A feasibility study on simultaneous data collection from multiple sensor RF tags with multiple subcarriers

Wireless and battery-less health monitoring of machinery and structures have been a dream in mechanical engi-neering. Particularly, simultaneous data collection from multiple sensors is required to detect failure or malfunction before it becomes fatal problem. In this paper, a concept of simultaneous data collection from multiple sensor RF tags with multiple subcarriers is proposed and its feasibility is examined. To facilitate the inclusion of sensor data in RF tag and to obtain the number of available communication channels, an analog modulation of digitally generated subcarriers is employed. The unavoidable mutual interference among subcarriers, stemming from the pulse shape of subcarrier in RF tags, is eliminated by a swift interference rejection method. We examined the feasibility and the performance of the concept with a two-subcarrier prototype in which the interference rejection is executed in a software defined radio platform. It is shown that the proposed concept is feasible. In order to evaluate the effect of the interference rejection method, we examined the correlation between the original sensor data and the recovered sensor data in a worst case interference environment. It is shown that the correlation coefficient is significantly improved from 0.00 to 0.91.

I. Introduction

In many engineering measurements, we need to monitor readings of multiple sensors. A typical example is the health monitoring test of machinery and structures –– airplanes, artificial satellites and civil engineering structures - to detect damage and malfunction before a fatal failure. In a health monitoring of machinery, single or multiple vibration sources are applied to a target and the transient responses at multiple points are synchronously measured in terms of magnitude and phase. Simultaneous data collection from multiple points is essential to detect the phase which shows the indication of resonance. Wiring of sensors is a serious problem particularly in rotating machinery, lightweight or large scale structures. For example, vibration testing of an artificial satellite as shown in Fig. 1 needs a large number of accelerometers whose data is collected with wire harnesses. The preparation of wire harnesses takes time and labor, and there are some positions that wired accelerometers can not be attached.