Change In Permittivity Research Articles

Evolution of structural and functional properties of the Fe/BaTiO3 system guided by mechanochemical and thermal treatment

Multiferroic systems are attractive to the researches worldwide due to diversity of existing applications, as well as possible novel ones. In order to contribute to understanding of the processes that take place within the structure of such a system, we subjected it to mechanochemical activation and thermal treatment. Powdery mixtures of iron and barium titanate in a mass ratio of 30% Fe and 70% BaTiO3 were activated in a planetary ball mill for time duration of 30 to 300 min and subsequently sintered at 1200?C in the atmosphere of air. During the activation the system undergoes structural phase transitions, whereby the content of iron and its oxides changes. The highest Fe content was observed in the sample activated for 270 min, with local maxima in crystallite size and microstrain values and a minimum in dislocation density. The complex dielectric permittivity changes in the applied radio frequency field, rangingfrom 176.9 pF/m in thesample activated for 90 min to 918.1 pF/m in the sample activated for 180 min. As the frequency of the field increases, an exponential decrease in the magnetic with a simultaneous increase in the electrical energy losses is noticeable. The system exhibits ferromagnetic resonance, whereby longer activation in the mill shifts the resonant frequency to higher values. Negative electrical resistance was observed in all analyzed samples. The activation time changes both the demagnetization temperature and the Curie temperature of the samples undergoing heating and cooling cycles in the external permanent magnetic field. Curie temperature is the highest in the sample activated for 240 min. Thermal treatment increases the initial magnetization of all samples, with the most pronounced increase of ~95% in the sample activated for 300 min.

WGM-Based Sensing of Characterized Glucose- Aqueous Solutions at mm-Waves

A newly-developed commercial coaxial probe kit (DAK-TL) is used to characterize the electromagnetic properties of glucose-loaded samples prepared at a range of concentrations 0.7–1.2 mg/ml similar to Type-2 normal diabetics in a broad range of frequencies from 300 MHz to 67 GHz using two different $50~\Omega $ open-ended coaxial probes. The objective is to determine the spectrum portion of the most sensitivity to slight variations in glucose concentrations and to identify the amount of change in the dielectric permittivity and loss tangent due to different concentrations of interest. The millimeter-wave range 50–67 GHz has shown to be promising for acquiring both high sensitivity and sufficient penetration depth for the most interaction between the glucose molecules and electromagnetic waves. Subsequently, the relative permittivity of the glucose-water mimicking samples are modeled in this mm-wave band using a single-pole Debye model with independent coefficients. The fitted Debye model is used to design a simple low-cost highly-sensitive integrated mm-wave sensing structure that utilizes the travelling-wave Whispering Gallery Modes (WGMs) launched in a dielectric disc resonator (DDR) when coupled to a dielectric image waveguide (DIG). The proposed sensor is used for continuous monitoring of glucose levels in blood mimicking aquatic solutions by tracking the variations in the magnitude and phase of the WGM transmission resonances in the mm-wave spectrum. This happens in reaction to the strong interactions of the coupled WGM evanescent field with the glucose samples loaded on top of the DDR inside a container. The sensor exhibits a high sensitivity performance (2.5–7.7 dB/[mg/ml]) for the two proposed DIG layouts, straight and curved, at the lower-order modes WGH 600 and WGH 700 of its five pure WGH modes supported in the frequency range 50–70 GHz as demonstrated by numerical simulations in a 3D full-wave EM solver and validated through proof-of-concept measurements.

Electromagnetic Technique for Hydrocarbon and Sand Transport Monitoring: Proof of Concept

Electromagnetic metering offers significant promise in the measurement of low-conductivity medium like in multiphase flow. Such measurements rely on the measurement of conductivity contrasts formed by two medium of substances, one substance being conductive and the other being non-conductive. In these conditions, it is assumed that the permittivity-induced displacement current is small compared to eddy current induced by conductivity, therefore the displacement current is usually ignored. The present study demonstrates, through solution of the electromagnetic forward problem and pilot tests, that the temporal, spatial and frequency related permittivity and conductivity changes are all captured by the induced electrical voltage measurement. Permittivity reflects in the amplitude and the conductivity reflects both in the amplitude and the phase angle of the voltage. The weight of each parameter to the voltage measurement is studied here. The findings of the study disclose that an electromagnetic metering system may offer advantages in continuously monitoring and measuring hydrocarbon contents and solid concentrations via both the amplitude and phase shift changes.

Computed Tomography-Based Modeling of Water Vapor-Induced Changes in Permittivity During Microwave Ablation.

Measurements of tissue permittivity with small open-ended coaxial probes during microwave tissue heating have been plagued by high variability as tissue water becomes vaporized. Analysis of such variability has been hampered by a lack of direct visualization of the measurement volume. The objective of this study was to determine if X-ray computed tomography (CT) could be used to visualize the measurement volume and then predict dielectric permittivity based on the visualized tissue composition. CT attenuation at 120kVp was measured at the end of an open-ended coaxial probe during microwave ablation of ex vivo liver (2.45GHz at 50 W delivered for 5minutes). Tissue composition was estimated from attenuation maps and used to predict dielectric properties based on established mixture equations. Predicted permittivity was then compared to measured values using error metrics and linear regression. There was a good agreement between measured and modeled permittivity during 5-minute ablations at 2.45GHz (r = 0.94, p < .001). Normalized root mean squared errors were below 17% in permittivity modeling at 2.45GHz. CT-based model predictions of dielectric properties are feasible in ex vivo liver. The models may facilitate real-time imaging-based permittivity mapping.

A fully electronically tunable millimeter wave lab-in-waveguide nano-fluidic sensor

In this paper, we report an ultra-sensitive millimeter wave (mm-wave) reflection liquid sensor, which is electronically tunable, non-invasive, and label-free. The reflection liquid sensor is based on the impedance match technique. It is implemented in a rectangular waveguide structure, which makes the interaction between mm-wave and liquid under test (LUT) in a closed environment, forms a nano-fluidic lab-in-waveguide liquid sensor, and isolates the interference of surroundings. The reflection liquid sensor shows high sensitivity to permittivity change of the LUTs. Taking the ethanol-distilled water as benchmark, a more than 62 dB ethanol-distilled water contrast is experimentally achieved. The detection limit is 0.05% ethanol in volumetric concentration with a 4 dB signal difference, which is the best performance of the microwave and mm-wave liquid sensors publicly reported until now. The ultra-sensitive reflection sensor can be used for bio-chemical sensing. The lab-in-waveguide biosensor is also compatible with microfluidics.

Simple and low-cost object detection method based on observation of effective permittivity change

The permittivity of a material is generally larger than that of air. When an object is present near an electric wire, the effective permittivity of the space around the wire becomes larger than that without the object. It follows that in the presence of an object, the velocity of the signal propagating along the wire decreases and the propagation delay time increases. This change can be easily detected by a simple electronic circuit composed of standard semiconductor devices. The principle of this object detection method can be used not only for proximity sensors but also for the detection or measurement of phenomena involving changes in permittivity.

Microfluidic Sensor Based on Composite Left-Right Handed Transmission Line

In this paper, we propose a novel metamaterial-based microfluidic sensor that permits the monitoring of properties of the fluid flowing in the microfluidic reservoir embedded between the composite left–right handed (CLRH) microstrip line and the ground plane. The sensor’s working principle is based on the phase shift measurement of the two signals, the referent one that is guided through conventional microstrip line and measurement signal guided through the CLRH line. At the operating frequency of 1.275 GHz, the CLRH line supports electromagnetic waves with group and phase velocities that are antiparallel, and therefore the phase “advance” occurs in the case of CLRH line, while phase delay arises in the right-handed (RH) frequency band. The change of the fluid’s properties that flow in the microfluidic reservoir causes the change of effective permittivity of the microstrip substrate, and subsequently the phase velocity changes, as well as the phase shift. This effect was used in the design of the microfluidic sensor for the measurement of characteristics of the fluid that flows in the microfluidic reservoir placed under the CLRH line. The complete measurement system was developed including the Wilkinson power divider that splits the signal between conventional RH and CLRH section, transmission lines with the microfluidic reservoirs, and a detection circuit for phase shift measurement. Measurement results for different fluids confirm that the proposed sensor is characterized by relatively high sensitivity and good linearity (R2 = 0.94). In this study, the practical application of the proposed sensor is demonstrated for the biomass estimation inside the microfluidic bioreactors, which are used for the cultivation of MRC-5 fibroblasts.

Feasibility Study of Hydration Monitoring Using Microwaves–Part 2: Measurements of Athletes

Hydration is a key consideration for athletes, where even mild levels of dehydration may negatively impact performance. Existing methods of assessment are either inaccurate or impractical for use in field settings, motivating the search for new approaches. Extremity microwave measurement is a promising method for ongoing hydration monitoring, owing to the inherent differences in dielectric properties with varying tissue water content. This paper reports on a feasibility study of in vivo hydration assessment using microwave measurements in athletes undergoing acute water loss during exercise. We developed and then tested a system for performing reliable microwave property estimation at the forearm. This system was used to measure hydration status in varsity wrestlers before and after a training session. A relationship between estimated permittivity and body weight change due to water loss was found, showing promise for the use of microwaves to assess hydration status. No significant relationship with attenuation was found. A novel method of assessing changes in hydration status is described, which may be of practical use for athletes in guiding fluid replacement during and after exercise.

Ground-penetrating radar measurements of subsurface structures of lacustrine sediments in the Qaidam Basin (NW China): Possible implications for future in-situ radar experiments on Mars

The stratigraphic profile of paleolakes on Mars preserves a record of past climatic, hydrological and sedimentary environment. Radar could be used to detect the structure and distribution of buried lacustrine sediments. But orbiter radar sounders rarely detect the internal structure or the bottom of the ancient Martian lake deposits. Future Martian missions will employ ground-penetrating radar (GPR) onboard rovers to investigate the shallow subsurface structure of paleolake basins. In this case, ground experiments are necessary to test the potential of GPR detection. This study reports on GPR experiments operating at 100 MHz and 200 MHz carried out in the Qaidam Basin, one of the analogue sites for Martian paleolake environments, to detect the subsurface structure of lacustrine sediments and measure the relative permittivity of sediments with both laboratory instrument and GPR data. Two GPR measurements were performed on top of yardangs representing layered lacustrine sedimentary outcrops. Another survey site is a polygonal patterned ground, which is a common landform in the Qaidam Basin and on Mars. The observations revealed by GPR experiments show that (1) sediments of three sites have varied compositions, density and porosity, and have a wide range of relative permittivity values, from 1.56 to 4.56; (2) the detection depth of our measurements could reach 20 m; (3) The interfaces between sedimentary layers can be seen in radargrams, but reflectors in radargrams may not always match with exposed layers of the yardang outcrops due to the undetected change of permittivity values or thin thickness of layers; (4) A distinct and continuous reflector is observed beneath the polygonal terrain which we interpret as a subsurface layer with low water/brine content. Our ground experiments suggest that a similar GPR on Martian rover could detect the near-surface structure of lacustrine sediments, e.g. deposition anomaly, interfaces of drastic permittivity change such as buried ice/brine considering that the design frequency is close to our equipment.

Cell Model Approaches for Predicting the Swelling and Mechanical Properties of Polyelectrolyte Gels

We present two successive mean-field approximations for describing the mechanical properties and the swelling equilibrium of polyelectrolyte gels in contact with a salt solution. The first mean-field approximation reduces the many-chain problem of a gel to a corresponding single chain problem. The second mean-field step integrates out the degrees of freedom of the flexible chain and the ions. It replaces the particle-based description of the polyelectrolyte with suitable charge distributions and an effective elasticity term. These simplifications result in a computationally very efficient Poisson-Boltzmann cell-gel description. Despite their simplicity, the single chain cell-gel model shows excellent and the PB model very good agreement with explicit molecular dynamics simulations of the reference periodic monodisperse network model for varying chain length, polymer charge fraction, and external reservoir salt concentrations. Comparisons of our models to the Katchalsky model reveal that our approach is superior for strongly charged chains and can also predict the bulk moduli more accurately. We further discuss chain length polydispersity effects, investigate changes in the solvent permittivity, and demonstrate the robustness of our approach to parameter variations coming from several modeling assumptions.

Dielectric and ferroelectric properties of BTFCO thin films

Single phase Bi3.25La0.75Ti2.5Nb0.25Fe0.125Co0.125O12 (BTFCO) thin films were deposited on Pt/TiO2/SiO2/Si substrates by RF-magnetron sputtering. Ferroelectric domain switching, including 180° and non-180° domains walls, was observed in polarization- electrical field hysteresis loops. The coercive field Ec of the materials, linking with zero polarization, is near 100 kV/cm. Dielectric permittivity changing with DC electric field shows one permittivity peak near 50 kV/cm, which suggests that field induced switching of 180° domains is completed at 50 kV/cm. Further increasing the DC field causes the decrease of dielectric permittivity, which can be attributed to the decrease of density of 90° domain walls. The difference between the Ec and the field for permittivity peak show that the switching field of 180° domain is lower than that of 90° domains in BTFCO ferroelectric films.

Study on epsilon crossover wavelength tuning of heavily doped germanium-on-silicon in mid-infrared range.

In this paper, we demonstrate that n-type heavily doped germanium (Ge) can serve as a sort of CMOS-compatible, permittivity crossover wavelength (at which the real part of permittivity changes sign) wide range adjustable epsilon-zero material in mid-infrared (MIR). The antimony (Sb) doped Ge films with high doping concentrations have been highly crystalline grown on silicon substrates with the molecular beam epitaxy (MBE) process. Our results reveal that the crossover wavelength of doped germanium is highly tunable by adjusting the carrier concentration and crystallinity of the films simultaneously. By optimizing dopant flux and substrate temperature, the maximum carrier concentration can be achieved as high as 1.6×1020cm-3, resulting in a very short crossover wavelength of 4.31 µm, which is very difficult to realize in group IV semiconductors. The heavily doping process also enables it possible to observe the room temperature photoluminescence (PL) from direct band transition of germanium films.

Microwave Limiters Implemented by Coupled Dielectric Resonators Based on a Topological Defect Mode and CT-Symmetry Breaking

We present a microwave realization of a reflective topological limiter based on an explicit self-induced violation of a charge-conjugation (CT) symmetry. The starting point is a bipartite structure created by coupled dielectric resonators with a topological defect placed at the center and two lossy resonators placed on the neighboring sites of the defect. This defect supports a resonant mode if the CT-symmetry is present, while it is suppressed once the symmetry is violated due to permittivity changes of the defect resonator associated with high irradiances of the incident radiation. This destruction leads to a suppression of transmittance and a subsequent increase of the reflectance while the absorption is also suppressed.

Soil Moisture Estimation by GNSS Multipath Signal

Global navigation satellite system (GNSS) multipath signals received by a geodetic-quality GNSS receiver can be used to estimate the water content of soil around the antenna. The direct signals from satellite to GNSS antenna are the most valuable signals in geodetic measurement, such as positioning, navigation, GNSS control network, deformation monitoring, and so on. However, the GNSS antenna also captures the reflected signals from the ground, which contain information of surrounding environment, so that useful information about the reflection surface can be inferred by analyzing the reflected signal. This technique is termed as GNSS-interferometric reflectometry. The signal-to-noise ratio (SNR) data recorded by a receiver contains SNR component of reflected signals, which is related to the soil moisture of the ground. The changes of soil moisture content will cause the change of soil permittivity and reflectivity which are the key factors that make further change of the SNR of reflected signals. We used the measured data to evaluate the correlation between amplitude of multipath induced SNR time series and real soil moisture. An improved soil moisture estimation algorithm based on multipath induced SNR amplitude data is proposed in this paper. The performance of the proposed soil moisture estimation method is evaluated using the 15-month data recorded by PBO H2O GNSS station and a 14-day experiment in Wuhan, China. The experimental results show that the estimated soil moisture has a strong correlation with the real soil moisture and the estimation accuracy in terms of root-mean-square error (RMSE) is 0.0345 cm3cm−3 and 0.0339 cm3cm−3, respectively. Meanwhile, the application scope of the method is given.

Cylindrical Cavity Sensor for Distinction of Various Driveability Index Gasoline with Temperature Robustness.

In this paper, a cylindrical cavity sensor based on microwave resonant theory is proposed to distinguish between various driveability index gasolines under temperature variations. The working principle of the proposed sensor is based on the fact that the change in permittivity of gasoline samples inside cavity sensor will also cause a change in resonant frequency. The proposed sensor has good sensitivity in terms of resonant frequency separation, which enables it to capture the minute permittivity changes and distinguish different gasolines. By using a normal gasoline permittivity of 2.15 and changing sensor dimension parameters, the sensor was designed by high-frequency structure simulator (HFSS). The designed sensor has a resonant frequency of 7.119 GHz for the TM012 mode with a 19.2 mm radius, a 35 mm height, and one-port coupling probe of 8 mm height. The proposed cylindrical cavity sensor shows advantages of excellent resonant characteristics of small cavity size and small sample amount. To optimize and verify the parameters of the sensor, many experiments have been carried out using HFSS and a vector network analyzer (VNA). Consequently, the proposed sensor is proven to be robust to temperature changes in terms of resonant frequency separation. The minimum frequency separation to distinguish gasoline samples is found to be larger than 29 MHz with reflection coefficients under −11 dB for temperature changes from −35 °C to 0 °C. The consistency of experimental and theoretical results also are presented, which guarantees accuracy of the sensor for the distinction of gasoline.

Multichannel filter application of a magnetized cold plasma defect in periodic structure of ZnS/TiO2 materials

In this article, transmission spectra of multilayer structure of zinc sulfide (ZnS) and titanium dioxide (TiO2) with defect of magnetized cold plasma (MCP) have been calculated theoretically by using characteristics transfer matrix method. The transmission spectra versus frequency have been analyzed for symmetric and asymmetric structure. Due to have a multiple band gaps in the asymmetric structure, we have taken the asymmetric structure for analysis with the parameters of MCP and the thicknesses of the dielectric materials. It is well known that magnetized cold plasma is an abnormal material because the permittivity changes with applied external magnetic field, and shows tunable photonic band gap for permittivity of the MCP. Now, the transmission spectra of the asymmetric structure versus frequency by inserting one or two magnetized cold plasma layer were analyzed with the variation of incident angles, the parameters of MCP, and the thicknesses of ZnS and TiO2 material. The analyzed transmission spectra of asymmetric structure with the variation of electron density, thicknesses of dielectric materials were obtained better results with defect of two plasma layers as compare to the defect of one layer of plasma. These obtained results reveal that the defect of two magnetized cold plasma layers of one dimensional asymmetric structure of ZnS, TiO2 may be used for the tunable multichannel filter at microwave region.

Measurement of Metal Velocity in Sand Casting during Mold Filling

Melt turbulence during mold filling is detrimental to the quality of sand castings. In this research study, the authors present a novel method of embedding Internet of Things (IoT) sensors to monitor real-time melt flow velocity in sand molds during metal casting. Cavities are incorporated in sand molds to position the sensors with precise registration. Capacitive and magnetic sensors are embedded in the cavities where melt flow velocity is calculated by using an oscillator, the frequency of which is sensitive to changes in the close field permittivity, and change in magnetic flux, respectively. Their efficiency is investigated by integrating the sensors into 3D sand-printing (3DSP) molds for conical-helix and straight sprue configurations to measure flow velocities for aluminum alloy 319. Experimental melt flow velocities are within 5% of estimations from computational simulations. A major benefit of 3DSP is the geometrical freedom for complex gating systems necessary to reduce turbulence and access to mold volume for sensor integration during 3DSP processing. Findings from this study establish the opportunity of embedding IoT sensors in sand molds to monitor metal velocity in order to validate simulation results (2–5% error), compare gating systems performance, and improve foundry practice of manual pouring as a quality control system.

Electrophysical properties of woven polymer mesh fabrics

ABSTRACTThe investigation was performed on three woven mesh fabrics made of polyethylene terephthalate (PET), polyamide (PA) 6.6 monofilaments, and PA 6.6 with carbon filament (CF). The dielectric properties were examined as functions of frequency at room conditions and as functions of frequency and temperature under the vacuum. It was observed at lower frequency higher changes of dielectric permittivity for the sample with CFs at room conditions. For PET and PA 6.6, dielectric permittivity in the vacuum was steady and little lower; furthermore, dielectric spectra showed the existence of γ‐, β‐, and α‐relaxations. The dc volume electrical resistivity was investigated in the function of relative humidity at room temperature for PA 6.6 and PA 6.6 with CF. For the sample with the CF, a decrease in the dc electrical resistivity of nine orders of magnitude in the direction with CF was registered as compared to the direction without a conductive filament. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48456.

Ultra-sensitive plasmonic sensing based on gold nanostrip arrays.

The extra-narrow reflection feature in angular dependence of reflectivity of periodic gold nanostrip arrays presents interest for sensing application. We explore its behavior in a modified dielectric environment and characterize the capability for sensing small changes in the dielectric permittivity of the environment.

Metamaterial for Hydrogen Sensing.

A hydrogen sensor based on plasmonic metasurfaces is demonstrated to exhibit the industry-required 10 s reaction time and sensitivity. It consists of a layer of either Y or WO3 sandwiched between a top Pd nanodisk and a Au mirror at the base. The phase change layer (Y, WO3) reacts with hydrogen, and the corresponding change of the refractive index (permittivity) is detected by the spectral shift of the resonance dip in reflectance at the IR spectral window. This direct reflectance readout of the permittivity change due to hydrogen uptake is fast and is facilitated by radiation field enhancement extending into the phase change volume. Numerical modeling was used to elucidate the effects that real and imaginary parts of the refractive index exert on the spectral shifts of resonance. The mechanism of sensor performance is outlined, and a possibility to tune its spectral range of operation by the diameter of the Pd nanodisk and thickness of the phase change material makes this design applicable to other molecular detection applications including surface-enhanced IR absorption.