

Fig. 1. An example of UWB pulse, radiated by the radar.

R

u0(t)

Rmax

ΔR ΔR

u1(t)

Rmin

Fig. 2. Back-and-forth motion of the object.

zcu1(t-tR)

u0(t)

u1(t-tR)×u0(t) u1(t-tR)×u0(t)dt∫0nT

0

Fig. 3 CorrelatorFig. 3. Correlator.

Fig. 4. The form of a signal when 0

R λΔ .

Immoreev I. and Ivashov S.

36 Ultrawideband and Ultrashort Impulse Signals, 15-19 September, 2008, Sevastopol, Ukraine

0 0

0 0

0

arg ( ) ( )

sin 4 4 sin( )

cos 4 4 sin( )

4sin( )

c sz t jz t

R Rt

arctgR R

t

R R t

π π θλ λ

π π θλ λ

πθ

λ

⎡ ⎤+ =⎢ ⎥⎣ ⎦⎛ ⎞⎛ ⎞Δ ⎟⎜ ⎟⎜ ⎟⎟⎜ + Ω +⎜ ⎟⎟⎜ ⎜ ⎟⎟⎜⎜ ⎟⎝ ⎠⎜ ⎟= =⎜ ⎟⎟⎜ ⎛ ⎞⎟⎜ Δ ⎟⎟⎜⎜ ⎟+ Ω + ⎟⎜⎜ ⎟⎟⎜⎜ ⎟⎟⎜⎜ ⎝ ⎠⎝ ⎠

⎡ ⎤= +Δ Ω +⎣ ⎦

Then the law of movement of object ( )R t will be:

( )( ) sinR t R R t θ= +Δ Ω + .

If the equipment of a radar allows to define distance up to object R , that, subtracting her from ( )R t , it is possible to define the law of movement of object precisely: ( )sinR t θΔ Ω + .

4. PROTOTYPES OF RADARS All the models of radars are created and tested with respect to the pointed principles.

4.1. MODEL # 1 Figure 5 demonstrates external views of this UWB radar model. The major specifications of prototype are given below:

Operation range 8 m; Pulse power 10 mW; Average power 80 μW; Width of the antenna's pattern: 80 Duration of radiated radio pulses 2 ns;

Model # 1 is intended for medical researches. Fig. 6 demonstrates the results of remote measuring physiological parameters.

At the Fig. 6 we demonstrate the time diagrams of signals corresponding heart and respiratory beats, which were detected by the UWB radar. The amplitude of radar output signals is directly proportional to the amplitude of thorax and heat beats.

To appreciate the accuracy of radar measurements and quality of information concerning patient’s heart activity obtained using UWB radar, we compared data collected with the radar and a medical cardiograph. The comparison was led in instantaneous (from beat to beat) variations of systole period (what is know as variability of cardiac rhythm). Fig. 7 demonstrates the measurement data depending on the number of a beat, which were obtained simultaneously with using radar (red line) and a cardiograph (blue line). The coefficient of correlation between these measurements was calculated. In this experiment, we have a correlation coefficient ≈ 0.91.

4.2. MODEL # 2 Fig. 8 demonstrates views of the Model # 2.

Model # 2 is intended for measurements of pulse. In Fig.9 the output data of this radar are shown.

Fig. 5. The appearance of the UWB radar.

Fig. 6. Time diagrams of heart and respiratory beats

Интервалы радара Интервалы кардиографа Уср. радар Уср.кардиограф

9492908886848280787674727068666462605856545250484644424038363432302826242220181614121086420

600

580

560

540

520

500

480

460

440

420

400

380

360

340

320

300

280

260

240

220

200

Fig. 7. Variability of cardiac rhythm.

Fig. 8. The second model of the radar.

Remote Monitoring of Human Cardio-Respiratory System Parameters by Radar and Its Applications

Ultrawideband and Ultrashort Impulse Signals, 15-19 September, 2008, Sevastopol, Ukraine 37

4.3. MODEL # 3 Fig. 10 demonstrates views of the Model # 3 of the UWB radar in process of the measurement of speed of a pulse's wave. This model consists of two radars - sensors which measure pulse on different vessels.

In Fig. 11 we show the output data of two sensors of the Model # 3.

Speed of a pulse's wave is the important diagnostic factor for cardiac and vascular diseases. Model # 3 can simultaneously measure variability of an cardiac rhythm. It is the universal craniological tool.

4.4. MODEL # 4 This model combines functions of radar for measurement of breath and electrocardiograph. This device is intended for “Home Medicine”. The data from the device are transferred on a wireless line to mobile phone and further to the medical center.

Fig. 12 demonstrates views of the Model # 4 of the UWB radar in use.

The results of medical tests of the above mentioned four models of radars have confirmed the

Fig. 9. The output data of the Model #2 of the radar.

Radar 2

Radar 1

Fig. 10. Model #3 of the radar.

Fig. 11. The output data of the third prototype of the radar

Fig. 12. Model #4 of the UWB radar.

Fig. 13. The general view of the radar.

Fig. 14. The radar is in Taiwan maternity hospital.

Immoreev I. and Ivashov S.

38 Ultrawideband and Ultrashort Impulse Signals, 15-19 September, 2008, Sevastopol, Ukraine

potentialities of UWB radars for monitoring person's breath and cardiac activity both at home and in hospital. The combination of UWB radar specific features, like noncontact and remote measurement, portability and simple operation, allows UWB radar to be recommended for wide usage in medical practice.

4.5. MODEL # 5 Medical UWB radar destined for remote and contactless monitoring of patients in hospital. The radar has the following parameters:

operation range: 0.6m ÷ 3.5m; signal spectrum: ∼ 500 MHz; pulse power: 9 mW; average power: 0.05mW;

The medical radar was used in reanimation chambers of the Russian cardiac hospital for long-term monitoring of the patients after operation on heart. Fig. 13 demonstrates the general view of the radar at its location nearby of a ceiling of chamber.

The similar radar was used in Taiwan maternity hospital for the same monitoring of the preterm-born infants (Fig. 14). These radars have shown high accuracy of measurement of breath and pulse.

5. CONCLUSION The review of fields of application for UWB radars confirms that UWB radars can be successfully applied in all cases when we need a high accuracy remote monitoring moving objects at short distances. Features of work of UWB radars are described in detail in [1-13].

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opportunities, unusual problems, system features”, Proceeding of Moscow State Technical University, # 4, 1998.

2. Immoreev I., “Main Features of UWB Radars and Differences from Common Narrowband Radars”. In book “Ultrawideband Radar Technology”. Edited Taylor, J.D.;CRC Press, Boca Raton, London, New Work, Washington, 2000.

3. Immoreev, I.;Ten questions on UWB [ultra wide band radar]. Aerospace and Electronic Systems

Magazine, IEEE Volume 18, Issue 11, Nov. 2003 Page(s):8-10.

4. Immoreev, I.Y.; Taylor, J.D.;Ultrawideband radar special features & terminology. Aerospace and Electronic Systems Magazine, IEEE, Volume 20, Issue 5, March 2005 Page(s):13-15.

5. Immoreev, I.Y.; Samkov, S.; Teh-Ho Tao; Short-distance ultra wideband radars. Aerospace and Electronic Systems Magazine, IEEE, Volume 20, Issue 6, June 2005 Page(s):9-14.

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8. Immoreev, I.J.; Taylor, J.D.; Radar conversion and evolution, Application of the Conversion Research Results for International Cooperation, 1999. SIBCONVERS '99. The Third International Symposium, Volume 2, May 18-20, 1999 Page(s):351-353.

9. Immoreev, I.; Vovshin, B.; Features of ultrawideband radar projecting, Radar Conference, 1995., Record of the IEEE 1995 International, 8-11 May 1995 Page(s):720-725.

10. Zaitsev, A.V.; Immoreev, I.Ya.; The scope of application of a reciprocity principle in the theory of antennas at radiation and reception of ultra-wideband signals, Ultrawideband and Ultrashort Impulse Signals, 2004 Second International Workshop 19-22 Sept. 2004 Page(s):97-100.

11. Immoreev, I.J.; Ultrawideband systems-features and ways of development, Ultrawideband and Ultrashort Impulse Signals, 2004 Second International Workshop, 19-22 Sept. 2004 Page(s):37-41.

12. Immoreev, I.J.; Sudakov, A.A.; Analysis of a joint action's opportunity of ultra-wideband and narrow-band communication systems in the same frequency band, Signals, Circuits and Systems, 2003. SCS 2003. International Symposium on, Volume 1, 10-11 July 2003 Page(s):117-120, Vol. 1.

13. Immoreev, I.J.; Sinyavin, Features of ultra-wideband signals' radiation, P.G.S.A.N.; Ultra Wideband Systems and Technologies, 2002. Digest of Papers. 2002 IEEE Conference on, 21-23 May 2002 Page(s):345-349.