Proposal for a PhD Thesis - Institute of Microelectronics - A*Star

PhD Project Proposal
Title: Integrated circuits for energy transfer & management in implantable
microsystems
Period: 2010–2012 (3 years)
Supervisor: Dr. Minkyu Je
E-mail: jemk@ime.a-star.edu.sg
Laboratory: Institute of Microelectronics (IME), A*STAR, Singapore (http://www.ime.astar.edu.sg)
Since energy is such an essential resource in implantable biomedical systems, it must be
efficiently transferred and managed. To supply energy to implanted devices, wireless
electromagnetic energy transfer is an effective and proven technique. It involves
transmitting electromagnetic energy into the body and collecting it via a coil or antenna.
Low-frequency electromagnetic energy transfer is currently used in cochlear implants,
radio-frequency identification (RFID) implants, retinal prosthetics, and neurostimulators.
Near-field wireless energy transfer results in electromagnetic fields that can heat tissue and
generate electromagnetic interference on nearby electronics. Hence, the wireless link
must meet regulatory guidelines. For small implanted applications, where volume
constraints limit the size of the receive coil, the practical range of energy transfer is limited
to a few centimeters. So, researchers have worked on design optimization and invention
of new techniques to increase the transfer distance and efficiency. Going further, energy
gathering is most useful and flexible when harvesting ambient energy, in which the source
of energy exists inherently as part of the system. An emerging approach that exploits true
ambient energy is vibrational and thermal energy harvesting from the user’s movement
and skin temperature respectively.
The voltage converter is another important component in the energy subsystem. For a
biomedical device, it must be optimized for the voltage and current required by the load.
Energy-efficient CMOS circuits operate off a supply voltage at or below 1 V, and most
biomedical applications require currents between a few microamps to a few milliamps. To
generate these voltages, a step-down (buck) converter is required. When only a small
step-down is required, a low drop-out (LDO) linear regulator is a simple and robust
approach; however, for a large step-down, the efficiency of an LDO is poor and switching
regulators are preferred. The two main voltage converter topologies are switched
capacitor–based and inductor/transformer–based switching converters.
In this PhD thesis project, it is proposed to develop high-efficiency energy transfer circuits
interfacing with a micro-coil for wireless energy transfer and ambient energy harvesters,

and voltage converters delivering optimal supply to the load. The new circuit design
should be able to meet the simultaneous requirements of very small form factor and high
efficiency down to very low energy level, which are critical for implantable microsystems.
The main objectives of the PhD thesis are as follow:
1. To study the governing mechanisms which determine the power transfer and
conversion efficiency.
2. To develop advanced approaches and techniques to design the high-efficiency
energy transfer and conversion circuits.
3. To demonstrate the developed energy transfer and management circuits within
actual implantable microsystems such as a sensorized prosthetic vascular graft.
The major activities of the PhD thesis will include literature study, modeling of energy
transfer coils and energy harvesters, circuit design, simulation and layout, test setup
development, and electrical/in-vitro/in-vivo testing. Most of these activities will be based
on the facilities run in the Integrated Circuits and Systems Laboratory at IME, where the
relevant CAD tools and test equipments are available. In-vitro and in-vivo testing will be
carried out under collaboration with Bio Electronics Programme at IME and National
University Hospital (NUH), Singapore.