Wireless sub-mm sized distributed brain implants have been proposed as the next frontier of Brain-Machine Interface (BMI) design to achieve untethered, high-density neural recording and stimulation. Simultaneously improving the wireless power transfer (WPT) efficiency and reducing the specific absorption rate (SAR) will be crucial for its clinical success. Towards these goals, we present an EM simulation method, a lumped equivalent circuit model, and a theoretical analysis to accurately predict the power delivered to the recording/ stimulating nodes, as well as the power dissipated in biological tissues and all other lossy elements within the system. This comprehensive framework also explains how increasing the distance between the transmit coil and the scalp can beneficially reduce the SAR without undermining the WPT efficiency. This work presents a rigorous prediction technique for transmission loss and tissue heating towards performance optimization.

A novel Brain-Machine Interface (BMI) system based on a distributed network of implantable wireless sensors was proposed. Small CMOS "Neurograin" chips (0.5x0.5 mm2) with on-chip antenna are designed to harvest near-field RF energy at ~1 GHz, and backscatter 10 Mbps BPSK modulated data asynchronously and periodically. A "Skinpatch" software-defined radio (SDR) receiver is realized on a commercial USRP running GNU Radio programs. It down-converts the reflected waves from the Neurograins and performs data recovery. In this BMI prototype demonstration, 32 Neurograins will be wirelessly powered, while a Skinpatch USRP will recover their backscattered packets in real-time.

A 100-ch fully head-implantable wireless broadband neural recording system was developed. It features 100 parallel wideband (0.1Hz ~ 7.8 kHz) neural recording channels, a medical grade 200mAh Li-ion battery recharged inductively at 2 MHz, and data telemetry using both 3.2/3.8GHz FSK wireless and 850nm IR laser data link. All active electronics are hermetically sealed in a titanium enclosure with a sapphire window. Custom 100 individual hermetic feedthroughs enable connection to the microelectrode intracortical array. This wireless implant has been validated both on-bench and in freely moving pig and monkey models.

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.

The first blue/green laser diode demonstrations reported in the summer of 1991 presented a hope that viable light-emitting devices based on the wide-bandgap II-VI compound were truly possible. In this paper we place those developments into the context of the 30-year research effort which has opened the possibility for the new laser diode, LED, and display devices operating in the short visible wavelengths. Active research interests worldwide have led to rapid progress in the field, culminating in the recent demonstration of room-temperature continuous wave diode lasers.>