Google Search
C6: Novel applications
Portable systems that record and process electrical signals produced by the brain will revolutionize medical healthcare, regenerative medicine and consumer electronics. While short-term recordings of the electroencephalogram (EEG) are usually performed in a lab employing hard-wired wet electrodes, signal acquisition outside of medical facilities requires dry sensors for convenience and long-term capability. They mostly include on-site signal processing to compensate for high contact resistances and artifacts. However, the active component raises the energy budget and consequently reduces the runtime of a mobile system.
We present a thermoelectric generator (TEG)-based, integrated power supply for energy autonomous active EEG electrodes. The supply consists of a TEG for power generation, a heat transfer structure funneling heat through the generator, a passive heat sink dissipating heat into the environment and will further be equipped with a power conversion ASIC for low input voltages. For thermal evaluation, the system is implemented on top of a stainless-steel disc-electrode. Heating of the electrode by body warmth results in a heat flux across the generator and consequently in electric power generation. The system design aims at high energy output while retaining small size and weight.
Two different generator types are evaluated: A compact micro-TEG with high module Seebeck voltage (TEG1, micropeltTPG-651) and a macroscopic generator with low electrical resistance (TEG2, Quick-Cool32-06-1.2). At ambient conditions (RT=24°C) and immobile subject, the generators produce an average voltage of TEG1=80mV (8.7uW for matched load conditions) and TEG2=20mV (34.5uW) when placed on the human forehead. For a walking subject (1.5m/s), the output increases to TEG1=135mV (24.6uW) and TEG2=40mV (137.9uW). The output characteristics of both generators are promising for powering a future CMOS-based EEG front-end including amplification and filtering (Gain=45dB, BW=150Hz, CMMR>50dB, P=10uW). The increased-voltage micro-TEG or the increased-power macro-TEG will be superior depending on the usage scenario and the voltage-dependent converter efficiency.