Biomedical implants hold the promise of dramatically improving health and well-being by, for example, enabling people to pro-actively monitor health through real-time tracking of internal body chemistry (e.g. pH, glucose, lactate, tissue oxygen), treat diseases through targeted and tailored drug delivery, treat neural disorders through neural prostheses, etc. However, this vision is only possible if implants become much smaller with longer lifetimes. The current state of the art in integrated circuit and micro-sensor design and manufacturing could enable cubic millimeter sized implants that would greatly reduce trauma to the patient and improve continuous health monitoring. However, power systems have lagged behind and become a barrier to implant miniaturization. Very small batteries would quickly become depleted and then the entire implant would have to be surgically replaced. The goal of this project is to overcome this power problem by wirelessly transmitting power to the biomedical implants using low frequency magnetic fields that easily penetrate the human body. These magnetic fields will excite a magnetoelectric power receiver that will be part of the implant. The magnetoelectric receiver will convert the magnetic fields to electricity which will then be properly conditioned to power the implant. The Principle Investigator (PI) and affiliated researchers will explore two competing types of magnetoelectric devices and characterize them especially in terms of uncertainties related to the position and alignment of the implant and associated power receiver. New fabrication processes will be developed that enable micro-scale magnetoelectric devices to generate more power, thus enabling further miniaturization for biomedical implants. In addition to enabling the miniaturization of implants, the work to be accomplished by this project could have broader benefits for the state of the art in both sensing and wireless power transfer.
The goal of this project is to explore the use of low frequency magnetic fields coupled with magnetoelectric power receivers to transmit power to biomedical implants. The target goal is to safely supply 100 microwatts per cubic millimeter, which would enable a wide range of implanted sensors and therapeutic devices. Low frequency magnetic fields are attractive because of their very low absorption in human tissue and encapsulating structures. Two classes of magnetoelectric devices will be investigated: laminates of magnetostrictive and piezoelectric material, and jointly fabricated permanent magnet / piezoelectric structures. The two approaches will be compared given alignment and orientation uncertainties and issues associated with human tissue interaction. Specifically, researchers will characterize the surrounding tissue's role in degrading the quality factor of the resonant magnetoelectric power receivers. The key relationships for power generation by this method as well as performance limits will be elucidated and experimentally validated, which will serve as a basis for system design. A new microfabrication process will be developed to enable high power transducers through the use of much thicker active materials (i.e. piezoelectric and magnetostrictive). Finally, a system to control the DC voltage used by the implant from the external transmitter will be developed and validated to remove the need for large onboard passive components associated with traditional power electronics. The efficacy of the external control method will be fully characterized with respect to stability of the DC voltage and robustness to system uncertainties. The results of this research will establish the basis for much smaller, more ubiquitous biomedical implants by overcoming the issue of delivering power at sufficient densities.
