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In this paper, we present a self-powered wireless sensor system for structural health monitoring of highway bridges. The system consists of an energy harvesting material, power conditioning circuitry, a sensor, an analog-to-digital converter, and a wireless transmitter. The energy harvesting material is a recently discovered NiMnCoIn magnetic shape memory alloy (MSMA), which converts mechanical vibrations first into a magnetization change and then, with assistance from a pick-up coil, into an alternating current (ac) output. The ac output of the MSMA is converted to a direct current (dc) voltage for powering a sensor and circuitry. Measurement results from a self-powered rectifier (SPR) and a six-bit successive approximation register analog-to-digital converter (SAR ADC) are presented, and implementation considerations are presented for the sensor and wireless transmitter. The SPR produces dc output voltages larger than 700 mV for loads larger than 100 kΩ with peak input amplitudes >;400 mVpk. A four-stage rectifier-multiplier is also implemented utilizing the proposed SPR as the first stage. The implemented SAR ADC is functional with a 0.9-V dc supply voltage (Vdd) and achieves an improved performance with a Vdd of 1.8 V, where the SAR ADC achieves a measured integral nonlinearity and differential nonlinearity of +1.2/-1.9 least significant bit and +1.3/-0.99 LSB, respectively. The SPR and SAR ADC are fabricated in a standard 0.5-μm CMOS process. The proposed sensor system can be fully optimized due to co-design capabilities. The lack of batteries makes this system ideal for deployment in bridge monitoring systems.
Date of Publication: Feb. 2013