Microwave Dielectric Spectra Research Articles

Effects of Carasau Dough Composition on the Microwave Dielectric Spectra up to 20 GHz

Carasau bread is a traditional product from Sardinia (IT). This flat bread is experiencing industrial advancement, through automation, and has great market potential. However, there is lack of understanding of how the composition (water content, salt, and yeast concentration) affects the product quality. In this work, a microwave dielectric spectroscopy study is performed to investigate how the composition of Carasau bread doughs influences the spectra of this food product up to 20 GHz. A third-order Cole–Cole model was used for the physical and quantitative understanding of the electromagnetic properties of this food product. Then, it has been studied how salt, yeast, and water variations affected the model parameters. This work could pave the route to the development of non-destructive, contactless microwave sensors for Carasau bread quality assessment.

Soil salinity estimation: Effects of microwave dielectric spectroscopy and important frequencies

AbstractThe microwave dielectric constant is a key bridge in establishing the relationship between microwave remote sensing and soil salinity (electrical conductivity, EC). However, the response between microwave dielectric spectrum type, frequency, and soil salinity is still unclear. The purpose of this study is to reveal the dielectric spectrum and frequency range closely related to soil salinity. In this study, 129 surface soil samples were collected, and soil EC and microwave dielectric spectrum (frequency range of 0.3–20 GHz) were measured. Four variable selection methods were used to select important spectral variables, and the relationship between these spectral variables and soil salt was constructed using a random forest model. The results showed that the combination of (real part) and (imaginary part) revealed the most implicit information related to soil salinity. Considering the important spectral variables, the model accuracy was generally improved to the full‐dielectric spectrum model (the ratios of the performance to the interquartile distance (RPIQ) improved by 0.11–0.40); furthermore, the variable iterative space shrinkage (VISSA) method could most effectively select important spectral variables (RPIQ = 2.32). The selected spectral‐RF models could provide important frequencies for estimating soil salinity; moreover, the low‐frequency range (0.3–4 GHz) and new important frequency ranges (e.g., 7 and 15 GHz) able to respond to soil salinity were identified. This study provides a new strategy for monitoring the soil salinization risk using multiple frequencies microwave remote sensing techniques.

Dielectric relaxation and thermodynamical parameters of hydrogen bonded complexes for Heptanamide and Pentanamide with halogenated phenols in benzene

In the experiment and dielectric relaxation setup at 303 K, X-band (9.34 GHz) and J-band (7.22 GHz) microwave benches were employed. In benzene, dielectric experiments were done on hydrogen-bonded complexes of Heptanamide and Pentanamide with 4-bromophenol, 4-chlorophenol, 4-iodophenol, and 4-fluorophenol. Microwave dielectric spectra for binary mixtures of alkanamides with Halogenated phenols have been determined over the frequency range of 10 MHz to 20 GHz at 303 K. Dielectric properties such as (ε׳), (ε''), (ε0) and (ε∞) have been investigated. The geometries are optimized at B3LYP with 6-311G++ basis set. Dipole moments of the binary mixtures are calculated from the dielectric data using Higasi’s method and compared with the theoretical results. The relaxation periods (τ0) for ternary liquid combinations were measured using Higasi's approach. According to the ternary data, the relaxation time is highest for 1:1 complexes. According to the system under examination, the relaxation time value increases as the concentration of solute increases. For various ternary mixes and molecular conformations of these systems, the relaxation periods (τ0) of the two bands are compared. The dielectric relaxation energy parameters of thermodynamics (ΔFε, ΔHε, ΔSε) of amides with halogenated phenols in benzene were calculated and compared to the associated viscosity parameters.

Domain contribution to the aging characteristics in BaTiO3 ceramics

The domain contribution to the aging characteristics of BaTiO3 (BTO) ceramics in a DC electric field was quantitatively investigated using microwave dielectric spectroscopy. The BTO aging effect was related to its domain size (DS): the reduction in the apparent permittivity by the DC electric field, Δε, increased with decreasing BTO DS. Inspection of the microwave dielectric spectra revealed that dipole polarization governed the overall aging effect regardless of the BTO DS, and that the ionic and electronic polarizations contributions were small. Substitutional loading of acceptor Mg2+ into the Ti4+ site decreased the BTO’s DS because defect pairs consisting of and its counterpart acted as nucleation sites for new domain walls. Magnesium-loaded BTO (Mg-BTO) had smaller Δε values (attributed to dipole polarization) than BTO for similar DS. The – defect complex effectively clamped the domain walls, thereby suppressing domain wall migration in the presence of an electric field. The measured permittivity decrease under a DC field was 423 for BTO but 246 for Mg-BTO with a similar DS, corresponding to a 41.8% improvement.

Dielectric behavior of adulterated milk with urea and water

Milk adulteration, especially by adding urea, is one of the major health concerns. In this work, we report a dielectric methodology to detect the existence of polar adulteration like urea and water in milk. The microwave dielectric spectra of whole milk, skim milk and their mixture with varying contents of water or urea was measured. An obvious dielectric relaxation was observed for these systems. The dielectric relaxations were well represented by the superposition of two relaxation processes which are attributable to free water and water adsorbed on protein, urea-water co-clusters and urea-water co-clusters adsorbed on protein for both milk-water systems, urea aqueous solution and both urea-milk systems respectively. The relaxation of lower frequency was identified as the dipole orientation polarization of water or urea-water co-clusters adsorbed on protein in milk mixtures. Significant differences in dielectric parameters, relaxation time and relaxation strength, between these systems were analyzed by comparing between skim and whole milk with different water contents and among water, skim and whole milk with different urea contents. The results show that microwave dielectric spectroscopy may provide a way or a choice for monitoring of water and urea in adulterated milk.

Microwave absorbing and shielding properties of inhomogeneous conductors and high-loss dielectrics

Microwave dielectric spectra of the relaxor ferroelectric PbMg1/3Nb2/3O3 single crystals, (Nb + In) co-doped rutile ceramics, inhomogeneous conducting polyaniline pellets, composites of poly(ethylene terephthalate) and multi-walled carbon nanotubes were used for calculation of transmission and reflection spectra of the material slabs in the free space and estimation of absorbing and shielding properties of the materials. Studied high-permittivity high-loss materials with a strong and broad dielectric dispersion in the microwave range were shown to have a high potential for microwave shielding and absorbing applications. Broadband (two decades of frequency) 40 dB shielding and high attenuation constant were demonstrated in the microwave range.

Effects of concentration on the microwave dielectric spectra of aqueous urea solutions

Several models of relaxation for the dielectric spectra of aqueous urea solutions in the microwave region are compared. The spectra are shown to contain two main Debye components arising from the rotational motions of urea and water molecules. Two essentially different concentration regions in urea solutions are identified. The first is characterized by a small increase in the mobility of water molecules (τ1 = 7.8 ps) and the existence of hydrated urea molecules (τ2 = 19 ps). Due to the aggregation of urea molecules, the relaxation times for the latter process grow considerably in highly concentrated solutions. At the same time, faster molecular motions (τ3 = 6 ps) are observed for water molecules.

Temperature transformation of microwave dielectric spectra of Rochelle salt in the dynamic conductance model

The temperature transformation of submillimeter dielectric spectra of Rochelle salt is analyzed within the framework of dynamic conductance model. The branched network of hydrogen bonds and crystallization water molecules in Rochelle salt is supposed to form a quasi-localized vibrational mode in the crystal spectrum. This mode determines the resonant dielectric response at helium temperatures, which with an increase in temperature is transformed into the relaxation response of diffusion motion.

Variations in the concentration of microwave dielectric spectra in a water-acetonitrile system

Relaxation models for describing the microwave dielectric spectra of acetonitrile (AN) solutions are presented. It is noted that the models, which contain two fundamental Debye spectral components, can be used for most concentrations. The separate influence of polar and nonpolar molecules in groups of AN molecules on the initial structure of water in the solution is established and found to have different signs. A schematic of the concentration’s structural transition from water to pure AN is given. It is concluded that integrated clusters consisting of water and AN molecules are found in the system’s region of medium concentrations (0.4–0.6 m.f. AN), where the motions of water molecules are slowed down and it is stabilized due to the hydrophobic hydration of nonpolar AN groups. It is shown that the AN molecules are more tightly bound compared than pure AN due to the formation of AN-H2O bonds over the range of concentrations.

Microwave dielectric spectra and molecular interaction in a binary mixture of ethanolamine with diethanolamine

Microwave dielectric spectra for binary mixtures of ethanolamine with diethanolamine have been determined over the frequency range of 10MHz to 20GHz, at different temperatures, using a time domain spectroscopy (TDS) method at 11 concentrations. The values of the dielectric loss (ε″) have been plotted against the dielectric constant (ε′) in the complex plane. The static dielectric constant (ε0), dielectric constant at high frequency (ε∞), and relaxation time (τ) have been determined using the Debye model, a single relaxation process. The dielectric behavior indicates a change of phase from a semi-solid to a liquid state. The effects of molecular size and number of OH group molecules on H-bond molecular interactions from Kirkwood correlation factors are presented.

Suppression of the anomaly of low-frequency permittivity in ferroelectric triglycine sulfate by microwaves

Microwave dielectric spectra of ferroelectric triglycine sulfate are measured in the littlestudied frequency range from 90 to 150GHz, and the suppression of low-frequency dielectric anomaly by microwaves at these frequencies is investigated. It is shown that suppression occurs only in the range of non-Debye dielectric dispersion. An additional dispersion mechanism based on the activation-diffusion model of orientational polarization and transit-time effects for quasi-free carriers is proposed to explain the microwave impact.

Anion-Dependence of Fast Relaxation Component in Na-, K-Halide Solutions at Low Concentrations Measured by High-Resolution Microwave Dielectric Spectroscopy

High-resolution microwave dielectric spectra of NaX, KX (X: F, Cl, Br, I) aqueous solutions of c = 0.05 and 0.1 M measured in the frequency range 0.2-26 GHz at 10 °C are analyzed. The dielectric relaxation (DR) spectrum of each solution, which deviates slightly from the bulk-water spectrum, is mathematically divided into the bulk-water spectrum and the spectrum of solute particles covered with a water layer using a mixture theory by assuming the existence of continuous bulk-water phase. The solute spectra above 3 GHz are fitted with a linear series of pure water component (γ dispersion with DR frequency fw), fast Debye component-1 with DR frequency f1 (>fw), and slow Debye component-2 with DR frequency f2 (<fw). Component-2 is only found for the fluorides. The sum of dispersion amplitudes of γ and components -1 and -2 for NaX and KX are found to be almost irrespective of X and equal to the pure water level, indicating that components -1 and -2 are from the water modified by ions, thus denoted as "hypermobile water" and "constrained water" (not rigidly bound to ion), respectively. Below 3 GHz, sub-GHz dispersion component is detected and assigned as a relaxation response of counterion cloud. The resulting limiting-molar conductivities of NaX and KX are in good agreement with the literature data measured at much lower frequencies. The estimated number of hypermobile water molecules is found to increase from 9 to 31 for NaX and from 9 to 37 for KX with increasing anion size. Thus, except for the fluorides, it is reported that the modified water by salt ions exhibits only Debye component-1 other than γ dispersion, indicating the existence of a water-ions collective hypermobile mode in each solution.

Microwave dielectric spectra and molecular relaxation in formamide–N,N-dimethylformamide binary mixtures

The dielectric dispersion and absorption spectra of formamide (FA), N,N-dimethylformamide (DMF) and their binary mixtures are investigated in the frequency range of 500 MHz to 20 GHz at 30 °C in view of the organic synthesis by microwaves heating using amides solvents. The concentration dependent values of molecular reorientation relaxation times lower than that of the ideal mixing behaviour have been attributed to the cooperative dynamics of H-bonded FA–DMF structures. The molar ratio of stable adduct is 2:1 of FA to the DMF, which is determined from the concentration dependent excess static dielectric constant and the relaxation time plots of these binary mixtures. Electrode polarization effect and ionic conduction in FA and DMF were investigated from their dielectric dispersion spectra in the low frequency region of 20 Hz to 1 MHz.

Infrared and THz Soft-Mode Spectroscopy of (Ba,Sr)TiO3 Ceramics

We performed a study of the temperature dependence of the dielectric response of (Ba,Sr)TiO 3 (BST) ceramics for the whole composition range in a wide frequency range by means of Fourier transform infrared, time-domain THz, microwave and low-frequency dielectric spectroscopy. Room-temperature spectra of the paraelectric dielectric response were compared with the results of first-principle simulations within the effective Hamiltonian approach with a good semi-quantitative agreement. It is shown that in the paraelectric phase away from the transition temperature, the complex THz soft mode, consisting of two overlapping heavily damped oscillators, fully accounts for the low-frequency dielectric properties. However, close to T C additional central-mode type dispersion, apparently caused by the pre-transitional polar clusters, is to be expected in the microwave dielectric spectra.

Molecular reorientation in ionic liquids: A comparative dielectric and magnetic relaxation study

We have used 2H magnetic relaxation to study the single-particle reorientation of the 1-ethyl-3-methylimidazolium ([emim] +) ion in two prototypical low-viscosity ionic liquids comprising the bis(trifluoromethylsulfonyl)imide ([Tf 2N] −) and dicyanimide ([(CN) 2N] −) anions. Hydrodynamic analysis reveals extremely low (‘subslip’) coupling factors not captured by existing theories. Comparison with the microwave dielectric spectrum of [emim][Tf 2N] shows that the dominant diffusive component of the dielectric response can be rationalized by single-particle reorientation of the cations.

Electronic trap effect of spectral sensitizing dye adsorbed on the surface of silver chloride

Using spectral sensitizing technology，silver halide microcrystals can be sensitized to the visible light region. The spectral sensitizing technology is important to the modern information recording and storage，solar energy transfer and storage, and the photoelectronic devices. The photoelectron decay characteristic of silver chloride microcrystals，which is adsorbed with green sensitizing cyanine dye，is studied by microwave absorption and dielectric spectrum detection technology. The model of photoelectron decay is set up. Electron trap effect of the dye in the silver halide surface is analyzed based on the photoelectron decay model and the photoelectron decay characteristic. The results show that when the mono-molecular dye is adsorbed on the surface，shallow electron traps are created; when the J-aggregated dye is adsorbed on the surface，deep electron traps are created. The critical dose of dye that seperates the shallow electron trap and deep electron trap effects is 0.2ml of dye (with concentration of 5.0mg/ml) per 40g AgCl emulsion.

A novel microwave absorption and dielectric spectrum detection technology in photoelectron dynamic study for solar cells

The photoelectron property is directly related to the light-energy conversion efficiency of solar cells. In this paper, the photoelectron dynamic of semiconductor was analyzed. The diffusion of electrons has influence on the dielectric function of the solar cell material. And the amplitude variance of the imaginary and real part of the dielectric function is in direct proportion to the dynamic process of free and shallow-trapped electrons. Based on the untouched detection technique, the method is present to detect the amplitude change of the microwave signal which is passing through the material whose dielectric function changes after exposure. A 35 GH z oscillator was used as a microwave source. The absorption and dispersion microwave signals, which contain the dynamic information of free and shallow-trapped electron signal, are split respectively with phase-sensitive instrument. The photoelectron character of n-type Si(100) thin film was investigated by the novel equipment, and the lifetime of different kinds of electrons with the resolution of 1 ns was obtained. The equipment can be directly used in the study of the optoelectronic conversion mechanism of solar cells.

Self-assembled structure of cyanine dyes: J-aggregates characteristics on optical information storing microcrystals

Dye sensitization is a fundamental function for solar cell and silver halide (AgX) microcrystal to increase the optoelectronic conversion efficiency. In this paper, the spectral properties and self-assembled structure of three types of cyanine dyes, adsorbed both on (100) surface of 0.4 μm AgBr cubic crystal and (111) surface of 1.8 μm AgBr tabular crystal, were studied with combination of spectroscopy and atomic force microscopy (AFM) technique. Rectangular aggregation structure is formed on the crystal faces of (100) and (111) for both anionic and cationic dyes, while herringbone-stacking structure is formed by an-ionic-cationic dye, and a J-band spectrum is correspondingly detected. The photoelectron property of dyesensitized samples was also investigated with microwave absorption and dielectric spectrum detection technology. After excited by a 355 nm fast-pulse laser, the photoelectron decay process of anionic-cationic dye sensitized sample is the fastest. This indicates that the affection of anionic-cationic dye aggregates to the photoelectron decay is the biggest, and the sensitization is more efficient.

Investigation of decay characteristics of photoelectrons in nanoparticales of cubic AgBr sensitized by NiS

NiS nanoparticales as a sensitizer is added to cubic silver bromide emulsion for the chemical sensitization. The decay curves of free photoelectrons and shallow-trapped electrons in the cubic silver bromide emulsion sensitized by NiS nanoparticales with the continuous increase of sensitization time are measured by the microwave absorption and dielectric spectrum techniques. The courses of decay of photoelectrons in the cubic silver bromide emulsion sensitized by NiS nanoparticales vis sensitization time is analyzed. The influence of electron traps in silver bromide microcrystals on the behavior of the photoelectrons' movement is discussed. The relationships between the effects of electron traps and the depth of traps with sensitization time are analyzed. By comparing the decay characteristics of the unsensitized and the sensitized samples, the optimum sensitization time under the present experimental conditions is 80 min.

Investigation of photoelectron action in cubic AgCl emulsion doped with formate ions

In recent years, the formate ion (HCO2−) as a kind of hole-to-electron converter has attracted much attention of photographic researchers. The formate ions can trap photo-generated holes, eliminate or reduce the electron loss caused by electron–hole recombination in latent image formation process. Through the hole-to-electron conversion, it can also release an extra electron or electron carrier, improving photosensitivity. In this paper the microwave absorption and dielectric spectrum detection technique is used to detect the time evolution behaviour of free photoelectrons generated by 35ps laser pulses in cubic AgCl emulsions doped with formate ions. The influence of different doping conditions of formate ions on the photoelectron decay kinetics of AgCl is analysed. It is found that when the HCO2− content is 10−3mol/mol Ag and the doping position is 90% the electron decay time and lifetime reach their maxima due to the efficient trap of holes by formate ions.