An overview of the recent wideband transcutaneous wireless communication techniques <s> D. Electromagnetic, Optical, and Body Channel <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> D. Electromagnetic, Optical, and Body Channel <s> As neuroprosthetic control systems continue to advance and increase in channel density, there will be a constant need to deliver data at higher bandwidths in and out of the body. Currently, RF telemetry and inductive coupling are the most commonly used methods for transmitting power and electronic data between implants and external systems, and state of the art systems can deliver data rates up to hundreds of kilobits per second. However, it is difficult to operate implanted medical RF links at higher data rates due to electromagnetic compatibility (EMC) constraints. In this study, we investigate the potential for hybrid telemetry systems that use constant-frequency RF inductive links for power and transcutaneous infrared (IR) signals for data. We show that with commercially available infrared communication components, data rates of up to 40 Mbits per second can be transmitted out across 5 mm of skin with an internal device power dissipation under 100 mW. <s> BIB002 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> D. Electromagnetic, Optical, and Body Channel <s> This paper presents a novel inductive link for wireless transmission of power and data to biomedical implantable microelectronic devices using multiple carrier frequencies. Achieving higher data bandwidth without compromising the power efficiency is the driving force to use two separate carriers. Two separate pairs of coils have been utilized for inductive power and forward data transmission. One major challenge, however, is to minimize the interference among these carriers especially on the implantable side, where size and power are highly limited. Planar power coils with spiral shape are optimized in geometry to provide maximum coupling coefficient, k. The data coils are designed rectangular in shape and wound across the power coils diameter to be oriented perpendicular to the power coil planes. The goal is to maximize data coils direct coupling, while minimize their cross-coupling with the power coils. The effects of coils geometry, relative distance, and misalignments on the coupling coefficients have been modeled and experimentally measured. <s> BIB003 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> D. Electromagnetic, Optical, and Body Channel <s> With the increasing number of portable and implantable personal health care devices, there is a strong demand to control their communication in a single wireless network. Recently, the IEEE 802.15 WBAN task group has discussed the combining of wearable and implantable body sensor networks (BSNs) [1], but no real chip implementation has been reported. In this paper, the implementation of a unified BSN as shown in Fig. 24.9.1 is described.. The unified BSN combines low-power body-channel communication (BCC) [2] and versatile medical implant communication service (MICS) [3] using a network controller located on the human body. This unified BSN has 2 main advantages over the conventional BSNs. First, the MICS band antenna shared with the BCC electrode can be attached directly to human skin to shorten the communication distances among the controller and implanted radios, relaxing their sensitivity and selectivity requirements. Second, due to low path loss of the human body channel, low-power communication is possible among the wearable devices [4]. In addition, the on-body sensors do not need external antennas because the bio-signal sensing electrode functions as the interface for data transmission. <s> BIB004 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> D. Electromagnetic, Optical, and Body Channel <s> Acquiring neural signals at high spatial and temporal resolution directly from brain microcircuits and decoding their activity to interpret commands and/or prior planning activity, such as motion of an arm or a leg, is a prime goal of modern neurotechnology. Its practical aims include assistive devices for subjects whose normal neural information pathways are not functioning due to physical damage or disease. On the fundamental side, researchers are striving to decipher the code of multiple neural microcircuits which collectively make up nature's amazing computing machine, the brain. By implanting biocompatible neural sensor probes directly into the brain, in the form of microelectrode arrays, it is now possible to extract information from interacting populations of neural cells with spatial and temporal resolution at the single cell level. With parallel advances in application of statistical and mathematical techniques tools for deciphering the neural code, extracted populations or correlated neurons, significant understanding has been achieved of those brain commands that control, e.g., the motion of an arm in a primate (monkey or a human subject). These developments are accelerating the work on neural prosthetics where brain derived signals may be employed to bypass, e.g., an injured spinal cord. One key element in achieving the goals for practical and versatile neural prostheses is the development of fully implantable wireless microelectronic ?brain-interfaces? within the body, a point of special emphasis of this paper. <s> BIB005 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> D. Electromagnetic, Optical, and Body Channel <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> BIB006 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> D. Electromagnetic, Optical, and Body Channel <s> Improving communication with implantable systems remains an important topic of research due to the limitations in power dissipation and the simultaneous need for high data rates. Neural recorders generate well above 10Mb/s data [1], which needs to be transmitted out-of-body. Multichannel stimulators, such as epiretinal implants, need control data in the range of several Mb/s for the into-body link [2]. Up to now, RF has been the dominant form of transcutaneous communication. One major issue is the crosstalk between the RF power link and the data signal. Therefore, dual-band telemetry is common in order to spectrally separate the data and power transfer. The standards reach from UWB transmitters [1], MICS band [3], to customized [2] RF receivers, often using sophisticated digital encoding. Also, orthogonal alignment has been used for the data and power coils to suppress crosstalk. Such RF communication needs a 2nd pair of coils, and the state-of-the-art power consumption ranges from 1.5 to 3nJ/b at rates of 120kb/s to 2.5Mb/s [3]. <s> BIB007 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> D. Electromagnetic, Optical, and Body Channel <s> This paper introduces a new modulation technique, called pulse harmonic modulation (PHM), for wideband, low power data transmission across inductive telemetry links that operate in the near-field domain. The use of sharp and narrow pulses, similar to impulse-radio ultrawideband (IR-UWB) in the far-field domain, leads to significant reduction in the transmitter power consumption. However unlike IR-UWB, where all pulses are the same, in PHM each bit consists of a pattern of pulses with specific time delays and amplitudes, which minimize the intersymbol interference (ISI) across the receiver coil. This helps achieve a high data rate without reducing the inductive link quality factor and selectivity, which are necessary to block interferers. The received signal consists of an oscillation pattern that is amplitude modulated by the amplitude and timing of the successively transmitted pulses to facilitate data demodulation with low bit-error rate (BER). The main application of the PHM is expected to be in the neuroprostheses, such as brain-computer interfaces (BCIs) or cochlear/retinal implants, which need to transfer large volumes of data across the skin. It may also be used in short-range proximity-based digital communications with high-throughput wireless devices. This paper describes the PHM theoretical foundation and demonstrates its operation with a proof-of-concept prototype setup, which achieves a data rate of 5.2 Mbps at 1 cm coil separation with a BER of 10- 6 . <s> BIB008
Even though the majority of the transcutaneous wireless communication links utilize RF EM fields, researchers have begun using optical links for this purpose as well as the human body as the transmission channel to address some of the EM limitations. Optical links have the potential to reach bandwidths well above that of the current RF links, and they do not suffer from power carrier interference BIB005 . However, lasers and LEDs that can offer such a wide bandwidth are not yet as power efficient as their RF counterparts, and they can be very sensitive to misalignments. Light scattering and absorption in the tissue are two major problems that limit the use of optical links to areas that Tx and Rx are very close or the tissue is transparent such as the cornea, lens, and vitreous humor in retinal implants BIB002 , BIB007 . Using the human body as the communication channel has been tried in 80's, and gained more attention in recent years BIB001 , BIB004 . Using lower carrier frequencies within 30~70 MHz results in power saving, and the electrical signal attenuation Fig. 3 . PHM conceptual waveforms including their key parameters BIB008 . (a) (b) Fig. 2. (a) A pair of planar spiral coils (PSC) with relatively strong coupling can be used for transcutaneous power transfer. A second pair of coils can be wound symmetrically across the PSC pair for data transfer such that their fluxes are orthogonal and minimize the power carrier interference when the coils are perfectly aligned. (b) It is possible to use other symmetrical geometries, such as figure-8 coils, to attenuate the effects of external common mode magnetic fields BIB006 , BIB003 . through the body is less than the EM fields. In this method electrodes are used instead of antennas, which are smaller but not comfortable on the skin. Nonetheless, body channel seems to be a good option when there is a need for communication between two or more implantable devices.