Passive Displacement Sensing Using Backscatter RFID with Multiple Loads
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The document discusses a method for wirelessly sensing the bend or displacement of an object using a low-cost passive RFID device, which overcomes power consumption issues found in previous approaches. A displacement sensor attached to a hand changes the scattering properties of an RFID tag during movement, enabling applications in gestural interfaces and virtual reality. The research concludes that three impedance states are necessary to determine an unknown load state while considering channel variations.
Passive Displacement Sensing Using Backscatter RFID with Multiple Loads
- 1. Passive Displacement Sensing using Backscatter RFID with Multiple Loads Jonathan Becker, Carnegie Mellon University Joshua Griffin, Disney Research Matthew Trotter, Disney Research
- 2. Goal Wirelessly sense the bend or displacement of an object with a low cost passive device. Prior Approaches • Piezoresis:ve materials • Fiber op:cs Problem with Prior Approaches May require analog-‐to-‐digital converters and transmiAng circuitry to sense bend – rela:vely high power consump:on Key Insight Use a displacement sensor aDached to hand to change scaDering proper:es of a backscaDer RFID tag as the hand bends and straightens. Applica8ons • Gestural interfaces • Virtual Reality • Mo4on capture 2 For example, see: • Olson et. al., “Piezoresistive strain gauges for use in wireless component monitoring systems” in 2008 IEEE Sensors Applications Symposium • Jahed et. at., “Enhanced resolution fiber optic strain sensor based on mach-zehnder interferometer and displacement sensing principles” in IEEE ELECO 2009
- 3. Diagram of 3-State RFID Tag Test Setup Want to determine this value D = Antenna Separation Can vary in time H ~Channel unknown a priori vv Z Z Z ⇔Γ ⇔Γ ⇔Γ 22 11 3 Displacement Sensor RFID Reader
- 4. Why are 3-States Needed? Γ1v = H Γ1 − Γv( ) Γ12 = H Γ1 − Γ2( ) Γv = Γ1 − Γ1v Γ12 Γ1 − Γ2( ) Known Known Known Unknown (Value desired)Unknown 4 Reference: S. Capdevila, L. Jofre, J. Romeu, and J. C. Bolomey, “Multi-Loaded Modulated Scatterer Technique for Sensing Applications,” IEEE Trans. Instrum. Meas., vol. 62, no. 4, pp. 794–805, 2013.
- 5. Sketches of Hand Mounted Displacement Transducer Straight Bent 5
- 6. Demo of Hand Mounted Displacement Sensor 6
- 7. Fig. 4 from Paper: Sensor in Test Setup Covered Microstrip Displacement Sensor for Precision Measurements 7 Sensor Parts Side by Side
- 8. Controlled Measurement Test Setup Displacement Sensor RF Switches Known Loads Tag Antenna Reader Antenna (not shown) 8
- 9. Results with Different Antenna Separations 9
- 10. Conclusions • Demonstrated a 5.8 GHz RFID tag with a sensor that detects displacement passively • Need a total of three impedance states to determine an unknown load state with an unknown channel – The first two impedance states contain channel information • Future work – Design a printed circuit board version of the tag – Integrate a charge pump into the circuit (passive tag) 10
- 12. Live Results: Hand Mounted Displacement Transducer 12
- 13. Why Use Three Loads? Removing DC offset creates ambiguity: Change in a load vs. moving antenna? DC Offset Removed Move Antenna Change Load Similar Rotation 13
- 14. Why Use Three Loads? (Cont.) Move Antenna Remove DC Offset Change Load Third load removes ambiguity created by DC block 14
- 15. Prototype 5.8 GHz 2-State RFID Tags 15