With the majority of delegates staying through the final paper in the last session, Darnell’s second annual nanoPower Forum finished strong. Leading off the final day, Kevin O’Handley, Vice President with Ferro Solutions, presented "New Means of Powering and Recharging Electronic Devices."
O’Handley discussed Ferro Solutions efforts to develop an efficient, wireless mechanism for transmitting electrical power to tiny receivers that could be implanted easily in patients for a range of new therapeutic devices. The technology is expected to be applied initially to neurostimulators.
Current implantable batteries, for instance, are about an inch in diameter and require several hours to recharge using induction from an external charging coil to an implanted receiving coil. Ferro Solutions proposes instead a novel thin-film device that would convert changes in an external magnetic field to an electrical voltage with high efficiency. The company will develop new thin-film deposition techniques and millimeter- and micron-scale designs for producing layered magnetorestrictive and electroactive films.
Unlike induction coil devices, O’Handley observed, "Our thin-film technology would scale well to much smaller receivers. This technology would enable devices the size of a few grains of rice that could be implanted without surgery in many different parts of the body – both less expensive and less risky for the patient."
Several papers on the last day of nPF 08 discussed aspects of electromagnetic energy harvesting. Richard Waters, CTO with Lumedyne Technologies presented, "Development of an Electro-Magnetic Transducer for Energy Harvesting of Kinetic Energy and its Application to MEMS-scale Devices."
Dr Waters present a novel electro-magnetic transducer for converting ambient kinetic energy into useful electrical power. The prototypes have demonstrated rectified dc power production of 18mW at 1-g (9.83 m/s2) of acceleration, and peak-to-peak voltage production of 2V at an applied acceleration of only 0.0027g.
"The voltage sensitivity of the transducer for low vibration levels indicates that a micro-scale version of the concept based on MEMS technology should be feasible," Dr. Waters concluded.
Dr. S.K Panda with the National University of Singapore discussed, "Stray Magnetic Energy Harvesting in Power Lines thought Inductive Coupling for Wireless Sensor Nodes." He demonstrated that the magnetic energy generated by a 50 Hz, 4A, 230Vac current carrying power line/cable can be transferred to the sensor node via inductive coupling.
The magnetic energy harvesting technique is based on the concept of electromagnetic law of induction. The prototype of the inductive energy transfer system has been designed and developed to convert harvested ac voltage into dc voltage which then charge the storage capacitor until the preset energy storage level.
The stored energy is released to the linear regulator to provide a constant 3.3V to the RF AM transmitter that requires 132° of energy for communication. Finally, the self-powered wireless RF transmitter working prototype is capable of transmitting 10 packets of 12 digital bits of information over a range of up to 70 meters in open field with line of sight.
Near the end of the Forum, Dr. Zoya Popovic with the University of Colorado at Boulder discussed an "Integrated Rectenna and Power Management Design for RF Far Field Energy Harvesting." She presented an innovative approach for delivering wireless power to batteryless sensors at very low power levels and high efficiency.
Broadband multi-frequency rectenna arrays which independently receive and rectify two orthogonal wave polarizations provide dc power with decreased variations in a multipath environment. The dc power extracted from 2-18GHz electromagnetic radiation is managed by high efficiency power processing circuitry. Experimental results were presented for an integrated switched capacitor power converter realized in a fully-depleted silicon on insulator (FD-SOI) process.