Directional amplitude backscatter modulation with suppressed Doppler based on rotating resonant loop

Abstract

The directional amplitude backscatter modulation with suppressed Doppler is demonstrated based on the scattering from a symmetrically rotating resonant loop. The concept is studied theoretically and experimentally with perfectly compatible results. The symmetrical rotation of the scatterer and the effect of radial resonance, as the two crucial points to realize the idea, are highlighted through the comparison between the symmetric and non-symmetric cases, and the results obtained for scatterers with and without radial resonance. The presented backscattering modulation technique provides an amplitude modulating waveform which is uniquely linked to the directional reradiation pattern of the rotating loop scatterer in a definite resonant mode. With the pure directional amplitude modulation (DAM) induced on the backscattered wave, the envelope waveform can be accurately retrieved form the received signal using the In-phase and Quadrature (IQ) representation. The contribution of the background in a real environment can be detected and removed to obtain the exact modulating waveform. This property of the proposed backscattering modulation method can be applied for sensing, localization, and identification purposes with high sensitivity, read range, and robustness.

Motion-Modulated Chipless RFID

“…This illustration proves the directional amplitude modulation induced by the rotating loop in both configurations. However, the phase of the received signal is constant over the time only for the symmetric configuration and it is sinusoidally varying for the non-symmetric case, which demonstrates that a pure directional amplitude modulation can be achieved only when both the symmetry property and the Doppler suppression due to resonance is utilized simultaneously [36].…”

“…The last type of motion-modulated chipless tags is proposed as direction-modulated tags [36]. Following the two previous types [phase (Doppler) and polarization modulated tags], this type of tags should modulate the backscattered wave just in magnitude (and not in phase or polarization) during the motion.…”

“…In other words, this specific scatterer can modify the magnitude of the backscattered wave proportional to its reradiation pattern when it is rotated around its symmetry axis (z-axis), while the phase and polarization of the backscattered wave are not modified at all. Note that during the rotation, different points of the loop have a non-zero radial velocity towards the incidence direction, however, the phase of the induced current is not modulated due to the resonance effect, which means the Doppler effect is suppressed by the resonance of the scatterer [36].…”