Loss Tangent Parameters Research Articles

Design and analysis of a compact multi-band annular ring antenna for UWB applications

In this paper a compact annular ring micro strip patch antenna with modified ground plane is proposed for UWB applications. The dimensions of proposed antenna are 30 × 26 × 1.6 mm3 which was designed on FR4 substrate with the thickness of 1.6 mm, εr = 4.4 and loss tangent parameter 0.02. To enhance the impedance bandwidth of the antenna ground plane is modifiedby extruding an inverted L shape stub and defected with multiple I shaped slots. The radiator consists of annular ringpatch, two circular stubs and one rectangular stub is included to the patch to improve the bandwidth. To design and simulate the proposed antenna CST Studio Suite 2018 is used. The proposed antenna is found with UWB frequency range of 3.1–10 GHz (S11 < −13 dB). Multiple frequency bands are observed in UWB frequency range 3.18 GHz, 6.75 GHz and8.67 GHz with the reflection coefficients of −49.6 dB, −50.2 dB and −45.7 dB respectively. VSWR is less than 2 for the total UWB frequency range. Proposed antenna is better option for UWB applications specially First and third frequency bands (3.18 GHz and 8.67 GHz) are suitable for Radio location (G59) services and second frequency band (6.75 GHz) is suitable for satellite and TV broadcasting applications. Performance of the proposed antenna is evaluated in terms of size, radiation efficiency and radiation patterns and it is better compared with existed systems.

Electrical properties of CsPbX3 (X=Cl, Br) perovskite quantum dot/poly(HEMA) cryogel nanocomposites

Quantum dot-filled polymer nanocomposites are recent of interest due to the improvement of the properties and possibility of use in diverse application areas. In this study, poly(HEMA) cryogels and CsPbCl3 and CsPbBr3 perovskite quantum dots were separately synthesized and then perovskite quantum dots/cryogel nanocomposites were formed for the first time. After comprehensive characterizations of the nanocomposites, the dielectric properties of those structures were studied using impedance spectroscopy. All characterization methods revealed the effective formation of the quantum dot/cryogel nanocomposites. The real part of the dielectric components of the nanocomposites decreased concerning the pure cryogel. For the CsPbCl3 quantum dots filled nanocomposites, the imaginary part of the dielectric component and the loss tangent parameter increased almost by the factors of ∼1.8 and ∼2.2, respectively. On the other hand, for the CsPbBr3 quantum dots filled cryogel, the imaginary part of the dielectric component and the loss tangent parameter values decreased by the factors of ∼2.6 and ∼2 respectively. The large dielectric losses in the case of CsPbCl3 quantum dot-based nanocomposite were attributed to the high existence of surface traps on the surface of the CsPbCl3 quantum dots.

Impact of heat treatment of milk on acid gelation

Heat treatment of milk is applied in the manufacture of cultured dairy products, primarily to increase viscosity and improve texture. Denatured whey proteins are recognised as mostly responsible for causing these textural changes. The higher isoelectric pH of whey protein triggers earlier acid-induced gelation. Rheological properties of acid gels made from heated milk exhibit significantly higher storage moduli (and lower fracture strain) due to alterations in gel microstructure and the contribution of covalent disulphide bonding. Gels prepared from heated milks also exhibit an increase in the loss tangent parameter due to loss of calcium phosphate crosslinks conferring a greater mobility within casein particles that are already part of the network. Casein interactions are mostly weak in these types of gels, and the balance between inter and intraparticle interactions, as well as the impact of denatured whey protein deposition on the particle surfaces, are discussed for their influence on acid gelation.

Blood Glucose Level Monitoring Using an FMCW Millimeter-Wave Radar Sensor

In this article, a novel sensing approach is presented for glucose level monitoring where a robust low-power millimeter(mm)-wave radar system is used to differentiate between blood samples of disparate glucose concentrations in the range 0.5 to 3.5 mg/mL. The proposed radar sensing mechanism shows greater capabilities for remote detection of blood glucose inside test tubes through detecting minute changes in their dielectric properties. In particular, the reflected mm-waves that represent unique signatures for the internal synthesis and composition of the tested blood samples, are collected from the multi-channels of the radar and analyzed using signal processing techniques to identify different glucose concentrations and correlate them to the reflected mm-wave readings. The mm-wave spectrum is chosen for glucose sensing in this study after a set of preliminary experiments that investigated the dielectric permittivity behavior of glucose-loaded solutions across different frequency bands. In this regard, a newly-developed commercial coaxial probe kit (DAK-TL) is used to characterize the electromagnetic properties of glucose-loaded samples in a broad range of frequencies from 300 MHz to 67 GHz using two different 50 Ω open-coaxial probes. This would help to determine the portion of the frequency spectrum that is more sensitive to slight variations in glucose concentrations as indicated by the amount of change in the dielectric constant and loss tangent parameters due to the different concentrations under test. The mm-wave frequency range 50 to 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. The processed results have indicated the reliability of using mm-wave radars in identifying changes in blood glucose levels while monitoring trends among those variations. Particularly, blood samples of higher glucose concentrations are correlated with reflected mm-wave signals of greater energy. The proposed system could likely be adapted in the future as a portable non-invasive continuous blood glucose level monitoring for daily use by diabetics.

Effect of insoluble calcium concentration on endogenous syneresis rate in rennet-coagulated bovine milk

The rennet coagulation of milk has been extensively studied. Mathematical modeling of the gelation process has been performed, mainly for the purpose of predicting the gel point. Rheological profiles of rennet gels during aging (long reaction times) have indicated that the gel stiffness (modulus) attains a maximum and thereafter decreases. We wanted to model this type of behavior and used the Carlson model, which includes terms for the proteolysis of κ-casein hairs (creating active sites) and the crosslinking of these activated sites. To account for the observed decrease in the gel modulus with time, we modified the Carlson model by adding an exponential decay term, which we ascribe to endogenous syneresis. We believe that this decay (i.e., syneresis rate) would likely be influenced by the mobility of bonds within casein micelles (in gels as indicated by the rheological loss tangent parameter). To modify the internal structural bonding of casein micelles, reconstituted skim milk was acidified to pH values 6.4, 6.0, 5.8, 5.6, and 5.4, or EDTA was added to milk at concentrations of 0, 2, 4, and 6mM, and the final pH values of EDTA-treated samples were subsequently adjusted to pH 6.0. These treatments were then used to prepare rennet gel samples that were monitored by dynamic low amplitude oscillatory rheometry. When the modified Carlson model was fitted to the actual experimental storage modulus values of each sample, it fitted the data reasonably well (especially the pH trial data). As the pH values of milk decreased, the modulus values at infinite reaction time (G′∞) increased; however, G′∞ decreased with an increase in the EDTA concentration. In the pH trial, the rate constants for the proteolysis of κ-casein hairs and the crosslinking of these activated sites exhibited a maximum at pH 5.6 and 6.0, respectively. The rate constant for endogenous syneresis increased at pH values <6.0. The rate constant for endogenous syneresis was significantly positively correlated (r≥0.96) with the loss tangent values of gels (indicating greater mobility), probably due to the loss of insoluble calcium phosphate crosslinking within micelles, which was significantly negatively correlated (r≥0.81) with the rate constant for endogenous syneresis. In the EDTA trial, with an increase in the EDTA concentration no maximum was observed in the rate constants related to proteolysis of κ-casein hairs or crosslinking of these activated sites. The rate constant for endogenous syneresis decreased at higher EDTA levels. The different rheological/modeling behavior in the EDTA trials was likely due to the very significant inhibition of rennet gelation induced by the use of EDTA, which also resulted in extremely long reaction times. Our modified Carlson model fit our experimental pH trial data very well, which indicates that the rennet gel system has the potential to synerese from the start; indeed this ability is an innate property of the casein micelle. Endogenous syneresis was enhanced by the loss of insoluble calcium phosphate crosslinking within casein micelles as this increased bond mobility within rennet gels.

Assessment of carbon steel microbiologically induced corrosion by electrical impedance spectroscopy

A methodology to analyse electrochemical impedance spectroscopy (EIS) data for the study of microbiologically induced corrosion is proposed. The proposed methodology is based on the loss tangent behaviour of EIS spectra for sterile and bacteria-inoculated environments. Loss tangent parameters were obtained by fitting the EIS data to the Cole–Cole dispersion model using a genetic algorithm. Two electrochemical cells were implemented to expose carbon steel probes to sterile and inoculated media for two bacteria consortia, acid-producing bacteria (APB) and sulphate-reducing bacteria (SRB). The APB tests were exposed for 96 h and the SRB tests for 144 h. A microbial count was carried out during each experiment. The EIS spectra were measured during exposure for sterile and inoculated media. The spectra were fitted to a multi Cole–Cole dispersion model, and loss tangent parameters were obtained.

Extracting characteristic impedance in low-loss substrates

A method to determine the characteristic impedance of transmission lines considering the substrate loss is presented. The extracted data shows that at microwave frequencies the finite loss tangent parameter impacts the characteristic impedance even in a low-loss substrate.

Effect of sodium hexametaphosphate concentration and cooking time on the physicochemical properties of pasteurized process cheese

Sodium hexametaphosphate (SHMP) is commonly used as an emulsifying salt (ES) in process cheese, although rarely as the sole ES. It appears that no published studies exist on the effect of SHMP concentration on the properties of process cheese when pH is kept constant; pH is well known to affect process cheese functionality. The detailed interactions between the added phosphate, casein (CN), and indigenous Ca phosphate are poorly understood. We studied the effect of the concentration of SHMP (0.25–2.75%) and holding time (0–20min) on the textural and rheological properties of pasteurized process Cheddar cheese using a central composite rotatable design. All cheeses were adjusted to pH 5.6. The meltability of process cheese (as indicated by the decrease in loss tangent parameter from small amplitude oscillatory rheology, degree of flow, and melt area from the Schreiber test) decreased with an increase in the concentration of SHMP. Holding time also led to a slight reduction in meltability. Hardness of process cheese increased as the concentration of SHMP increased. Acid-base titration curves indicated that the buffering peak at pH 4.8, which is attributable to residual colloidal Ca phosphate, was shifted to lower pH values with increasing concentration of SHMP. The insoluble Ca and total and insoluble P contents increased as concentration of SHMP increased. The proportion of insoluble P as a percentage of total (indigenous and added) P decreased with an increase in ES concentration because of some of the (added) SHMP formed soluble salts. The results of this study suggest that SHMP chelated the residual colloidal Ca phosphate content and dispersed CN; the newly formed Ca-phosphate complex remained trapped within the process cheese matrix, probably by cross-linking CN. Increasing the concentration of SHMP helped to improve fat emulsification and CN dispersion during cooking, both of which probably helped to reinforce the structure of process cheese.

Rheological, textural and melting properties of commercial samples of some of the different types of pasteurized processed cheese

The detailed rheological and textural properties of commercially available samples of the three major categories of pasteurized processed cheese in the USA, that is, pasteurized process American cheese (PPA), pasteurized process cheese product (PPP) and pasteurized process cheese food (PPF), were analysed. All samples had similar pH values, ranging from 5.65 to 5.87, but most were ∼5.7. Even within each of the categories considerable differences were observed in textural and melting behaviour. The samples with the lowest melt and the lowest loss tangent parameter from the rheological tests were two PPF and one PPA samples. These two PPF samples also had the highest hardness and adhesiveness force. Significant correlations were observed between several textural, rheological and melting properties.

Effect of Trisodium Citrate Concentration and Cooking Time on the Physicochemical Properties of Pasteurized Process Cheese

The effects of the concentration of trisodium citrate (TSC) emulsifying salt (0.25 to 2.75%) and holding time (0 to 20min) on the textural, rheological, and microstructural properties of pasteurized process Cheddar cheese were studied using a central composite rotatable design. The loss tangent parameter (from small amplitude oscillatory rheology), extent of flow (derived from the University of Wisconsin Meltprofiler), and melt area (from the Schreiber test) all indicated that the meltability of process cheese decreased with increased concentration of TSC and that holding time led to a slight reduction in meltability. Hardness increased as the concentration of TSC increased. Fluorescence micrographs indicated that the size of fat droplets decreased with an increase in the concentration of TSC and with longer holding times. Acid-base titration curves indicated that the buffering peak at pH 4.8, which is due to residual colloidal calcium phosphate, decreased as the concentration of TSC increased. The soluble phosphate content increased as concentration of TSC increased. However, the insoluble Ca decreased with increasing concentration of TSC. The results of this study suggest that TSC chelated Ca from colloidal calcium phosphate and dispersed casein; the citrate-Ca complex remained trapped within the process cheese matrix. Increasing the concentration of TSC helped to improve fat emulsification and casein dispersion during cooking, both of which probably helped to reinforce the structure of process cheese.

Effect of gelation temperature on the properties of skim milk gels made from plant coagulants and chymosin

Reconstituted skim milk was gelled at 25–40°C with the plant-origin coagulants from Cynara cardunculus L. or Cynara humilis L. or with fermentation-produced chymosin. Gel formation and ageing were monitored by low amplitude oscillatory rheology and confocal scanning laser microscopy. Arrhenius plots for the rate of milk gelation were also determined. Plant coagulants had shorter gelation time (tg) at 25°C, 35°C and 40°C, and higher initial rate of increase in G′ values at all temperatures tested. The firmest gels at long ageing times were produced by chymosin at 30°C and 32°C. At a gelation temperature of 25°C, the differences in rheological and microstructural characteristics between plant coagulants and chymosin were considerable; plant coagulants had shorter tg and higher G′ values. For the lowest gelation temperatures, plant coagulants had smaller activation energy values for gelation. Most of the gelation results were similar between plant coagulants, but some differences were found in the values of tg, the rate of increase in G′ and loss tangent parameter. The characteristics of gels produced with plant coagulants were influenced less by the changes in temperature compared with chymosin-produced gels, which may be an important consideration in using plant-origin coagulants in the production of cheeses with a wider range of gelation temperatures.

Effects of Added Plasmin on the Formation and Rheological Properties of Rennet-Induced Skim Milk Gels

Elevated plasmin enzyme activity has been suggested as a likely cause of impaired functional properties that occur in milk from cows either in their latelactational period or that are experiencing mastitis. However, there are conflicting reports on the impact of plasmin on rennet coagulation properties of milk. The effects of added plasmin on the rheological properties, at small and large deformation, of rennet-induced gels were investigated. The microstructure of rennet-induced gels was studied, using confocal scanning laser microscopy. Porcine plasmin was added to reconstituted milk, and samples were incubated at 37°C for between 0.5 to 8h. The hydrolysis reaction was terminated using soybean trypsin inhibitor. The extent of degradation of caseins was determined with SDS-PAGE. The extent of breakdown of αs- and β-caseins increased with incubation time with plasmin. Storage modulus of rennet gels decreased linearly with increasing degradation of caseins. There was an increase in the loss tangent parameter of the gels with increasing casein degradation, indicating a more liquid-like gel character. Gelation time decreased until approximately 3h of incubation with plasmin (when the amounts of intact αs- and β-caseins were ∼46 and 50%, respectively); thereafter, gelation time increased considerably. Yield stress of rennet-induced gels decreased with increasing casein breakdown. When the level of casein hydrolysis was high (<40% of intact caseins), the microstructure of rennet-induced gels was drastically altered. Even when there were low levels of casein hydrolysis, the rheological properties of rennet gels were altered, which could have negative impacts on cheese yield and texture.

Dynamic viscoelastic properties of antimicrobial tissue conditioners containing silver–zeolite

Objectives: The purpose of this study was to determine the effects of including the antimicrobial silver–zeolite (SZ) on the dynamic viscoelastic properties of various tissue conditioners. Methods: The dynamic viscoelastic properties of five commercially available tissue conditioners: Visco-gel (VG), GC Soft-Liner (SL), FITT (FT), SR-Ivoseal (IV) and Shofu Tissue Conditioner (TC) containing SZ were evaluated after 1 and 28 days of water- and artificial saliva immersions with the use of complex modulus and loss tangent parameters. Values for these two parameters for each tissue conditioner were statistically analyzed by one- and two-way ANOVA and Bonferroni’s test. Results: Complex modulus and loss tangent values of TC were not significantly different among specimens containing 0, 2, 5 and 10 wt.%-SZ, respectively. In FT and TC containing 2 wt.%-SZ, these values were not significantly different between 1 and 28 days in both water- and saliva immersions. Conclusion: The results suggest that incorporating SZ does not affect TC’s inherent dynamic viscoelastic properties, while the other tissue conditioners investigated may be found to have changed viscoelastic properties as a consequence of the inclusion of SZ.

Characterisation of materials behaviour in microwave joining of ceramics

In this paper, attempts made for optimising the process parameters of the microwave welding of ceramic materials using a ridge waveguide are presented. The dielectric constant and the loss tangent parameters are measured using a HP85070 dielectric probe kit and also a network analyzer that works in the frequency range of 500 MHz–20 GHz at room temperature. These two parameters are measured in order to understand the penetration power of the microwave, and the ability of the material to convert absorbed energy into heat. The properties of the joint such as flexural strength, grain size, composition, porosity and other related properties are compared with respect to the parent materials. From the results obtained, it can be concluded that the quality of joint produced is reasonably good, with a joint strength of 60–95% of the flexural strength of the parent material.