UBC Theses and Dissertations

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UBC Theses and Dissertations

Low-power temperature sensing system for biomedical applications Afkhami Ardakani, Hasan


Implantable sensors have been used to improve monitoring and diagnosis of health-related parameters while allowing patients to lead a relatively normal life. Using data from such sensors, one can detect abnormal conditions at early stages and facilitate the prevention of potentially serious consequences. Recent technological advances in integrated circuits, wireless communications, and physiological sensing allow miniature, lightweight, ultra-low-power, intelligent monitoring devices. In this thesis, we focus on an electro-thermally active stent technology for management of in-stent restenosis (i.e., re-narrowing of artery at the stented site). Various studies reporting hyperthermia treatments of restenosis through stent heating have shown promising results, i.e., moderate local heating prevents restenosis by limiting cell proliferation. To remotely warm up the stent, we intend to harvest power from a dedicated source outside of the patient’s body and convert it to heat. However, if there is no control over temperature, the stent temperature may increase unboundedly, which would have adverse effects. The main objective of this thesis is to design a low-power, accurate temperature sensing system with a small footprint. Further, the required power to operate the temperature sensor should be harvested. In this work, two different temperature telemonitoring systems have been designed and laid out in a 65-nm CMOS technology. Both systems have been fabricated and successfully validated. The first telemonitoring system converts the sensed temperature directly to a frequency in an unlicensed band and transmits it to an external reader. The system operates from a supply voltage of 0.7 V and a power consumption of 100 µW. The measured sensitivity of the system is 1.1 MHz/°C within the frequency band of 902 to 928 MHz. This system is capable of detecting temperature change to as low as 1 °C. The sensor interface circuit of our second telemonitoring system converts the temperature to duty-cycle and sends sensory data out using an on-off-keying modulation system. The pulse width of the transmitted signal is proportional to e temperature. Measurement results of a proof-of-concept prototype show that the system operates from a supply voltage of as low as 0.6 V while consuming 115 µW.

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