Device In Frequency Domain Research Articles

Investigation on motion characteristics of an Anti-pitching Generating WEC (AGWEC) considering the viscous effect

Anti-pitching Generating Wave Energy Converter (AGWEC) uses the relative pitch motion between floating bodies to push the hydraulic energy storage PTO movement, which reduces the relative pitch between floating bodies while generating power. In this paper, based on the CFD method and the potential flow theory with viscosity modification, the motion characteristics of AGWEC in waves are studied. The viscous dissipation term is introduced into the boundary condition of potential flow, and the viscous modified potential flow theory method is established. The Eigenfunction Expansion Matching (EEM) method and Impulse Response Function (IRF) method are used to analyze the motion response of the device in frequency domain and time domain respectively. At the same time, compared with the results of CFD method based on Star-CCM+, the universality of the two methods is proved, and the motion characteristics of the AGWEC based on (non)linear PTO system and the variation law with the relevant parameters are obtained under different floating body axial spacing and wave frequency.

Offline Health Diagnosis of Power Device Based on Nonintrusive Inductively Coupled Approach

Understanding the causes of a power device’s defect plays a crucial role in failure and reliability analyses, and hence, the need of health diagnosis. Health diagnosis involves the measurement of predefined electrical parameters of a power device under its usual operating condition and the analyses of their deviations from their norms. Instead of the conventional direct measurements of voltage and current waveforms in time domain, this paper proposes a nonintrusive measurement method that measures the ON-state impedance of a power device in frequency domain. The proposed method eliminates direct electrical contact with the device-under-test, and it has the ability to detect the deviation of the ON-state impedance from its norm for health diagnosis purpose.

Characterization of Dynamic Self-Heating in GaN HEMTs Using Gate Resistance Measurement

This paper reports on a new method for the characterization of transistors transient self-heating based on gate end-to-end resistance measurement. An alternative power signal is injected to the device output (between drain and source) at constant gate-to-source voltage. The dependence of gate resistance with temperature is used to extract the thermal impedance of the device in frequency domain via electrical measurement. This new method is validated on common-gate AlGaN/GaN high-electron-mobility transistors on Si substrate under different experimental conditions, which demonstrates its potential to provide complete dynamic self-heating models for power transistors.

Frequency-domain vs continuous-wave near-infrared spectroscopy devices: a comparison of clinically viable monitors in controlled hypoxia

The Near-infrared spectroscopy (NIRS) has not been adopted as a mainstream monitoring modality in acute neurosurgical care due to concerns about its reliability and consistency. However, improvements in NIRS parameter recovery techniques are now available that may improve the quantitative accuracy of NIRS for this clinical context. Therefore, the aim of this study was to compare the abilities of a continuous-wave (CW) NIRS device with a similarly clinically viable NIRS device utilising a frequency-domain (FD) parameter recovery technique in detecting changes in cerebral tissue saturation during stepwise increases of experimentally induced hypoxia. Nine healthy individuals (6M/3F) underwent a dynamic end-tidal forced manipulation of their expiratory gases to induce a stepwise induced hypoxia. The minimum end-tidal oxygen partial pressure (EtO2) achieved was 40 mm Hg. Simultaneous neurological and extra-cranial tissue NIRS reading were obtained during this protocol by both tested devices. Both devices detected significant changes in cerebral tissue saturation during the induction of hypoxia (CW 9.8 ± 2.3 %; FD 7.0 ± 3.4 %; Wilcoxon signed rank test P < 0.01 for both devices). No significant difference was observed between the saturation changes observed by either device (P = 0.625). An observably greater degree of noise was noticed in parameters recovered by the FD device, and both demonstrated equally variable baseline readings (Coefficient of variance 8.4 and 9.7 % for the CW and FD devices, respectively) between individuals tested. No advantageous difference was observed in parameters recovered from the FD device compared with those detected by CW.

Comparison of Near-Infrared Oximeters in a Liquid Optical Phantom with Varying Intralipid and Blood Content.

The interpretation of cerebral tissue oxygen saturation values (StO2) in clinical settings is currently complicated by the use of different near-infrared spectrophotometry (NIRS) devices producing different StO2 values for the same oxygenation due to differences in the algorithms and technical aspects. The aim was to investigate the effect of changes in scattering and absorption on the StO2 of different NIRS devices in a liquid optical phantom. We compared three continuous-wave (CW) with a frequency domain (FD) NIRS device. Responsiveness to oxygenation changes was only slightly altered by different intralipid (IL) concentrations. However, alterations in haematocrit (htc) showed a strong effect: increased htc led to a 20-35% increased response of all CW devices compared to the FD device, probably due to differences in algorithms regarding the water concentration.

Generalized Continuum Sensitivity Formula for Shape Optimization of High-Frequency Devices in Frequency Domain

This paper presents a generalized continuum design sensitivity formula that is applicable to any shape design problems of high-frequency devices in frequency domain. The derived sensitivity formula is expressed in terms of surface integrals over a part of the interface between different materials and of the conducting boundary undergoing shape modification during iterative design process. Using the proposed approach, it is easy to deal with the shape optimization concerning conducting surfaces as well as dielectric contours. The method has been successfully applied to the optimization of high-frequency waveguides where the numerical implementation is thoroughly investigated from the viewpoint of constructing adjoint systems and calculating sensitivity values.

Changes in optical properties of tissue during acute wound healing in an animal model

Changes of optical properties of wound tissue in hairless rats were quantified by diffuse photon density wave methodology at near-infrared frequencies. The diffusion equation for semi-infinite media was used to calculate the absorption and scattering coefficients based on measurements of phase and amplitude with a frequency domain device. There was an increase in the absorption and scattering coefficients and a decrease in blood saturation of the wounds compared with the nonwounded sites. The changes correlated with the healing stage of the wound. The data obtained were supported by immunohistochemical analysis of wound tissue. These results verified now by two independent animal studies could suggest a noninvasive method to detect the progress of wound healing.

Optical Properties of Wounds: Diabetic Versus Healthy Tissue

Diffuse photon density wave (DPDW) methodology at Near Infrared frequencies has been used to calculate absorption and scattering from wounds of healthy and diabetic rats. The diffusion equation for semi-infinite media is being used for calculating the absorption and scattering coefficients based on measurements of phase and amplitude with a frequency domain device. Differences observed during the course of healing in the two populations can be correlated to the delayed healing observed in diabetics. These results are encouraging and further work will focus on the implementation of this device to the clinical setting as a monitoring tool in chronic diabetic wounds.