al., Long range passive RADAR interrogation of subsurface acoustic passive wireless sensors using terrestrial television signals, IEEE Sensors ndash

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(1)Passive RADAR interrogation of passive cooperative targets: long range illumination of SAW delay lines using high power sources J.-M Friedt, M. Paquit1 1. W. Crochot, commons.wikipedia.org/. now with AR Electronique. FEMTO-ST/Time & Frequency, Besançon, France jmfriedt@femto-st.fr https://www.ettus.com/ https://www.kubii.fr/. Slides at http://jmfriedt.free.fr/sawsymposium2021.pdf sequel to M. Paquit & al., Long range passive RADAR interrogation of subsurface acoustic passive wireless sensors using terrestrial television signals, IEEE Sensors 20 (13) 7156–7160 (2020) 1 / 15.

(2) emitter fc. fc. ref ADC. I Passive RADAR: using existing electromagnetic sources for RAdiofrequency Detection And Ranging (time delay and Doppler shift for target velocity) I Popular with universities and amateurs: no need to be allowed to emit a strong signal (PR ∝ PE /d 4 ) I Range resolution solely determined by bandwidth ∆f ∆R = c/(2∆f ) ⇒ ∆f %⇒ ∆R & I Beamwidth ' azimuth resolution determined by antenna size wrt λ I Sythetic Aperture RADAR: move transmitting and/or receiving antenna sur to simulate a large aperture and hence improved azimuth resolution 1 2 3 Demonstrated using Ettus Research E312 or B210 SDR platforms using frequency stacking. Need for two coherent (same LO, same sampling rate) channels to sample reference and surveillance signals. ADC. target. Passive bistatic RADAR (PBR). fs xcorr. 1 S.T. Peters & al., In Situ Demonstration of a Passive Radio Sounding Approach Using the Sun for Echo Detection, IEEE Trans. Geosci. and Remote Sensing 56 (12) 7338 (Dec. 2018) 2 S. Prager & al., Ultrawideband Synthesis for High-Range-Resolution Software-Defined Radar, IEEE Trans. Instrum. Meas. 69 3789-–3803 (2020) 3 O. Toker & al., A Synthetic Wide-Bandwidth Radar System Using Software Defined Radios, 7th International Electronic Conference on Sensors and Applications (15–30 November 2020). 2 / 15.

(3) Passive wireless cooperative target I Design considerations I separate relevant signal from clutter: delay echo by at least 1 µs I compact: avoid 100 m coaxial cable to delay by 1 µs two-way trip I sensing capability: delay dependence with physical environment. ⇒ acoustic delay line since most non-cooperative sources will be wideband (6= resonator) I Deployment scenario: passive wireless sensor buried in concrete/soil and periodically probed I Challenge: radiofrequency emission regulations Use existing high power broadband sources to illuminate SAW delay line and short range reception of the signal SAW delay line as cooperative target for non-cooperative source PBR measurement. 4. 4 M.. Paquit & al., Long range passive RADAR interrogation of subsurface acoustic passive wireless sensors using terrestrial television signals, IEEE Sensors 20 (13) 7156–7160 (2020) 3 / 15.

(4) I YXl/128◦ LNO. Reflective delay line layout. I 50% or 70% metallization ratio I aperture=1000 µm 1000 um. 1600 um. 3200 um. I floating potential .... 1600 um. I ... reflective mirrors I delays T, 2T, 3T (T=870 ns) I chip size: 7200 µm×1800 µm 3.68 um. I 20 dB time-domain insertion losses. 7.36 um. 0. |S11| (dB). -10 -20 -30 -40 -50 -60 510. 520. 530. 540. 550. frequency (MHz). 2. 128 LNO: K ' 5.7%: sensor bandwidth ' 31 MHz @ 538 MHz, 1/K 2 finger pairs5 in inter-digitated transducer (IDT). |S11| (dB). -20. ◦. -30. red=0.5/0.5. -40. blue=0.5/0.3. -50 -60 -70. 5 D.. 0.5. 1.0. Morgan, Surface Acoustic Wave Filters – With Applications to Electronic Communications and Signal Processing, 2nd Ed., Academic Press (2007), pp.158–160, & teaching by V. Plessky. 1.5. 2.0. 2.5. 3.0. time (us). 4 / 15.

(5) Digital Video Broadcast-Terrestrial non-cooperative source Static emitter (e.g. DVB-T or GSM tower), static or moving receiver(s) I 128◦ LNO: K 2 ' 5.7%: sensor bandwidth ' 31 MHz I DVB-T 8 MHz wide channels but ... I ... Clermont Ferrand (45.7726 N, 2.9644 E) transmits DVB-T on three adjacent channels (European 28, 29 and 30) centered on 530, 536 and 546 MHz. I 11.8 km range to the 1465 m high emitter I One 6-element directional Yagi-Uda antenna towards reference signal and a dipole in close contact to the surface holding the sensor connected to a dipole Puy du Dôme DVB-T emitter characteristics antenna (cf Ground Penetrating RADAR layout) 5 / 15.

(6) Digital Video Broadcast-Terrestrial non-cooperative source Static emitter (e.g. DVB-T or GSM tower), static or moving receiver(s) I 128◦ LNO: K 2 ' 5.7%: sensor bandwidth ' 31 MHz I DVB-T 8 MHz wide channels but ... I ... Clermont Ferrand (45.7726 N, 2.9644 E) transmits DVB-T on three adjacent channels (European 28, 29 and 30) centered on 530, 536 and 546 MHz. I 11.8 km range to the 1465 m high emitter I One 6-element directional Yagi-Uda antenna towards reference signal and a dipole in close contact to the surface holding the sensor connected to a dipole Geographical settings antenna (cf Ground Penetrating RADAR layout) 6 / 15.

(7) Hardware for radiofrequency signal reception channel1 channel2. 546 MHz CH30. 538 MHz CH29. 530 MHz CH28. power (a.u.). I SDR: bandwidth challenge 6e+06 I USB3 on RPi4 for maximum transfer bandwidth + ADC avoid the Ethernet/USB sharing bottleneck of RPi3 5e+06 I single channel B210 measurement: 56 Msamples/s ... fs=30 MHz LO= I ... streamed to 8 GB RAM Raspberry Pi 4 (RPi 4) 538 MHz 4e+06 and stored to RAMdisk. I Custom software 6 for transferring 8-bit data (Over 3e+06 The Wire (otw) format) and storing 8-bit IQ samples to file 2e+06 I RPi4 6 GB/56 MS/s IQ bytes=57 second records I RPi4 6 GB/2×30 MS/s IQ bytes=53 seconds I AD9361 radiofrequency frontend local oscillator 1e+06 ∈ [70 : 6000] MHz I Baseband spectrum displays the three channels −→ 0 -15 -10 -5 0 5 I Switch the RPi4 to “performance” (1.5 GHz clock frequency (MHz) rate) mode: echo performance > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor. 10. 15. 6 https://github.com/jmfriedt/sentinel1_pbr/ 7 / 15.

(8) Signal extraction: direct signal interference (DSI) removal. 7. W. Feng, J.-M. Friedt, G. Cherniak, Z. Hu, M. Sato, Direct path interference suppression for short range passive bistatic SAR imaging based on atomic norm minimization and Vandermonde decomposition, IET Radar, Sonar and Navigation (2019). 1e+09. N. fs=30 MHz Ts=33 ns=10 m SAW sensor echoes. 8e+08. cross correlation (a.u.). I The surveillance channel receives the direct signal from the emitter as well I The DVB-T is not exactly noise (autocorrelation=Dirac) but includes some repetitive structure in R time and frequency (ambiguity function s(t)s ∗ (t − τ ) exp(j2πft) · dt = autocorrelation when Doppler shift is null) I Identify direct signal from reference antenna and subtract from surveillance shifted n times, n ∈ [0 : N] with N large enough to remove multipath but small enough to keep target echoes I weights identified as least square error solution7 : assemble matrix of time-delayed copies of reference measurement, and pseudo-inverse to identify weight of each vector in surveillance: −→. 6e+08. no DSI removal. 4e+08. 0 1 2 3 4 5 6 7 8. 2e+08. 0 -3. -2. past. -1. 0. time(us). 1. future. 2. 3. I n d e x 1=−N ; I n d e x 2=N ; % a n a l y z e d e l a y N∗dt , c o u l d be p o s i t i v e o n l y n u m r a n g e s h i f t =( I n d e x 2−I n d e x 1 +1) ; % i f r e f c h a n n e l i s known X1=z e r o s ( nt , n u m r a n g e s h i f t ) ; f o r kk=I n d e x 1 : I n d e x 2 % by W. Feng & a l t e=kk+a b s ( I n d e x 1 ) +1; i f kk<=0 X1 ( : , t e ) =[ s i g n a l r e f (0−kk +1: end ) ; z e r o s (0−kk , 1 ) ] ; e l s e X1 ( : , t e ) =[ z e r o s ( kk −1 ,1) ; s i g n a l r e f ( 1 : end−kk +1) ] ; end end s i g n a l m e a s=s i g n a l m e a s −X1∗( p i n v ( X1 ) ∗ s i g n a l m e a s ) ; % l e a s t s q u a r e 8 / 15.

(9) Measurement range assessment 05 cm 10 cm 15 cm 20 cm 25 cm 30 cm 35 cm 40 cm 45 cm 50 cm. 15 cm. 2e+08. 1e+08. 1. 1.5. 2. 2.5. time (us). -4. -2. 0. time (us). 2. 4. 2.17 us (no echo). 3. 1e+08. 2. 15-20 cm. 10 cm. 3e+08. 3. 2.47 us. ho. returned power (a.u.). 4e+08. 4. ec. correlation (a.u.). 2.43 us. 5 cm. 5e+08. 2e+08. 1.63 us. 1.67 us. o2 ech. 3e+08. 0.87 us. 5. o1. 4e+08. 6. 0.87 us. ec h. correlation (a.u.). 5e+08. 1. no echo 0. 0. 10. 20. 30. range (cm). 40. 50. X : time delayed copies of ref sur = sur − X · (X t · X )−1 X ) ·sur ) | {z } pinv (X ). |. {z. weights. xcorr = iFFT [FFT (ref ) ·. }. FFT ∗ (sur )] 9 / 15.

(10) Temperature measurement I Range from surveillance dipole to sensor dipole: 10 cm – lighter heating the sensor I 128◦ LNO: ' 74 ppm/K. 15 10. unwrapped phase (rad). phase (rad). 20. 6.1 rad. 5. 15. 10. 1st echo. 5. 0.87 us. 0. 2nd echo. 1.67 us. -5. φ=2πfτ =2πx538x0.87 =2941 rad dT=dφ/(φxS), S=74 ppm/K => dT=27 K @ dφ=6 rad. 20. 12.3 rad. φ=2πfτ =2πx538x0.87 =2941 rad dT=dφ/(φxS), S=74 ppm/K => dT=27 K, 55 K @ dφ=6, 12 rad. 25. 5.8 rad 6.1 rad. 25. 30. 0. 100. 200. 300. 400. time (s). 500. 600. 3rd echo. 0 700. 0. 100. 200. 300. 400. 500. time (s). 10 / 15.

(11) 0.4 0 -0.4 -20 0.4 0 -0.4 -20. ph (rad). X=-15 Y=10. -10. -5. 0. 5. 10. ph (rad). -15. slope 0.014 rad/cm. X=-7.5 Y=10. -15. -10. -5. 0. 5 X=0 Y=10. slope -0.041 rad/cm. -15. -10. 10. -5. 0. 5. 10. slope 0.010 rad/cm. X=+7.5 Y=10. -15. -10. -5. 0. 5. 10. 0.4 0 -0.4 -20 0.4 0 -0.4 -20 0.4 0 -0.4 -20 0.4 0 -0.4 -20. Experiment2. || (a.u.). X=-15 Y=10. -15. 3e+08 2e+08 1e+08 0 -20. || (a.u.). 10. 6e+08 4e+08 2e+08 0 -20. || (a.u.). X=-15 Y=10. sensor position -15. -10. -5. 0. 5. 10. X=-7.5 Y=10. -15. -10. -5. 0. -15. -10. -5. 0. -10. -5. 0. 5. 10. slope 0.027 rad/cm. X=-7.5 Y=10. slope -0.002 rad/cm. -15. -10. -5. 0. 5. 10. slope 0.009 rad/cm slope 0.006 rad/cm. -15. -10. -5. X=0 Y=10. 0. 5. 10. slope 0.054 rad/cm. X=+7.5 Y=10. -15. -10. -5. 0. 5. 10. surv. antenna position (cm). || (a.u.). 2.5e+08 1.5e+08 5e+07 -20 4e+08 3e+08 2e+08 1e+08 -20. sensor position. slope -0.041 rad/cm. surv. antenna position (cm). sensor positions 7.5. sensor position. ph (rad). 0.4 0 -0.4 -20. Phase. slope -0.034 rad/cm. ph (rad). ph (rad) ph (rad). 0.4 0 -0.4 -20. 5. 10. || (a.u.). I Here near field measurement: max(|returned power|) hints at sensor position along measurement line. Experiment1. X=0 Y=10. 5. cm 2.5 −20 0 -15 -10 -5 0 surveillance antenna positions surv. antenna position (cm) 8 W. Feng, J.-M Friedt, G. Goavec-Merou, M. Sato, Passive radar delay and angle of arrival measurements of multiple acoustic delay lines used as passive sensors, IEEE Sensors 19 (2) 594–602 (2019). 10. || (a.u.). I Synthetic aperture RADAR azimuth compression 8 : iFFT along surveillance antenna positions (N items). ph (rad). I Phase along azimuth: ϕ = 2π ∆d sin ϑ0 λ. || (a.u.). I Range compression: correlation along time axis (M items). || (a.u.). I Matrix (M × N) with M time-domain acquisitions for N surveillance antenna positions separated by ∆d < λ/2. ph (rad). Spatial separation of sensors. X=+7.5 Y=10. 5. 10. 4e+08 3e+08 2e+08 1e+08 0 -20 4e+08 3e+08 2e+08 1e+08 0 -20 5e+08 4e+08 3e+08 2e+08 1e+08 0 -20 6e+08 4e+08 2e+08 0 -20. X=-15 Y=10. sensor position -15. -10. -5. 0. 5. 10. X=-7.5 Y=10. -15. -10. -5. 0. -15. -10. -5. 0. -15. -10. -5. 0. 5. 10. X=0 Y=10. 5. 10. X=+7.5 Y=10. 5. 10. surv. antenna position (cm). Magnitude 11 / 15.

(12) with sensor. 4e+08 2e+08 0 -2. -1. past 0 future 1. 482. 498 506. 200000 150000. 5 kW. 100000. 3. Eiffel tower emitter spectrum. 530. 4. 546. 5 kW. 8 MHz. 50000 0 480. |S11| (dB). 2. time (us). 250000. power (a.u.). echo3. no sensor. 6e+08. echo2. 8e+08. echo1. I 50 kW at 482 and 506 MHz (32 MHz wide) and tentative 5 kW @ 498 & 530 MHz. cross correlation (a.u.). Same in Paris ... Eiffel tower, measurement 4.25 km away. 500. 520. 540. 560. frequency (MHz). 0 -5 -10 -15 -20 -25 -30 -35. SAW sensor characterization. 480. 490. 500. 510. 520. Only a single channel in each 30-MHz wide band.. 0. 1. 2.4 us. 1.6 us. 0.8 us. |S11| (dB). frequency (MHz) 0 -10 -20 -30 -40 -50 -60 -70. 2. time (us). 3. 4. 12 / 15.

(13) Same in Paris ... Eiffel tower, measurement 4.25 km away I 50 kW at 482 and 506 MHz (32 MHz wide) and tentative 5 kW @ 498 & 530 MHz. 1.7 us 0.9 us 2.5 us. 30 20 10 0 -10 0. 100. 200. 482. 498 506. 200000 150000. 5 kW. 100000. Eiffel tower emitter spectrum. 400. 500. 530. 600. 546. 5 kW. 8 MHz. 50000 0 480. |S11| (dB). 300. time (s). 250000. power (a.u.). lighter. lighter. phase (rad). 40. 500. 520. 540. 560. frequency (MHz). 0 -5 -10 -15 -20 -25 -30 -35. SAW sensor characterization. 480. 490. 500. 510. 520. Consistent temperature measurement @ 4.5 cm.. 0. 1. 2.4 us. 1.6 us. 0.8 us. |S11| (dB). frequency (MHz) 0 -10 -20 -30 -40 -50 -60 -70. 2. time (us). 3. 4. 13 / 15.

(14) How does it compare with energy harvesting? Series of investigations at Univ. of Tôkyô on rectenna for electromagnetic smog energy harvesting I H. Nishimoto, Y. Kawahara, T. Asami, Prototype Implementation of Ambient RF Energy Harvesting Wireless Sensor Networks, IEEE Senseors conference (2010) I R. Vyas, H. Nishimoto, M. Tentzeris, Y. Kawahara, T. Asami, A battery-less, energy harvesting device for long range scavenging of wireless power from terrestrial TV broadcasts, Proc. IEEE MTT-S International Microwave Symposium (2012) I R.J. Vyas, B.B. Cook, Y. Kawahara, M. Tentzeris, E-WEHP: A Batteryless Embedded Sensor-Platform Wirelessly Powered From Ambient Digital-TV Signals, IEEE Trans. Microwave Theory and Techniques (2013) −→ 6.3 km from Tôkyô Tower to Univ. of Tôkyô Hongo campus: -9 dBm resulting from 37 dBm integrated over 9 channels (54 MHz bandwidth) to power a MSP430 & PIC24F low-power microcontrollers + radiofrequency digital communication interface but 60 s charge time This work: 77 dBm emitted at a range of 11.8 km ⇒ Free Space Propagation Loss leads to -31.5 dBm received power at SAW sensor with 20 dB loss ⇒ -51.5 dBm backscattered power and Free Space Propagation Loss to surveillance: -58.5 dBm received power ideally @ 10 cm = 266 µVRMS but 1 MS correlation collected in 30 ms 14 / 15.

(15) Conclusion I Demonstration of long range (>10 km) powering of SAW delay line for short range (<20 cm) passive wireless transducer probing in the context of shallow buried sensors I Embedded, COTS hardware for passive bistatic RADAR probing of cooperative targets I Demonstration with VHF SAW reflective delay lines and DVB-T transmitters. I Need for subtracting Direct Signal Interference to recover SAW sensor backscattered signal.. S. Müller, wikimedia.org. Taxiarchos228, wikimedia.org. Applicable throughout Europe at least (example of German emitters: 100 kW EIRP) & China 9 http://www.com-tech.it/download/ChannelStructure.pdf. 9 15 / 15.

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