An overview of the recent wideband transcutaneous wireless communication techniques <s> I. INTRODUCTION <s> In the hearing prosthesis, stimulation is presented through an array of 20 electrodes located in the scala tympani. Any two electrodes can be configured as a bipolar pair to conduct a symmetrical, biphasic, constant-current pulsatile stimulus. Up to three stimuli can be presented in rapid succession or effectively simultaneously. For simultaneous stimulation, a novel time-division current multiplexing technique has been developed to obviate electrode interactions that may compromise safety. The stimuli are independently controllable in current amplitude, duration, and onset time. Groups of three stimuli can be generated at a rate of typically 500 Hz. Stimulus control data and power are conveyed to the implant through a single transcutaneous inductive link. The device incorporates a telemetry system that enables electrode voltage waveforms to be monitored externally in real time. The electronics of the implant are contained almost entirely on a custom designed integrated circuit. Preliminary results obtained with the first patient to receive the advanced implant are included. > <s> BIB001 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> I. INTRODUCTION <s> Since the original demonstration that electrical activity generated by ensembles of cortical neurons can be employed directly to control a robotic manipulator, research on brain–machine interfaces (BMIs) has experienced an impressive growth. Today BMIs designed for both experimental and clinical studies can translate raw neuronal signals into motor commands that reproduce arm reaching and hand grasping movements in artificial actuators. Clearly, these developments hold promise for the restoration of limb mobility in paralyzed subjects. However, as we review here, before this goal can be reached several bottlenecks have to be passed. These include designing a fully implantable biocompatible recording device, further developing real-time computational algorithms, introducing a method for providing the brain with sensory feedback from the actuators, and designing and building artificial prostheses that can be controlled directly by brain-derived signals. By reaching these milestones, future BMIs will be able to drive and control revolutionary prostheses that feel and act like the human arm. <s> BIB002 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> I. INTRODUCTION <s> The next generation of implantable high-power neuroprosthetic devices such as visual prostheses and brain computer interfaces are going to be powered by transcutaneous inductive power links formed between a pair of printed spiral coils (PSC) that are batch-fabricated using micromachining technology. Optimizing the power efficiency of the wireless link is imperative to minimize the size of the external energy source, heating dissipation in the tissue, and interference with other devices. Previous design methodologies for coils made of 1-D filaments are not comprehensive and accurate enough to consider all geometrical aspects of PSCs with planar 3-D conductors as well as design constraints imposed by implantable device application and fabrication technology. We have outlined the theoretical foundation of optimal power transmission efficiency in an inductive link, and combined it with semi-empirical models to predict parasitic components in PSCs. We have used this foundation to devise an iterative PSC design methodology that starts with a set of realistic design constraints and ends with the optimal PSC pair geometries. We have executed this procedure on two design examples at 1 and 5 MHz achieving power transmission efficiencies of 41.2% and 85.8%, respectively, at 10-mm spacing. All results are verified with simulations using a commercial field solver (HFSS) as well as measurements using PSCs fabricated on printed circuit boards. <s> BIB003 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> I. INTRODUCTION <s> Motivated by the success of cochlear implants for deaf patients, we are now facing the goal of creating a visual neuroprosthesis designed to interface with the occipital cortex as a means through which a limited but useful sense of vision could be restored in profoundly blind patients. We review the most important challenges regarding this neuroprosthetic approach and emphasize the need for basic human psychophysical research on the best way of presenting complex stimulating patterns through multiple microelectrodes. Continued research will hopefully lead to the development of and design specifications for the first generation of a cortically based visual prosthesis system. <s> BIB004 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> I. INTRODUCTION <s> We have used a well-known technique in wireless communication, pulse width modulation (PWM) of time division multiplexed (TDM) signals, within the architecture of a novel wireless integrated neural recording (WINeR) system. We have evaluated the performance of the PWM-based architecture and indicated its accuracy and potential sources of error through detailed theoretical analysis, simulations, and measurements on a setup consisting of a 15-channel WINeR prototype as the transmitter and two types of receivers; an Agilent 89600 vector signal analyzer and a custom wideband receiver, with 36 and 75 MHz of maximum bandwidth, respectively. Furthermore, we present simulation results from a realistic MATLAB-Simulink model of the entire WINeR system to observe the system behavior in response to changes in various parameters. We have concluded that the 15-ch WINeR prototype, which is fabricated in a 0.5-mum standard CMOS process and consumes 4.5 mW from plusmn1.5 V supplies, can acquire and wirelessly transmit up to 320 k-samples/s to a 75-MHz receiver with 8.4 bits of resolution, which is equivalent to a wireless data rate of ~ 2.56 Mb/s. <s> BIB005 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> I. INTRODUCTION <s> This brief presents a standalone closed-loop wireless power transmission system that is built around a commercial off-the-shelf (COTS) radio-frequency identification (RFID) reader (TRF7960) operating at 13.56 MHz. It can be used for inductively powering implantable biomedical devices in a closed loop. Any changes in the distance and misalignment between transmitter and receiver coils in near-field wireless power transmission can cause a significant change in the received power, which can cause either a malfunction or excessive heat dissipation. RFID circuits are often used in an open loop. However, their back telemetry capability can be utilized to stabilize the received voltage on the implant. Our measurements showed that the delivered power to the transponder was maintained at 11.2 mW over a range of 0.5 to 2 cm, while the transmitter power consumption changed from 78 mW to 1.1 W. The closed-loop system can also oppose voltage variations as a result of sudden changes in the load current. <s> BIB006 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> I. INTRODUCTION <s> We present an inductively powered 32-channel wireless integrated neural recording (WINeR) system-on-a-chip (SoC) to be ultimately used for one or more small freely behaving animals. The inductive powering is intended to relieve the animals from carrying bulky batteries used in other wireless systems, and enables long recording sessions. The WINeR system uses time-division multiplexing along with a novel power scheduling method that reduces the current in unused low-noise amplifiers (LNAs) to cut the total SoC power consumption. In addition, an on-chip high-efficiency active rectifier with optimized coils help improve the overall system power efficiency, which is controlled in a closed loop to supply stable power to the WINeR regardless of the coil displacements. The WINeR SoC has been implemented in a 0.5-μ m standard complementary metal-oxide semiconductor process, measuring 4.9×3.3 mm2 and consuming 5.85 mW at ±1.5 V when 12 out of 32 LNAs are active at any time by power scheduling. Measured input-referred noise for the entire system, including the receiver located at 1.2 m, is 4.95 μVrms in the 1 Hz~10 kHz range when the system is inductively powered with 7-cm separation between aligned coils. <s> BIB007 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> I. INTRODUCTION <s> We have presented the design methodology along with detailed simulation and measurement results for optimizing a multiband transcutaneous wireless link for high-performance implantable neuroprosthetic devices. We have utilized three individual carrier signals and coil/antenna pairs for power transmission, forward data transmission from outside into the body, and back telemetry in the opposite direction. Power is transmitted at 13.56 MHz through a pair of printed spiral coils (PSCs) facing each other. Two different designs have been evaluated for forward data coils, both of which help to minimize power carrier interference in the received data carrier. One is a pair of perpendicular coils that are wound across the diameter of the power PSCs. The other design is a pair of planar figure-8 coils that are in the same plane as the power PSCs. We have compared the robustness of each design against horizontal misalignments and rotations in different directions. Simulation and measurements are also conducted on a miniature spiral antenna, designed to operate with impulse-radio ultra-wideband (IR-UWB) circuitry for back telemetry. <s> BIB008
ranscutaneous data telemetry is a key function in a group of implantable medical devices, known as neuroprostheses, which substitute sensory or motor modalities that are lost due to injuries or diseases BIB004 . Eliminating hardwired interconnects in these devices to keep the skin intact is necessary to improve the patient comfort and safety against the risks of infection and mechanical damage. Cochlear implants and visual prostheses need a large volume of data from external artificial sensors to interface with a large number of neurons and produce sensations with high enough quality and resolution that can support desired functions such as speech recognition or functional vision BIB004 ,  . The flow of information in these neuroprosthetic devices is mainly from outside (e.g. an artificial sensor) into the body and eventually to the central nervous system (CNS). This direction of dataflow is often referred to as the forward telemetry or downlink. The same neuroprosthetic devices often need to inform the external processing components of the system about the neuronal response immediately after stimulation to properly adjust the stimulation parameters BIB001 . There is also information about the internal operation of the implant that needs to be sent out to close feedback loops or ensure safe operation of the system BIB006 . This direction of dataflow that sends information from inside towards out of the body is often referred to as back telemetry or uplink. The data volume and required bandwidth for the downlink is much higher than uplink in the aforementioned applications. There is another group of neuroprosthetic devices, known as invasive brain-computer interfaces (iBCI), that collect a massive amount of neural data from the CNS or peripheral nervous system (PNS) and send it across the skin to the external components of the system to be further processed in Manuscript received April 15, 2011 . This work was supported in part by the National Institutes of Health, grant NIBIB-5R21EB009437, and the National Science Foundation under award ECCS-824199. Maysam Ghovanloo is with the GT-Bionics lab, School of Electrical and Computer Engineering at the Georgia Institute of Technology, Atlanta, GA 30308, USA (phone: 404-385-7048; email: mgh@gatech.edu). order to infer the patients' intentions BIB005 - BIB007 . The processed information can then be used to access computers, drive wheelchairs, or control the users' environments or motorized prosthetic limbs. The same neuroprosthetic devices need a transcutaneous downlink to adjust implantable device parameters such as gain and bandwidth, and possibly add sensory feedback through neural stimulation for better control of the movements and for a richer and more natural experience of the prosthetic limb BIB002 . The data volume and necessary bandwidth for the downlink is much lower in iBCI applications than the uplink. There are several common design challenges among both categories of transcutaneous wireless link applications, which relate to the extremely limited space and power availability in the human body. There is also significant electromagnetic (EM) field absorption in tissue, stemming from its predominantly water content and conductive volume conductor that increases exponentially with frequency  . Hence, the higher the carrier frequency, the lower the EM field penetrates in the tissue and the more loss it experiences, which turns into heat. In neuroprostheses, high bandwidth needs to be achieved at the lowest possible carrier frequencies. In other words, the information content of every carrier cycle in wideband transcutaneous wireless links often needs to be much higher than similar free space wireless communications. Yet another challenge that also relates to the tissue volume conductor is the effects of surrounding environment on the electrical characteristics of the coils and antennas that establish the transcutaneous wireless link. Fig.  1 shows a simplified view of an implanted and an external coil in homogeneous tissue environment. These coils and antennas need to be specifically designed and optimized considering the tissue environment BIB003 - BIB008 . In this paper different types of transcutaneous wireless links have been described along with some of the most recent solutions that researchers have devised to address the above common challenges.