This contribution introduces a novel, dielectric waveguide based, permittivity sensor. Next to the fundamental hybrid mode theory, which predicts exceptional wave propagation behavior, a design concept is presented that realizes a pseudo-transmission measurement approach for attenuating feed-side reflections. Furthermore, a transmission line length independent signal processing is introduced, which fosters the robustness and applicability of the sensor concept. Simulation and measurement results that prove the sensor concept and validate the high measurement accuracy, are presented and discussed in detail.

In a free-space method using a pair of horn antennas with dielectric lenses, we demonstrated that the permittivity of a sample can be estimated with good accuracy by equalizing a measured transmission coefficient of a sample to a transmission coefficient for a Gaussian beam, which is approximately equal to the transmission coefficient for a plane wave multiplied by a term that changes the phase. In this permittivity estimation method, because the spot size at the beam waist in a Gaussian beam needs to be determined, we proposed an estimation method of the spot size by employing the measurement of the Line in Thru-Reflect-Line calibration; thus, no additional measurement is required. The permittivity estimation method was investigated for the E-band (60-90 GHz), and it was demonstrated that the relative permittivity of air with a thickness of 2mm and a sample with the relative permittivity of 2.05 and a thickness of 1mm is estimated with errors less than ±0.5% and ±0.2%, respectively. Moreover, in measuring a sample without displacing the receiving horn antenna to avoid the error in measurement, we derived an expression of the permittivity estimation for S parameters measured using a vector network analyzer, and demonstrated that the measurement of a sample without antenna displacement is valid.

The equivalent anisotropic material parameters of metal dummy fills in a CMOS chip were extracted through an eigenmode analysis of a unit-cell of a space filled with metal dummies. The validity of the parameters was confirmed by comparing the S-parameters of a parallel-plate waveguide with the metal dummy fills and their effective material properties. The validity of the effective material properties was also confirmed by using them in a simulation of an on-chip dipole antenna.

A broadband approach to estimate the relative permittivity of dielectric cuboids has been proposed for materials of weak frequency dispersive characteristic. Our method involves a numerical iterative scheme with appropriate initial values carefully selected to solve for the relative permittivity in a wide range of frequencies. Good agreements between our method and references have been observed for nylon and acrylic samples. An applicable range relation between the minimal thickness, the frequency range and the dielectric property of the material has also been discussed.

We propose a new swept-frequency measurement method for the electromagnetic characterization of materials. The material is a multilayer cylinder that pierces a rectangular waveguide through two holes in the narrow waveguide walls. The complex permittivity and permeability of the material are calculated from measured S-parameters as an inverse problem. To this aim, the paper develops a complete electromagnetic formulation of the problem, where the effects of material insertion holes are taken into consideration. The formulation is validated through the measurement of ferrite and water samples in the S-band.

The effective permittivity of the two-dimensional multilayered periodic structures which consist of the rectangular dielectric cylinders is examined numerically. The original periodic structure is replaced with a simple structure such as the dielectric slab. By using the reflectance of the periodic structure obtained by the FDTD method, the effective permittivity of the dielectric slab, which has the same reflectance as that of the periodic structure, is obtained by using the transcendental equation. In order to reduce the procedure to obtain the reflectance from the multilayered periodic structures, the reflectance from one-layered structure is used. The range of the application and validity of this procedure is examined.

A simple, low reflection, and highly-efficient pilot-plant scale microwave irradiation reactor for woody biomass pretreatment was fabricated. Pretreatment is an essential process for effective bioethanol production. The fabricated reactor consists of 8 microwave irradiators which are attached to a metal pipe. The woody biomass mixture which contains water and organic acid flows through the metal pipe and is heated by microwaves at a total power of 12,kW. To design the microwave irradiators, we used a 3D Finite Element Method (FEM) simulator, which was based on the measured complex permittivity data of the woody biomass mixture. The simulation results showed that the reflection coefficient $|S_{11}|$ from the reactor was less than -30,dB when the woody biomass mixture temperature was between 30$^{circ}$C and 90$^{circ}$C. Finally, we experimentally confirmed that the fabricated irradiation reactor yielded a microwave absorption efficiency of 79%.

Underfill materials are used in a packaging of millimeter wave IC. However, there are few reports for dielectric properties of underfill materials in millimeter wave region. A cut-off circular waveguide method is one of a powerful technique to evaluate precisely complex permittivity in millimeter wave region. This method may be useful not only for low-loss materials, but also for mid-loss ones with loss tangent of 10$^{-2}$ order. In this paper, an evaluation technique based on the cut-off circular waveguide method is presented to measure mid-loss underfill materials. As a result, the relative permittivity $arepsilon_{r}$ and the loss tangent tan$delta$ are in the range of 2.8$sim $3.4 and (1.0$sim$1.6)$ imes10^{-2}$, respectively. Also, the measurement precision is 2.3% for $arepsilon_{r} approx 3$ and 40% for tan$delta approx 10^{-2}$.

Four calculation techniques for the Q-factor determination of resonant structures are compared on the basis of the influence of the VNA measurement uncertainty. The influence is evaluated using Monte Carlo calculations. On the basis of the deviation, the dispersion, and the effect of nearby resonances, the circle fitting method is the most appropriate technique. Although the 3dB method is the most popular technique, the Q-factors calculated by this method exhibit deviations, and the sign and amount of the deviation depend on the measurement setup. Comparisons using measurement data demonstrate that the uncertainty of the dielectric loss tangent calculated by the circle fitting method is less than a third of those calculated by the other three techniques.

Ultra-wideband pulse radar exhibits high range resolution, and excellent capability in penetrating dielectric media. With that, it has great potential as an innovative non-destructive inspection technique for objects such as human body or concrete walls. For suitability in such applications, we have already proposed an accurate permittivity estimation method for a 2-dimensional dielectric object of arbitrarily shape and clear boundary. In this method, the propagation path estimation inside the dielectric object is calculated, based on the geometrical optics (GO) approximation, where the dielectric boundary points and its normal vectors are directly reproduced by the range point migration (RPM) method. In addition, to compensate for the estimation error incurred using the GO approximation, a waveform compensation scheme employing the finite-difference time domain (FDTD) method was incorporated, where an initial guess of the relative permittivity and dielectric boundary are employed for data regeneration. This study introduces the 3-dimensional extension of the above permittivity estimation method, aimed at practical uses, where only the transmissive data are effectively extracted, based on quantitative criteria that considers the spatial relationship between antenna locations and the dielectric object position. Results from a numerical simulation verify that our proposed method accomplishes accurate permittivity estimations even for 3-dimensional dielectric medium of wavelength size.

Ultra-wideband (UWB) pulse radar has high range resolution and permeability in a dielectric medium, and has great potential for the non-destructive inspection or early-stage detection of breast cancer. As an accurate and high-resolution imaging method for targets embedded in a dielectric medium, extended range points migration (RPM) has been developed. Although this method offers an accurate internal target image in a homogeneous media, it assumes the permittivity of the dielectric medium is given, which is not practical for general applications. Although there are various permittivity estimation methods, they have essential problems that are not suitable for clear, dielectric boundaries like walls, or is not applicable to an unknown and arbitrary shape of dielectric medium. To overcome the above drawbacks, we newly propose a permittivity estimation method suitable for various shapes of dielectric media with a clear boundary, where the dielectric boundary points and their normal vectors are accurately determined by the original RPM method. In addition, our method iteratively compensates for the scattered waveform deformation using a finite-difference time domain (FDTD) method to enhance the accuracy of the permittivity estimation. Results from a numerical simulation demonstrate that our method achieves accurate permittivity estimation even for a dielectric medium of wavelength size.

In this paper, a new swept-frequency method for the measurement of the complex permittivity and permeability of materials is proposed. The method is based on the S-parameters measurement of a cylindrical material placed inside a rectangular waveguide, where the axis of the cylinder is perpendicular to the narrow waveguide walls. The usage of cylinders in measurement is beneficial because they are easy to fabricate and handle. A novel exact solution of the field scattered by the cylinder is developed. The solution is based on expanding the field in a sum of orthogonal modes in cylindrical coordinates. Excitation coefficients relating the cylindrical scattered field to the waveguide modes are derived, and are used to rigorously formulates the S-parameters. Measurement are performed in the S-band with two dielectric materials (PTFE, nylon), and in the X-band with one magnetic material (ferrite epoxy). The measurement results agree with those from the literature.

The waveguide-penetration method is a method to measure the electrical properties of materials. In this method, a cylindrical object pierces a rectangular waveguide through a pair of holes at the centre of its broad walls. Then, the complex permittivity and permeability of the object are estimated from measured S-parameters after TRL calibration. This paper proposes a new calibration algorithm for the waveguide-penetration method. Reference materials with known electrical properties are fabricated in cylindrical shapes to fit into the holes in the waveguide and are used as calibration standards. The algorithm is formulated using the property of equal traces in similar matrices, and we show that at least two reference materials are needed to calibrate the system. The proposed algorithm yields a simpler means of calibration compared to TRL and is verified using measurements in the S-band. Also, the error sensitivity coefficients are derived. These coefficients give valuable information for the selection of reference materials.

Various studies of specific absorption rates (SARs) using liquid phantoms imitating human body tissues have been widely carried out in electromagnetic compatibility (EMC) research fields. In order to establish accurate SARs for measurement, a faithful mockup of human body tissue is needed. Therefore, knowledge of the accurate measurement of sample materials with high permittivity and high loss is very important. In this study, the complex permittivity of tap water, ethanol, methanol and isopropanol is measured by the open-ended cut-off circular waveguide reflection method. The effectiveness of the method presented here of measuring a liquid phantom with high-permittivity and high-loss is also confirmed by comparing the measured results with the results obtained by the TM010 circular cavity resonator method. At this time, the effects on the input impedance under variations of the insertion length and termination conditions were studied. Then the complex permittivity of tap water, ethanol, methanol and isopropanol was measured at frequencies ranging from 0.5 to 3.0 GHz using the measurement procedure above. As a result, we confirmed the frequency characteristics of the complex permittivity for a wide variety of high-loss liquid materials.

This paper proposes a novel metamaterial structure, which equivalently indicates negative permittivity, for the purpose of applying it to a near-field imaging and/or diagnostics of electromagnetic properties by using a surface plasmon in microwave frequency range. The proposed structure consists of a conducting wire lattice with conducting spheres embedded at the mid-point of the wire. It is shown that a spatial dispersion of the wire lattice can be reduced significantly by the sphere. It is also shown that this structure can successfully be applied to an excitation of the surface plasmon in the microwave frequency range by adequately cutting into a thin slab.

A circular cavity resonance method is improved to measure the frequency dependence of complex permittivity of a dielectric plate by using multimode TE0m1 with integer m. The measurement principle is based on a rigorous analysis by the Ritz-Galerkin method. A new circular cavity with lowered height is designed from a mode chart of a cavity to decrease the number of unwanted modes near the TE0m1 modes. A copper cavity having 20 GHz for the TE011 mode was constructed based on this design. For glass cloth PTFE, RT/duroid 6010 and FR-4 dielectric plates, the frequency dependences are measured from resonant frequencies for the TE0m1 (m = 1, 2, 3 ...) modes. These measured results agree well with ones measured by using the conventional four different size cavities with TE011 mode. It is verified that the designed cavity structure is useful to measure the frequency dependence of low loss dielectric plates.

The Waveguide-Penetration method is a permittivity measurement technique where a columnar object pierces a rectangular waveguide through a pair of holes at the center of its broad walls. The permittivity of the object is estimated from measured S-parameters . This paper demonstrates a scheme for analyzing permittivity measurement errors in the Waveguide-Penetration method. The sources of errors are categorized into systematic and random error sources. Systematic errors in the values of the sample and waveguide holes diameters, the effect of sample's length, and the influence of ambient temperature are investigated and corrected for. Potential random error sources such as imperfect TRL calibration elements, VNA thermal noise, sample loading, and test-port cable flexure are analyzed and their contribution to random errors are estimated.

In this paper, an evaluation method for electromagnetic wave absorber with anisotropic reflection properties is discussed. Anisotropic absorber panels have an axis of anisotropy (principal axis). In order to specify the principal axis, the evaluation method based on the diagonalization of reflection coefficient matrix is used. Also, the permittivity of absorber materials is considered.

The construction of EM absorber and frequency selective shielding has been investigated by using two dimensional metal fiber array (MFA) composites. The MFA composite shows a resonant type frequency dispersion in the complex relative permittivity spectra (εr = εr' - jεr") having a negative εr' region. The frequency characteristics of the conventional ferrite-rubber EM absorber can be improved by combining with the negative permittivity property of the MFA composite. A frequency selective shielding can be achieved by the evanescent EM wave propagation in the layered MFA composite structure.

This paper presents a measurement method for determining effective conductivity of copper-clad dielectric laminate substrates in the millimeter-wave region. The conductivity is indirectly evaluated from measured resonant frequencies and unloaded Q values of a number of Whispering Gallery modes excited in a circular disk sample, which consists of a copper-clad dielectric substrate with a large diameter of 20-30 wavelengths. We can, therefore, obtain easily the frequency dependence of the effective conductivity of the sample under test in a wide range of frequency at once. Almost identical conductivity is predicted for two kinds of WG resonators (the copper-clad type and the sandwich type) with different field distribution; it is self-consistent and provides the important foundation for the method if not for the alternative method at this moment. We measure three kinds of copper foils in 55-65 GHz band, where the conductivity of electrodeposited copper foil is smaller than that of rolled copper foil and shiny-both-sides copper foil. The measured conductivity for the electrodeposited copper foil decreases with an increase in the frequency. The transmission losses measured for microstrip lines which are fabricated from these substrates are accurately predicted with the conductivity evaluated by this method.