Wireless powering for implantable device networks

The miniaturization of electronic systems has allowed to realize mm-sized implanted devices for all kinds of applications, ranging from sensing of relevant biological parameters to drug delivery and nerve stimulation. However, all those systems require a power source and batteries are normally too big or requiring to be periodically recharged/replaced. Given the limited and discontinuous amount of energy that can be harvested inside the body, Wireless Power Transfer (WPT) is a promising solution. There are multiple ways to perform in-body WPT, using inductive, ultrasound, and RF energy sources. Finding a generic solution to the problem of wirelessly powering implantable devices is perceived today as an impossible challenge. This is especially true if we consider wearable, low-weight, and comfortable power transmitters out of the body. Each powering method presents different advantages/disadvantages. Inductive powering is insensitive to the human body and interfaces between air and tissue, but very sensitive to misalignment. Ultrasound powering has very low path losses in the human body but is affected by 99.9% attenuation on the interface skin/air. RF powering has the advantage to have field power decaying as the inverse of distance, instead of the inverse of distance squared (as it happens in the inductive powering). However, it suffers from significant absorption into the body and interface reflections. Recently people have tried to exploit the human body, which can act as a conductor itself to transfer power, in a similar fashion as 802.15.6 human body communication. Other research groups are looking at various ways of harvesting vibrational, light, or temperature gradient sources. This Ph.D. aims to develop efficient WPT technology for miniature implantable solutions based on these novel concepts. The candidate will perform a detailed literature study. A suitable mathematical model and simulation environment will be developed. The core research task will be in the design of very energy-efficient energy harvester and power management circuits. The candidate will be able to design and have their own ASIC manufactured. Finally, the ASIC will be tested in a suitable in-vitro model.