Accurate THz Ellipsometry Using Calibration in Time Domain

2021 ◽  
Author(s):  
Zahra Mazaheri ◽  
Can Koral ◽  
Antonello Andreone
Keyword(s):  
Time Domain ◽  
Parameter Extraction ◽  
Calibration Procedure ◽  
Thz Spectroscopy ◽  
Angle Of Incidence ◽  
Liquid Form ◽  
Calibration Methods ◽  
Wide Range ◽  
Transmission Measurements ◽  
High Absorption

Abstract We report on the realisation of a customized THz Time Domain Spectroscopic Ellipsometer (THz-TDSE) based on fiber-coupled photoconductive antennas, operating in a wide range of incident angles and allowing also standard transmission spectroscopy without any optical realignment. To ensure accurate parameter extraction for a broad range of materials, we developed a fast and effective algorithm-assisted method to calibrate the setup and compensate for the nonideality in the response of the THz system. The procedure allows to minimise errors induced by imperfect response of the antennas and polarizers, imprecise setting of the impinging and receiving angles in the goniometric mechanical arms, and unavoidable mismatches in the THz beam optics. Differently from other calibration methods applied in the literature, our approach compares in time domain the ellipsometric derived electric field s- and p-polarised components at a given angle of incidence with the reconstructed ones, attained by using the complex dielectric function of a known sample. The calibrated response is determined with high precision by setting the system in transmission mode. In order to validate the technique, ellipsometric measurements have been carried out at various angle of incidences on a number of materials both in solid and liquid form, and their data compared with what obtained by conventional THz spectroscopy. Results show that THz-TDSE accompanied with an accurate calibration procedure is an effective technique for material characterization, especially in case of samples with a high absorption rate that are not easily investigated through transmission measurements.

scholarly journals Solute Transport Measurements in Different Soil Types using Time Domain Reflectometry

2001 ◽  
Vol 32 (2) ◽  
pp. 99-114 ◽  
Author(s):  
Magnus Persson
Keyword(s):  
Solute Transport ◽  
Time Domain ◽  
Calibration Method ◽  
Calibration Procedure ◽  
Solute Concentration ◽  
Time Domain Reflectometry ◽  
Soil Types ◽  
Undisturbed Soil ◽  
Transport Measurements ◽  
Calibration Methods

During recent years, time domain reflectometry (TDR) has proved to be a valuable tool for both water content (θ) and bulk electrical conductivity (σa) measurements. To allow resident solute concentration (Cr) measurements, a calibration procedure is necessary for the relationship between σa and Cr. Two main calibration approaches exist. Direct calibration allows for Cr measurements with varying θ, while the indirect calibration method is used for conditions with constant θ. In this paper, three methods of achieving direct calibration parameters are presented and evaluated in three different soil types. Calibrations are made in both disturbed and undisturbed soil columns as well as in the field. It was shown that there were only small differences between calibration methods in homogeneous sand. In other soils, choosing the correct calibration is important. In clay soils solute transport measurements are difficult to take under conditions with varying θ, therefore it is suggested that only the indirect calibration approach should be used. When using TDR it is important to be aware of the accuracy of the TDR system in order to interpret data correctly. Some error sources are thus also briefly discussed.

scholarly journals MOSAIK and FMI-Based Co-Simulation Applied to Transient Stability Analysis of Grid-Forming Converter Modulated Wind Power Plants

2021 ◽  
Vol 11 (5) ◽  
pp. 2410
Author(s):  
Nakisa Farrokhseresht ◽  
Arjen A. van der Meer ◽  
José Rueda Torres ◽  
Mart A. M. M. van der Meijden
Keyword(s):  
Power System ◽  
Time Domain ◽  
Power Plants ◽  
Transient Stability ◽  
Renewable Energy Sources ◽  
Critical Factor ◽  
Primary Control ◽  
Simulation Approach ◽  
Wide Range ◽  
Grid Side

The grid integration of renewable energy sources interfaced through power electronic converters is undergoing a significant acceleration to meet environmental and political targets. The rapid deployment of converters brings new challenges in ensuring robustness, transient stability, among others. In order to enhance transient stability, transmission system operators established network grid code requirements for converter-based generators to support the primary control task during faults. A critical factor in terms of implementing grid codes is the control strategy of the grid-side converters. Grid-forming converters are a promising solution which could perform properly in a weak-grid condition as well as in an islanded operation. In order to ensure grid code compliance, a wide range of transient stability studies is required. Time-domain simulations are common practice for that purpose. However, performing traditional monolithic time domain simulations (single solver, single domain) on a converter-dominated power system is a very complex and computationally intensive task. In this paper, a co-simulation approach using the mosaik framework is applied on a power system with grid-forming converters. A validation workflow is proposed to verify the co-simulation framework. The results of comprehensive simulation studies show a proof of concept for the applicability of this co-simulation approach to evaluate the transient stability of a dominant grid-forming converter-based power system.

scholarly journals Comparing optical performance of a wide range of perovskite/silicon tandem architectures under real-world conditions

Nanophotonics ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Manvika Singh ◽  
Rudi Santbergen ◽  
Indra Syifai ◽  
Arthur Weeber ◽  
Miro Zeman ◽  
...  
Keyword(s):  
Solar Cells ◽  
Real World ◽  
Solar Spectrum ◽  
Photocurrent Density ◽  
Angle Of Incidence ◽  
Optical Study ◽  
Optical Performance ◽  
Tandem Solar Cells ◽  
Bottom Cell ◽  
Wide Range

Abstract Since single junction c-Si solar cells are reaching their practical efficiency limit. Perovskite/c-Si tandem solar cells hold the promise of achieving greater than 30% efficiencies. In this regard, optical simulations can deliver guidelines for reducing the parasitic absorption losses and increasing the photocurrent density of the tandem solar cells. In this work, an optical study of 2, 3 and 4 terminal perovskite/c-Si tandem solar cells with c-Si solar bottom cells passivated by high thermal-budget poly-Si, poly-SiOx and poly-SiCx is performed to evaluate their optical performance with respect to the conventional tandem solar cells employing silicon heterojunction bottom cells. The parasitic absorption in these carrier selective passivating contacts has been quantified. It is shown that they enable greater than 20 mA/cm2 matched implied photocurrent density in un-encapsulated 2T tandem architecture along with being compatible with high temperature production processes. For studying the performance of such tandem devices in real-world irradiance conditions and for different locations of the world, the effect of solar spectrum and angle of incidence on their optical performance is studied. Passing from mono-facial to bi-facial tandem solar cells, the photocurrent density in the bottom cell can be increased, requiring again optical optimization. Here, we analyse the effect of albedo, perovskite thickness and band gap as well as geographical location on the optical performance of these bi-facial perovskite/c-Si tandem solar cells. Our optical study shows that bi-facial 2T tandems, that also convert light incident from the rear, require radically thicker perovskite layers to match the additional current from the c-Si bottom cell. For typical perovskite bandgap and albedo values, even doubling the perovskite thickness is not sufficient. In this respect, lower bandgap perovskites are very interesting for application not only in bi-facial 2T tandems but also in related 3T and 4T tandems.

scholarly journals A Possible Way for the Detection and Identification of Dangerous Substances in Ternary Mixtures Using THz Pulsed Spectroscopy

Sensors ◽  
2019 ◽  
Vol 19 (10) ◽  
pp. 2365 ◽  
Author(s):  
Vyacheslav A. Trofimov ◽  
Svetlana A. Varentsova
Keyword(s):  
Spectral Properties ◽  
Main Pulse ◽  
Ternary Mixtures ◽  
Thz Spectroscopy ◽  
Time Intervals ◽  
Detection And Identification ◽  
Dangerous Substances ◽  
Spectral Intensities ◽  
Absorption Frequencies ◽  
High Absorption

We discuss an effective tool for the detection and identification of substances in ternary mixtures with similar spectral properties using a broadband reflected THz signal. Nowadays, this is an urgent problem; its effective solution is still far off. Two ternary mixtures of the explosives (RDX+TNT+HMX and RDX+TNT+PETN) were used as the examples for demonstration of the efficiency of the method proposed. The identification is based on the pulsed THz spectroscopy. We follow the spectral intensities together with the use of integral correlation criteria. They use the spectral line dynamics of the THz pulse reflected from the substance under investigation and that of the standard THz signal from database. In order to increase the accuracy and reliability of the identification, we analyze the partial non-overlapping time intervals, containing the main pulse of the reflected THz signal and the sequential sub-pulses. The main pulse is shown to contain information about high absorption frequencies (ν > 2.6 THz) of the mixture components. In the sub-pulses, the absorption frequencies of the components are detected in the range of low (ν < 2.6 THz) and high (ν > 2.6 THz) frequencies. The opportunity of distinguishing the mixtures with similar spectral properties is also shown.

Application of time-domain THz spectroscopy for studying blood plasma of rats with experimental diabetes

2014 ◽  
Vol 22 (3) ◽  
pp. 185-188 ◽  
Author(s):  
O. P. Cherkasova ◽  
M. M. Nazarov ◽  
I. N. Smirnova ◽  
A. A. Angeluts ◽  
A. P. Shkurinov
Keyword(s):  
Blood Plasma ◽  
Time Domain ◽  
Experimental Diabetes ◽  
Thz Spectroscopy

Unsteady Conjugate Heat Transfer Investigation of a Multistage Steam Turbine in Warm-Keeping Operation With Hot Air

2018 ◽  
Author(s):  
Piotr Łuczyński ◽  
Dennis Toebben ◽  
Manfred Wirsum ◽  
Wolfgang F. D. Mohr ◽  
Klaus Helbig
Keyword(s):  
Heat Transfer ◽  
Conjugate Heat Transfer ◽  
Flow Patterns ◽  
Operating Conditions ◽  
Angle Of Incidence ◽  
Time Step ◽  
Hot Air ◽  
Wide Range ◽  
Vortex Systems ◽  
Operating Points

In recent decades, the rising share of commonly subsidized renewable energy especially affects the operational strategy of conventional power plants. In pursuit of flexibility improvements, extension of life cycle, in addition to a reduction in start-up time, General Electric has developed a product to warm-keep high/intermediate pressure steam turbines using hot air. In order to optimize the warm-keeping operation and to gain knowledge about the dominant heat transfer phenomena and flow structures, detailed numerical investigations are required. Considering specific warm-keeping operating conditions characterized by high turbulent flows, it is required to conduct calculations based on time-consuming unsteady conjugate heat transfer (CHT) simulations. In order to investigate the warm-keeping process as found in the presented research, single and multistage numerical turbine models were developed. Furthermore, an innovative calculation approach called the Equalized Timescales Method (ET) was applied for the modeling of unsteady conjugate heat transfer (CHT). The unsteady approach improves the accuracy of the stationary simulations and enables the determination of the multistage turbine models. In the course of the research, two particular input variables of the ET approach — speed up factor (SF) and time step (TS) — have been additionally investigated with regard to their high impact on the calculation time and the quality of the results. Using the ET method, the mass flow rate and the rotational speed were varied to generate a database of warm-keeping operating points. The main goal of this work is to provide a comprehensive knowledge of the flow field and heat transfer in a wide range of turbine warm-keeping operations and to characterize the flow patterns observed at these operating points. For varying values of flow coefficient and angle of incidence, the secondary flow phenomena change from well-known vortex systems occurring in design operation (such as passage, horseshoe and corner vortices) to effects typical for windage, like patterns of alternating vortices and strong backflows. Furthermore, the identified flow patterns have been compared to vortex systems described in cited literature and summarized in the so-called blade vortex diagram. The comparison of heat transfer in the form of charts showing the variation of the Nusselt-numbers with respect to changes in angle of incidence and flow coefficients at specific operating points is additionally provided.

Gain-phase margins-based delay-dependent stability analysis of pitch control system of large wind turbines

2019 ◽  
Vol 41 (13) ◽  
pp. 3626-3636 ◽  
Author(s):  
Omer Turksoy ◽  
Saffet Ayasun ◽  
Yakup Hames ◽  
Sahin Sonmez
Keyword(s):  
Control System ◽  
Stability Analysis ◽  
Wind Turbines ◽  
Time Domain ◽  
Dynamic Performance ◽  
Pitch Control ◽  
Wide Range ◽  
Delay Dependent ◽  
Delay Dependent Stability ◽  
Large Wind

This paper investigates the effect of gain and phase margins (GPMs) on the delay-dependent stability analysis of the pitch control system (PCS) of large wind turbines (LWTs) with time delays. A frequency-domain based exact method that takes into account both GPMs is utilized to determine stability delay margins in terms of system and controller parameters. A gain-phase margin tester (GPMT) is introduced to the PCS to take into GPMs in delay margin computation. For a wide range of proportional–integral controller gains, time delay values at which the PCS is both stable and have desired stability margin measured by GPMs are computed. The accuracy of stability delay margins is verified by an independent algorithm, Quasi-Polynomial Mapping Based Rootfinder (QPmR) and time-domain simulations. The time-domain simulation studies also indicate that delay margins must be determined considering GPMs to have a better dynamic performance in term of fast damping of oscillations, less overshoot and settling time.

scholarly journals Time-domain THz spectroscopy of the characteristics of hydroxyapatite provides a signature of heating in bone tissue

PLoS ONE ◽  
2018 ◽  
Vol 13 (8) ◽  
pp. e0201745
Author(s):  
Marie Plazanet ◽  
Jordanka Tasseva ◽  
Paolo Bartolini ◽  
Andrea Taschin ◽  
Renato Torre ◽  
...  
Keyword(s):  
Bone Tissue ◽  
Time Domain ◽  
Thz Spectroscopy
Sign in / Sign up

Export Citation Format

Share Document