This article describes a feasibility study of a novel trans-scleral tonometer based on the use of an instrumented form of digital palpation tonometry. Similar to manual digital palpation tonometery, trans-scleral tonometer utilizes two force probes offset by a fixed distance. Force indentation data from these probes have been shown to correlate with the intraocular pressure (IOP) of the eye. Enucleated porcine eyes were used to experimentally validate the approach. The observed hysteresis in the force data was analyzed using an analytical model that accounts for the outflow of the aqueous humor. The predictions of the model indicate that the primary reason behind the observed hysteresis is stress relaxation (accommodation) in the visco-elastic corneo-scleral shell. Experimental data from eye distention and indentation tests were then used to infer the conditions under which the novel tonometer would be expected to have an accuracy of ±1 mmHg. Analysis of the data shows that indentation rates should be kept below 0.5 mm/s for a pressure range of 10-35 mmHg. Two commonly used pressure control protocols were tested in an effort to ensure accurate IOP values during the palpation tests. Due to the large increase of IOP during digital palpation, the trans-scleral (intra-vitreous) pressurization was found to be inadequate, leading to clogging of the line by the displaced vitreous. No such problems were identified when the eye was pressurized through the cornea and into the anterior chamber. Force data from multiple palpation experiments are used to generate calibration curves for a two-probe conceptual tonometer. The calibration showed that a 10 mN of force variation corresponds to 1 mmHg of IOP change. A possible implementation using a contoured facial mask is also presented.
Combined thermionic emission and tunneling of hot electrons (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. This paper describes a numerical and experimental investigation into the formation of a nanometer-sized tunneling gap based on the combined action of electrostatic, elastic and Lorentz forces. Experimental data reported here were used to tune the model and extract estimates for the size of the tunneling area and the gap size, respectively. The effect of changing the strength of the magnetic field was also investigated. The presented one-dimensional (1D) analysis of the relative magnitudes of these forces indicates possible stable operation. © IOP Publishing Ltd.
Interest in using electrostatics for active nano-assembly has grown significantly over the last five years. One common electret structure for such electrostatic constructs is the silicon-silicon dioxide interface. In this paper, an experimental and mathematical analysis of the process of writing negative charge spots in Si-SiO2 is presented. It is demonstrated that controlling the spread of the charge can reduce the spot size and the drop in written potential. Simulation results of a one-dimensional charging model that assumes tunnelling of electrons through the oxide and trapping within SiO2 are presented and compared with the experimental data. The model assumes charge trapping at the Si-SiO2 interface and none at the oxide-air interface or within the oxide bulk. Conducted experiments also show that although the lateral spread of charge places a lower limit on the minimum spot size in silicon-silicon dioxide structures, the use of a hydrophobic hexamethyldisilazane layer can be effective in improving the size stability of the written electrical spots.