C.L. Britton

Operation of a gated field emitter using an individual carbon nanofiber cathode

We report on the operation of an integrated gated cathode device using a single vertically aligned carbon nanofiber as the field emission element. This device is capable of operation in a moderate vacuum for extended periods of time without experiencing a degradation of performance. Less than 1% of the total emitted current is collected by the gate electrode, indicating that the emitted electron beam is highly collimated. As a consequence, this device is ideal for applications that require well-focused electron emission from a microscale structure.

Multiple-input microcantilever sensors

A surface-micromachined micro-electro-mechanical-system (MEMS) process has been used to demonstrate multiple-input chemical sensing using selectively coated cantilever arrays. Cantilever motion due to absorption-induced stress was readout using a custom-designed, eight-channel integrated circuit. Combined hydrogen and mercury vapor detection was achieved with a palm-sized, self-powered module with spread-spectrum telemetry reporting.

Datasheet Driven Silicon Carbide Power MOSFET Model

A compact model for SiC Power MOSFETs is presented. The model features a physical description of the channel current and internal capacitances and has been validated for dc, CV, and switching characteristics with measured data from a 1200-V, 20-A SiC power MOSFET in a temperature range of 25°C to 225°C. The peculiar variation of on-state resistance with temperature for SiC power MOSFETs has also been demonstrated through measurements and accounted for in the developed model. In order to improve the user experience with the model, a new datasheet driven parameter extraction strategy has been presented which requires only data available in device datasheets, to enable quick parameter extraction for off-the-shelf devices. Excellent agreement is shown between measurement and simulation using the presented model over the entire temperature range.

PHENIX inner detectors

Abstract The timing, location and particle multiplicity of a PHENIX collision are determined by the Beam–Beam Counters (BBC), the Multiplicity/Vertex Detector (MVD) and the Zero-Degree Calorimeters (ZDC). The BBCs provide both the time of interaction and position of a collision from the flight time of prompt particles. The MVD provides a measure of event particle multiplicity, collision vertex position and fluctuations in charged particle distributions. The ZDCs provide information on the most grazing collisions. A Normalization Trigger Counter (NTC) is used to obtain absolute cross-section measurements for p–p collisions. The BBC, MVD and NTC are described below.

An integrated CMOS time interval measurement system with subnanosecond resolution for the WA-98 calorimeter

The time interval measurement system of the WA-98 calorimeter is presented. This system consists of a constant fraction discriminator (CFD), a variable delay circuit, a time-to-amplitude converter (TAC), and a Wilkinson analog-to-digital converter (ADC) all realized in a 1.2-/spl mu/m N-well CMOS process. These circuits measured the time interval between a reference logic signal and a photomultiplier tube (PMT) signal that had amplitude variations of 100:1 and 10-ns rise and fall times. The system operated over the interval range from 2 ns to 200 ns with a resolution of /spl sim//spl plusmn/300 ps including all walk and jitter components. The variable delay circuit allowed the CFD output to be delayed by up to 1 /spl mu/s with a jitter component of /spl sim/0.04% of the delay setting. These circuits operated with a 5-V power supply. Although this application was in nuclear physics instrumentation, these circuits could also be useful in other scientific measurements, medical imaging, automatic test equipment, ranging systems, and industrial electronics.

A multi-channel ADC for use in the PHENIX detector

A custom CMOS analog to digital converter was designed and a prototype 8-channel ADC ASIC was fabricated in a 1.2 /spl mu/m process. The circuit uses a Wilkinson-type architecture which is suitable for use in multi-channel applications such as the PHENIX detector. The ADC design features include a differential positive-ECL input for the high speed clock and selectable control for 11 or 12-bit conversions making it suitable for use in multiple PHENIX subsystems. Circuit topologies and ASIC layout specifics, including power consumption, maximum clock speed, INL, and DNL are discussed. The ADC performed to 11-bit accuracy.

In vivo application of a minimally invasive oximetry based perfusion sensor

Pulse oximetry is an optical technique based on the differences in absorption of blood oxygenated and deoxygenated hemoglobin, which can be used for sensing blood flow in tissue. The inadequacy of current systemic blood flow measurements to detect changes in the local perfusion of transplanted and/or diseased organs has led us to develop a novel micro-sensor for this purpose. For this paper, we present in vivo results from a preliminary study performed to quantify the effectiveness and SNR of the sensor using a rat model. The results indicate that the sensor is able to detect changes in perfusion to the target organ in correlation to a standard laser-Doppler reference signal.

Monolithic circuits for the WA98 lead class calorimeter

Two monolithic circuits developed for readout of a 10000 element lead glass calorimeter are described. The first contains 8 channels with each channel comprising a charge integrating amplifier, two output amplifiers with gains of one and eight, a timing filter amplifier and a constant fraction discriminator. This IC also contains a maskable, triggerable calibration pulser and circuits needed to form 2 by 2 and 4 by 4 energy sums used to provide trigger signals. The second IC is a companion to the first and contains 16 analog memory channels with 16 cells each, eight time-to-amplitude converters and a 24-channel analog-to-digital converter. The use of the analog memories following the integration function eliminates the need for delay cables preceding it. Characterizations of prototypes are reported, and features included to ease integration of the ICs into a readout system are described.<<ETX>>

Implantable sensor for blood flow monitoring after transplant surgery

A limited number of techniques are employed in clinical medicine for regional tissue perfusion assessment. These methods are marginally effective and are not well suited for implantation due to the inability to miniaturize the associated technologies. Consequently, no standardized techniques exist for real-time, continuous monitoring of organ perfusion following transplantation. In this paper, a brief overview of the relevant clinical techniques employed for regional tissue perfusion assessment is given with particular emphasis on post-surgical monitoring of transplanted organs. The ideal characteristics for a perfusion monitoring system are discussed and the development of a new, completely implanted local tissue monitoring system is summarized. In vivo and in vitro data are presented that establish the efficacy of this new technology, which is a photonics-based sensor system uniquely suited for continuous tissue monitoring and real-time data reporting. The suitablity of this sensor technology for miniaturization, which enables implantation for monitoring localized tissue perfusion, is discussed.

Battery-powered, wireless MEMS sensors for high-sensitivity chemical and biological sensing

Researchers at Oak Ridge National Laboratory (ORNL) are developing selectively coated cantilever arrays in a surface-micromachined MEMS process for very high sensitivities in chemical and biological sensing. Toward this end, we have developed a one-dimensional (1-D) 10-element microcantilever array that we have coated with gold for mercury sensing and palladium for hydrogen sensing. Ultimately we will coat each element with a different coating. Currently, measurements have been performed using a companion analog 1.2-/spl mu/m CMOS eight channel readout chip also designed at ORNL specifically for the microcantilever arrays. In addition, we have combined our sensors with an ORNL-developed RF-telemetry chip having on-chip spread spectrum encoding and modulation circuitry to improve the robustness and security of sensor data in typical interference- and multipath-impaired environments. We have also provided for a selection of distinct spreading codes to serve groups of sensors in a common environment by the application of code-division multiple-access techniques. Our initial system is configured for use in the 915-MHz Industrial, Scientific, and Medical (ISM) band. The entire package is powered by four AA batteries.