A Displacement Sensor Based on a Normal Mode Helical Antenna

Abstract

This paper presents a passive displacement sensor based on a normal mode helical antenna. The sensor consists of an external helical antenna and an inserting dielectric rod. First, the perturbation theory is adopted to demonstrate that both the electric intensity and magnetic intensity have a noticeable gradient change within the in-and-out entrance of the helical antenna, which will cause the sensor to experience a resonant frequency shift. This phenomenon was further verified by numerical simulation using the Ansoft high frequency structure simulator (HFSS), and results show the linear correlation between the retrieved resonant frequency and the displacement. Two sets of proposed sensors were fabricated. The experiments validated that the resonant frequency shifts are linearly proportional to the applied displacement, and the sensing range can be adjusted to accommodate the user’s needs.

A Capacitively-Fed Inverted-F Antenna for Displacement Detection in Structural Health Monitoring

“…There are a number of displacement sensors in Table 3. The helical antenna [27] is for built-in application; the patch antenna fed by capacitive microstrip lines [33] and the patch antenna with overlapping sub-patch [34] have great sensitivity with small measuring range, which is suitable for crack propagation monitoring; the sensor with complementary split-ring resonators [44] can measure two-dimensional displacement; and the inverted-F antenna-based sensor [45] is designed for the measurement of displacement on metal surfaces. Compared with the sensor in [23], the CFIFA-based sensor has higher sensitivity, and by adjusting the dimensions of the CFIFA, the CFIFA-based sensor can obtain a larger measuring range.…”

“…Among the passive RFID-based sensors, patch antenna sensors have been widely adopted in structural health monitoring due to their simple configuration, multimodality, low cost and other advantages [ 27 , 28 ]. Passive RFID-based patch antenna sensors can recognize local damage or a failed bearing capacity of individual members; they also help identify structural deformation in terms of strain or displacement and serve as an important detection measurand in SHM.…”

A bolt loosening detection method based on patch antenna with overlapping sub-patch

“…Xue et al proposed a displacement sensor based on a normal mode helical antenna, a passive wireless crack sensor based on a patch antenna with an overlapping sub-patch, and a crack sensor based on a patch antenna fed by capacitive microstrip lines. [35][36][37] Caizzone et al proposed a crack sensor based on two mutual coupling planar-inverted F antennas. 38 The unstressed antenna sensor focuses on the relative movement of the antenna components, and it has the advantage of being simple to install and detachable, thus, the unstressed antenna sensor can be used as the strain sensor to measure bolt loosening.…”

Long-Range Displacement Meters Based on Chipped Circular Patch Antenna

“…By analyzing the shift of the resonant frequency, the crack width can be obtained. Xue et al [23] also proposed a displacement sensor that is composed of a helical antenna and a dielectric rod antenna. When the relative displacement of the helical antenna and the dielectric rod occurs, which can be equivalent to the displacement deformation of the structure, the resonant frequency of the sensor will shift.…”