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A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
A low cost approach to acoustic filters acting asGPR cooperative targets for passive sensing
J.-M Friedt & A. Hugeat
FEMTO-ST Time & Frequency, Besançon, FranceContact: [email protected]
References and slides at http://jmfriedt.free.fr
July 8, 2015
IWAGPR2015 – Firenze, Italy
http://jmfriedt.free.fr
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Outline
• What are RADAR cooperative targets ?• Why GPR cooperative targets ?• Radiofrequency acoustic transducers as cooperative targets• Software optimization for dual sub-surface and sensor monitoring• Low cost demonstration using off-the shelf radiofrequency filters
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
What are RADAR cooperativetargets ?
1 target whose backscattered signal isrepresentative of its state (identification,measurement)
2 active targets: radar beacons (racon), IFF
3 passive targets: buried dielectric reflectors
4 this work: use of radiofrequency transducersbased on surface acoustic wave propagation(RF filters)
H. Stockman, Communication by means of reflected powerProc. IRE 36 (Oct. 1948) pp.1196–1204(picture from http://geogdata.csun.edu/~aether/pdf/volume_05a/rosol.pdf)
IWAGPR2015 – Firenze, Italy
http://geogdata.csun.edu/~aether/pdf/volume_05a/rosol.pdf
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
What are RADAR cooperativetargets ?
1 target whose backscattered signal isrepresentative of its state (identification,measurement)
2 active targets: radar beacons (racon), IFF
3 passive targets: buried dielectric reflectors
4 this work: use of radiofrequency transducersbased on surface acoustic wave propagation(RF filters)
A. Glinsky, Theremin: Ether Music And Espionage, Uni-versity of Illinois Press (2005)
http://madmikesamerica.com/2010/08/the-thing-and-the-curious-life-of-leon-theremin/thing2/
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
What are RADAR cooperativetargets ?
1 target whose backscattered signal isrepresentative of its state (identification,measurement)
2 active targets: radar beacons (racon), IFF
3 passive targets: buried dielectric reflectors
4 this work: use of radiofrequency transducersbased on surface acoustic wave propagation(RF filters)
A. Glinsky, Theremin: Ether Music And Espionage, Uni-versity of Illinois Press (2005)
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
What are RADAR cooperativetargets ?
1 target whose backscattered signal isrepresentative of its state (identification,measurement)
2 active targets: radar beacons (racon), IFF
3 passive targets: buried dielectric reflectors
4 this work: use of radiofrequency transducersbased on surface acoustic wave propagation(RF filters)
D. J. Thomson, D. Card, and G. E. Bridges, RF CavityPassive Wireless Sensors With Time-Domain Gating-BasedInterrogation for SHM of Civil Structures, IEEE SensorsJournal . 9 (11) (Nov. 2009), pp.1430-1438
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
What are RADAR cooperativetargets ?
1 target whose backscattered signal isrepresentative of its state (identification,measurement)
2 active targets: radar beacons (racon), IFF
3 passive targets: buried dielectric reflectors
4 this work: use of radiofrequency transducersbased on surface acoustic wave propagation(RF filters)
C.T. Allen, S. Kun, R.G Plumb, The use of ground-penetrating radar with a cooperative target, IEEE Trans-actions on Geoscience and Remote Sensing, 36 (5) (Sept.1998) pp. 1821– 1825
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Why GPR cooperative targets ?
• Complement buried structure information with physical quantitymeasurement
• Accessible quantities: temperature, stress (pressure), identifier (ID)• Measurement range: depends on RADAR cross section – typical
losses in the 30-40 dB range
Passive cooperative target (no local battery source) for extended lifeexpectancy (limited by packaging)
Envisioned applications:
• pipe tagging/stress/temperature• soil moisture 1
• concrete temperature 2
1L. Reindl & al., Radio-requestable passive SAW water-content sensor, IEEETrans. Microwave Theory & Techniques, 49 (4), (Apr. 2001), pp. 803–808
2J. Kim, R. Luis, M.S. Smith, J.A. Figueroa, D.C. Malocha, B.H. Nam, Concretetemperature monitoring using passive wireless surface acoustic wave sensor systemSensors and Actuators A 224 (Febr. 2015), pp.131–139
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
SAW basicsDemonstrated with dedicated readers for Surface Acoustic Wave (SAW)transducers (Transense, CTR, Sengenuity, RSSI, SenSanna, Frec|n|sys, SENSeOR).
M1
M2
M3
IDT
typical dimensions:10 mm x 4 mm
@ 100 MHz
• Sensor: φ = 2π · D/λ = 2πD · f /c with dc/c(T , σ) known• GPR is wideband pulse generator ⇒ delay line architecture.• This work aims at providing GPR-compatible SAW sensors ...• ... or divert existing SAW filters for sensing purpose.
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Radiofrequency acoustic (SAW)transducers as cooperative targets
• from a user perspective, an electrical dipole• physics: conversion of incoming RADAR pulse
to an acoustic (mechanical) wave throughinverse piezoelectric effect
• acoustic wave propagates on the surface of thepiezoelectric substrate at a speed of3000-5000 m/s
• the acoustic wave is reflected by patternedmirrors, reaches the transducer and isconverted back to an electromagnetic pulse(RADAR echo) ⇒ tag or sensor
Piezoelectricity is linear process: returned power isa fraction of incoming power, no threshold
Unlike RFID which requires power while being operated, SAW transducers are ideally
suited for GPR interrogation
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Radiofrequency acoustic (SAW)transducers as cooperative targets
• from a user perspective, an electrical dipole• physics: conversion of incoming RADAR pulse
to an acoustic (mechanical) wave throughinverse piezoelectric effect
• acoustic wave propagates on the surface of thepiezoelectric substrate at a speed of3000-5000 m/s
• the acoustic wave is reflected by patternedmirrors, reaches the transducer and isconverted back to an electromagnetic pulse(RADAR echo) ⇒ tag or sensor
Piezoelectricity is linear process: returned power isa fraction of incoming power, no threshold
Unlike RFID which requires power while being operated, SAW transducers are ideally
suited for GPR interrogation
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Software optimization for dualsub-surface and sensor monitoring
• Separate sensor response fromsubsurface reflectors by delaying echobeyond any possible interfacereflection (2 µs = 4 mm long sensor at4000 m/s)
• Short term response = buriedstructures (“clutter”)
• Long term response = buried sensor
Available GPR only allows for a small num-ber of samples (
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Software optimization for dualsub-surface and sensor monitoring
• Separate sensor response fromsubsurface reflectors by delaying echobeyond any possible interfacereflection (2 µs = 4 mm long sensor at4000 m/s)
• Short term response = buriedstructures (“clutter”)
• Long term response = buried sensor
Solution: define two time windows, one fo-cusing on the subsurface structures (e.g. 0-200 ns) and another on the sensor (e.g.1000-1200 ns)
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Software optimization for dualsub-surface and sensor monitoring
• Separate sensor response fromsubsurface reflectors by delaying echobeyond any possible interfacereflection (2 µs = 4 mm long sensor at4000 m/s)
• Short term response = buriedstructures (“clutter”)
• Long term response = buried sensor
Only software re-design, hardware re-mains the same (reconfigure start delay ofthe stroboscopic measurement)
⇒ demonstrated on Mal̊a ProEx GPRhttps://sourceforge.net/projects/proexgprcontrol/
IWAGPR2015 – Firenze, Italy
https://sourceforge.net/projects/proexgprcontrol/
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Low cost demonstration usingoff-the shelf radiofrequency filters
• Dedicated transducers require cleanroom fabrication capability ableto handle piezoelectric substrates
• Design considerations:• transducer transfer function must match GPR pulse spectrum• delay must be within measurement range of GPR• reflective transducer operation (most filters operate in transmission)
Measurement example, using an TDK/Epcos B3607 filter:
-8
-7
-6
-5
-4
-3
-2
-1
0
100 120 140 160 180 200 220 240 260
|S11| (
dB
)
frequency (MHz)
0
0.005
0.01
0.015
0.02
0.025
0.03
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
retu
rned
pow
er (
a.u.)
time (us)IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Low cost demonstration usingoff-the shelf radiofrequency filters
• Dedicated transducers require cleanroom fabrication capability ableto handle piezoelectric substrates
• Design considerations:• transducer transfer function must match GPR pulse spectrum• delay must be within measurement range of GPR• reflective transducer operation (most filters operate in transmission)
Measurement example, using an TDK/Epcos B3607 filter:
-8
-7
-6
-5
-4
-3
-2
-1
0
100 120 140 160 180 200 220 240 260
|S11| (
dB
)
frequency (MHz)
0
0.005
0.01
0.015
0.02
0.025
0.03
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
retu
rned
pow
er (
a.u.)
time (us)
power supply(heater)
resistance
TX
RX
Pt100 probe
monitoring
100 MHz
unshielded
antennas
SAW
sensor
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Low cost demonstration usingoff-the shelf radiofrequency filters
• Dedicated transducers require cleanroom fabrication capability ableto handle piezoelectric substrates
• Design considerations:• transducer transfer function must match GPR pulse spectrum• delay must be within measurement range of GPR• reflective transducer operation (most filters operate in transmission)
Measurement example, using an TDK/Epcos B3607 filter:
0 100 200 300 400 500 600 700 800
trace number (a.u.)
2.75
2.8
2.85
2.9
2.95
3
time (us)
-5
0
5
10
15
0 100 200 300 400 500 600 700 800u
nw
rap
ped
ph
ase
(rad
)time (s)
25
30
35
40
45
50
0 100 200 300 400 500 600 700 800
tem
per
atu
re (
deg
C)
time (s)
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Signal processing stepsConverting the echo delays to a meaningful measurement:
1 multiple echoes from the sensor to get rid of RADAR-targetdistance dependence
2 phase measurement of each returned echo: cross-correlation
3 for single echo (eg SAW filter):phase of the Fourier transformof the main spectrumcomponent (assuming constantRADAR-target distance)
4 SAW delay lines will usually bemore narrowband than RADARpulse ⇒ long echo⇒ improved SNR
5 sub-sampling period resolution:polynomial fit of the cross-correlation maximum
6 danger: multiple nearby cross-correlation peaks ⇒ risk of 2πrotation: ϕ = 2πD/λ = 2πD · f /c ⇒ dϕT = −2πDf /c · dcT/cwhere dcT/c(LiNbO3) = 60 ppm/K. If D = 1 cm, 2π phase rotationon LiNbO3/128 for 35 K at 100 MHz (cLNO128 ' 4000 m/s).
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Signal processing stepsConverting the echo delays to a meaningful measurement:
1 multiple echoes from the sensor to get rid of RADAR-targetdistance dependence
2 phase measurement of each returned echo: cross-correlation3 for single echo (eg SAW filter):
phase of the Fourier transformof the main spectrumcomponent (assuming constantRADAR-target distance)
4 SAW delay lines will usually bemore narrowband than RADARpulse ⇒ long echo⇒ improved SNR
5 sub-sampling period resolution:polynomial fit of the cross-correlation maximum
6 danger: multiple nearby cross-correlation peaks ⇒ risk of 2πrotation: ϕ = 2πD/λ = 2πD · f /c ⇒ dϕT = −2πDf /c · dcT/cwhere dcT/c(LiNbO3) = 60 ppm/K. If D = 1 cm, 2π phase rotationon LiNbO3/128 for 35 K at 100 MHz (cLNO128 ' 4000 m/s).
-10
-5
0
5
10
0 20000 40000 60000 80000 100000
phase (rad)
time (s)
72 ns232 ns
20
30
40
50
60
70
80
90
100
0 20000 40000 60000 80000 100000
temp. (degC)
time (s)
time difference
2450 MHz LiNbO3/128 device
IWAGPR2015 – Firenze, Italy
A low costapproach to
acoustic filtersacting as GPR
cooperativetargets for
passive sensing
J.-M Friedt & al.jmfriedt@femto-
st.fr
What are RADARcooperativetargets ?
Why GPRcooperativetargets ?
Radiofrequencyacoustictransducers ascooperativetargets
Softwareoptimization fordual sub-surfaceand sensormonitoring
Low costdemonstrationusing off-the shelfradiofrequencyfilters
Conclusion andperspectives
Conclusion and perspectives• Extend the range of applications of (Ground Penetrating) RADAR
by monitoring physical quantities• Use existing instruments for probing cooperative targets 3• Acoustic transducers provide a compact solution ...• ... ideally suited to GPR interrogation.• Software enhancement dedicated
to sensor monitoringPerspectives:
• software improvement for real timedisplay of the sensor visibility andphysical quantity value (calibration)
• beyond physical quantity: chemicalcompound detection (dedicated sensordesign)
Acknowledgement: TDK/Epcos kindly provided sam-
ples of the B39111B5232H310 and B39191B5087H810
filters, with support of S. Ballandras (Frec|n|sys).3J.-M Friedt, A. Saintenoy & al, High-overtone Bulk Acoustic Resonators as
passive Ground Penetrating Radar cooperative targets, J. Appl. Phys 113 (13), 2013IWAGPR2015 – Firenze, Italy
What are RADAR cooperative targets ?Why GPR cooperative targets ?Radiofrequency acoustic transducers as cooperative targetsSoftware optimization for dual sub-surface and sensor monitoringLow cost demonstration using off-the shelf radiofrequency filtersConclusion and perspectives