Todd Kaiser

Passive Telemetric Readout System

A technique for remote query monitoring of environmental parameters such as pressure, humidity, complex permittivity, temperature, strain, and gases such as carbon dioxide, oxygen, and ammonia is presented. Resonant peak passive telemetry is used for wireless remote monitoring. The resonance frequency of an inductor-capacitor sensor circuit changes with the surrounding environmental parameter, and a detector circuitry, which employs a loop antenna, is used to remotely identify the resonance frequency. Mutual coupling between the antenna and the sensor inductor enables wireless monitoring. Various detection techniques available for monitoring the sensor resonance frequency are examined, and a new method is presented for automated and continuous wireless detection of sensor resonance frequency. Results are presented for different sensor resonance frequencies using various sensor capacitance values. The designed system can effectively detect sensor resonance frequency variation in the range of 20 kHz-10 MHz with the highest achievable resolution of 0.01 MHz. Sensor resonance frequency changes that occur faster than 1 s cannot be detected. The automated continuous wireless remote sensor platform design provides significant advantage over past systems, and the entire design is simple, easy to use, and widely applicable for in vivo, in vitro, and in situ monitoring

Silicon nitride biaxial pointing mirrors with stiffening ribs

Gold-coated silicon nitride mirrors designed for two orthogonal rotations were fabricated. The devices were patterned out of nitride using surface micromachining techniques, and then released by a sacrificial oxide etch and bulk etching the silicon substrate. Vertical nitride ribs were used to stiffen the members and reduce the curvature of the mirrored surfaces due to internal stress in the nitride and the metal layer. This was accomplished by initially etching the silicon substrate to form a mold that was filled with nitride to create a stiffening lattice-work to support the mirrored section. Mirror diameters ranging from 100 mm to 500 mm have been fabricated, with electrostatic actuation used to achieve over four degrees of tilt for each axis.

Ionizing Radiation Detector for Environmental Awareness in FPGA-Based Flight Computers

Ionizing radiation has a detrimental effect on digital electronics which need to operate in extraterrestrial environments. Modern reconfigurable digital fabrics are enabling new architectures for flight computers, which can exploit environmental awareness to increase their fault tolerance. In this paper, we present the design, modeling, and characterization of a radiation sensor which can be coupled with a reprogrammable hardware fabric to provide spatial information about radiation events that can cause logical faults. The sensor uses a wide area PN junction as its fundamental sensing element. As radiation passes through the sensor, electron hole pairs are created. The internal electric field of the PN junction sweeps the charge carriers in opposite directions which are ultimately sensed by orthogonally placed electrodes on the top and bottom of the sensor. This XY grid provides the spatial location of an ionizing radiation strike, which can be fed to the coupled computer fabric for environmental awareness. A reverse bias voltage is applied to the sensor in order to fully deplete the substrate for maximum charge carrier generation. The sensor is designed to detect the spatial location of radiation strikes of energy levels, which can cause faults in commercial field programmable gate arrays substrates.

A pendulous oscillating gyroscopic accelerometer fabricated using deep-reactive ion etching

A silicon pendulous oscillating gyroscopic accelerometer (POGA) was fabricated using deep-reactive ion etching (DRIE) and silicon wafer bonding technologies. A POGA is the micromachining-compatible analog of the pendulous integrating gyroscopic accelerometer (PIGA), which is the basis of the most sensitive accelerometers demonstrated to date. Gyroscopic accelerometers rely on the principle of rebalancing an acceleration-sensing pendulous mass by means of an induced gyroscopic torque. The accelerometer is composed of three individual layers that are assembled into the final instrument. The top layer uses wafer bonding of an oxidized wafer to a handling wafer to create a silicon-on-oxide wafer pair, in which the oxide layer provides electrical isolation between the mechanical members and the handling layer. The middle layer is a two-gimbal torsionally-supported silicon structure and is in turn supported by an underlying drive/sense layer. The micromachined POGA operated according to gyroscopic accelerometer principles, having better than milligram resolution and dynamic ranges in excess of 1 g (open loop) and approximately 12 mg (closed loop).

Increasing Radiation Tolerance of Field-Programmable- Gate-Array-Based Computers Through Redundancy and Environmental Awareness

Radiation-tolerant computing is of great importance to the aerospace community because future missions demand more computational power. Of special interest to the aerospace community are flight computers implemented on static random-access-memory-based field-programmable gate arrays. Such computer systems allow the in-flight reconfiguration of hardware that enables the practical deployment of truly reconfigurable computers. However, commercial static random-access-memory-based field-programmable gate arrays are uniquely susceptible to ionizing radiation. This paper introduces a computer architecture for static random-access-memory-based field-programmable gate arrays that resists failures caused by ionizing radiation. The approach extends the widely accepted fault mitigation practice of triple modular redundancy and configuration memory scrubbing by adding spare circuitry and environmental awareness through an ionizing radiation sensor. This paper describes the design of the system in addition to a theore...

A Wireless Sensor Interrogator Design for Passive Resonant Frequency Sensors Using Frequency Modulation Spectroscopy

This paper presents a wireless sensor interrogator design based on frequency modulation spectroscopy (FMS). The wireless sensor interrogator is capable of wireless detection and tracking of the resonant frequency of a passive inductor-capacitor circuit. The wireless interrogator has been successfully simulated and implemented in hardware. Compared to other wireless sensor interrogation techniques, FMS enables not only detection, but also tracking of the sensors changing resonant frequency over time. The theory of FMS is discussed briefly, followed by the results from both the simulation and the hardware implementation. The hardware implementation of the wireless sensor interrogator is able to lock onto and track the resonant frequency of a passive inductor-capacitor resonant circuit.

Large area molded silicon nitride micro mirrors

Large area molded torsional micromirrors have been fabricated from thin films of low-pressure chemical vapor deposition silicon nitride. Optical surfaces as large as 400 /spl mu/m in diameter with surface deviations less than 0.33 /spl mu/m have been fabricated from 1.5-/spl mu/m-thick layers of silicon nitride. Surface flatness was achieved by molding latticed silicon nitride fins to the backside of the mirrors. Fins as deep as 28 /spl mu/m were constructed by deep reactive ion etching bulk silicon to produce molds for the fins prior to silicon nitride deposition. Mirrors with fins were shown to be insensitive to temperature effects within the range of 50-120 /spl deg/C. An optical switch with insertion loss less than 2 dB was constructed with the mirrors, demonstrating their potential as switch elements in optical systems.

Comparison of xenon lamp-based and led-based solar simulators

Rapid advances in high intensity light emitting diodes (LEDs) have provided sufficient tools to design LED solar simulators to accurately mimic the sun. LEDs offer numerous advantages over lamp-based technology currently used. However, these advantages have not been harnessed because of limitations in creating a solar simulator with the highest rating (AAA) for spectral match, temporal stability, and light uniformity. Oriels VeraSol is one of the first LED, triple A solar simulators. The VeraSol-LED was compared to the equally rated Oriel Sol3A-xenon lamp solar simulator by measuring the current-voltage (I-V) response and spectral response (SR) for a variety of solar cells. Both simulators effectively mimic the sun; however, the results demonstrate the LED-based simulator produced a more stable, flexible, and accurate match to AM1.5G than the xenon lamp-based simulator with similar marks in the quality of PV cell response.

Position sensitive radiation detector integrated with an FPGA for radiation tolerant computing

A position sensitive radiation sensor was modeled, developed and fabricated then interfaced with a field programmable gate array (FPGA) to create a radiation hardened computing platform. The system exploits environmental information from the sensor in order to determine regions within the FPGA that may have been affected by radiation. The spatial radiation sensor provides the computer system with the location of radiation strikes. This information is used by the computer system to avoid and repair effected circuits on the programmable fabric. By giving the recovery circuitry insight into the location where a fault may have occurred, the latency between detection of a fault and repair can be reduced. This provides an additional level of reliability by more efficiently detecting and correcting faults in SRAM-based FPGAs faults compared to the traditional voting and sequential search approaches.

Experimental Conformation of Ionizing Sensing for Space Radiation Environmental Awareness

A prototype system has demonstrated the capability to use a custom-designed multi-channel sensor to monitor high energy radiation strikes by coupling the silicon sensing elements with a radiation tolerant computer system. The computer system uses triple modular redundant soft processors and custom signal conditioning circuitry to monitor single event effects caused by high energy particles passing through semiconductor materials. The operation of the system was confirmed by exciting the radiation sensing elements with high energy Krypton ions from a cyclotron and monitoring the number of current spikes generated by the generation of electron-hole pairs as the ions lose kinetic energy through collisions within the silicon lattice of the sensors.