Master's thesis presentation Charlie Erndin Dahlberg

Supervisor: Per Lundgren
Examiner: Maria Asplund
Opponents: Theodor Hult Berényi and Simon Imark

Abstract: Intracranial pressure monitoring is conventionally done via an external ventricular drain or an implant probe where a wire protrudes through the skull.
Such methods are cumbersome, costly, highly invasive and they constitute a significant risk of infection with each procedure. For long-term intracranial pressure monitoring, new types of implants which can be left inside of the patient are required, in order to minimize the amount of surgery. Such implants can not be powered by batteries as batteries require changing. This thesis instead turns towards energy harvesting, and aims toward investigating whether energy can be harvested from the human brain by the means of a piezoelectric cantilever harvester, in order to power a pressure sensor implant.

A literature review was conducted in order to examine the current state-of-the-art of energy harvesting inside the human body. A PZT (lead zirconate titanate) cantilever harvester was simulated together with a simple brain model in order to see how much power can be generated by placing the harvester on the brain surface. Results show that a simple 7x7 mm2 thin plate bimorph PZT harvester can generate up to 2.6 nW. The system power requirements would for a sensor implant with a transceiver would however reach at least 200 μW. Thus, a wake-up receiver system should be used where measurements are only taken sparsely for short durations. The current design would allow for 30 seconds of measurements to be taken per month. These
results indicate that human brain energy harvesting is capable of powering sensor implants.

Additionally, a phantom brain test rig was constructed and pressurized in order to mimic the pressure dynamics inside the human brain.