Vibration Sensing using Doppler-modulated Chipless RFID Tags

Abstract

The paper describes how chipless tags attached to non-metal vibrating objects can be utilized to sense the frequency and amplitude of mm-vibration without any calibration process, and to identify the tag from large distances in low microwave frequency band. It is demonstrated that micro-Doppler harmonics induced by vibrating high-resonant scatterers are more detectable than those induced by the vibrating object itself while the scatterers provide great area efficiency. Presented methods for vibration sensing and identification are experimentally validated for sub-millimeter vibrations at distances up to 8 meters.

Motion-Modulated Chipless RFID

“…The other Doppler-modulated chipless tag realized based on vibration is shown in Fig. 4 [33]. The chipless tag is considered with a rectangular loop scatterer which is aligned such that the backscattered wave (generated by the fundamental mode of the loop) preserves the same polarization as the incident wave (z-aligned).…”

“…The loop has a one-dimensional vibration along the direction of the incident wave (y-axis) which induces a sinusoidal phase modulation on the backscattered wave same as the rotational case, while the modulation index for the vibration case is defined as β = 2π D/λ where D is the vibration amplitude. Since the modulation scheme is the same for the rotating dipole and the vibrating loop, the differential RCS of the vibrating loop is also expressed by ( 13) [33]. The performance of the vibrational Doppler-modulated chipless tag in terms of identification and read range is almost similar to the rotational case [33] which is not presented here to avoid redundancy.…”

“…Since the modulation scheme is the same for the rotating dipole and the vibrating loop, the differential RCS of the vibrating loop is also expressed by ( 13) [33]. The performance of the vibrational Doppler-modulated chipless tag in terms of identification and read range is almost similar to the rotational case [33] which is not presented here to avoid redundancy. However, it should be mentioned that the β value in practical vibrations is usually quite small (due to the small vibration amplitude respect to the wavelength) which cause to reduce the differential RCS level significantly [see (13)].…”

“…However, it should be mentioned that the β value in practical vibrations is usually quite small (due to the small vibration amplitude respect to the wavelength) which cause to reduce the differential RCS level significantly [see (13)]. Nevertheless, it is demonstrated in [33] that resonant scatterers such as a rectangular loop can be utilized to sense the vibration characteristics (amplitude and frequency) more efficiently and at larger distances compared to when chipless tags are not attached to the vibrating surface. Accordingly, the measurement results related to the vibration sensing using Doppler-modulated chipless tag is presented in the next part.…”

“…The measurement setup for vibration sensing is shown in Fig. 8(a) [33]. The vibration is produced using a loud speaker which is fed by a LF signal generator with the sinusoidal voltage of V 0 sin(2π f m t ) where f m = 68 Hz.…”