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Improved reflection technique for the permittivity measurement of ferrites using slotted coaxial samples
摘要： This paper presents the effect of magnetic permeability on the permittivity measurement using coaxial line reflection technique. It discusses in detail about the design aspects, analysis and simulation of the slotted co-axial sample and fixture for dielectric characterization of the ferrites and garnets possessing both dielectric and magnetic properties. This technique makes use of improved coaxial fixture and APC 07 compatible slotted coaxial sample geometry to measure the complex permittivity of the ferrite material. Permittivity is calculated from the impedance of sample loaded fixture, which is independent of magnetic permeability, because of air slot cut in the coaxial hollow cylindrical sample along the length. Characterization data of dielectrics and ferrites is used in design of ferrite circulators, and pulse magnets for particle accelerator applications. This is also used in many other RF applications including design of dielectric resonator for spin wave line width measurement of ferrites. Design work is aimed at accurate measurement of complex permittivity; using reflection measurement in coaxial fixture over a wide frequency range of 20 kHz to 1 GHz. Reflection measurement technique is further explored for accurate measurement of complex permittivity.
关键词： Complex permittivity,Network analyzer,Coaxial open ended fixture,Wide band measurement technique
更新于2025-09-23 15:23:52
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[IEEE NAECON 2018 - IEEE National Aerospace and Electronics Conference - Dayton, OH, USA (2018.7.23-2018.7.26)] NAECON 2018 - IEEE National Aerospace and Electronics Conference - Impact of dielectric and magnetic losses on the negative index characteristics of a chiral material with first-order sideband dispersion
摘要： Electromagnetic propagation in chiral materials under first-order dispersion is examined for negative indices under non-conductive losses. Three loss scenarios are considered, viz., dielectric (complex permittivity) losses; magnetic (complex permeability) losses; and a combination of both types of losses to investigate the overall impact of the losses on the emergence of negative index bands.
关键词： complex permittivity and permeability,loss compensation,plane wave polarization,material dispersion,negative index bands,Negative refractive index
更新于2025-09-23 15:22:29
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Dual-prism based terahertz time-domain attenuated total reflection spectroscopy and its application to characterise the hydration state of L-threonine in solution
摘要： To investigate the hydration state of amino acids, terahertz time-domain attenuated total internal reflection (THz TD-ATR) spectroscopy is often adopted to measure the complex permittivity. However, the classical THz TD-ATR spectroscopy system has only a single ATR prism and requires prism cleaning for different measuring modes, increasing the time consumed and easily introducing errors due to the changing environment. To accelerate the measurements and avoid the influence of environmental fluctuations, in this paper, we designed and built a dual-prism based THz TD-ATR spectroscopy: two ATR prisms with and without samples setting on the optical rail can be sequentially switched to optical systems for easily and rapidly collecting both sample and reference ATR spectra. According to the measurements of deionised water, the dual-prism based THz TD-ATR spectroscopy system can measure the sample complex permittivity rapidly and with high accuracy. The complex permittivity of L-threonine in aqueous solution is measured and analysed via the proposed system, and the hydration numbers of L-threonine solutions in different concentrations are quantitatively characterised. It is believed that the dual-prism based THz TD-ATR technique is a powerful tool for quickly and accurately investigating the hydration of amino acids.
关键词： Terahertz spectroscopy,Complex permittivity,Time-domain attenuated total internal reflection,Amino acid hydration
更新于2025-09-23 15:22:29
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Characterization of the lossy dielectric materials using contour mapping
摘要： The imaginary part of the complex permittivity of a lossy dielectric material is large and couples with its real part. The resonant frequency of a cavity with the sample depends not only on the real part of the complex permittivity of the sample but also the imaginary part, resulting in serious ambiguity in determining the sample’s complex permittivity. This work proposes a contour mapping method to determine the complex permittivity. The full-wave simulation gives us the contours of the resonant frequency and the quality factor, which are functions of the relative dielectric constant and the loss tangent. By mapping the measured resonant frequency and the measured quality factor, one can uniquely determine the complex permittivity of the sample. Five liquids were examined, including three low-loss materials for benchmarking and two lossy materials. The measured complex permittivities of the three low-loss materials agree very well with the other methods. As for the lossy materials, the measured relative dielectric constant and the loss tangent of alcohol are 6.786 and 0.895, respectively. Besides, the measured dielectric constant of glycerin is 6.811, and its loss tangent is 0.562. The proposed contour mapping technique can be employed to measure the complex permittivity of liquids and solids from lossless to lossy materials.
关键词： lossy dielectric materials,resonant frequency,contour mapping,complex permittivity,quality factor
更新于2025-09-23 15:21:21
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Complex Permittivity Measurement of Paraffin Phase-Change Material at 26 GHz–1.1 THz Using Time-Domain Spectroscopy
摘要： We report complex permittivity measurement of hexatriacontane films at the frequency range of 26 GHz–1.1 THz. Hexatriacontane (C36H74) has a melting point of 75 ?C that exhibits a 15% volumetric change which is crucial in developing low-loss RF microactuators with large displacement. In this work, we employ time-domain spectroscopy to measure the transmission coefficient of the paraffin samples in the frequency range of 0.3–1.1 THz. In order to extract the dielectric constant and accurately estimate the small values of loss tangent, we developed a propagation model which measured data are fitted to through a new least-squares minimization method. A Debye relaxation model is used to model the frequency dependence of the permittivity. Described method is rapidly convergent with minimum amount of signal processing. This method can be used to determine the complex permittivity of the materials by devising an appropriate function for the frequency dependence of the complex permittivity. Transmission through 20 samples of paraffin with various thicknesses is measured and the average permittivity is found to be 2.25 with standard deviation of 0.028. The loss tangent is monotonically increasing with frequency and the maximum value is 6.32×10?3 at 1.1 THz. Our study demonstrates that paraffin is a low-loss dielectric which makes it an attractive candidate for development of electro-thermo-mechanical actuators for sub-millimeter- and millimeter wave (mmW) variable capacitors, low-loss reconfigurable antennas, and phase shifters.
关键词： Terahertz,Time-domain spectroscopy,Loss tangent,Millimeter wave,Alkane,Paraffin,Complex permittivity
更新于2025-09-23 15:21:21
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Dielectric replica measurement: A new technique for obtaining the complex permittivity of irregularly shaped objects
摘要： Dielectric measurements provide valuable information about the properties of materials, and could be used to classify and identify the source of objects, in fields such as archaeology. Current methods of identification are all partly destructive, so an innovative electromagnetic method developed by the authors, based on resonant cavity perturbation (RCP), provides an attractive, non-destructive alternative. A problem with traditional RCP is that the changes in frequency and Q-factor vary with the object's shape; however we overcome this by creating a replica of the object, from a material whose dielectric properties are known. Then, by combining three separate perturbations with orthogonal field directions, due firstly to the object and then to its replica, we eliminate the shape dependency, and thus determine the object's dielectric constant and loss factor. After developing the theory of this novel DRM technique, we demonstrate the principle using a set of geometric shapes made in both polytetrafluoroethylene (PTFE) and a 3D printed material. Further measurements then enable second-order terms to be included in the model, improving its accuracy. Finally, DRM is shown to be capable of distinguishing two irregularly shaped objects of different materials. Potential applications of DRM include determining the provenance of pottery, glasses and flints, and distinguishing ivory from bone. These would be of interest to customs and environmental agencies, as well as museum curators and archaeologists.
关键词： resonant cavity,3D printing,artefact,network analyser,Dielectric measurement,archaeology,complex permittivity,non-destructive testing
更新于2025-09-19 17:15:36
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Plasmonics of Au/Polymer Core/Shell Nanocomposites for Thermoresponsive Hybrid Metasurfaces
摘要： We investigate the temperature-dependent optical response of ordered lattices of non-interacting gold-core/poly(N-isopropylacrylamide)-shell nanoparticles (NPs), a system with proven photothermal and sensing capabilities. For the first time on this system, we exploited in situ Spectroscopic Ellipsometry (SE) to determine the complex, temperature-dependent optical properties of the lattice, a key piece of information which, however, is often overlooked. In doing so, we take full advantage of large-scale colloidal self-assembly, which makes NP lattices accessible to conventional SE. A quantitative interpretation of the SE data is obtained through an effective model based on the actual characteristics of the NPs and their dielectric environment. The model allows to estimate temperature-dependent morphological parameters, such as the distance between the gold cores and the substrate, also yielding the complex permittivity of the plasmonic NP lattice. Thus, by combining the high sensitivity of SE with proper modelling, we provide a comprehensive characterization of thermoresponsive NP lattices. The approach proposed here is instrumental to the analysis and design of functional hybrid metasurfaces with plasmonic functionalities, including particle-to-film coupled systems.
关键词： spectroscopic ellipsometry,PNIPAM,localized surface plasmon resonance,complex permittivity,core-shell particles
更新于2025-09-19 17:13:59
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[IEEE 2019 XXIVth International Seminar/Workshop on Direct and Inverse Problems of Electromagnetic and Acoustic Wave Theory (DIPED) - Lviv, Ukraine (2019.9.12-2019.9.14)] 2019 XXIVth International Seminar/Workshop on Direct and Inverse Problems of Electromagnetic and Acoustic Wave Theory (DIPED) - Waveguide Millimeter Wave Measurement Cell with Minimum Reflection Coefficient for Complex Permittivity Determination of Bioactive Liquids
摘要： An original waveguide millimeter wave measurement cell for complex permittivity determination of bioactive high-loss liquids was studied numerically and experimentally. This measurement cell consisted of round metal waveguide, Teflon inserted and glass capillary with liquid under test inside. The main features of the measurement cell are as follows. Waveguide connections (matching elements) to input and output waveguides have minimum reflection coefficient. The capillary with the high loss liquids under test located not in the electromagnetic field maximum as usual, but at an angle to the wave propagation along the waveguide cell. The advantages of such capillary location were discussed in the paper. This waveguide millimeter wave measurement cell was compared with the symmetrical waveguide millimeter wave measurement cell for complex permittivity determination.
关键词： millimeter waves,reflection coefficient,Microwave resonator,complex permittivity,bioactive liquids,frequency spectrum,waveguide
更新于2025-09-16 10:30:52
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AIP Conference Proceedings [AIP Publishing APPLIED PHYSICS OF CONDENSED MATTER (APCOM 2019) - Strbske Pleso, Slovak Republic (19–21 June 2019)] APPLIED PHYSICS OF CONDENSED MATTER (APCOM 2019) - Cured epoxy resin dielectric characterization based on accurate waveguide technique
摘要： Complex permittivity of a substrate plays an important role in designing a compact and robust antenna. Thus, measuring complex permittivity must be done carefully in order to achieve accurate and reliable result. Waveguide is a widely used technique to determine complex permittivity of a dielectric material. In this paper the permittivity of cured epoxy resin is determine using waveguide technique, within the G-band frequency range. It determines the complex permittivity by analyzing only the measured transmission coefficient of the material and easily noise affected reflection coefficient is not used. Sample is only partially loaded in the waveguide to avoid the resonance during measurement. Therefore, results obtained are accurate and reliable. Also, the estimated real part of complex permittivity is in a good agreement with available data from other work.
关键词： complex permittivity,epoxy resin,G-band frequency,waveguide technique,dielectric material
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Atlanta, GA, USA (2019.7.7-2019.7.12)] 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Measurement of Dielectric Constants of Liquid Crystals Using Double-Ridged Waveguide Cavity
摘要： Liquid crystals (LCs) are widely used in reconfigurable microwave devices for their voltage tunable dielectric constant and loss. For the design of materials and devices, accurate measurements of the complex permittivity of LCs are required. This paper presents a method of performing microwave characterizations of LCs using a double ridged waveguide cavity and the perturbation method. To realize the broadband test and make operating frequency points distribute uniformly, the multi-mode technique is introduced and 6 modes (TE1,0,2n-1,n= 1, 2, 3, 4, 5, 6) are chosen as operating modes to work at 5-22 GHz by one cavity. Besides, the sample loading area in the double-ridged waveguide cavity is much smaller and the sample volume required is only about 0.02 ml. Several LCs are measured: a certain commercial mixture MM (Merck), and M1~M3, as developed LC compositions with large dielectric anisotropy and low microwave losses.
关键词： perturbation method,liquid crystals,complex permittivity,multi-mode
更新于2025-09-11 14:15:04