Srihari Rajgopal

Personal Navigation via High-Resolution Gait-Corrected Inertial Measurement Units

In this paper, a personal micronavigation system that uses high-resolution gait-corrected inertial measurement units is presented. The goal of this paper is to develop a navigation system that uses secondary inertial variables, such as velocity, to enable long-term precise navigation in the absence of Global Positioning System (GPS) and beacon signals. In this scheme, measured zero-velocity duration from the ground reaction sensors is used to reset the accumulated integration errors from accelerometers and gyroscopes in position calculation. With the described system, an average position error of 4 m is achieved at the end of half-hour walks.

Personal navigation via shoe mounted inertial measurement units

We are developing a personal micronavigation system that uses high-resolution gait-corrected inertial measurement units. The goal of this project is to develop a navigation system that use secondary inertial variables, such as velocity, to enable long-term precise navigation in the absence of Global Positioning System (GPS) and beacon signals. In this scheme, measured zero velocity durations from the ground reaction sensors are used to reset the accumulated integration errors from the accelerometers and gyroscopes in position calculation. We achieved an average position error of 4 meters at the end of half-hour walks.

Stainless steel capacitive pressure sensor for high pressure and corrosive media applications

This paper reports an assembly-type, stainless steel (SS) capacitive gage pressure sensor comprising three key elements: two SS dies and a commercial SS Swagelok fitting that also serves as the package. The sensor is realized by placing a patterned silicon dioxide film deposited on the thinner of the two SS dies (diaphragm die) against a silicon nitride film deposited on the other SS die (backing plate) and housing the combination in a Swagelok fitting. Pressure measurements up to 1500 psi have been demonstrated using corrosive and benign media. Tested media include 45% wt. potassium hydroxide (KOH), 25% wt. tetramethylammonium hydroxide (TMAH), deionized (DI) water, and nitrogen gas. Extended-duration tests with a sensor subjected to KOH solution for 30 days demonstrate excellent repeatability. Random pressure fluctuation tests over a 15-day period also demonstrate good repeatability.

A Silicon Carbide Accelerometer for Extreme Environment Applications

A polycrystalline silicon carbide (poly-SiC) surface-micromachined capacitive accelerometer is designed, fabricated and tested. Leveraging the superior thermo-mechanical and chemical resistance properties of SiC, the device is a first step toward cost-effective implementation of a new class of extreme environment accelerometers, for example for high temperature vibration and shock measurements, even thought this initial work is at room temperature. The accelerometer described herein is designed for a range of 5000 g and a bandwidth of 18 kHz, specifications consistent with commercially available piezoelectric devices for high-level mechanical impact measurements. Test results demonstrate the sensor achieving a resolution of 350 mg/√Hz at 1kHz with a sensitivity of 12 μV/g and a bandwidth of 10 kHz at room temperature.

Dual-gate silicon carbide (SiC) lateral nanoelectromechanical switches

We present demonstration and experimental results of four-terminal nanoscale electromechanical switches with a novel dual-gate design in a lateral configuration based on polycrystalline silicon carbide (poly-SiC) nanocantilevers. The switches operate at both room temperature and high temperature up to T 500oC in ambient air with enhanced control over the distributed electrostatic actuation force, and also enable recovery from stiction at contact. We have experimentally demonstrated multiple switching cycles of these nanomechanical switches with different actuation control schemes, and active release from stiction by exploiting a repulsive mechanism. In combination with modeling of cantilever deflection, the experiments help reveal the coupled electromechanical behavior of the device when making contact during switching operations, and suggest possible correlation between the switch degradation observed over cycles and the elastic deformation of nanocantilevers.

3-D microfabricated electrodes for targeted deep brain stimulation

This work presents a novel 4-sided, 16-channel deep brain stimulation electrode with a custom flexible high-density lead for connectivity with pulse generation electronics. The 3-dimensional electrode enables steering the current field circumferentially. The electrode is fabricated in pieces by micromachining and microfabrication techniques; the pieces are then assembled mechanically to form the electrode, after which the lead is connected. The electrode is modeled by finite element analysis and tested in vitro to validate the design concept, i.e., targeted stimulation. Simulation and experimental results for a targeted stimulation show close agreement. With a symmetric bipolar stimulation configuration, within a 3 mm radius, the electric potential in front of the activated side is at least 3.6 times larger than that on the corresponding two adjacent, not-activated sides, and 9 times larger than the corresponding opposite, not-activated side.

Micro flow sensor using polycrystalline silicon carbide

A thermal flow sensor has been fabricated and characterized, consisting of a center resistive heater surrounded by two upstream and one downstream temperature sensing resistors. The heater and temperature sensing resistors are fabricated from nitrogen-doped(n-type) polycrystalline silicon carbide(poly-SiC) deposited by LPCVD(low pressure chemical vapor deposition) on LPCVD silicon nitride films on a Si substrate. Cavities were etched into the Si substrate from the front side to create suspended silicon nitride membranes carrying the poly-SiC elements. One upstream sensor is located from the heater and has a sensitivity of /sccm with rise time in a dynamic range of 1000 sccm. N-type poly-SiC has a linear negative temperature coefficient and a TCR(temperature coefficient of resistance) of from room temperature to .

Nanomechanical non-volatile memory for computing at extreme

A computing platform that works under extreme conditions (> 250 °C and at radiation > 1 Mrad) can be attractive in a number of important application areas, including automotive, space and avionics. Nanoelectromechanical systems (NEMS) switches have emerged as promising candidates for computing in harsh environment. Designing reliable memory specifically non-volatile memory is a major challenge for these computing systems. In this paper, we propose a novel non-volatile memory (NVM) design for reliable operation in extreme environment using NEMS structure. It exploits a common failure mode in these devices, namely stiction. Unlike traditional charge-based memories, it relies on the mechanical state of a NEMS switch as information carrier. We analyze device and circuit-level design issues to enable robust NVM array implementation with NEMS devices.

High-temperature (>500°C) reconfigurable computing using silicon carbide NEMS switches

Many industrial systems, sensors and advanced propulsion systems demand electronics capable of functioning at high ambient temperature in the range of 500–600°C. Conventional Si-based electronics fail to work reliably at such high temperature ranges. In this paper we propose, for the first time, a high-temperature reconfigurable computing platform capable of operating at temperature of 500°C or higher. Such a platform is also amenable for reliable operation in high-radiation environment. The hardware reconfigurable platform follows the interleaved architecture of conventional Field Programmable Gate Array (FPGA) and provides the usual benefits of lower design cost and time. However, high-temperature operation is enabled by choice of a special device material, namely silicon carbide (SiC), and a special switch structure, namely Nano-Electro-Mechanical-System (NEMS) switch. While SiC provides excellent mechanical and chemical properties suitable for operation at extreme harsh environment, NEMS switch provides low-voltage operation, ultra-low leakage and radiation hardness. We propose a novel multi-layer NEMS switch structure and efficient design of each building block of FPGA using nanoscale SiC NEMS switches. Using measured switch parameters from a number of SiC NEMS switches we fabricated, we compare the power, performance and area of an all-mechanical FPGA with alternative implementations for several benchmark circuits.

Silicon carbide pressure sensor for high temperature and high pressure applications: Influence of substrate material on performance

We have studied the effect of substrate material related to thermal mismatch for silicon carbide (SiC) diaphragm-based capacitive pressure sensors. Two sets of devices, with identical dimensions and fabrication processes were made on poly-SiC and Si substrates. Designed for a maximum pressure of 4.83 MPa (700 psi), these devices were operated in small-deflection mode and tested at room temperature and 500oC. At room temperature, the SiC- and Si-substrate devices showed sensitivities of 6.5E-04 and 6.1E-04 fF/Pa, nonlinearities of 5.0% and 3.9%, and resolutions of 0.2% and 0.3%, respectively. At 500oC, the SiC- and Si-substrate devices showed sensitivities of 1.2E-02 and 1.1E-02 fF/Pa, nonlinearities of 2.6% and 3.8%, and resolutions of 0.5% and 1.8%, respectively. For the chosen design parameters, the results show little influence of substrate material on sensor performance.