Eniko T Enikov

Abstract:

Novel prognostic sensors and reasoner algorithms are the core technology for detecting defects caused by accumulation of fatigue damage in electrical and mechanical systems over time. However, serious technical challenges to implementing a general health management strategy for helicopters and military aircraft still exist. For example, severe heat and vibration make it difficult to distinguish fault signatures from environmental noise. Moreover, bearing loads are very dynamic, making it difficult to distinguish subtle wear-out signatures from normal acoustic patterns. Detection can be improved by increasing the number of sensor locations, but this option is unattractive from the standpoint of added cost, weight, and data overhead of such a system. © 2011 IEEE.

Abstract:

This article describes the design of a novel trans-scleral tonometer based on the use of multiple force sensors forming a mechanical stiffness sensor. The approach is akin to an instrumented form of digital palpation tonometry in which manual paplation is used to infer the stiffness, and hence, the intraocular pressure of the eye. Force indentation data from multiple probes has been shown to correlate with the intraocular pressure (IOP) using encucleated porcine eyes. A noticeable amount of hysteresis has been observed during indentations at higher rate. Analysis of the experimental data indicates that stress relaxation (accommodation) in the visco-elastic corneo-scleral shell is the primary factor of the observed hysteresis. Further tests under different indentation rates show that the novel tonometer is expected to have an accuracy of ±1 mmHg when the indentation rate is kept below 0.5 mm/sec for pressure range of 10-35 mmHg. Using a calibrated finite element model of the measurement, the effect of lateral and angular misalignment is also examined. The results show that the position and orientation of the tactile sensor has to be controlled to within ±1 mm and ±3° in order to achieve a target accuracy of ±1 mmHg. © 2012 Society for Experimental Mechanics.

Abstract:

A novel stress-insensitive piezoresistor in the shape of an annulus has been developed to be used in conjunction with a piezoresistive bridge for temperature-compensated force measurements. Under uniform stress conditions, the annular resistor shows near-zero stress sensitivity and a linear response to temperature excitation within test conditions of 24-34 °C. Annular resistors were placed in close proximity to stress-sensitive elements in order to detect local temperature fluctuations. Experiments evaluating the performance of the temperature compensator while testing force sensitivity showed a thermal rejection ratio of 37.2 dB and near elimination of low-frequency noise (drift) below 0.07 Hz. Potential applications of this annular resistor include use in multi-axis force sensors for force feedback microassembly, improvements in the simplicity and robustness of high precision microgram sensitive balances, higher accuracy for silicon diaphragm-based pressure sensors and simple temperature compensation for AFM cantilevers. © 2011 IOP Publishing Ltd.

Abstract:

Combined thermionic emission and tunneling of hot elec- Trons (thermo-tunneling) has emerged as a potential new solid- state cooling technology. Practical implementation of thermo- Tunneling, however, requires the formation of a nanometer-sized gap spanning macroscopically significant surfaces. Thermo- Tunneling is a term used to describe combined emission of hot electrons (thermionic emission) and tunneling of electrons through a narrow potential barrier between two surfaces (field emission). Thermo-tunneling of hot electrons across a few- nanometer gap has application to vacuum electronics, flat panel displays, and holds great potential in thermo-electric cooling and energy generation. Development of new thermo-tunneling applications requires creation of a stable nanometer gap be- Tween two surfaces. This presentation is focused on our effort to investigate the stability of the the thin flexible structure under electrostatic and lorenz forces opposing each other. In this pre- sentation, we report the result of numerical simulation with some mathematical simplifications. The mathematical model used for the numerical simulation is well studied in the literature. Us- ing forth-order partial differential beam equation, we studied the steady state solutions of the thermo-tunneling beam model using Galerkin method.Essential output parameters of the model in- clude a central contact area measured by its length (delta) and the thermo-tunneling current. Both parameters are determined as a function of the externally applied external potential and magnetic field. Numerical solutions of the model show two possi- ble operating modes: (1) symmetric deformation with negligibly small current; and (2) asymmetric mode where the B-field con- Trols the current and contact area. Under practical values for the externally applied magnetic and electric fields, it has been shown that the second mode is only possible for electrode with very low work functions, e.g. below 0.5 eV. Therefore, novel materials such as Diamond-like carbon films are likely to be essential in thermo-tunneling applications. Copyright © 2012 by ASME.