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A LOW COST RADAR SYSTEM FOR HEARTBEAT DETECTION Dr. Eric K. Walton The Ohio State University ElectroScience Laboratory 1330 Kinnear Road, Columbus, OH 43212 Mr. Benjamin K. Ozcomert Upper Arlington High School, Upper Arlington OH. THIS PROJECT SPONSORED BY ESL - CERF.
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A LOW COST RADAR SYSTEM FOR HEARTBEAT DETECTIONDr. Eric K. WaltonThe Ohio State University ElectroScience Laboratory1330 Kinnear Road, Columbus, OH 43212Mr. Benjamin K. OzcomertUpper Arlington High School, Upper Arlington OH
THIS PROJECT SPONSORED BYESL - CERF The Ohio State University ElectroScience Laboratory Consortium on Electromagnetics and Radio Frequencies (ESL-CERF)
CERF; LOW COST RADAR • Frequency Synthesizer • Windfreak SynthNV module • based on the Analog Devices wideband fractional-N synthesizer chip (with integrated VCO) • Analog Devices ADF-4350 • This mixed-signal chip can output signals in the 137-4,400 MHz range. • This chip has enabled a number of very low cost modules to be developed. • Our cost was $574. • This module is very simple to set up and use. • The USB port controls the device as well as providing power. • signal output port • RF reference signal input port available as option. • power sense port • The optional reference signal input port can be used for setting up several units coherently. • The power sense port can be used to measure a received signal level, a • nd thus this small unit can independently be used as a scalar network analyzer. • The internal microprocessor can be programmed to operate independently by setting it to a particular frequency and power level. • It can even be programmed to perform a step frequency scan automously. Photo of Windfreak SynthNV module
BASED ON ANALOG DEVICES ADF 4350Wideband synthesizer with integrated VCO
Spectrum Analyzer Testing FROM SPECTRUM ANALYZER TESTING; NOTE THE SIDELOBE STRUCTURE 1.5 GHZ 3.0 GHZ 3.8 GHZ
CERF; LOW COST RADAR • I/Q Mixer (DEMODULATOR) • There are a large number of UWB mixers available, • Most require associated components (amps for LO and LP filters and amps for the IF output. • We wanted to operated down to DC. • We selected the Polyphase Microwave quadrature demodulator as a compromise between cost and performance. • Bandwidth from 0.5 to 4.0 GHz with built in LO amplifier and I/Q low pass filters. • Characteristics; • LO/RF freq. 500-4,000 MHz • I/Q bandwidth DC-275 MHz (50Ω) • Input IP3 +30 dBm • Input P1 +12 dBm • Amp. Imbal. +/- 0.05 dB • Phase Error +/- 0.5 Deg. • LO Power +0 dbm • DC supply +/- 5 VDC • This unit was purchased and tested using bench top laboratory equipment and was found to meet specifications. • The unit was offered to The OSU ESL at an educational discount price of only $918.75. A photo of the unit is given in figure 7. $918.75. Polyphase Microwave Inc.; 1111 W 17TH ST, STE 200 Bloomington, IN 47404
CERF; LOW COST RADARA/D CONVERTER • MEASUREMENT COMPUTING USB-7202 • ONE A/D PER CHANNEL • UP TO 8 SIMULTANEOUS • INDEPENDENT RANGE SETTINGS • 16-BITS • USB POWERED • 100 KS/S CUMULATIVE RATE • (IE; 50 KS/S EACH CHAN. FOR TWO ETC.) • SIMULTANEOUS SAMPLING • DOUBLE SPEED IN BURST MODE (32 K INTERNAL FIFO) $399
CERF; LOW COST RADAR TESTING RESULTS 0.5-4.4 GHz 1-12 GHz ridge-waveguide UWB horns 3 DB SPLITTER SYNTH USB I I/Q MIXER A/D 3.25 AND 5.88 INCH DIAMETER SPHERES Q USB COMPUTER
CERF; LOW COST RADAR IN PHASE AND QUADRATURE COMPONENTS VS. FREQUENCY EXAMPLE RESULTS FOR 5.88 IN. DIA. SPHERE
EXAMPLE STABILITY TEST IT IS CRITICAL THAT THE RADAR SYSTEM BE STABILE AND REPEATABLE FROM SCAN TO SCAN SO THAT SCANS CAN BE DIRECTLY COMPARED AND SO THAT THE BACKGROUND CAN BE SUBTRACTED FROM THE DATA OF INTEREST AS WELL AS SO THAT THE “THRU” DATA CAN BE USED FOR NORMALIZATION. As a stability test, the empty target support at the beginning of the series can be compared to the one at the end; (time elapsed = 20 minutes) Note the difference is less than -25 dB.
STABILITY TEST; TIME DOMAIN • IF WE LOOK AT THE EMPTY VS. EMPTY DATA IN THE TIME DOMAIN, WE NOTE THAT THE MOST STABILE REGION IS NEAR THE ANTENNA COUPLING REGION. (difference below -35 dB) • IT IS LESS STABILE AT TIMES GREATER THAN 20 ns. This may be simply due to people moving around near the measurement system.
CERF; LOW COST RADAR Green = no-target data Blue = raw sphere data Red = sphere data divided by thru data DB FREQUENCY (MHZ)
CERF; LOW COST RADAR FULL TIME SCALE Coupling in pow. Divider (thus negative time) DB TIME DOMAIN (ns)
CERF; LOW COST RADAR DB TIME (ns) NOTE; background subtraction suppresses the room clutter (background) by more than 30 dB. Normalization to the “thru” connection removes the effects of system and cables. (IE: moves the response from 11.2 ns to 4.2 ns. {antennas and propagation distance remain})
CERF; LOW COST RADAR We can also do this for the 3.25 in diam sphere
FULL CALIBRATION EXAMPLE LET US DO A FULL CALIBRATION TO REFERENCE SPHERES USING EXACT SPHERE RCS FOR REFERENCE. H. L. Thal Jr., “Exact Circuit Analysis of Spherical Waves,” IEEE Transactions on Antennas and Propagation, vol. AP-26, No. 2, March 1978. SET OF TEST TARGETS AND REFERENCE SPHERES APPROX 20 INCHES RADAR 1-12 GHZ RIDGED WAVEGUIDE HORNS STYROFOAM COLUMN
FULL CALIBRATION EXAMPLE MEASURE TARGETS OF INTEREST (S21 VS. FREQ.) SUBTRACT BACKGROUND (EMPTY TARGET SUPPORT) TRANSFORM TO TIME DOMAIN ZERO OUT ALL EXCEPT TARGET ZONE TRANSFORM BACK TO FREQUENCY DOMAIN NORMALIZE TO REFERENCE SPHERE MULTIPLY BY EXACT RCS OF REFERENCE SPHERE Note units of complex voltage and complex meters.
FULL CALIBRATION EXAMPLE FOR THE FOLLOWING EXAMPLE, WE WILL USE A 3.5 INCH DIAM. SPHERE AS THE REFERENCE, AND A 2.5 INCH DIAM. SPHERE AS THE TARGET OF INTEREST. THAT WAY, WE CAN DOUBLE CHECK OUR ACCURACY BY COMPARING THE CALIBRATED 2.5 INCH MEASURED RCS VALUES WITH THE EXACT SOLUTION FOR THE 2.5 INCH SPHERE TARGET. The set of measurements on the different targets took place over a period of approximately 1 hour.
FULL CALIBRATION EXAMPLE NOTE THE I/Q BALANCE NOTE THE GAIN DROP-OFF OF THE RADAR NOTE THE RESULT OF SUBTRACTING THE EMPTY SUPPORT DATA.
FULL CALIBRATION EXAMPLE INCREASING NOISE NOTE THE RESULT OF SUBTRACTING THE BACKGROUND AND THEN NORMALIZING TO (DIVIDING BY)THE REFERENCE SPHERE DATA.
FULL CALIBRATION EXAMPLE ESPECIALLY REMOVE THE DIRECT HORN TO HORN COUPLING TERM SET ALL OUTSIDE THIS TARGET ZONE TO ZERO NEXT WE TRANSFORM THE SUBTRACTED & NORMALIZED DATA TO THE TIME DOMAIN.
FULL CALIBRATION EXAMPLE PLOT OF THE EXACT RCS (DBSM) OF THE 3.5 INCH SPHERE .
FULL CALIBRATION EXAMPLE(FINAL CALIBRATION RESULT) NOTE THE AGREEMENT BETWEEN THE CALIBRATED TARGET AND THE EXACT CALCULATION.
FULL CALIBRATION EXAMPLE WE CAN ALSO DO THIS FOR A 0.75 INCH DIAM SPHERE AS A TARGET. NOTE AGREEMENT
FULL CALIBRATION EXAMPLE IN THIS CASE, THE TARGET OF INTEREST IS A 50 CALIBER BULLET (NOSE ON) 0.75 “ D SPHERE EXACT BULLET WE INCLUDE THE EXACT RCS OF THE 0.75 INCH DIAM. SPHERE AS A REFERENCE.
FULL CALIBRATION EXAMPLE WE ALSO DID A MOM CALCULATION FOR THAT 50 CAL BULLET (Thanks; THE HONG LEE)
FULL CALIBRATION EXAMPLE Overlay theoretical with experimental RCS (DBSM). BROADSIDE RCS (DBSM) NEAR NOSE ON BULLET RADAR DATA FREQ NOT “TOO” BAD.
FULL CALIBRATION EXAMPLE • CONCLUSIONS; • WE CAN BUILD A STEP FREQUENCY SYNTHESIZED RADAR USING MODERN MIXED SIGNAL MICROCHIPS FOR LESS THAN $2000. • IT IS FULLY SOFTWARE CONTROLLED. • USB INTERFACE TO LAPTOP • FULLY PROGRAM CONTROLLED IN MATLAB (IN OUR CASE) • WE CAN MEASURE RADAR TARGETS VERSUS FREQUENCY AND TRANSFORM THE RESULTS TO THE TIME DOMAIN. • WE CAN PERFORM FULL CALIBRATIONS ON THE DATA TO YIELD RADAR SCATTERING IN DBSM. • WITH GOOD DYNAMIC RANGE • AND GOOD TIME STABILITY. • WE CAN ALSO USE THIS RADAR IN THE SINGLE FREQUENCY MODE TO MEASURE DOPPLER.
HUMAN HEARTBEAT One of our goals is to extract I/Q Doppler waveform signatures from the human heartbeat. This is an I/Q Doppler measurement done with an ESL network analyzer on a volunteer. MEASURED USING NETWORK ANALYZER IN CW VS. TIME MODE. Q 1.5 GHZ Note the repeating I/Q pattern synchronized with the heartbeat. We hope to collect more of this type of data using our new portable radar and to compare the I/Q signature with MRI or EKG data. I/Q PATTERN 10 HEARTBEATS I
HUMAN HEARTBEAT [HOW CAN WE ASCRIBE MEANING TO THESE TRAJECTORIES?] 1.5 GHz Trajectory (EKW volunteer) 1.5 GHz Trajectory (EKW volunteer) 2.0 GHz Trajectory (EKW volunteer) 2.0 GHz Trajectory (EKW volunteer) MEDICAL INTERPRETATIONS?
FULL CALIBRATION EXAMPLE QUESTIONS? DR. ERIC K. WALTON THE OHIO STATE UNIVERSITY ELECTROSCIENCE LABORATORY 1330 KINNEAR ROAD COLUMBUS, OHIO 43212 Walton.1@osu.edu Office 614/292-5051; cell 614/537-5609 6. Acknowledgements The authors wish to thank The Ohio State University ElectroScience Laboratory Consortium on Electromagnetics and Radio Frequencies (ESL-CERF) (sponsors of this project) as well as Polyphase Corporation for their assistance.