Detection of Radio-Frequency Electronics by Acoustic Modulation of Radar Waves

Transcription

1 UNCLASSIFIED // APPROVED FOR PUBLIC RELEASE Detection of Radio-Frequency Electronics by Acoustic Modulation of Radar Waves Dr. Gregory J. Mazzaro The Citadel, The Military College of South Carolina Charleston, SC, Andrew J. Sherbondy, Kyle A. Gallagher, Kelly D. Sherbondy United States Army Research Laboratory Adelphi, MD UNCLASSIFIED // APPROVED FOR PUBLIC RELEASE

2 Presentation Overview Nonlinear Radar Concept, Motivations Recent Advancements Acoustic Radar: Current Research Acousto-RF Interaction: Concept Experiments: Near & Standoff United States Army Research Laboratory vehicle-mounted radar Results & Future Work 2

3 Nonlinear Radar Concept Tx electronic target Rx P refl = ap in 2 Target presence/location is indicated by receiving frequencies that were not transmitted. Applications: locate personal electronics during emergencies detect electronically-triggered devices Advantages: It is easier to separate targets from clutter because most clutter is linear. Disadvantages: Targets require high incident power to drive them into non-linear behavior. Received responses are usually very weak compared to the transmitted probe signals. 3

4 Nonlinear Radar Results For targets-of-interest and relevant frequency bands, harmonic radar is preferred. It is difficult to filter out self-generated intermodulation. The 2 nd harmonic (2f 0 ) tends to be strongest. A memoryless power-series model for device nonlinearity has been sufficient for describing received radar responses. The traditional (Friis-based) radar equation can be tweaked to accurately model (linear) transmission and (nonlinear) interaction & reception. M m Erefl t ameinc t P m 1 M 2 M! PT GT M GR M R M 2 2M 2 4 R Transmit frequencies in L-Band/UHF (800 MHz to 1 GHz) appear to be advantageous. Linearization by filtering and feed-forward cancellation at f 0 provides SNR high enough to detect weak target responses at 2f 0. Moving-target indication and synthetic-aperture imaging have been accomplished via harmonic radar. 4

5 Presentation Overview Nonlinear Radar Concept, Motivations Recent Advancements Acoustic Radar: Current Research Acousto-RF Interaction: Concept Experiments: Near & Standoff United States Army Research Laboratory vehicle-mounted radar Results & Future Work 5

6 Acoustic Radar: Doppler Rx ± n f audio Tx RF Txaudio f audio DUT target is stationary The acoustic source vibrates the target. The target produces positive & negative frequency shifts. n f audio n f audio target moves away from radar target moves towards radar 6

7 Acoustic Radar: Doppler Rx Tx RF ± n f audio The frequency shifting may be modeled as frequency modulation (FM). Txaudio f audio DUT E refl T audio t ~ E refl f frf 5faudio frf 4faudio frf 3faudio frf 2faudio frf faudio frf frf faudio frf 2faudio frf 3faudio frf 4faudio frf 5faudio 7

8 Acoustic Radar: Metal-Metal Rx Tx RF ± n f audio The acoustic source vibrates the target. The conductive junctions within the target connect and disconnect. Txaudio f audio DUT The re-radiation from the junctions (target) is stronger and weaker. most junctions (dipoles) disconnected 8 most junctions connected

9 Acoustic Radar: Metal-Metal Rx Tx RF ± n f audio The metal-metal effect may be modeled as amplitude modulation (AM). Txaudio f audio DUT E refl T audio t ~ E refl f frf 5faudio frf 4faudio frf 3faudio frf 2faudio frf faudio frf frf faudio frf 2faudio frf 3faudio frf 4faudio frf 5faudio 9

10 Presentation Overview Nonlinear Radar Concept, Motivations Recent Advancements Acoustic Radar: Current Research Acousto-RF Interaction: Concept Experiments: Near & Standoff United States Army Research Laboratory vehicle-mounted radar Results & Future Work 10

11 Short-Distance Experiment audio amplifier LabWorks PA-138 LabWorks MT-161 shaker Adelphi Laboratory Center Building 204 audio generator Agilent 33220A f audio f audio fiberglass rod DUT ~2 ft distance coupler HP 778D-12 Keysight N5171B RF generator ± k f audio Tektronix RSA6114A spectrum analyzer P rec Schwarzbeck BBHA-9120-E antenna Goal: Establish proof-of-concept for detection by acousto-rf interaction. 11

12 Near-Field Measurements 800 MHz carrier no target present Goal: Reproduce previous results (metal filings, mechanical shaker) using an antenna and useful targets. 12

13 Near-Field Measurements handheld FRS radio 800 MHz carrier 800 MHz RF 400 Hz audio 800 MHz RF Hz audio The radio produced a measurable response at the expected frequencies. 13

14 Near-Field Measurements 800 MHz carrier quart-sized bag containing metal filings 800 MHz RF 2x400 Hz audio 800 MHz RF + 2x400 Hz audio Metal filings produce additional frequencies (which confirmed results presented by our colleagues). + 3x400 Hz audio 14

15 Standoff Experiment : 600, 800, 1000, 1500, 2000, 3000, 4000, 5000, 6000 MHz f audio : 50, 100, 200, 400, 800 Hz Adelphi Laboratory Center Building 507 Keysight RF generator N5171B 1 mw HP 778D-12 or coupler HP 779D Schwarzbeck antenna BBHA-9120-E Tx/Rx 10 ft DUT spectrum Tektronix RSA-6114A analyzer P rec audio Agilent generator 33220A f audio LabWorks audio PA-138 amplifier fiberglass rod f audio (½ in) LabWorks MT-161 shaker Goals: Observe results similar to short-distance test; achieve detection over-the-air, farther away. 15

16 Standoff Experiment shaker rod DUT antenna ALC Building 507 audio amplifier coupler audio generator laptop, Matlab cables RF generator spectrum analyzer audio amplifier shaker coupler rod DUT antenna 16

17 Standoff Measurements corner reflector, 18 inches red = target present black = target absent 17

18 Standoff Measurements corner reflector, 12 inches red = target present black = target absent 18

19 Standoff Measurements corner reflector, 6 inches red = target present black = target absent Radar calibration targets produce the acoustic-rf response. 19

20 Standoff Measurements Motorola MD200R Uniden GMR1636 handheld radios metal shavings red = target present black = target absent 20

21 Standoff Measurements Motorola MD200R Uniden GMR1636 metal shavings red = target present black = target absent 21

22 Standoff Measurements painted metal landmine Our acoustic radar can indeed see both metallic and electronic targets. red = target present black = target absent 22

23 Standoff Measurements Motorola MD200R radio red = radio, complete blue = radio, empty black = target absent Uniden GMR1636 radio 23

24 Standoff Measurements Motorola MD200R radio red = radio, complete blue = radio, empty black = target absent Uniden GMR1636 radio The response received from each radio may be attributed to its printed circuit board / antenna. 24

25 Standoff Measurements red = radio vibrating, reflector behind blue = radio vibrating, reflector absent (MD200R) green = radio absent, reflector vibrating black = radio absent, reflector present 25

26 Standoff Measurements red = radio vibrating, reflector behind blue = radio vibrating, reflector absent (MD200R) green = radio absent, reflector vibrating black = radio absent, reflector present 26

27 Standoff Measurements red = radio vibrating, reflector behind blue = radio vibrating, reflector absent green = radio absent, reflector vibrating black = radio absent, reflector present 27

28 Standoff Measurements A vibrating conductive target may be seen clearly in the presence of a very reflective clutter object. green = radio absent, reflector vibrating black = radio absent, reflector present 28

29 Summary & Future Work Acoustic radar is a form of nonlinear radar which generates a response by altering a radar wave with acoustic energy by frequency shifting (toward/away from the radar) or by connecting & disconnecting conductive junctions within the target A short-range (2-ft) experiment indicated that all targets-of-interest produce an acoustic-radar response. A standoff (10-ft) experiment indicated that target responses may be captured by transmitting only 1 mw, using a single antenna, and more strongly by exploiting the metal-metal effect. With additional time & funding perform more exhaustive sweeps of and f audio, and generate the acoustic energy using a loudspeaker. 29

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