Wireless Data and Power Transmission Aiming Intracranial Epilepsy Monitoring

This study presents a wireless power and data transmission system to overcome the problems in intracranial epilepsy monitoring associated with transcutaneous wires. Firstly, a wireless power transfer link based on inductive coupling is implemented and a power management unit for the implant is designed. 4-coil resonant inductive link scheme is exploited since it exhibits a high efficiency and optimal load flexibility. Power management unit consists of an active rectifier, a low drop-out voltage regulator which is biased internally with a supply independent current source; all implemented as integrated circuit. Wireless power link provides 10 mW under 1.8 V dc to the load, more specifically the electrodes and read-out electronics. Wireless data communication is realized using the same frequency, 8.4 MHz, as the power link. Load shift keying is performed for uplink (from implant to external) communication by switching an integrated modulator which, in fact, detunes the resonance. Modulated signal is recovered on the external device by means of an integrated self-referenced ASK demodulator. Data rate is adapted for a fast ripple (< 500 Hz) detection system which requires 300 kbps communication. The measurements show that the system works at 36% power transfer efficiency without communication link and the efficiency drops to 33% with 300 kbps uplink data transfer. Finally, in-vitro tests that emulate the real operation scenario are performed thanks to the two-polymer packaging and almost the same power transfer efficiency is achieved under same operation conditions.

Analysis and optimization of passive UHF RFID systems

Jari-Pascal Curty

Radio Frequency IDentification (RFID) is an automatic identification method, relying on storing and remotely retrieving data using devices called RFID tags or transponders. An RFID tag is a small object that can be attached to or incorporated into a product, animal or person. RFID tag contains antenna to enable it to receive and respond to Radio-Frequency (RF) queries from an RFID reader or interrogator. Passive tags require no internal power source, whereas active tags require a power source. As of today (2005), the ubiquitous computing and ambient intelligence ideas are making their way. In order for these to become a reality, a number of key technologies are required. Briefly, these technologies need to be sensitive, responsive, interconnected, contextualised, transparent and intelligent. RFID is such a technology and more particularly passive RFID tags. But, in order to deliver the necessary characteristics that could trigger ambient intelligence, there are some challenges that need to be addressed. Remote powering of the tags is probably the most important. Issues concerning the antenna-tag interface, as well as the rectifier design, that allows the RF signal to be converted to Direct Current (DC) are in pole position. Secondly, the communication link and the reader should be optimized. The RF signal that contains the tag data suffers from a power of four decay with the distance between tag and reader. As a result, both the reader sensitivity and the tag backscattered power efficiency have to be maximized. Long-range powering, as well as sufficient communication quality, are the guidelines of this work. This research project proposes a linear two-port model for an N-stage modified-Greinacher full wave rectifier. It predicts the overall conversion efficiency at low power levels where the diodes are operating near their threshold voltage. The output electrical behavior of the rectifier is calculated as a function of the received power and the antenna parameters. Moreover, the two-port parameters values are computed for particular input voltages and output currents for the complete N-stage rectifier circuit using only the measured I-V and C-V characteristics of a single diode. Also presented in this work is an experimental procedure to measure how the impedance modulation at the tag side affects the signal at the reader. The method allows the tag designer to efficiently predict the effect of modulator design at system level and gives an useful instrument to choose the most appropriate impedances. Finally, the design of a fully integrated remotely powered and addressable RFID tag working at 2.45 GHz is described. The achieved operating range at 4 W Effective Isotropically Radiated Power (EIRP) reader transmit power is 12 m. The Integrated Circuit (IC) is implemented in a 0.5 μm silicon-on-sapphire technology. A state of the art rectifier design achieving 37% of global efficiency is embedded to supply energy to the transponder. Inductive matching and a folded-dipole antenna are key elements to achieve these performances. The necessary input power to operate the transponder is about 2.7 μW.

EPFL2006

Remotely powered PPM demodulator by inductive coupling for rodent applications

Catherine Dehollain, Enver Gürhan Kilinç, Franco Maloberti, Kerim Türe

A low-power pulse position modulation (PPM) demodulator has been developed for remotely powered batteryless implantable devices. The required power for the implantable device is provided by the magnetic coupling with the external array of powering of coils placed under the living space of the animal. The remote powering is turned off 6 % of one bit duration during data transmission. The remote powering link is optimized to deliver power at 13.56 MHz frequency. The power is transferred from 30 mm distance with 21 % efficiency. An integrated full-wave rectifier and voltage regulator generate 1.8 V supply voltage from induced signal. The integrated PPM demodulator consumes only 27.8 lW and has 8.33 kb/s data rate. The presented entire system and basic blocks are integrated using a 0.18 mu m CMOS technology. Experimental results verify the effectiveness of the PPM demodulator and the downlink communication system.

Springer Verlag2016

Analysis and optimization of passive UHF RFID systems

Jari-Pascal Curty

EPFL2006