Wireless Displacement Sensing Enabled by Metamaterial Probes for Remote Structural Health Monitoring

Abstract

We propose and demonstrate a wireless, passive, metamaterial-based sensor that allows for remotely monitoring submicron displacements over millimeter ranges. The sensor comprises a probe made of multiple nested split ring resonators (NSRRs) in a double-comb architecture coupled to an external antenna in its near-field. In operation, the sensor detects displacement of a structure onto which the NSRR probe is attached by telemetrically tracking the shift in its local frequency peaks. Owing to the NSRR's near-field excitation response, which is highly sensitive to the displaced comb-teeth over a wide separation, the wireless sensing system exhibits a relatively high resolution (<1 μm) and a large dynamic range (over 7 mm), along with high levels of linearity (R2 > 0.99 over 5 mm) and sensitivity (>12.7 MHz/mm in the 1–3 mm range). The sensor is also shown to be working in the linear region in a scenario where it is attached to a standard structural reinforcing bar. Because of its wireless and passive nature, together with its low cost, the proposed system enabled by the metamaterial probes holds a great promise for applications in remote structural health monitoring.

An Equivalent Circuit Model for Nested Split-Ring Resonators

“…In a practical sensing application, after the fabrication, d and l can be adjusted to determine f res before the NSRR is installed as a sensor. By the coupling between a transceiver antenna and the NSRR, the resonance of NSRR can be observed in the form of a peak at the reflection coefficient of the antenna [30], [31]. Therefore, in these simulations, the whole measurement setup is simulated including the antennas.…”

“…The distance between the antenna and the NSRR is set to 10 cm. The setup employed to carry out the measurements is covered in detail in [30].…”

“…In the first set of simulations, the NSRRs are excited by a plane wave in horizontal polarization (E-field parallel to the orientation of the strips) [30]. The goal of this simulation is to see the effect of N on the NSRR resonance frequency.…”

“…The NSRR structure was further modified for displacement and strain sensing by splitting it into two mechanically independent halves and electrically connecting these two parts by a thin wire [30]. This modified NSRR structure was demonstrated to provide significant advantages in structural health monitoring, where wireless, passive, and compact sensors with the capability of measuring very small displacements are in high demand [30]- [33]. Despite having the superiority over 0018-9480 © 2017 IEEE.…”

Displacement Measurement Realized By Near-field Coupling Between Multiple Coils

“…(4)(5)(6)(7)(8) A variety of sensing techniques have been developed for contactless displacement sensing in the past decades, for example, the eddy current, capacitive, optical, and inductive displacement sensors. (4,9,10) Optical sensors have better accuracy, stability, and linearity than all other sensors, but they are usually bulky and costly owing to the requirements of a laser, lens, and electronic components.…”