Wireless SAW Strain Sensor Using Orthogonal Frequency Coding

Abstract

Wireless sensors offer a unique solution for many applications where wired designs may not be feasible. This paper presents the design and experimental results of a passive, wireless surface acoustic wave (SAW) strain sensor using orthogonal frequency coding (OFC) for the device identification. The sensor operates at a frequency of 915 MHz with a bandwidth of 68 MHz. A vector network analyzer is used to interrogate the sensor from a range of 60 cm (2 ft), with further range possible by increased transmitter output power or averaging. The sensor is bonded directly to a steel cantilever test structure and could be attached directly to other structures. An external connection site facilitates an antenna, with bond wires joining the connection site to the SAW die. A 3-D printed package protects the sensor while allowing the antenna to be mounted externally from the sensor package. Experimental results show that the wireless SAW strain sensor performs comparably to a wired, commercial strain gage. In addition, the strain sensitivity is extracted for this SAW OFC strain sensor embodiment which describes the frequency shift with the applied strain (−1.80 ppm/με).Index Terms-Wireless sensor, saw sensor, surface acoustic wave (saw), structural health monitoring (shm), saw strain sensor.

An Impedance-Loaded Orthogonal Frequency-Coded SAW Sensor for Passive Wireless Sensor Networks

“…The previous OFC SAW sensors have large coding capacity for multi-sensors operation while the problem of multiple measurands coupling is hard to resolve [28][29][30], since the principle of these sensors is based on the effect of the measurand on the velocity of the surface acoustic wave. In this article, the proposed impedance-loaded OFC SAW sensor is packaged properly so it could be isolated from the measurands, so the problem of multiple measurand coupling could be avoided.…”

“…Since the phase shift value has a minus effect on orthogonality, the large capacity of OFC coding is kept for this sensor. Compared with previously presented passive wireless OFC SAW sensors [28][29][30][31], this proposed sensor could avoid the multiple measurands coupling for the first time in addition to having a large coding capacity for wireless sensor networks in Table 1. Table 1.…”

“…To expand the capacity of SAW sensors, an OFC SAW sensor based on the principle of orthogonal frequency-coded division is proposed in [28][29][30]. This sensor could expand the capacity in a limited bandwidth using code diversity.…”

Nonlocal Damage Mechanics for Quantification of Health for Piezoelectric Sensor

“…Guided waves such as Lamb waves and SAW have been explored for detection of surface and subsurface defects/delamination [11][12][13][14]. Recently, highly sensitive strain sensors employing SAW resonator have been developed for SHM applications [15][16][17]. It was demonstrated that the strain induced in the structure could be sensed using SAW sensors, and macroscale damage could be quantified.…”

High-temperature static strain langasite SAWR sensor: Temperature compensation and numerical calibration for direct strain reading

“…For the reasons discussed so far, sensors that are small, robust, allow for flexible packaging, and which offer the possibility of operating wirelessly and battery-free are very attractive for harsh-environment applications. Surface acoustic wave (SAW) sensors have the potential to address all these requirements due to their robustness, simplicity of packaging, ease and cost efficiency of use [3], [5], [6], [12]. In particular, the wireless sensing and battery-free operation capabilities are extremely attractive for harsh-environment operation, since they diminish or eliminate the need for maintenance; allow operation at temperatures where no battery or energy scavenging method is feasible; dispenses additional circuitry at the sensor level, thus also reducing bulkiness, and improves reliability.…”