The Measurement of Conductivity and Permittivity of Semiconductor Spheres by an Extension of the Cavity Perturbation Method

A technique based on cavity perturbation theory is described with which one can determine the microwave conductivity and dielectric permittivity of a small sphere of completely arbitrary conductivity. These properties follow from the measured frequency shift and quality change occurring when the sample is inserted into a region of maximum electric field in a cavity resonator. The range of validity of the quasi-static internal field approximation is discussed, and curves are provided for extending the measuring technique beyond this range. The extended theory is valid for the entire conductivity range from zero to infinity. Measurements on several samples of known conductivity and permittivity in which the approximation is not satisfied are seen to agree with the theory. For highly conductive materials, the present method is closely related to the "eddy current loss" measuring technique discussed by others. The two methods are compared from the point of view of perturbation theory in order to determine their relative merits. Because the measuring technique employs a spherical sample, it may be applied profitably to materials with nonisotropic carrier nobilities and to semiconducting materials for which contact fabrication techniques are poorly known.     

High-frequency paramagnetic susceptibility and cavity parameters

In a study on the relation between HF susceptibility and cavity parameters a discussion of higher-order effects is included and demagnetizing effects of the HF field are dealt with. Final formulas are given for an ellipsoidal sample in a collinear region of the HF field and for arbitrary orientation of the HF field with respect to the static field. The relation between the eigenfrequency and the admittance of the cavity is deduced by means of an unusual but more direct formalism which exploits the Poynting vector as basic quantity.     

Rapid electromagnetic warming of cells and tissues

We describe a system for thawing frozen cell suspensions and tissues by electromagnetic absorption. A 25-ml sample is heated in a cylindrical resonant cavity, which is excited in three modes all close to 434 MHz. Maximum warming rates are over 10 degrees C/s (600 C/min), and a frozen sample may be brought from -65 degrees C to room temperature in < 30 s, with final spatial differences of < 20 degrees C. Samples may be frozen externally, or cooled within the cavity at typically 1 degree C/min. We have also used the resonant cavity to measure the permittivity and conductivity of the sample at temperatures from -83 degrees C to +8 degrees C. By measuring the heat capacity of the sample, we have calculated the power deposited in it as a function of its temperature. The system is currently being used to investigate the effect of warming rate on cell survival.     

Cavity Model for the Slot Radiation of an Enclosure Excited by Printed Circuit Board Traces With Different Loads

Traces on a printed circuit board (PCB) couple to the cavity consisting of the PCB ground plane and a metallic enclosure cover. We introduce this common-mode coupling of a PCB trace to the cavity field by an analytical model that is verified with 3-D simulations using HFSS. The cavity field causes radiated emission from the slots of the cavity. For an accurate calculation of the cavity field inside the enclosure and the radiated emission, we consider the radiation loss by a multiport approach. Comparisons of the analytical results for the radiated field to measurements show good agreement. Radiated emission can be calculated for arbitrary geometric enclosure shapes as a function of frequency, position of the trace on the PCB, and trace load/driver impedances.      

基于瞬态微波光电导测试仪的谐振腔传感器设计

利用微波谐振腔微扰原理建立了应用于测量半导 体和发光材料的谐振腔的传感器模型。采用HFSS 仿真软件对谐振腔参数和结构进行仿真。仿真结果表明,采用矩形孔时,微波谐振腔中具有 符合实验要求 的电场形式以及电场强度;实验结果也表明,样品在采用矩形耦合孔的谐振腔获得了较强的 信号。将不同 的样品放置于谐振腔中,并用纳秒激光脉冲照射,获得了较理想的动力学曲线,证明该谐振 腔的实用性, 为下一步测量样品的介电常数和电导率等物理参数等实验奠定了基础。     

A simple method for accurate loss tangent measurement ofdielectrics using a microwave resonant cavity

A simple yet rigorous method has been developed to enable the loss tangent of dielectrics, having a known relative permittivity, to be accurately measured using a waveguide resonant cavity. The novel method eliminates the need for any physical measurement, either on the cavity or dielectric sample under test. The only electrical parameters that need to be measured are resonant frequencies and Q-factors of a reference cavity and those of the same cavity loaded with the dielectric sample. One of the advantages of the new technique is that dielectrics, of arbitrary shape, can be characterized at very high microwave frequencies. The new method has been verified through measurement over X-band     

On the attenuation of transient fields by imperfectly conducting spherical shells

Exact formulas for the electric and magnetic fields at any arbitrary point within a cavity region completely enclosed by a conducting spherical shell of arbitrary size are derived under the assumption that the exciting electromagnetic field is a linearly polarized, monochromatic, plane wave falling on the external surface of the shell. It is shown that the polarization of the electromagnetic field at the center of the cavity is the same as the polarization of the incident wave. From a knowledge of this steady-state solution, the time history of the electromagnetic field at the center of the cavity is calculated for the case where the incident wave is a Gaussian pulse. Numerical information on the effectiveness of the aluminum and copper shields under steady-state and transient conditions is provided for several pulse durations, shield sizes, and wall thicknesses.     

Shift of the complex resonance frequency of a dielectric-loadedcavity produced by small sample insertion holes

The presence of small sample insertion holes in a cylindrical cavity produces a shift in the complex resonance frequency of the cavity. A mathematical model is proposed to compute the shift when the cavity oscillates in an axially symmetric TM_0mp mode The treatment applies to samples with arbitrary complex permittivity. The model is compared to other treatments and checked against measured results     

Novel open-resonator for a quasioptical gyrotron

A new kind of open-resonator for a quasioptical gyrotron—an axisymmetrical quasioptical cavity of oblique roiation at arbitrary angle (AQCORAA)—is proposed. Using scalar diffraction theory and an approximate method, the field distributions in the AQCORAA are derived, and the influence of rotating angle on the field distributions is analysed. The stored field energy in the cavity is also obtained.     

Propagation of ELF waves below an inhomogeneous anisotropic ionosphere

The ionospheric anisotropy is considered with horizontal magnetic field either for transverse (East-West or West-East) or for longitudinal (South-North) propagation. For transverse propagation in a vertically stratified medium the differential equations of the various field components are uncoupled and a closed form solution is given for identical exponential height variation of the components of tensor conductivity. For arbitrary height variation of the tensor conductivity numerical solutions are obtained after expressing the surface impedance below the ionosphere in terms of a Riccati-type differential equation. The West-East direction of propagation exhibits a lower attenuation constant than the East-West direction forf < 1000cps. This is contrary to the expectations based on a model of a homogeneous anisotropic ionosphere. For longitudinal propagation the differential equations of the various field components are coupled, with the coupling being particularly strong above theDregion. The differential equations are simplified by assuming no coupling in the lower ionosphere and strong coupling above a pre-selected altitudey_{1}. For exponential height variation of the tensor conductivity components the closed form solution differs negligibly from the isotropic case. For arbitrary height varition of the tensor conductivity numerical solutions are obtained similarly as for the transverse propagation. Over most of the frequency range the attenuation figures for South-North propagation are intermediate between the corresponding figures for West-East and East-West propagation.     

大失谐情况下的V-型三能级原子与光场相互作用

本文研究了一个V-型三能级原子与光场的相互作用．在原子与场大失谐情况下,处于基态能级可绝热消除,即此模型可化为非简并Raman耦合模型;进而提出了其改进型有效哈密顿量;最后得到了简并Raman耦合模型的有效哈密顿量,并借助于矩阵求出了任意时刻波函数的解。     

Measurement of material properties with a tunable resonant cavity

A tunable resonant cavity is used to measure the complex permittivity of dielectrics and the surface conductivity of metals with high precision. The analytical approximations, traditionally used in the cavity perturbation techniques, have been replaced with a rigorous numerical solution of the electromagnetic field distribution inside the rotationally symmetric cavity filled with inhomogeneous dielectrics. The measured values of the unloaded Q factor are compared with the numerically computed values over the tuning range. The least-squares data fitting procedure yields simultaneously the values of the loss tangent and the surface conductivity, and their standard deviations.<>     

Source Coding With Feed-Forward: Rate-Distortion Theorems and Error Exponents for a General Source

In this work, we consider a source coding model with feed-forward. We analyze a system with a noiseless, feed-forward link where the decoder has knowledge of all previous source samples while reconstructing the present sample. The rate-distortion function for an arbitrary source with feed-forward is derived in terms of directed information, a variant of mutual information. We further investigate the nature of the rate-distortion function with feed-forward for two common types of sources- discrete memory- less sources and Gaussian sources. We then characterize the error exponent for a general source with feed-forward. The results are then extended to feed-forward with an arbitrary delay larger than the block length.     

Electromagnetic scattering from three-dimensional cavities via aconnection scheme

The electromagnetic scattering from arbitrary three-dimensional cavities is presented. To alleviate computational constraints for three-dimensional problems, a connection scheme is developed based on microwave network theory. This scheme allows the cavity to be divided into sections and each section to be analyzed independently of the rest of the cavity. Each section of the cavity is represented by a generalized admittance matrix which if formulated via a boundary-integral equation approach. Using the concept of input and load admittance, the aperture admittance matrix of the cavity can be derived by cascading the admittance matrices of individual sections. Once the cavity aperture admittance matrix is obtained, the aperture electric field and the backscattered field are found by the standard generalized network formulation. Numerical results are compared against modal solutions of regularly shaped cavities with good agreement. This connection scheme leads to a reduction in computational resources, especially for cavities with one dimension much larger than the other two     

On the electromagnetic field in a cavity fed by a tangentialelectric field in an aperture in its wall

Heretofore, the electromagnetic field produced by a specified tangential electric field in an aperture in the wall of an arbitrarily shaped cavity has most often been expanded in terms of cavity modes. An alternative approach, that of the electric field integral equation is presented. In this approach, the cavity field is expressed as the field of a surface density of tangential electric current, or a surface density of tangential magnetic current, or a combination of surface densities of tangential electric and magnetic currents on the boundary of the cavity. Each surface density is characterized by a single tangential vector function which is determined by the integral equation requiring that the part of the electric field tangent to the boundary of the cavity must reduce to the specified tangential electric field in the aperture and zero elsewhere on the boundary of the cavity. The electric field integral equation method is specialized to more easily determine the field inside an arbitrary cylindrical cavity excited by a tangential electric field in an aperture in its lateral wall. The method is further specialized to a circular cavity     

Convergence of the reverberation chambers to the equilibrium analyzed with the finite-difference time-domain algorithm

Over recent years, reverberation chambers have been analyzed by many numerical techniques. This contribution studies how the finite-difference time-domain algorithm converges to the steady state conditions as a function of the cavity Q factor, changing the wall conductivity or the internal lossy media. By lowering the reflection coefficient of the chamber walls, the computation time could be considerably reduced without a significant effect on the field distribution for any analyzed antennas. The field distributions are strongly correlated when the conductivity of the wall is one hundredth of the copper conductivity or greater, whereas when the conductivity is lower the correlation between field distributions is low.     

Quantitative Formulations of Electrophysiological Sources of Potential Fields in Volume Conductors

The noninvasive measurement of electrical potentials at the surface of the body (e.g., the electrocardiogram) has long been considered an important tool in clinical diagnosis. Electrophysiological modeling and simulation is valuable as an aid in the interpretation of such potential recordings. In all cases, the potential field can be considered to arise from bioelectric sources operating in a volume conductor. This paper concentrates on the appropriate quantitative formulation for these sources. Such sources arise from excitable cells undergoing action potentials (primary sources) or at passive boundaries between regions of different conductivity (secondary sources). These sources are described and discussed for arbitrary cell shapes, circular cylindrical cells, conductive media with piecewise constant conductivity, and for syncytial tissue whose macroscopic properties are anisotropic.     

Programmable Temperature Control System for Biological Materials

A system was constructed which allows programmable temperature?time control for a 5 cm3 sample volume of arbitrary biological material. The system also measures the parameters necessary for the determination of the sample volume specific heat and thermal conductivity as a function of temperature, and provides a detailed measurement of the temperature during phase change and a means of calculating the heat of the phase change.     

Measurement of the microwave conductivity of a polymeric materialwith potential applications in absorbers and shielding

The microwave conductivity of a new material, the polymer poly-p-phenylene-benzobis-thiazole (PBT) made conductive by ion-implantation doping with iodine, is measured at 9.89 GHz as a function of temperature using the cavity perturbation technique applicable to thin films of arbitrary shape. The DC and microwave conductivities of PBT are seen to approach asymptotically the low-temperature limit predicted by Mott's energy-dependent hopping model. The potential utilization of conductive polymers in microwave absorbers and electromagnetic interference (EMI) shielding is examined using layered media EM theory     

High-Accuracy Wide-Range Measurement Method for Determination of Complex Permittivity in Reentrant Cavity: Part A --- Theoretical Analysis of the Method

New mathematical method for calculation of complex electric permittivity (epsilon) of a wide range of materials from the direct measured parameters of a reentrant cavity containing a sample of material is presented. Condition of resonance is drawn based on analysis of electromagnetic field distribution in the cavity with a sample. Accuracy of the obtained algorithm (convergences of series) and method of shortening iterative solution is discussed in detail.