An overview of the recent wideband transcutaneous wireless communication techniques <s> A. Reactive vs. Radiative <s> A 402-405 MHz MICS band transceiver has been developed for implantable medical applications. The transceiver offers exceptionally low power consumption whilst providing a high data rate. The circuit features a unique ultra low power wakeup system enabling an average sleep current of less than 250 nA. The transmit and receive current is less than 5 mA when operating at a data rate of up to 800 kbps. System integration is high and only 3 external components (crystal and 2 decoupling capacitors) and a matching network are required. The transceiver can also operate in the 433 MHz ISM band. The key system design features and performance of this transceiver are presented in this paper. <s> BIB001 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> A. Reactive vs. Radiative <s> In this paper, an overview of near field UHF RFID is presented. This technology recently received attention because of its possible use for item-level tagging where LF/HF RFID has traditionally been used. We review the relevant literature, discuss basic theory of near and far field antenna coupling in application to RFID, and present some experimental measurements. <s> BIB002 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> A. Reactive vs. Radiative <s> Printed spiral coils (PSCs) are viable candidates for near-field wireless power transmission to the next generation of high-performance neuroprosthetic devices with extreme size constraints, which will target intraocular and intracranial spaces. Optimizing the PSC geometries to maximize the power transfer efficiency of the wireless link is imperative to reduce the size of the external energy source, heating of the tissue, and interference with other devices. Implantable devices need to be hermetically sealed in biocompatible materials and placed in a conductive environment with high permittivity (tissue), which can affect the PSC characteristics. We have constructed a detailed model that includes the effects of the surrounding environment on the PSC parasitic components and eventually on the power transfer efficiency. We have combined this model with an iterative design method that starts with a set of realistic design constraints and ends with the optimal PSC geometries. We applied our design methodology to optimize the wireless link of a 1-cm 2 implantable device example, operating at 13.56 MHz. Measurement results showed that optimized PSC pairs, coated with 0.3 mm of silicone, achieved 72.2%, 51.8%, and 30.8% efficiencies at a face-to-face relative distance of 10 mm in air, saline, and muscle, respectively. The PSC, which was optimized for air, could only bear 40.8% and 21.8% efficiencies in saline and muscle, respectively, showing that by including the PSC tissue environment in the design process the result can be more than a 9% improvement in the power transfer efficiency. <s> BIB003 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> A. Reactive vs. Radiative <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> BIB004 </s> An overview of the recent wideband transcutaneous wireless communication techniques <s> A. Reactive vs. Radiative <s> We have developed a miniature telemetry system that captures neural, EMG, and acceleration signals from a freely moving insect and transmits the data wirelessly to a remote digital receiver. The system is based on a custom low-power integrated circuit that amplifies and digitizes four biopotential signals as well as three acceleration signals from an off-chip MEMS accelerometer, and transmits this information over a wireless 920-MHz telemetry link. The unit weighs 0.79 g and runs for two hours on two small batteries. We have used this system to monitor neural and EMG signals in jumping and flying locusts. <s> BIB005
The area around any radio frequency transmitter can be divided into three regions: near field (0~λ), transition zone (λ~2λ), and far field (2λ~∞), where λ is the carrier signal wavelength. Considering limitations in the choice of carrier frequencies for transcutaneous communications (< 1 GHz, λ > 30 cm) and the proximity of the transmitter (Tx) and receiver (Rx) in these applications, it can be concluded that almost all transcutaneous communications are within near field. In this region the field decays with distance, d, very rapidly at a rate of 1/d 3 and the relationship between electric and magnetic fields are quite complicated BIB002 ,  . When the coils and antennas are much smaller than λ, interactions between coils and antennas in the near field are further divided into reactive (0~λ/2π) and radiative (λ/2π ~λ) regions. In the reactive region, energy is stored in the field very close to the antenna and it can return back to the antenna in a regenerative fashion without radiation if it is not absorbed by the Rx antenna or the surrounding medium. Interactions between the Tx and Rx antennas in this region are modeled and analyzed in the form of loosely coupled coils that constitute a transformer or parallel plate capacitors. Coils' mutual coupling in this case is highly dependent on their geometries, relative distance, and orientation. The coils' self resonance frequency (SRF) often limits the choice of carrier frequencies to 0.1 ~ 50 MHz. Since tissue is quite transparent in this frequency range, the loss mechanisms are mainly due to the coils' parasitic components BIB003 . In the radiative near field region, there is only radiant energy and no storage, although the relationship between magnetic and electric field components is quite different from the far field. Various Industrial-Scientific-Medical (ISM) bands have been employed in this region for body area networks (BAN) or for recording from freely behaving animals when it is possible to keep the antenna outside the subject's body BIB004 , BIB005 . However, for fully implanted devices, the band that is mostly used in the radiative near field region is the Medical Implant Communication Service (MICS), which uses frequencies between 402 and 405 MHz with less than 300 kHz bandwidth per channel. The main advantage of the MICS, which offers a range of up to 2 m, over inductive coupling is eliminating the need for the external transceiver to touch the patient's skin. However, the highest reported data rates of 800 kBps are neither sufficient for neuroprosthetic devices nor iBCIs BIB001 .