Low power CMOS, IC, biosensor and wireless power transfer techniques for wireless sensor network application
The emerging field of wireless sensor network (WSN) is receiving great attention due to the interest in healthcare. Traditional battery-powered devices suffer from large size, weight and secondary replacement surgery after the battery life-time which is often not desired, especially for an implantable application. Thus an energy harvesting method needs to be investigated. In addition to energy harvesting, the sensor network needs to be low power to extend the wireless power transfer distance and meet the regulation on RF power exposed to human tissue (specific absorption ratio). Also, miniature sensor integration is another challenge since most of the commercial sensors have rigid form or have a bulky size. The objective of this thesis is to provide solutions to the aforementioned challenges.^ The focus of this presentation is on integration of technologies for implantable wireless sensor network. Firstly, a low power IC for the radio, which consumes most of the power, is fabricated using CMOS technology. This transceiver harvests energy from 915MHz RF radiation power signal. Also, the powering signal provides reference clock to the IC for low power frequency synthesis. A simple receiver is implemented on chip for multi-node access. Then wireless powering techniques were studied to improve the current work. Wireless power transfer (WPT) link distance for implantable devices in prosthetic arm application (targeted muscle reinnervation) is less than 10 cm. At this distance, wireless power transfer using magnetic resonance coupling (MRC) can be much more effective in power transfer efficiency. By focusing on this point, a design technique using band pass filter theory allows transferring power selectively to a specific target device. Selective WPT enables multi-node access without having to use any further techniques, greatly simplifying the system. A low power SoC is designed to comply with the proposed WPT technique, also dedicated for glucose detection using 180nm CMOS technology. The IC is composed of a low power transmitter based on injection locked ring oscillator. The wireless sensor IC receives power wirelessly from MRC through 27 MHz (ISM band) and transmits in 405 MHz (MICS band). Since our glucose sensor is an amperometric sensor, the IC detects current from the biosensor and mirrors it to an internal ring oscillator, which presents the glucose level in frequency (I-F conversion). Frequency variation due to temperature can be calibrated out through an internal reference clock. Total power consumption of the system is around 20 µW. To complete the system, a glucose sensor is designed and fabricated with graphene petals on carbon fiber. Efforts were focused on flexible, robust and sensitive glucose sensor based on multilayered graphene petals (GP) on thin carbon fiber (CF) tow. GP/CF electrode was decorated with the mixture of Pt nanoparticles (PtNPs), polyaniline (PANI), glucose oxidase (GOx), and nafion. PtNP are electrodeposited onto the graphene for its catalytic behavior toward hydrogen peroxide, which is generated in the process of glucose oxidase (GOx) oxidizing glucose, acting as an electron-transfer promoter. The GOx/PANI/PtNP/GP/CF biosensor showed highly flexible characteristics with good sensitivity and it showed more than 90% of its sensitivity after 4 weeks in phosphate buffered saline (PBS) solution.^
Pedro P. Irazoqui, Purdue University.
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