Evaluation of the Skin Surface Hydration in Vivo by Electrical Measurement

Reviews existing instrumental techniques suitable for industrial measurement of capacitance in the range 0.1-10 pF, including resonance, oscillation, charge/discharge and AC bridge methods. It shows that in order to achieve high measurement sensitivity and good signal-to-noise ratio, the effects of stray capacitances on the measurement systems must be minimised. Several intrinsically stray-immune measuring circuits are described, including an audio-frequency transformer-ratio-arm bridge and a charge/discharge measuring circuit capable of operating at frequencies up to several MHz. The active guard method and suitable guard driving techniques for reducing the effects of strays on the measurement of grounded capacitances sensors are described. Techniques for reducing the baseline drift of the capacitance measuring circuits, such as auto-balancing and auto-calibration, etc., are also discussed.

https://iopscience.iop.org/article/10.1088/0022-3735/21/3/001/pdf

Electronic transducers for industrial measurement of low value capacitances

Void fraction measurements for vertical flow in a small diameter tube (9.53 mm) were taken using two non-intrusive capacitive void fraction sensors. The sensors were needed to measure the void fraction of water - air two-phase flow under normal gravity and microgravity conditions. Void fraction data were collected with: (1) a sensor having helical wound electrodes that was used to collect data under normal gravity and microgravity conditions, (2) a sensor having concave plate electrodes, used to collect data at normal gravity. This paper covers the calibration results for both sensors and some of the problems associated with the helical wound design. Nonlinearity in the helical sensor is addressed, with improvements shown in the concave plate sensor. Comparisons are made between the capacitive sensors, quick-closing valves and a gamma densitometer.

https://iopscience.iop.org/article/10.1088/0957-0233/7/8/011/pdf

Void fraction measurements in gas - liquid flows using capacitance sensors

Restoration of the epidermal barrier is a requirement for burn wound closure. A rapid, reliable, and noninvasive measure of the rate of restoration of the epidermal barrier is not readily available. To monitor the reformation of the epidermal barrier, we measured surface electrical capacitance on cultured skin substitutes (human keratinocytes and fibroblasts attached to collagen-glycosaminoglycan substrates) and split-thickness skin autografts grafted to patients. Data were collected from four patients with burns and one pediatric patient with a congenital hairy nevus comprising > 60% total body surface area. Capacitance measurements were performed at days 7, 10, 12, 14, and 28 by direct contact of the capacitance probe for 10 seconds to the cultured skin substitutes or split-thickness autograft. On postoperative days 7, 10, 12, 14, 21, and 28, the surface electrical capacitance of cultured skin substitutes after 10 seconds of sampling was 2468 +/- 268, 1443 +/- 439, 129 +/- 43, 200 +/- 44, 88 +/- 20, and 74 +/- 19 picofarads (mean +/- standard error of the mean), respectively. Surface electrical capacitance for split-thickness autograft on the same days was 1699 +/- 371, 1914 +/- 433, 125 +/- 16, 175 +/- 63, 110 +/- 26, 271 +/- 77 picofarads, respectively. Surface electrical capacitance in all of the grafts decreased with time. Cultured skin substitutes had approximately the same 10-second capacitance values as split-thickness autograft during 3 weeks of healing and approached values for uninjured skin (32 +/- 5 picofarads) by 12 days. Measurement of surface electrical capacitance is a direct, inexpensive, and convenient index for noninvasive monitoring of epidermal barrier formation.

Surface electrical capacitance as an index of epidermal barrier properties of composite skin substitutes and skin autografts.

A helical capacitance sensor is proposed to measure the void fraction of gas-liquid two-phase flow in a small tube with 5 mm diameter in this paper. The structure of helical capacitance sensor is analyzed by using the finite-element method (FEM) and the orthogonal array testing strategy. According to simulation, the optimal structure of helical capacitance sensor is suggested. The results of simulation and experiments show that the optimized sensor has a more homogeneous sensitivity field. The helical capacitance sensor demonstrates a good linearity between the capacitance value and the void fraction to be measured. In addition, the helical capacitance sensor has a good adaptability to different flow patterns.

Optimization of Helical Capacitance Sensor for Void Fraction Measurement of Gas-Liquid Two-Phase Flow in a Small Diameter Tube

Two new circuits for the accurate measurement of specimen capacitance and resistive loss are described. The capacitance measurements are unaffected by the specimen resistance when the parallel resistance is greater than 30 ?. The practicality of the circuit is enhanced by its use of coaxial cable to provide both connection to the sample and the inductance required for circuit operation. An important characteristic of the circuit is its ability to measure capacitance and resistance of very high loss specimens accurately.

New Methods of Measuring Capacitance and Resistance of Very High Loss Materials at High Frequencies

This paper describes a differential-gap varying method for measuring the dielectric constants and thicknesses of thin films. In this method, an electrode assembly of two high tension circular plate electrodes is used. The electrodes are arranged symmetically parallel to a grounded plate electrode that is jointly moved by a micrometer head. Many of the errors of the conventional method are eliminated in the method used here. It is also shown that this method serves as an experimental tool for simultaneous determination of the permitivity and the thickness

Manabu Nishikawa

Papers

New Methods of Measuring Capacitance and Resistance of Very High Loss Materials at High Frequencies

Determination of Dielectric Constant and Thickness of Thin Film Using Differential-Gap Varying, Method