Inductively coupled coil pair is the most common way of wirelessly transferring power to medical implants. However, the coil displacements and/or loading changes may induce large fluctuations in transmitted power into the implant if no adaptive control is used. In such cases, it is required to transmit excessive power to accommodate all the working conditions, which substantially reduces the power efficiency and imposes potential safety concerns. We have implemented a power transfer system with adaptive control technique to eliminate the power variations due to the loading or coupling coefficient changes. A maximum of 250mW power is transmitted through an optimized coil pair driven by Class-E power amplifier. Load shift keying is implemented to wirelessly transfer data back from the secondary to primary side over the same coil pair, with data rate of 3.3 kbps and packet error rate less than 10/sup -5/. A pseudo pulsewidth modulation has been designed to facilitate back data transmission along with forward power transmission. Through this back telemetry the system transmits the information on received power, back from implant to primary side. According to the data received, the system adjusts the supply voltage of the Class-E power amplifier through a digitally controlled dc-dc converter, thus varying the power sent to the implant. The key system parameters are optimized to ensure the stability of the closed-loop system. Measurements show that the system can transmit the 'just-needed' power for a wide range of coil separation and/or loading conditions, with power efficiency doubled when compared to the uncompensated link.

Design and analysis of an adaptive transcutaneous power telemetry for biomedical implants

A high data-rate frequency-shift keying (FSK) modulation protocol, a wideband inductive link, and three demodulator circuits have been developed with a data-rate-to-carrier-frequency ratio of up to 67%. The primary application of this novel FSK modulation/demodulation technique is to send data to inductively powered wireless biomedical implants at data rates in excess of 1 Mbps, using comparable carrier frequencies. This method can also be used in other applications such as radio-frequency identification tags and contactless smartcards by adding a back telemetry link. The inductive link utilizes a series-parallel inductive-capacitance tank combination on the transmitter side to provide more than 5 MHz of bandwidth. The demodulator circuits detect data bits by directly measuring the duration of each received FSK carrier cycle, as well as derive a constant frequency clock, which is used to sample the data bits. One of the demodulator circuits, digital FSK, occupies 0.29 mm/sup 2/ in the AMI 1.5-/spl mu/m, 2M/2P, standard CMOS process, and consumes 0.38 mW at 5 V. This circuit is simulated up to 4 Mbps, and experimentally tested up to 2.5 Mbps with a bit error rate of 10/sup -5/, while receiving a 5/10-MHz FSK carrier signal. It is also used in a wireless implantable neural microstimulation system.

A wideband frequency-shift keying wireless link for inductively powered biomedical implants

This paper presents Interestim-2B, a modular 32-site wireless microstimulating ASIC for neural prosthesis applications, to alleviate disorders such as blindness, deafness, and severe epilepsy. Implanted just below the skull along with a high-density intracortical microelectrode array, the chip enables leadless operation of the resulting microsystem, accepting power and data through an inductive link from the outside world and inserting information into the nervous system in the form of stimulating currents. Each module contains eight current drivers, generating stimulus currents up to /spl plusmn/270 /spl mu/A with 5-b resolution, /spl sim/100M/spl Omega/ output impedance, and a dynamic range (headroom voltage) that extends within 150 mV of the 5 V supply rail, and 250 mV of the ground level. As many as 64 modules can be used in parallel, to drive multiprobe arrays of up to 2048 sites, with only a pair of connections to a common inductive-capacitive (LC) tank circuit, while receiving power (8.25 mW/module) and data (2.5 Mb/s) from a 5/10-MHz frequency shift keyed carrier. Every 4.6 mm /spl times/ 4.6 mm chip fabricated in a 1.5-/spl mu/m, 2M/2P standard CMOS process through MOSIS, houses two modules and generates up to 65 800 stimulus pulses/s.

https://www.uta.edu/rfmems/Telemetry/papers/A%20Modular%2032-site%20wireless%20neural%20stimulation%20microsystem.pdf?origin=publicationDetail

A modular 32-site wireless neural stimulation microsystem

Although the microstrip antenna has been extensively studied in the past few decades as one of the standard planar antennas, it still has a huge potential for further developments The paper suggests three areas for further research based on our previous works on microstrip antenna elements and arrays One is exploring the variety of microstrip antenna topologies to meet the desired requirement such as ultrawide band (UWB), high gain, miniaturization, circular polarization, multipolarized, and so on Another is to apply microstrip antenna to form composite antenna which is more potent than the individual antenna The last is growing towards highly integration of antenna/array and feeding network or operating at relatively high frequencies, like sub-millimeter wave or terahertz (THz) wave regime, by using the advanced machining techniques To support our points of view, some examples of antennas developed in our group are presented and discussed

https://downloads.hindawi.com/journals/ijap/2012/428284.pdf

Some Recent Developments of Microstrip Antenna

Microwave scanning antennas, vol l, apertures

A method for the analysis of the near field of an antenna is presented; it can be used to deduce the parameters of the antenna near field by specific parameters of the far field. The deductive steps are: (1) deducing the discrete current distribution on the antenna aperture; (2) calculating the antenna near field. Some results are compared with given data, and the agreement is good. It can be widely used in assessment of the antenna near field.

A deductive method for antenna near-field computation in EMC prediction

This paper introduced a strategy for parallel implementation of the FDTD algorithm using a COW (cluster of workstations) parallel computing system Some computing examples were given to prove the feasibility, correctness and high efficiency of this method This method provides a solve-scheme for the EM computation of electrically large-sized complex objects and can be used in EMC analysis

A strategy for parallel implementation of the FDTD algorithm

This paper presents a practical and efficient design for a microstrip array antenna with beam squint. Its essential method is using a special feed network. Then the amplitude distribution on the array's aperture is tapered from the center to the ends, and the aperture phase is shifted from one end to the other. A microstrip array antenna with beam squint is developed, which shows that the design is correct.

Developing a kind of microstrip array antenna with beam squint

Making use of the two modified finite-difference time-domain (FDTD) methods, that is, ADI-FDTD and R-FDTD, we propose a new time domain method in this paper. The method is established from Maxwell curl and divergence equations. It inherits the advantages of both former methods, i.e., not only eliminating the restraint of the Courant-Friedrich-Levy (C-F-L) condition, with an efficient saving of CPU time, but also leading to a direct memory reduction of 33% in the storage of the field components. The formulation is presented and some results of numerical examples are compared to FDTD, ADI-FDTD and R-FDTD. Good agreement is observed.

A new FDTD algorithm - ADI/R-FDTD

In this paper the Finite-Difference Time-Domain (FDTD) method is used to investigate the effects of three types of acoustic diffusers on the field homogeneous characteristics in a reverberation chamber. This paper has three parts: the first one is the analysis of every type of diffuser attached alone on the wall surfaces in the chamber to improve the field uniformity. The second one presents the effect of three-dimensional Schroeder diffuser on the field uniformity in the chamber. And the last one investigates that the arbitrary combinations of the three kinds of diffusers homogenize the field of the chamber.

Gao Benqing

Papers

A deductive method for antenna near-field computation in EMC prediction

A strategy for parallel implementation of the FDTD algorithm

Developing a kind of microstrip array antenna with beam squint

A new FDTD algorithm - ADI/R-FDTD

The analysis of several diffusers in a reverberation chamber by FDTD method