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Microwave Frequencies (microwave + frequency)
Selected AbstractsEffect of Temperature (,5 to 130 °C) and Fiber Direction on the Dielectric Properties of Beef Semitendinosus at Radio Frequency and Microwave FrequenciesJOURNAL OF FOOD SCIENCE, Issue 6 2008N. Basaran-Akgul ABSTRACT:, The dielectric properties must be defined to design efficient radio frequency (RF) and microwave (MW) processes by the food manufacturers. The objective of this study was to understand how frequency, temperature, and muscle fiber orientation influence the dielectric properties. The eye of round (Semitendinosus) muscle was selected because it contains large, relatively uniform muscle cells with similar muscle fiber orientation and relatively uniform chemical composition throughout the tissue. Dielectric properties were measured using an open-ended coaxial probe technique at 27, 915, and 1800 MHz and temperatures between ,5 and 130 °C. Power penetration depth was calculated. Since many commercially prepared, thermally processed, ready-to-eat entrees are made with frozen meat, dielectric property measurements were started from ,5 °C. The dielectric constant and dielectric loss factors were often higher for muscle with the muscle fiber measured in a parallel orientation to the probe compared to samples of the same treatment (for example, fresh or frozen) in a perpendicular tissue orientation at the same frequency and temperature. Dielectric constant and loss values for frozen beef tended to be higher than fresh beef at the same temperature and frequency. Tissue orientation appeared to have a greater effect on dielectric loss values at lower frequencies. Penetration depth tended to be greater when the direction of propagation was perpendicular to the muscle fiber. [source] A New Compound with Ultra Low Dielectric Loss at Microwave FrequenciesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2009Ching-Fang Tseng A new ultra low loss microwave dielectric ceramic, Mg(Sn0.05Ti0.95)O3 (MSnT), was found and investigated. The compounds were prepared by the conventional solid-state route, and sintered at 1360°,1480°C for 2,6 h. The investigations show that the MgTi2O5 secondary phase was observed. Moreover, the dielectric properties were correlated with the formation second phase. The excellent microwave dielectric properties of Q×f=322 000 (GHz), ,r=17.4, and ,f=,54 ppm/°C were obtained from the new MSnT ceramics sintered at 1390°C for 4 h. [source] Giant Electric Field Tuning of Magnetic Properties in Multiferroic Ferrite/Ferroelectric HeterostructuresADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Ming Liu Abstract Multiferroic heterostructures of Fe3O4/PZT (lead zirconium titanate), Fe3O4/PMN-PT (lead magnesium niobate-lead titanate) and Fe3O4/PZN-PT (lead zinc niobate-lead titanate) are prepared by spin-spray depositing Fe3O4 ferrite film on ferroelectric PZT, PMN-PT and PZN-PT substrates at a low temperature of 90,°C. Strong magnetoelectric coupling (ME) and giant microwave tunability are demonstrated by a electrostatic field induced magnetic anisotropic field change in these heterostructures. A high electrostatically tunable ferromagnetic resonance (FMR) field shift up to 600,Oe, corresponding to a large microwave ME coefficient of 67,Oe cm kV,1, is observed in Fe3O4/PMN-PT heterostructures. A record-high electrostatically tunable FMR field range of 860 Oe with a linewidth of 330,380,Oe is demonstrated in Fe3O4/PZN-PT heterostructure, corresponding to a ME coefficient of 108,Oe cm kV,1. Static ME interaction is also investigated and a maximum electric field induced squareness ratio change of 40% is observed in Fe3O4/PZN-PT. In addition, a new concept that the external magnetic orientation and the electric field cooperate to determine microwave magnetic tunability is brought forth to significantly enhance the microwave tunable range up to 1000,Oe. These low temperature synthesized multiferroic heterostructures exhibiting giant electrostatically induced tunable magnetic resonance field at microwave frequencies provide great opportunities for electrostatically tunable microwave multiferroic devices. [source] Recent developments in nonlinear network design: Overview of integrated nonlinear microwave and millimeter-wave circuits workshopINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 5 2002Adalbert BeyerArticle first published online: 27 AUG 200 Abstract In the 1960s and 1970s the design of microwave networks containing nonlinear elements often consisted of trial and error routines. The required circuit performance was then achieved iteratively. With the knowledge of the physical property of the materials at microwave frequencies and its influence on active devices used in microwave networks, it is possible to reduce the time required to analyze new nonlinear circuits for microwave purposes. Advanced tools are necessary, which can analyze the network very quickly for a short development time. The basic requirements are a fast and accurate nonlinear measurement system and descriptions that match the real counterpart. This article shows the development of the nonlinear microwave network design for the last decade as a reflection of the workshop entitled Integrated Nonlinear Microwave and Millimeterwave Circuits. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12, 388,417, 2002. Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mmce10041 [source] Dielectric properties of pharmaceutical materials relevant to microwave processing: Effects of field frequency, material density, and moisture contentJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2010Paul W.S. Heng Abstract The rising popularity of microwaves for drying, material processing and quality sensing has fuelled the need for knowledge concerning dielectric properties of common pharmaceutical materials. This article represents one of the few reports on the density and moisture content dependence of the dielectric properties of primary pharmaceutical materials and their relevance to microwave-assisted processing. Dielectric constants and losses of 13 pharmaceutical materials were measured over a frequency range of 1,MHz,1,GHz at 23,±,1°C using a parallel-electrode measurement system. Effects of field frequency, material density and moisture content on dielectric properties were studied. Material dielectric properties varied considerably with frequency. At microwave frequencies, linear relationships were established between cube-root functions of the dielectric parameters ( and ) and density which enabled dielectric properties of materials at various densities to be estimated by regression. Moisture content was the main factor that contributed to the disparities in dielectric properties and heating capabilities of the materials in a laboratory microwave oven. The effectiveness of a single frequency density-independent dielectric function for moisture sensing applications was explored and found to be suitable within low ranges of moisture contents for a model material. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:941,957, 2010 [source] Low-Loss Microwave Dielectrics in the Spinel-Structured (Mg1,xNix)Al2O4 Solid SolutionsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010Cheng-Liang Huang Solid solutions of (Mg1,xNix)Al2O4 (x=0,1) have been prepared using the solid-state reaction method and their dielectric properties were measured at microwave frequencies. Formation of single-phase spinel-structured solid solutions was confirmed by X-ray diffraction analysis throughout the entire compositional range, and the measured lattice parameters varied linearly from 8.0810 Å at x=0 (MgAl2O4) to 8.0445 Å at x=1 (NiAl2O4) leading to a linear decrease in the unit cell volume from 527.71 to 520.59 Å3. The ionic polarizability obtained, however, increased with the increase of x to a maximum at x=0.25 and decreased thereafter. It shows only a small variance in the ,r with Ni substitution for Mg and a maximum ,r of 8.21 was achieved for (Mg0.75Ni0.25)Al2O4 in response to the highest ionic polarizability and relative density. However, the Q×f value can be significantly promoted up to a maximum value of 130 000 GHz (measured at 15.4 GHz) at x=0.25. In addition, substitution of Mg by Ni also helps to decline the ,f value from ,65 ppm/°C at x=0 to ,53.5 ppm/°C at x=0.25. [source] Human pericardial fluid at microwave frequenciesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2009Anil Lonappan Abstract This article reports a new method of analyzing pericardial fluid based on the measurement of the dielectric properties at microwave frequencies. The microwave measurements were performed by rectangular cavity perturbation method in the S-band of microwave frequency with the pericardial fluid from healthy persons as well as from patients suffering from pericardial effusion. It is observed that a remarkable change in the dielectric properties of patient samples with the normal healthy samples and these measurements were in good agreement with clinical analysis. This measurement technique and the method of extraction of pericardial fluid are simple. These results give light to an alternative in-vitro method of diagnosing onset pericardial effusion abnormalities using microwaves without surgical procedure. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 155,158, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24010 [source] A novel method of detecting cervical cancer using microwavesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2008Anil Lonappan Abstract This article communicates a new method of detecting cervical cancer based on the measurement of the dielectric properties of smear at microwave frequencies. The microwave measurements were performed by rectangular cavity perturbation in the S-band of microwave frequency with the smear samples from healthy persons as well as from cancerous patients. It is observed an appreciable change in the dielectric properties of cancerous samples with the normal healthy samples and these measurements were in good agreement with clinical analysis. This measurement technique is simple and the collection of smear is painless and nonsurgical in nature. The results show a new method of diagnosing cervical cancer using microwave measurement without any surgical procedures and suggest an alternative to Papanikolaou test or Papanicolaou test. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1552,1554, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23433 [source] A novel method of detecting HIV/AIDS using microwavesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2008Anil Lonappan Abstract HIV/AIDS is one of the most destructive epidemics in ever recorded history claims an estimated 2.4,3.3 million lives every year. Even though there is no treatment for this pandemic Elisa and Western Blot tests are the only tests currently available for detecting HIV/AIDS. This article proposes a new method of detecting HIV/AIDS based on the measurement of the dielectric properties of blood at the microwave frequencies. The measurements were made at the S-band of microwave frequency using rectangular cavity perturbation technique with the samples of blood from healthy donors as well as from HIV/AIDS patients. An appreciable change is observed in the dielectric properties of patient samples than with the normal healthy samples and these measurements were in good agreement with clinical results. This measurement is an alternative in vitro method of diagnosing HIV/AIDS using microwaves. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 557,561, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23143 [source] Analysis of female human breast tissues at microwave frequenciesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2008G. Bindu Abstract Complex permittivities of in vitro female human breast tissues have been measured at the ISM band using rectangular resonant cavity perturbation technique. Ranges of dielectric properties and water contents of these tissues are presented. The results show that benign and malignant breast tumors can be characterized based on the variation of the dielectric properties with respect to the dielectric parameters of the normal breast tissues. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 614,616, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23160 [source] Synovial fluid at microwave frequenciesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2007Anil Lonappan Abstract Arthritis is one of the most pervasive diseases that causes of disability. For most people arthritis pain and inflammation cannot be avoided as the body ages. The present communication reports the study on the synovial fluid has the main lubricant in joints collected from normal persons and those ailing from arthritis are subjected to the microwave study and the variations of the dielectric parameters are investigated. The in vitro measurements of synovial fluid samples are done using cavity perturbation technique in the frequency range of 2,3 GHz. It is observed that in this band, the dielectric constant of normal samples are higher than those of arthritis affected ones and conductivity of is higher in normal samples, which finds application in detecting arthritis using microwaves. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1700,1702, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22552 [source] Experimental investigation of breast tumor imaging using indirect microwave holographyMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2006M. Elsdon Abstract A novel indirect holographic technique for the early detection of breast cancer, which offers considerable benefits in terms of simplicity and expense, is presented and discussed. It is shown how this approach, usually employed at optical frequencies, can be adapted to image breast tumors at microwave frequencies. Practical results, using a simulated phantom, successfully demonstrate the validity of this technique. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 480,482, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21384 [source] Microwave dielectric properties of polybutylene terephtalate (PBT) with carbon black particlesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2005L. C. Costa Abstract The synthesis of composites based on polymers containing carbon as additives is rather relevant because it has been found that applications in several industries are increasing, particularly due to their unusual mechanical and electrical properties. By choosing the adequate doping concentrations, we can precisely control the electrical properties in the microwave frequencies, in order to tailor the desired behavior. In this study, we present the results of the complex-permittivity measurements, ,* = ,, , í ,,, at 2.7, 5, and 12.8 GHz, on polybutylene terephtalate (PBT), with different concentration of black carbon particles, using the resonant-cavity method. Measuring the shift in the resonant frequency of the cavity, ,f, caused by the insertion of the sample, we can calculate to the real part of the complex permittivity, ,,, while the measure of the change in the inverse of the quality factor of the cavity, ,(1/Q), allow us to calculate the imaginary part, ,,. Maxwell,Wagner,Sillars (MWS) and Looyenga mixture laws are applied to the obtained results. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 61,63, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20901 [source] Wind direction azimuthal signature in the Stokes emission vector from the ocean surface at microwave frequenciesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2001A. J. Camps Abstract An ocean polarimetric emission model is presented. It is found that skewness and upwind/cross-wind rms slopes are responsible for the first and second azimuthal harmonic, respectively. Atmospheric effects contribute significantly at low wind speeds, and at horizontal polarization at certain observation angles. Simulation results compare favorably with reported JPL,WINDRAD measurements. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 426,432, 2001. [source] Magnetoimpedance (MI) in amorphous wires: new materials and applicationsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2009Larissa V. Panina Abstract The discovery of the magnetoimpedance (MI) effect in 1994 had a strong impact on the development of magnetic sensors. Along with traditional areas of sensing applications (data storage, bio-medical electronics, robotics and security), the MI elements have a high potential for applications in smart sensory systems (self-sensing composites) operating at microwave frequencies owing to still very large MI ratios of 50,100% in Co-rich amorphous wires at GHz frequencies. Here we introduce two types of MI wire composites: 2D-arrays and mixtures of wire pieces. In such materials the effective permittivity has strong dispersion in a frequency band determined by a plasma frequency or a dipole resonance, respectively. If MI wires are used as constituent elements, this dispersion may be very sensitive to the magnetic properties of wires since the wire impedance determines the relaxation parameter of the effective permittivity. For example, increasing the wire impedance by establishing the magnetisation along the axis with an external magnetic field broadens the resonance band, decreases the reflection amplitude and may open a bandpass. Depending on the magnetic anisotropy in wires, tuning can be realized with both magnetic field and stress. It is foreseen that MI-wire composite materials could be suitable for large scale applications, in particular, for free space filters in secure wireless systems and for microwave nondestructive testing and control in civil engineering. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] AC impedance analysis and EMI shielding effectiveness of conductive SBR compositesPOLYMER ENGINEERING & SCIENCE, Issue 10 2006G.T. Mohanraj Flexible conductive polymer composites were prepared using styrene,butadiene rubber (SBR) as a matrix and conductive carbon black as filler. The filler loading was varied from 10 to 60 phr. The complex AC impedance and electromagnetic interference shielding effectiveness (EMI SE) of the composites were measured at the microwave frequencies of 7.8,12.4 GHz. The effect of variation in filler concentration and measurement frequency on the AC impedance and EMI SE of the composites were investigated. Equivalent circuits describing the conduction behavior of the composites were determined by means of Nyquist plots. The complex electric modulus of the composites was also determined. Increase in the filler loading increased the capacitive nature of the materials. The composites were better defined by a parallel resistor,capacitor circuit in series with a resistor. The EMI SE was found to pass through a maximum with increase in frequency. However, with the increase in filler loading and sample thickness of the material, the EMI SE was found to increase continuously. POLYM. ENG. SCI., 46:1342,1349, 2006. © 2006 Society of Plastics Engineers. [source] Passive microwave radiometer channel selection basedoncloudandprecipitation information contentTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 617 2006Sabatino Di Michele Abstract The information content of microwave frequencies between 5 and 200 GHz for rain, snow and cloud water retrievals over ocean and land surfaces was evaluated using optimal estimation theory. The study was based on large datasets representative of summer and winter meteorological conditions over North America, Europe, Central Africa, South America and the Atlantic obtained from short-range forecasts with the operational ECMWF model. The information content of rain, snow and cloud water was traded off against the uncertainties due to the natural variability of other variables that microwave observations are sensitive to. These are surface emissivity, land surface skin temperature, atmospheric temperature and moisture. The estimation of the underlying error statistics was based on ECMWF model forecast error statistics. The results suggest that a number of frequency bands are most suited for the retrieval of (i) rain over oceans: 15,18, 35,40, 80, 145, 118.75±10,14 GHz; rain over land: 85,100, 135,140 GHz, (ii) snow over land and oceans: 95,100, 140,150, 187 GHz, (iii) clouds over oceans: 40, 80,85 GHz; clouds over land: 90,100, 135,140 GHz. For radiometers designed for global and multi-season applications, several channels in all of the above frequency ranges would be desirable for optimizing channel usage in hydrometeor retrievals depending on the observed situation. Copyright © 2006 Royal Meteorological Society. [source] Einstein Lecture , Passion for precision,ANNALEN DER PHYSIK, Issue 9 2006T.W. Hänsch Abstract Optical frequency combs from mode-locked femtosecond lasers have link optical and microwave frequencies in a single step, and they provide the long missing clockwork for optical atomic clocks. By extending the limits of time and frequency metrology, they enable new tests of fundamental physics laws. Precise comparisons of optical resonance frequencies of atomic hydrogen and other atoms with the microwave frequency of a cesium atomic clock are establishing sensitive limits for possible slow variations of fundamental constants. Optical high harmonic generation is extending frequency comb techniques into the extreme ultraviolet, opening a new spectral territory to precision laser spectroscopy. Frequency comb techniques are also providing a key to attosecond science by offering control of the electric field of ultrafast laser pulses. In our laboratories at Stanford and Garching, the development of new instruments and techniques for precision laser spectroscopy has long been motivated by the goal of ever higher resolution and measurement accuracy in optical spectroscopy of the simple hydrogen atom which permits unique confrontations between experiment and fundamental theory. This lecture recounts these adventures and the evolution of laser frequency comb techniques from my personal perspective. [source] Complex permittivity of sodium chloride solutions at microwave frequenciesBIOELECTROMAGNETICS, Issue 4 2007A. Peyman Abstract The complex permittivity of aqueous solutions at 20,°C has been measured at concentrations between 0.001 and 5,mol/L and over a frequency range 0.13,20,GHz. The results were combined with literature values to derive empirical equations to predict the dielectric behavior of sodium chloride solutions between 0 and 5,mol/L and 5°C,35,°C. Bioelectromagnetics 28:264,274, 2007. © 2007 Wiley-Liss, Inc. [source] Influence of 400, 900, and 1900 MHz electromagnetic fields on Lemna minor growth and peroxidase activityBIOELECTROMAGNETICS, Issue 3 2005Mirta Tkalec Abstract Increased use of radio and microwave frequencies requires investigations of their effects on living organisms. Duckweed (Lemna minor L.) has been commonly used as a model plant for environmental monitoring. In the present study, duckweed growth and peroxidase activity was evaluated after exposure in a Gigahertz Transversal Electromagnetic (GTEM) cell to electric fields of frequencies 400, 900, and 1900 MHz. The growth of plants exposed for 2 h to the 23 V/m electric field of 900 MHz significantly decreased in comparison with the control, while an electric field of the same strength but at 400 MHz did not have such effect. A modulated field at 900 MHz strongly inhibited the growth, while at 400 MHz modulation did not influence the growth significantly. At both frequencies a longer exposure mostly decreased the growth and the highest electric field (390 V/m) strongly inhibited the growth. Exposure of plants to lower field strength (10 V/m) for 14 h caused significant decrease at 400 and 1900 MHz while 900 MHz did not influence the growth. Peroxidase activity in exposed plants varied, depending on the exposure characteristics. Observed changes were mostly small, except in plants exposed for 2 h to 41 V/m at 900 MHz where a significant increase (41%) was found. Our results suggest that investigated electromagnetic fields (EMFs) might influence plant growth and, to some extent, peroxidase activity. However, the effects of EMFs strongly depended on the characteristics of the field exposure. Bioelectromagnetics 26:185,193, 2005. © 2005 Wiley-Liss, Inc. [source] Spin-lattice relaxation of spin-½ nuclei in solids containing diluted paramagnetic impurity centers.CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2003Abstract Dynamic nuclear polarization of nuclei by means of paramagnetic electron spin locking (Hartmann-Hahn cross-polarization between paramagnetic electrons and nuclei, or NOVEL) is discussed. The theory is demonstrated by experiments executed at 2.4 and 9.6 GHz on a natural type Ib diamond. It is shown that the 13C polarization rate is independent of the microwave frequency, in agreement with theory. NOVEL polarization takes place only while the spin-locking pulse is on. The rate at which the nuclei are polarized is proportional to the electron polarization in the rotating frame. Therefore, the length of the spin-locking pulse is limited by the value of T1,(e), and because T1,(e) , T1(e) for diamond the effective NOVEL polarization rate of 13C nuclei is usually relatively low. A comparison between the relative effectiveness of 13C polarization rates between NOVEL and the solid-state effect is made for high and low paramagnetic impurity concentrations. The dependence of the 13C polarization rate on the paramagnetic impurity concentration has been determined for a suite of natural diamonds. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 19A: 44,49, 2003. [source] Time domain global modelling of EM propagation in semiconductor using irregular gridsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 4 2002Hsiao-Ping Tsai Abstract A two-dimensional finite volume time domain (FVTD) method using a triangular grid is applied to the analysis of electromagnetic wave propagation in a semiconductor. Maxwell's equations form the basis of all electromagnetic phenomena in semiconductors and the drift-diffusion model is employed to simulate charge transport phenomena in the semiconductor. The FVTD technique is employed to solve Maxwell's equations on an irregular grid and the finite box method is implemented on the same grid to solve the drift-diffusion model for carrier concentration. The locations of unknowns have been chosen to allow linking coupled Maxwell's equations and transport equations in a seamless way. To achieve suitable accuracy and computational efficiency, using irregular grid topology allows a finer mesh in doped region and at junction, and a coarser mesh in substrate and insulting regions. The proposed scheme has been implemented and verified by characterizing electromagnetic wave propagation at microwave frequency in a semiconductor slab with arbitrary doping profile. Copyright © 2002 John Wiley & Sons, Ltd. [source] Effect of Filler Content on the Dielectric Properties of PTFE/ZnAl2O4,TiO2 CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2008Sherin Thomas ZnAl2O4,TiO2 (ZAT)/polytetrafluoroethylene (PTFE) composites were prepared by powder processing method. The structure and microstructure of the composites were analyzed using X-ray diffraction and scanning electron microscopic techniques. The effect of different volume fraction of ZAT (0,0.6) on the dielectric properties of the composites was investigated at 1 MHz and at the microwave frequency of 7 GHz. The dielectric properties (relative permittivity and dielectric loss) were found to increase with the ZAT content. The samples with 60 vol.% of ZAT filler showed a relative permittivity of 3.9 and dielectric loss of 0.009, respectively, at 7 GHz. The variation of relative permittivity and dielectric loss showed only a very small variation with temperature in the range 25°,70°C for various ZAT/PTFE composites. The relative permittivity obtained experimentally were compared with that of the theoretical values predicted using modified Lichtenecker, Jayasundere,Smith, and Series mixing formulae. They were found to agree well with the predicted values for low filler content. [source] Microwave Dielectric Properties of A-Site Modified Ba(Co0.7Zn0.3)1/3Nb2/3O3 by La3+JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2008Jian Jiang Bian The sintering behavior, ordering state, and microwave dielectric properties of Ba1,xLa2x/3(Zn0.3Co0.7)1/3Nb2/3O3 Ceramics (0,x,0.06) were investigated in this paper. The X-ray diffraction (XRD) results show that all samples exhibit a single perovskite phase except for the sample with x,0.03. The sinterability is slightly improved by La doping. The long range order (LRO) degree on B-site is greatly increased with the increase of x value up to x=0.015 and then slightly decreased with the further increase of x due to the increasing amount of second phases. The dielectric constant at microwave frequency decreases slightly with the increase of x when x<0.015 and increases slightly with further increasing x for the samples sintered at 1375°C/10 h. The Q×f value increases with x up to x=0.015 and then decreases with further increase of x, which is consistent with the variation trend of LRO degree. The ,f value decreases slightly with the increase of x up to 0.006, then increases greatly with the further increase of x. An optimized dielectric properties of ,r=34, Q×f=63 159, GHz and ,f=5.21 ppm/°C were obtained for the x=0.01 sample sintered at 1425°C/10 h. [source] Improvement of Microwave Loss Tangent and Tunability of Ba0.55Sr0.45TiO3/MgO Composites Using the Heterogeneous Precipitation MethodJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Rui-Hong Liang Ba0.55Sr0.45TiO3/MgO composites were successfully prepared by the heterogeneous precipitation method and their structural, surface morphological, tunable properties, and dielectric properties at microwave frequency were systemically investigated. Compared with the sample prepared by the traditional solid-state method, the sample prepared by the heterogeneous precipitation method exhibits a smaller grain size, more uniform microstructure, higher tunability, and lower microwave loss, and these properties are very beneficial to the development of the microwave tunable devices application. Moreover, the effects of La2O3 doping on the dielectric and tunable properties of BST/MgO composites are investigated. The result shows that the La3+ -doped sample has higher tunability and lower microwave loss than the undoped one. [source] Human pericardial fluid at microwave frequenciesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2009Anil Lonappan Abstract This article reports a new method of analyzing pericardial fluid based on the measurement of the dielectric properties at microwave frequencies. The microwave measurements were performed by rectangular cavity perturbation method in the S-band of microwave frequency with the pericardial fluid from healthy persons as well as from patients suffering from pericardial effusion. It is observed that a remarkable change in the dielectric properties of patient samples with the normal healthy samples and these measurements were in good agreement with clinical analysis. This measurement technique and the method of extraction of pericardial fluid are simple. These results give light to an alternative in-vitro method of diagnosing onset pericardial effusion abnormalities using microwaves without surgical procedure. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 155,158, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24010 [source] A novel method of detecting cervical cancer using microwavesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2008Anil Lonappan Abstract This article communicates a new method of detecting cervical cancer based on the measurement of the dielectric properties of smear at microwave frequencies. The microwave measurements were performed by rectangular cavity perturbation in the S-band of microwave frequency with the smear samples from healthy persons as well as from cancerous patients. It is observed an appreciable change in the dielectric properties of cancerous samples with the normal healthy samples and these measurements were in good agreement with clinical analysis. This measurement technique is simple and the collection of smear is painless and nonsurgical in nature. The results show a new method of diagnosing cervical cancer using microwave measurement without any surgical procedures and suggest an alternative to Papanikolaou test or Papanicolaou test. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1552,1554, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23433 [source] A novel method of detecting HIV/AIDS using microwavesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2008Anil Lonappan Abstract HIV/AIDS is one of the most destructive epidemics in ever recorded history claims an estimated 2.4,3.3 million lives every year. Even though there is no treatment for this pandemic Elisa and Western Blot tests are the only tests currently available for detecting HIV/AIDS. This article proposes a new method of detecting HIV/AIDS based on the measurement of the dielectric properties of blood at the microwave frequencies. The measurements were made at the S-band of microwave frequency using rectangular cavity perturbation technique with the samples of blood from healthy donors as well as from HIV/AIDS patients. An appreciable change is observed in the dielectric properties of patient samples than with the normal healthy samples and these measurements were in good agreement with clinical results. This measurement is an alternative in vitro method of diagnosing HIV/AIDS using microwaves. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 557,561, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23143 [source] Analytical noise model of a high-electron-mobility transistor for microwave-frequency applicationMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2004Vandana Guru Abstract Noise analysis for AlGaAs/GaAs HEMT and AlGaAs/InGaAs/GaAs PHEMT is developed at microwave frequency using an accurate charge control approach. The small-signal parameters and the drain and gate-noise sources are calculated to determine the noise coefficients and correlation coefficients. Finally, the minimum noise figure is evaluated by incorporating the extrinsic noise sources and compared with the experimental data, which is in excellent agreement. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 410,417, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11396 [source] Relationship between the propagation characteristics of via and microstrip connecting angleMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 3 2003Wusheng Ji Abstract The microstrip-via-microstrip is a popular interconnect structure in multilayer circuits at microwave frequency. The microstrip connecting angle is an arbitrary angle due to layout and technical error. The relationship between the propagation characteristics of via and the microstrip connecting angle was analyzed by using the Ansoft simulator. The obtained results have important application value for the design of a similar multilayer circuit. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 225,228, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11021 [source] | ||||||||||||||||||||||