Eniko T Enikov

Abstract:

The development of new tonometers requires laboratory tests on enucleated eyes where the intraocular pressure (IOP) is usually controlled by the use of a fluid column (manometry). This article describes a novel eye pressure regulation system for IOP tests along with a new concept of mechanical palpation tonometry. Manometry is commonly regarded as an invasive technique that can measure precisely the pressure inside the eye. It is a common laboratory technique for evaluating changes in IOP over time, and for providing reference pressure by which all other tonometers can be evaluated. In general, the system consists of a fluid column (1 % saline solution) connected via PVC tubing to a three way valve. The valve is able to connect the column branch to a syringe with a 21G needle inserted into the vitreous humor and to a pressure transducer. The syringe needle is inserted in the eye through the side, with the tip located approximately in the middle of the vitreous chamber [1]. However, this method is prone to errors due to the gelatinous and highly fibrous nature of the vitreous matter that could easily clog the syringe needle and prevent the accurate pressure control and measurement. To resolve this difficulty, we report an alternative control of the IOP through the anterior chamber of the eye. In addition to the clogging, severed blood vessels in enucleated eyes result in large rate of leakage of intraocular fluid. With these modifications in place, it was demonstrated that the pressure sensing is fast and accurate, allowing investigation of mechanical trans-scleral palpation and the development of a new concept of mechanical palpation tonometry device. The device is based on multiple probes for measuring contact forces. Experimental data from the performance of the device are presented. Copyright © 2011 by ASME.

Abstract:

This paper describes the assembly experiments with a novel miniature assembly cell for micro-electromechanical systems (MEMS). The cell utilizes a transparent electrostatic gripper and uses several disparate sensing modalities for position control: computer vision for part alignment with respect to the gripper, a fiber-coupled laser, and a position sensitive detector (PSD) for part to assembly alignment. Assembly experiments indicate that the gripping force and stage positioning accuracy are sufficient for insertion of 500μm wide parts in 550 μm wide slots etched in silicon wafers. Details on the cell operation, the control algorithm used and their limitations are also provided. Potential applications of the developed assembly cell are assembly of miniature optical systems, integration of optoelectronics, such as laser diodes with CMOS, and epitaxial lift-off (ELO) of thin films used in optoelectronic devices. Copyright © 2004 by ASME.

Abstract:

This paper presents a low-cost hands-on experiment for a classical undergraduate controls course for non-electrical engineering majors. The setup consists of a small dc electrical motor attached to one of the ends of a light rod. The motor drives a 2-in propeller and allows the rod to swing. Angular position is measured by a potentiometer attached to the pivot point. A custom-designed circuit board produces the controlled voltage input to the motor. The target board is powered and communicates with the PC through its USB port using a virtual RS-232 port. A simple MATLAB/Simulink module has been created to read the pendulum angle and send a command signal to the motor. The module is based on Real-time Windows Target software, which allows a sampling rate of up to 200 Hz. Students are able to design and test classical PID and phase lead-lag controllers, as well as modern controllers, including state-space controller design combined with feedback linearization. A semester-long series of assignments is described that can be carried out without the need for a specialized laboratory or teaching assistants. The project was tested in a classical control systems design class of senior-level mechanical engineering students. Student feedback and survey data on the effectiveness of the modules are also presented.

Abstract:

A gas or vapor compressor is one of the key components of many engineering systems, such as certain designs of vapor compression refrigeration systems, cryo-coolers, air handlers. For meso-scale systems with linear dimensions of a few centimeters, conventional designs do not work efficiently because of rather large relative tolerances, and hence these meso-scale systems require micro-fabricated components for efficient operation. This paper presents a meso-scale centrifugal compressor fabricated by photo-lithographic techniques. A preliminary design based on 1-D flow analysis using air as the working fluid shows that a 50 mm diameter centrifugal compressor with a blade height of 200 μm gives a static pressure ratio of 1.12. In this design, the impeller has 10 full blades and 10 splitter blades. Each blade has the NACA profile 9510 with the maximum camber at 50% of the chord. These impeller blades have exit angles 35° with exit flow angles of 60°. A vaned diffuser having 20 equally spaced vanes with the same NACA profile is used to improve compressor efficiency. A 3-D compressible, viscous flow analysis has been done using a commercial finite volume software. The results of this analysis allowed the verification of the flow characteristics inside the meso-scale centrifugal compressor. The compressor has been fabricated using micro-fabrication techniques. The rotor and the stator are made by etching a silicon wafer by using DRIE (Deep Reactive Ion Etching) technique. A Pyrex wafer is then bonded to the stator for visual access inside the compressor.

Abstract:

Scanning probe microscopy(SPM)-based nanolithography with injected charges into layered electrets, such as silicon dioxide (SiO2) and silicon nitride, is a promising tool with far-reaching applications, such as controlled nano-assembly of macro-molecules and data storage. Despite its potential, some practical limitations exist. This paper describes an experimental investigation of the process of charging and charge dissipation in SiO2 using an AFM probe tip and surface potential (Kelvin probe) microscopy. The stability of charge bits on hexamethyl disilazane(HMDS)-treated SiO2 under low dielectric constant liquids, fluorocarbon, and benzene has been demonstrated. Results from a numerical simulation of a theoretical charging model, in which the charge traps are assumed to be localized on the silicon/SiO2 interface, are also presented. The charge transport mechanism considered is modified Fowler-Nordheim tunneling. © 2005 Elsevier B.V. All rights reserved.