Papers by Author: Yong Gui Dong

Abstract: A portable tester for accessing the electrical properties of human skin surface is reported. A pair of interdigital electrodes (IDE) that contact directly with the human skin, is used as the sensing element. The impedance of the sensing system is modeled as a resistance and a capacitance in series. A square wave signal is applied so that impedance of the IDE is measured in a charging/discharging way. The response voltages of the IDE at two excitation frequencies, 10 kHz and 600 Hz, are measured successively during one measurement cycle. Since the equivalent capacitance of skin performs different frequency-dependent property other than the resistance, their values can be resolved from the measured response voltages. A microprocessor-based system is implemented as a prototype battery-powered portable unit for household measurements. Good repeatability and satisfied accuracy have been obtained by experimental results.

Abstract: The major technical difficulty of time domain reflectometry (TDR) based cable fault location lies in the accurate measurement of the time of flight (TOF). The measurement of such time intervals is realized by a digital counter together with a reference clock. Theoretical analysis is established to prove that the resolution can be refined to nanosecond by averaging the counting results from a massive number of repetitive measurements. A microcontroller is used to generate a repetitive step signal in order to perform the repetitive test. 8 MHz clock and 8-bit digital counter are used to measure the time of flight. Experimental results showed that the timing resolution of the counter method is improved to nanosecond using the mean of 30,000 times of measurement results. A portable prototype for cable fault location is made to verify such a configuration. Test results showed that the position of the cable fault can be located with error of less than 0.1m.

Abstract: A pair of concentrically placed gold electrodes is utilized in contact with human skin surface for moisture evaluation. The electrical impedance spectroscopy is measured within a frequency range of 100Hz to 5MHz. It is showed that, in case of relatively dried stratum corneum, reproducibility of measured impedances will decrease significantly in lower frequency range. The integrality of impedance frequency locus is correspondingly dependent on skin moist state. On the other hand, in case of relatively wetted stratum corneum, an integral locus can be obtained and Cole-Cole arc model can be applied for quantitative calculation. The integrality of the locus is introduced as a supplemental parameter. Experimental results with moistened filter paper as well as human skin indicate that, the skin moisture can be better represented both graphically and quantitatively.

Abstract: A sealed air cooling local environment control apparatus that can provide constant working environment for precision instruments has been developed. Based on electrical analogy, the thermal network model has been derived, and the parameters of thermal conductance and capacitance in the model were measured in different test conditions. The obtained maximum relative errors between the measured values and the theoretical values are in the range of 0.6% to 6%, which indicates that the proposed theoretical model and the test method are feasible. The obtained parametes can help to understand the heat transfer properties of the apparatus, and the methods can be also as the reference for the test and rapid commissioning of other local environment control apparatus.

Abstract: Local environment control system (LECS) has been widely used in many areas as the necessary guarantee for most precision instruments. A sealed air cooling constant temperature box with dual-chamber structure that can provide constant working condition for precision instruments in-vehicle was developed. According to the heat transfer analysis of the double plate-fins heatsink, the heat radiation area and dimensions were determined based on electrical analogy. The air flow rate and temperature distribution of the system in heat steady-state was simulated by CFD software, and the results are consistent with that of experimental test. In different conditions, the thermal test results indicate that when the heat flow rate in the inner chamber is about 170 W, the temperature difference between inner chamber and environment is no more than 6.5 °C. The thermal design and test methods can be as the reference for the design of other precision instruments in-vehicle.

Abstract: The detection and characterisation of subsurface flaws in nonmetallic materials are very important for people’s health, lives, and environment. Possible damage must be detected early and reliably. A capacitive approach for detecting the subsurface cracks is discussed. A uniplanar capacitive sensor with multi-electrodes for obtaining the corresponding electrical capacitance information of the measured slab is presented. An experimental rig, which is composed of a uniplanar capacitive sensor of 8-electrodes and two engineering plastic samples, has been built for damage detection of nonmetallic material. Principal component analysis is used to extract relevant features from capacitance values for damage detection and identification. The simulated, as well as the preliminary experimental results show that the current approach is capable of detecting subsurface damages of nonmetallic materials and discriminating the flaws. The proposed approach is feasible and effective for damage detection and health monitoring.

Abstract: In case of mechanical system health monitoring, a need to develop normal-knowledge based novelty detection techniques is increasing. The negative selection algorithm, which is inspired from the operation mechanism of human immune system, is one of such approaches. Our approach is to apply the idea for the anomaly detection in the vibration time series of the rotor system. A real-valued negative selection algorithm based on Euclidean distance, as well as cosine similarity, has been implemented. By means of adding the corresponding coverage radius to each antibody elements, the detection efficiency of each antibody element is increased. The detection efficiency is evaluated with simulated data as well as vibration signal sampled from one rotor system. The results indicate that the algorithm can efficiently detect the anomaly in time series data. Moreover, the number of detectors in antibody set is less enough for potential application in online signal monitoring.