Theoretical and experimental investigation of two-layer circular patch antenna excited by a coaxial probe

In this article, we present two efficient closed-form models to examine thoroughly the dependence of resonant frequency, quality factor, probe reactance, input impedance, bandwidth, and gain on parameters such as patch radius, probe location, substrate electrical parameters, and air gap of a coax probe-fed circular patch antenna. The implementation of these models is very easy and the computation cost is very low. The proposed models show excellent agreements with experimental and simulation results. We have also investigated experimentally the gain patterns of a suspended substrate circular patch antenna.

Высокоселективный полосковый фильтр нижних частот с уровнем заграждения более 100 dB в широкой полосе

A new miniature strucuter of a highly selective low-pass filter (LPF) on a suspended substrate with a double-sided topology of stripline conductors has been proposed. The steepness of the slope of the frequency response of the filter and the depth of the stopband are determined by the zeros of the transmission coefficient, which number is equal to the order of the filter. The synthesis of a fifth-order low-pass filter prototype on a 0.5-mm thick alumina substrate with a relative permittivity εr = 9.8 was performed by numerical electrodynamic analysis of its 3D model. The filter passband cut-off frequency at the level of –1 dB fc = 1.75 GHz, and the length of the stopband at the −100 dB level extends to a frequency of 4.4 fc.

Laser Flash Raman Spectroscopy Method for Characterizing the Specific Heat of a Single Nanoparticle

Nanoparticles are widely used in composite materials, nanoscale devices, biological detectors and medical treatment. The thermophysical properties of a single nanoparticle are, therefore, important for both nanotechnology and nanoscience applications. However, property measurements are limited by the spatial resolution of conventional measurement methods, so there are not yet any effective measurement methods to characterize the thermophysical properties of a single nanoparticle. This paper describes a laser flash Raman spectroscopy method for measuring the specific heat of a single nanoparticle supported on a free-standing substrate based on a lumped parameter model for the nanoparticle coupled with a transient 2D thermal conduction model for the suspended substrate. A series of square laser pulses are assumed to be used to heat the supported single nanoparticle in a vacuum. The temperature increases in the single nanoparticle and the suspended substrate are then measured based on their Raman band shifts. The laser absorption coefficients of the nanoparticle and the substrate are then eliminated by comparing the temperature increases measured using different laser pulse widths. The specific heat of the nanoparticle and the thermal contact conductance between the nanoparticle and the substrate can then be extracted by fitting the temperatures of both the nanoparticle and the substrate. Case studies show that the method can accurately measure the specific heat of a single nanoparticle about 100 nm in diameter using ~1 ns pulse widths. The influence of the nanoparticle geometry and the thermophysical properties of the substrate are also discussed.