Yuto Kato

Stretchable electromagnetic-interference shielding materials made of a long single-walled carbon-nanotube–elastomer composite

By using long single-walled carbon nanotubes that possess a high aspect ratio and small diameter as fillers, we introduced electromagnetic interference (EMI) shielding to a fluorinated rubber without hardening and embrittling it. A sheet of this material with a thickness of 0.2 mm could decrease more than 90% of the strength of incident electromagnetic waves at microwave frequencies. Further, this material has a sufficient flexibility, which enables it to elongate to double its original length without any cracking, and has a higher mechanical strength than commercialized generic stocking (3.1 times the maximum tensile stress and 2.4 times the tear strength). Therefore, this material is useful for flexible and stretchable EMI shielding sheets that can wrap an arbitrarily shaped radiating object. This feature can be attributed to the fact that the carbon nanotubes could induce EMI shielding at a low loading level (only 1 wt%) without breaking the structure of the rubber matrix.

New Uncertainty Analysis for Permittivity Measurements Using the Transmission/Reflection Method

We have developed a new algorithm for the uncertainty analysis of permittivity calculations of high-loss materials using the transmission/reflection (T/R) method. In the T/R method, several calculation procedures are performed to derive the permittivity. In our method, the permittivity is derived from measured S-parameters by solving an equation in which S-parameters are included in the form (S21+ S12)+β(S11 + S22), where β is a weighted factor to be optimized to minimize the uncertainty. We confirmed its efficacy by doing numerical calculations, as well as using actual measurement data for several materials obtained with a waveguide fixture. We also considered the effect of the type of calibration method used on a vector network analyzer on the permittivity uncertainty, and quantitatively clarified that it is essential to develop a highly accurate S-parameter measurement system to perform permittivity measurements using the T/R method accurately.

Consideration of error model with cable flexure influences on waveguide vector network analyzers at submillimeter-wave frequency

In microwave and millimeter wave frequency region, systematic error terms, i.e. directivity, matching and tracking, in vector network Analyzer (VNA) can be corrected by a calibration process. However, it is difficult to correct the other random error terms, i.e. connection repeatability and flexure influences of cables attached to test ports, etc. In the waveguide VNA using frequency extension modules, fortunately, it is unnecessary to consider cable flexure influences of test ports in the measurement uncertainty due to no test port cables being used. However, LO and RF cables making connection from frequency extension modules to microwave VNA have a large impact on the uncertainty in the transmission phase measurements. This paper proposes and demonstrates an evaluation technique of cable flexure influences of RF and LO cables in the millimeter and submillimeter wave VNA using frequency extension modules. Then, new VNA error model considering the LO and RF cable flexure influences are discussed.

New uncertainty analysis and simplified verification method for permittivity measurements using the Transmission/Reflection method by utilizing a weighted factor

We have developed a new algorithm of uncertainty analyses for the permittivity calculation of high-loss materials using the Transmission/Reflection (T/R) method. In the T/R method, there are several calculation procedures to derive the permittivity. In our method, the permittivity is derived from measured S-parameters by solving an equation in which S-parameters are included by the form: (S21+S12)+β(S11+S22), where β is a weighted factor to be optimized in order to minimize the uncertainty. We compared uncertainties of the permittivity derived from different calculation procedures to confirm the efficacy of our method. We also proposed a simplified verification method for measurement results.

Study of reflection effect at fixture interfaces on permittivity measurements using the transmission/reflection method

We have evaluated the reflection effect at fixture interfaces in permittivity measurements using the transmission/reflection (T/R) method. In the T/R method, permittivity is derived from measured quantities without taken into account the reflections at fixture ends, thus they generate deviations of the results. From numerical calculations, we confirmed ripples due to multiple reflections are more pronounced in the frequency characteristic of the permittivity with increasing the reflection coefficient at fixture ends. We also performed permittivity measurements with the T/R method using four different types of fixtures. By comparing the resulting frequency characteristics of the permittivity, and by evaluating the uncertainties due to the connecting repeatability of fixtures, we clarified fixture-type dependence of the reflection effect on results of the T/R method.

Permittivity measurement using a long fixture to eliminate reflection effect at fixture ends

We have developed a correction method of the reflection effect at fixture interfaces on permittivity measurements using the transmission/reflection (T/R) method. In the T/R method using a coaxial fixture, ripples and gradients often appear in the frequency characteristics of measured permittivities caused by reflections at fixture ends. We proposed to use a long air line as a fixture to distinguish reflection signals at sample interfaces from those at fixture interfaces. Measured S-parameters are analyzed in the time-domain by gating unwanted reflection signals, and then replacing them with estimated S-parameters to eliminate their effects. We validated the developed procedure by numerical calculations.

Permittivity measurements for high-permittivity materials at NMIJ using resonator methods

This paper describes material characterizations for high-permittivity materials with the dielectric constant up to 3,000 by using resonator methods. Samples considered in this study are substrates with 0.5 mm in the thickness. Two types of measurement methods have been proposed: rectangular resonator method with controlling a sample insertion length, and waveguide reflection method with a sample terminated by a short circuit. Both methods have the advantage of providing nondestructive measurements. Numerical calculations for both and experimental measurements for the latter have been performed to investigate their validity and ranges of application.

Improvement of uncertainty analysis for waveguide VNA measurement at terahertz frequency

This paper describes a new measurement uncertainty analysis for scattering parameter measurements of waveguide devices in the frequency range from 750 GHz to 1.1 THz. The measurement uncertainty of Vector Network Analyzer (VNA) has already been analyzed from uncertainty of primary standards and repeatability. However, estimated uncertainties of waveguide VNA measurement over 110 GHz were underestimated in the case of comparison by two measurement systems at terahertz frequency. Other uncertainty contributions are connection torque deviation and effect from IF cables between VNA and frequency extension modules. By using new uncertainty model, results from two systems agreed within the uncertainty.

Improvement of Transmission/Reflection Method for Permittivity Measurement Using Long Fixtures With Time-Domain Analysis Approach

A transmission/reflection (T/R) method using a coaxial fixture is conventionally employed for permittivity measurements of high-loss materials. However, in this method, ripples often appear in the frequency characteristics of the measured permittivities owing to the reflections at the fixture ends. Although gating analysis for the time-domain signals have been employed to reduce these ripples, it cannot be applied to conventional T/R methods at microwave frequencies because of the short distance of the time interval between the required signal and unwanted signals to be eliminated in the gating process. To deal with the problem of eliminating the reflection effects at fixture interfaces, we used a long air line as a fixture, and analyzed the measured S-parameters by using the improved gating analysis in the time domain, where unwanted reflection signals in S-parameters in the time domain were eliminated while maintaining the continuity of the waveforms. We demonstrated its efficacy by performing numerical calculations, as well as using actual measurement data for polytetrafluoroethylene obtained with a PC-7 air line with the length of 30 cm. Furthermore, we developed a new algorithm for a rigorous uncertainty analysis of the time-domain analysis of S-parameters that considers the correlations between the measured S-parameters at different frequencies. By applying this algorithm, we evaluated the uncertainty of the proposed method for permittivity measurements.

Dynamic measurements of moisture content using microwave signal and its verification

This paper describes a dynamic method to measure the moisture content of grains such as rice and wheat. The proposed method does not require the value of bulk density or mass of the grains. Instead, it uses the attenuation and phase shift of the microwave signal through a microstrip transmission line. The static and dynamic measurements were performed for rice samples having different moisture contents from 11 % to 19 %. The results of the dynamic measurement showed close agreement with those of the static measurement. In addition, the ratio of amplitude change and phase shift is linearly dependent on the moisture content of the rice for both static and dynamic measurements.