Time synchronization is one of the important services in wireless sensor networks (WSN), and Bluetooth low energy (BLE) is one of the wireless protocols that has drawn a lot of attention recently, with applications in Internet of Things (IoT) and sensor fusion. Although, nonconnectable beacons are the most energy-efficient advertising mode of BLE, no synchronization service is defined for them in the BLE standard. Here, we presentBlueSync, a BLE compatible time synchronization protocol, which uses beacons for data transfer. As part of this study, we investigate the tradeoffs between energy efficiency, synchronization error, and speed by considering different drift-management methods and various synchronization packet configurations. Additionally, we propose a Discrete Adjustment technique that can improve energy efficiency in calculating timer ticks updates up to$15\times $without sacrificing accuracy.BlueSyncis implemented on two commercial BLE system on chips and tested in 10-min long sessions without any resynchronization. Experimental results show that depending on the settings,BlueSynccan achieve average synchronization errors as low as 320 ns per 60 s (single hop) and is the most accurate time synchronization reported on BLE to date.

Many wireless sensor networks benefit from one type of time synchronization protocols. However, due to different crystal oscillators and clock sources in the nodes, even with drift-management techniques, synchronization error starts increasing fast after a few to tens of seconds. To keep the error low in minute-long sessions, typically the master transmits packets periodically to reset the error. These extra packets increase power consumption of all nodes especially in long sessions. Here, we propose AdaptSync that uses the timing/error information of a short period of time at the beginning of a session to reduce the error in the rest of the session independent of the master. Implementation steps are discussed and tested on sensor nodes that use Bluetooth as the wireless link. Experimental results show that in 10-minute long sessions, average synchronization error is reduced 7x compared to normal synchronization.

Many wireless sensor networks rely on synchronization protocols to correlate measurements on different nodes. In order to save power in these applications, we consider two stages for the nodes as synchronization timeslot and the synchronous task that can run on different clock frequencies. Implemented on a Bluetooth Low Energy (BLE) chip, decreasing the clock frequency from 16 MHz to 1 MHz results in 2x and 7.5x reduction in crystal oscillator and timer run currents, respectively. Experimental results show that when the synchronization timeslot runs on the 16 MHz clock and then the clock frequency reduces to 1 MHz for executing the task, synchronization accuracies are similar to the case where only the high frequency clock is used.

Lithographically defined microelectrode arrays now permit high-density recording and stimulation in the brain and are facilitating new insights into the organization and function of the central nervous system. They will soon allow more detailed mapping of neural structures than has ever before been possible, and capabilities for highly localized drug-delivery are being added for treating disorders such as severe epilepsy. For chronic neuroscience and neuroprosthesis applications, the arrays are being used in implantable microsystems that provide embedded signal processing and wireless data transmission to the outside world. A 64-channel microsystem amplifies the neural signals by 60 dB with a user-programmable bandwidth and an input-referred noise level of 8$\mu{\hbox{V}}_{\rm rms}$before processing the signals digitally. The channels can be scanned at a rate of 62.5 kS/s, and signals above a user-specified biphasic threshold are transmitted wirelessly to the external world at 2 Mbps. Individual channels can also be digitized and viewed externally at high resolution to examine spike waveforms. The microsystem dissipates 14.14 mW from 1.8 V and measures 1.4$\times$1.55 cm$^2$.

This paper describes the development of a high-density electronic interface to the central nervous system. Silicon micromachined electrode arrays now permit the long-term monitoring of neural activity in vivo as well as the insertion of electronic signals into neural networks at the cellular level. Efforts to understand and engineer the biology of the implant/tissue interface are also underway. These electrode arrays are facilitating significant advances in our understanding of the nervous system, and merged with on-chip circuitry, signal processing, microfluidics, and wireless interfaces, they are forming the basis for a family of neural prostheses for the possible treatment of disorders such as blindness, deafness, paralysis, severe epilepsy, and Parkinson's disease.

This paper presents research at The University of Michigan on micromachined capacitive silicon accelerometers and gyroscopes with their interface electronics to satisfy the requirements for inertial navigation applications. The accelerometer systems developed employ in-plane (lateral), out-of-plane (z-axis), and single-chip 3-axis sensors with the interface electronics. The interface electronics forms a second-order electromechanical sigma-delta modulator together with the sensor and the system can be operated in both open and closed-loop. These devices can achieve better than 2 /spl mu/g//spl radic/Hz resolution with a range of /spl plusmn/1.35 g. The single-crystal silicon ring gyroscope provides 132 mV/deg/sec sensitivity and 10 deg/hour resolution.

Micromachined microsystems and Micro Electro Mechanical Systems (MEMS) have made possible the development of highly accurate and portable sensors and instrument for a variety of applications in the health care, industrial, consumer products, avionics, and defense. Design of low-power circuits for these applications, and use of micromachined sensors and actuators in combination with integrated circuits to implement even lower power microinstruments has now become possible and the focus of attention. This paper reviews the state of the art in the development of micromachined microsystems and MEMS, discusses low-power design approaches for microsystems, and reviews some recent development in power generation and energy harvesting from the environment.

An open-architecture microsystem that can be populated with a variety of sensors and actuators is described. The microsystem is designed for low-power wireless applications where small size and high sensor accuracy are important. It consists of an in-module microcontroller connected to multiple front-end transducers through an intramodule sensor bus. An external interface allows internally processed data to be output through either a hard-wired input/output port or a radio-frequency transmitter. The present microsystem is configured for environmental monitoring and measured temperature, barometric pressure, relative humidity, and acceleration/vibration. It occupies less than 10 cc, consumes an average of 530 /spl mu/W from 6 V, and transmits data up to 50 m. System features such as active power management, the intramodule sensor bus, generic bus interface circuitry, and in-module sensor compensation based on bivariate polynomials are discussed.

This paper presents a review of silicon micromachined accelerometers and gyroscopes. Following a brief introduction to their operating principles and specifications, various device structures, fabrication, technologies, device designs, packaging, and interface electronics issues, along with the present status in the commercialization of micromachined inertial sensors, are discussed. Inertial sensors have seen a steady improvement in their performance, and today, microaccelerometers can resolve accelerations in the micro-g range, while the performance of gyroscopes has improved by a factor of 10/spl times/ every two years during the past eight years. This impressive drive to higher performance, lower cost, greater functionality, higher levels of integration, and higher volume will continue as new fabrication, circuit, and packaging techniques are developed to meet the ever increasing demand for inertial sensors.