An Energy Autonomous 400 MHz Active Wireless SAW Temperature Sensor Powered by Vibration Energy Harvesting

• Main Authors: Zhu, Yao, Zheng, Yuanjin, Gao, Yuan, Made, Darmayuda I., Sun, Chengliang, Je, Minkyu, Gu, Alex Yuandong
• Other Authors: School of Electrical and Electronic Engineering
• Format: Article
• Language: English
• Published: 2016
• Subjects: Energy autonomous; Power management; SAW; SAW oscillator; Temperature sensor; Wireless; Low power; Vibration energy harvest
• Online Access: https://hdl.handle.net/10356/82823; http://hdl.handle.net/10220/40333
• Institution: Nanyang Technological University

An energy autonomous active wireless surface acoustic wave (SAW) temperature sensor system is presented in this paper. The proposed system adopts direct temperature to frequency conversion using a lithium niobate SAW resonator for both temperature sensing and high-Q resonator core in a cross-coupled RF oscillator. This arrangement simplifies the temperature sensor readout circuit design and reduces the overall system power consumption. A power conditioning circuit based on buck-boost converter is utilized to provide high efficiency power extraction from piezoelectric energy harvester (PEH) and dynamic system power control. The SAW resonator is fabricated in-house using a two-step lithography procedure while the RF oscillator as well as the PEH power conditioning circuit are implemented in standard 65-nm and 0.18- μm CMOS processes respectively. The measured RF transmitter output power is -15 dBm with a phase noise of -99.4 dBc/Hz at 1 kHz offset, achieving a figure of merit (FOM) of -217.6 dB. The measured temperature sensing accuracy is ±0.6 °C in -40 °C to 120 °C range. Fully powered by a vibration PEH, the proposed energy autonomous system has a self-startup voltage of 0.7 V and consumes an average power of 61.5 μW.