Wireless Strain Sensing for Spacecraft Application

Abstract

This paper presents the application of single antenna unpowered wireless transponder into the wireless strain sensor system, and also the usage of an external VCO for carrier frequency generation. The wireless strain sensing system is powered by solar energy. This system includes a wireless strain sensor that consumes about 6 mW, a wireless solar energy harvesting unit, and a frequency modulation/demodulation unit. To achieve such an ultralow power operation, a voltage-controlled oscillator (VCO) is used to convert the directcurrent (DC) strain signal to a high frequency oscillatory signal. Next, this oscillatory signal is transmitted by an unpowered wireless transponder. The single channel is capable of receiving the radio frequency (RF) carrier signal and reflecting the modulated strain signal out via the same antenna. The generic solar panel with energy harvesting circuit is used to power the strain sensor node for a short period of time. The frequency demodulation is based on a Phase Lock Loop (PLL) circuit that tracks the frequency of the received wireless signal and demodulates it into the original strain signal. The system features ultra-low power consumption, completely wireless sensing, solar powering, and portability. This system is also integrated onto portable printed circuit architecture for demonstration of its portability. In the future space program, this system could potentially be applied to both dynamic and static structural measurements. Although the challenge of extreme operational condition for WSS in space and the strict performance requirements, the application of WSS in space is promising and bears the potential in reduction of costs and payloads with great scalability and sensor flexibility.