Complex Permittivity Of Samples Research Articles

Direct Permittivity Reconstruction From Power Measurements Using a Machine Learning Aided Method

A machine learning aided (MLA) method is employed for the direct permittivity retrieval of dispersive and non-dispersive materials. The method requires low-cost measurements since it solely utilizes the amplitude of the transmission response ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$|S_{21}|$</tex-math> </inline-formula> ) to extract the complex permittivity. This precludes the need for a network analyzer, and therefore, the measurements can be performed using a power sensor. Unlike earlier works, however, the method introduced here does not require prior information about the dispersion model of the material under test (MUT), so it is applicable to a wider range of materials. The method is based on applying two artificial neural networks (ANNs) for the permittivity reconstruction of low and high-loss materials. The ANNs are trained using full-wave simulation results of a coaxial line loaded with different MUTs for the direct reconstruction of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon^\prime$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varepsilon^{\prime\prime}$</tex-math> </inline-formula> . As a proof of concept, several chemical liquids, their mixtures, and powdered samples were used to experimentally validate the technique within the 0.3–3 GHz band. The retrieved complex permittivities of samples were in good agreement with the reference data and those obtained by the well-known transmission/reflection Nicolson–Ross–Weir (NRW) method.

Microstructure induced dielectric loss in lightweight Fe3O4 foam for electromagnetic wave absorption

SummaryFe3O4 has been extensively applied in electromagnetic wave absorption field profiting from its advantageous magnetic loss, low cost and environmental benignity. Nevertheless, the inherent drawbacks of high density, low permittivity and easily magnetic aggregation are still the obstacles for pristine Fe3O4 becoming ideal absorbents. To overcome such limitations, a design mentality of constructing 3D structure shaped by curled 2D porous surface is proposed in this study. 3D structure overcomes the easy-agglomeration issue of 2D materials and meanwhile maintains their conductivity. The complex permittivity of samples is regulated by adjusting the microstructure of Fe3O4 to achieve optimum impedance matching. Defect induced polarization and interfacial polarization are the main loss mechanisms. Impressively, the density of S0.5 is only 0.05078 g/cm3 and the effective absorption bandwidth is up to 6.24 GHz (11.76-18 GHz) at 1.8 mm. This work provided a new insight for structurally improving the EMW absorption performance of pure magnetic materials.

Determination of complex permittivity of thin dielectric samples based on high-q microstrip resonance sensor

In this paper, a high quality factor microstrip resonator based on modified Minkowski fractal structure sensor is presented for determining the dielectric sample's complex permittivity. A high loaded quality factor value has been achieved by utilizing fractal structure, which is far greater than that of a typical rectangle microstrip antenna. Besides, the modified fractal radiation patch and the feeding section of the sensor result in a highly sensitive area to the tested materials. The sensing principle is implemented by detecting the electric fields perturbation of the resonator when different tested materials are placed over it. The complex permittivity change of the tested materials can be forecasted by transferring the acquired experimental relative resonant frequency shifts (Δf) and loaded QL values of the proposed sensor to a well-developed neural network system. To validate the proposed method, various standard dielectric samples including Teflon, PVC, and others are tested and analyzed. The experimental results are compared with published values with the maximum error of 4.9%.

Dual-prism based terahertz time-domain attenuated total reflection spectroscopy and its application to characterise the hydration state of L-threonine in solution

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.

High-Q sensor for permittivity detection based on spiral resonator

A high-quality factor microwave planar sensor with microfluidic channels for permittivity detection is proposed in this paper. The sensor is based on microstrip technology, and uses spiral subwavelength resonators to couple with the sample flowing in the microfluidic channel upon the sensor. Then the frequency shift and notch depth of the transmission response are related to the difference in complex permittivities between samples through a mathematic model, which will be used to extract the complex permittivities of samples afterwards. The sensor is designed with dual transmission lines to achieve better robustness and real-time measurement. After the simulation of samples in microfluidic channels, it turns out that the sensor is capable to distinguish samples whose permittivity has a difference of more than 2.56%. The quality factor of the sensor is 218 with empty load. It is validated to effectively distinguish mixture of water and air as well as water and ethanol with different fraction, which can be as low as 5%. The extracted permittivity is compared with theoretical value, which shows a good consistency.

Characterization of the lossy dielectric materials using contour mapping.

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.

Noniterative complex permittivity retrieval using calibration-independent waveguide measurements

Calibration-independent nonresonant measurements can be employed to eliminate the need for calibration before microwave measurements. These methods generally assume that the location of the sample in its measurement cell is known after the sample is positioned or shifted within the cell and that the length of the measurement cell is known. In addition, in general these methods necessitate some sort of numerical analysis to retrieve the complex permittivity of the sample. In this research paper, we propose a calibration-independent nonresonant waveguide method to first eliminate measurement errors arising from inaccurate knowledge of the location of the sample within its cell (after shifting) and arising from improper knowledge of the length of the measurement cell and second to determine the complex permittivity explicitly. In addition, our proposed method needs scattering parameter measurements from three different measurement configurations – another improvement with respect to a similar calibration-independent method requiring measurements from four different configurations. Furthermore, it does not necessitate that the sample be flushed to the measurement cell. We analyzed repeatability of cell connection and investigated uncertainty in the measurement of complex permittivity for a change in length of the sample and the cell and when air gap present between sample surfaces and guide walls. We validated the proposed method by measuring the complex permittivity of polyethylene sample and distilled water at X-band (8.2–12.4GHz).

Materials classification by partial least squares using S-parameters

This paper presents a simple and usable algorithm, which is called Partial Least Squares, to classify the samples in different thicknesses and frequency range. This model employed to reconstruct the samples using S-parameters which are collected by Vector Network Analyzer in Free Space Measurement method. The relationship of between S-parameters is showed to classify the materials using proposed model. The Partial Least Squares algorithm has a good potential to classify the different samples with non-contactless and non-destructive measurement method. The classification process will be easy by using the proposed model, due to its practical and simple usage. In addition, the extraction techniques, which are Nicolson Ross Weir, Newton–Raphson, and Genetic Algorithm, are used in order to extract the dielectric constant of samples, in this study. The Newton–Raphson algorithm is selected to obtain the complex permittivity of samples since it gives best results than other extracting techniques and the results are used for classification.

Characterizing the complex permittivity of high-κ dielectrics using enhanced field method.

This paper proposed a method to characterize the complex permittivities of samples based on the enhancement of the electric field strength. The enhanced field method significantly improves the measuring range and accuracy of the samples' electrical properties. Full-wave simulations reveal that the resonant frequency is closely related to the dielectric constant of the sample. In addition, the loss tangent can be determined from the measured quality factor and the just obtained dielectric constant. Materials with low dielectric constant and very low loss tangent are measured for benchmarking and the measured results agree well with previous understanding. Interestingly, materials with extremely high dielectric constants (ε(r) > 50), such as titanium dioxide, calcium titanate, and strontium titanate, differ greatly as expected.

Measurement of Complex Permittivity of Insulating Substrates with an Open-Ended Coaxial Resonator

A novel cavity perturbation technique utilizing open-ended coaxial resonator is presented in order to measure the complex permittivity of insulating substrates at microwave frequencies. This technique can afford quite high accurate measurement results without singularities, and simply. According to the operation frequency of the resonator, the geometric parameters of the resonator are designed. Based on the perturbation technique, a new formulaic method of data analysis has been proposed which can extract complex permittivity of samples, and with the resonant frequency and the quality factor shift, one can calculate the complex permittivity of the measured materials. Experiment has been conducted with the quartz and sapphire to verify the formulaic, and the test results fully verify the correctness of the proposed method.

High-Sensitivity Metamaterial-Inspired Sensor for Microfluidic Dielectric Characterization

A new metamaterial-inspired microwave microfluidic sensor is proposed in this paper. The main part of the device is a microstrip coupled complementary split-ring resonator (CSRR). At resonance, a strong electric field will be established along the sides of CSRR producing a very sensitive area to a change in the nearby dielectric material. A micro-channel is positioned over this area for microfluidic sensing. The liquid sample flowing inside the channel modifies the resonance frequency and peak attenuation of the CSRR resonance. The dielectric properties of the liquid sample can be estimated by establishing an empirical relation between the resonance characteristics and the sample complex permittivity. The designed microfluidic sensor requires a very small amount of sample for testing since the cross-sectional area of the sensing channel is over five orders of magnitude smaller than the square of the wavelength. The proposed microfluidic sensing concept is compatible with lab-on-a-chip platforms owing to its compactness.

Study of Dual Open Ended Coaxial Sensor System for Calculation of Phase Using Two Magnitudes

A dual open ended coaxial sensor system to determine complex permittivity was studied in detail. This paper focuses on determination of a reflection coefficient phase from two magnitudes using modified capacitance model from 300 kHz to 8 GHz. The phase information can then be used for calculation of the sample's complex permittivity. Factors such as range and limitation of the model, sample's permittivity, operating frequency, and size of sensor were investigated. Sensitivity of calculated phase with respect to small changes in measured magnitude was carried out.

Facile preparation and high microwave absorption of C/SiO2 composites with an ordered inter-filled string mesostructure

A kind of ordered inter-filled mesostructural C/SiO2 composites has been prepared by a combined processing of nanocasting method with hot-pressing sintering. In the composites, carbon particles can be incorporated, in the form of ordered nanowire arrays, into channels of mesoporous silica templates and endow the sintered composite with high electrical conductivity up to 1.47×103S/m. The electromagnetic interference (EMI) shielding efficiency (SE) of the C/SiO2 composite, with a thickness of 2.0mm, is as high as 35dB and dominated by microwave absorption in the X band (8.0–12.0GHz). The high complex permittivity of sample indicates that the large dielectric loss results in a significant effect on the microwave attenuation. Therefore, such conductive C/SiO2 composite ceramics with an inter-filled mesostructure will provide us with new applications as microwave absorbing materials.

A METRIC FUNCTION FOR FAST AND ACCURATE PERMITTIVITY DETERMINATION OF LOW-TO-HIGH-LOSS MATERIALS FROM REFLECTION MEASUREMENTS

We have derived a one-variable metric function for fast and accurate complex permittivity extraction of low-to-high-loss materials using re∞ection-only microwave non-resonant measurements at one frequency. The metric function can be modifled to facilitate fast computation of the complex permittivity of materials for various applications (e.g., relative complex permittivity measurement of low- loss materials). It is useful as a measurement tool for broadband measurements of complex permittivity of samples with substantiate lengths. In addition, the method is applicable for measurement of complex permittivity of dispersive materials or complex permittivity of non-dispersive samples in limited frequency-band applications, since it is based on point-by-point (or frequency-by-frequency) extraction. It is validated by a numerical analysis and measurements of a liquid sample.

Nondestructive Online &lt;emphasis&gt;In Vitro&lt;/emphasis&gt; Monitoring of Pre-Osteoblast Cell Proliferation Within Microporous Polymer Scaffolds

We present a system for the online, in vitro, nondestructive monitoring of tissue growth within microporous polymer scaffolds. The system is based on measuring the admittance of the sample over a frequency range of 10-200 MHz using an open-ended coaxial probe and impedance analyzer. The sample admittance is related to the sample complex permittivity (CP) by a quasi-static model of the probe's aperture admittance. A modified effective medium approximation is then used to relate the CP to the cell volume fraction. The change of cell volume fraction is used as a measure of tissue growth inside the scaffold. The system detected relative cell concentration differences between microporous polymer scaffolds seeded with 0.4, 0.45, 0.5, and 0.6 x 10(6) pre-osteoblast cells. In addition, the pre-osteoblast proliferation within 56 scaffolds over 14 days was recorded by the system and a concurrent DNA assay. Both techniques produced cell proliferation curves that corresponded to those found in literature. Thus, our data confirmed that the new system can assess relative cell concentration differences in microporous scaffolds enabling online nondestructive tissue growth monitoring.

The Measurements of the Complex Permittivities of Blood Samples in Quasi-Millimeter and Millimeter Wave Bands

We measured the complex permittivities of whole blood and blood plasma in quasi millimeter and millimeter wave bands using a coaxial probe method. The validity of these measurements was confirmed by comparing with those of a different measurement method, i.e., a dielectric tube method. It is shown that the complex permittivities of the blood samples are similar to those of water in quasi millimeter and millimeter wave bands. Furthermore, the temperature dependences of the complex permittivities of the samples were measured.

Data analysis of the extraction of dielectric properties from insulating substrates utilizing the evanescent perturbation method

The evanescent perturbation technique utilizing open-ended coaxial resonator probes was investigated as a nondestructive method for measuring the dielectric properties of insulating substrates in the microwave frequency region. As an investigative result, we have proposed a new formulaic method of data analysis by which the complex permittivity of samples, from changes in resonant frequency (f) and the quality factor of the resonance (Q), may be extracted in a concise and highly reproducible manner. The proposed formula has been developed based upon experimentation and detailed numerical studies of full-wave Maxwell equations coupled with physical observation and interpretation of experimental data. The new formula is applicable to both bulk and film samples with zero and finite tip-sample distances. The geometric factors derived were analyzed for variable parameters such as tip curvature, sample thickness, and tip-sample distance. Additionally, the calibration procedures necessary for experimental determination of these geometric factors were established.

Fabry–Perot‐based approach for the measurement of complex permittivity of samples inserted in resonant cavities

AbstractA new approach to measure the complex dielectric permittivity of materials placed inside a microwave resonant cavity is presented. We exploit the similarity between the microwave cavity and an optical cavity to develop a new measurement technique, which is used to obtain the complex permittivity of a polybutylene terephtalate (PBT). © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 106–108, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20390

Measurement of the moisture content with a cylindrical resonating cavity in TM/sub 010/ mode

A new resonating mode has been used in a cylindrical cavity to measure the moisture content and the specific mass of cigarettes. A simple theoretic calculation gives the relation between the sample complex permittivity and the characteristics of the cavity. A model is proposed to extract the moisture content and the specific mass from the complex permittivity. An experimental setup has been demonstrated. It uses a servo-controlled oscillator. This setup is ready to be tried on a production machine.

Waveguide permittivity measurement using variable-length samples and an uncalibrated reflectometer

A method is presented to measure the complex permittivity of samples inserted into waveguides. The method is based on reflection coefficient measurements for four different sample lengths, which are used to determine the complex propagation constant of the guide's fundamental mode. For simple waveguide geometries, the complex permittivity can be calculated, assuming a value of 1 for the relative permeability. Unlike classical waveguide techniques, this method does not require calibration of the reflectometer, and it can be used with samples that are narrower than the waveguide cross section's main dimension. By using narrower samples, the upper frequency limit of the method can be increased. Measurements in an X-band rectangular waveguide using the proposed method are presented and compared with results obtained with a cavity perturbation method. Very good agreement has been found over the frequency range prescribed for the method. Results are shown for completely filled and partially filled waveguides.