Spectral characteristics of microwave and infrared metamaterials with three-dimensional resonators

Spectral characteristics of metamaterials made of arrays of novel cylindrical resonators coupled with a substrate are simulated. It is shown that, apart from the usual modes, these resonators support additional modes due to a special shape of the resonators and to the presence of a dielectric substrate. In addition to the main resonance, the spectral characteristic has a resonance peak depending on the width of the transverse slit of the cylinder and the dielectric permittivity of the substrate. The dependences obtained in this work can be used to develop novel dynamically controlled metamaterials.     

多信道二维光子晶体滤波器

根据光波模在光子晶体线缺陷波导和环形谐振腔之间的耦合原理,在二维三角晶格光子晶体中设计了一款由线缺陷主波导、环形谐振腔、60°弯下载波导组成的多信道下载滤波器。利用平面波展开方法计算了完整光子晶体及线缺陷波导的能带结构;基于时域有限差分方法计算了各目标频率光信号在器件中的传输特性,分析了影响器件耦合效率的因素并对其进行了改进。分析表明:通过改变环形谐振腔内介质柱的半径可以调节光子晶体环形谐振腔的谐振频率,而改变线缺陷主波导与环形谐振腔之间耦合区域中介质柱的形状以及将直下载波导改换成60°弯下载波导可以提高线缺陷主波导、60°弯波导与环形谐振腔之间的耦合效率。计算结果显示:优化后的多信道二维光子晶体滤波器具备优良的选频功能,各目标频率光信号的透射率均达90%以上。与传统半导体介质材料器件相比,该器件体积较小,结构简单,易于大规模集成,很有应用前景。     

微波谐振腔含水率传感器的设计方法

构建了含水混合物介电特性模型,设计了基于此模型的开路同轴谐振腔传感器,并指出影响其传感特性的两个主要参数是保护盖介电常数和空载谐振频率.针对此问题,利用MATLAB对保护盖介电常数和空载谐振频率对传感器传感特性的影响进行了仿真和分析.加工了具有不同谐振频率的含水率传感器及不同介电常数的保护盖.实验结果表明,本文提出的模型能够很好地指导传感器的设计,同时选取Al2O3制作的保护盖和空载谐振频率为2.5G的同轴谐振腔具有较好的测量效果.     

基于微波谐振腔的湿度传感器

构建了含水混合物介电特性模型，设计了基于此模型的开路同轴谐振腔传感器，并指出影响其传感特性的两个主要参数是保护盖介电常数和空载谐振频率。鉴于此，针对保护盖材料及空载谐振频率对传感器传感特性的影响进行了全面分析和仿真。加工了具有不同谐振频率的微波谐振腔及不同材料的端口保护盖。实验结果表明，该模型能够很好地指导传感器的设计，同时选取Al2O3作为保护盖材料及具有空载谐振频率为2．5GHz的谐振腔，具有较好的测量效果。     

High-frequency microstrip cross resonators for circular polarization electron paramagnetic resonance spectroscopy

In this article we discuss the design and implementation of a novel microstrip resonator which allows absolute control of the microwaves polarization degree for frequencies up to 30 GHz. The sensor is composed of two half-wavelength microstrip line resonators, designed to match the 50 Omega impedance of the lines on a high dielectric constant GaAs substrate. The line resonators cross each other perpendicularly through their centers, forming a cross. Microstrip feed lines are coupled through small gaps to three arms of the cross to connect the resonator to the excitation ports. The control of the relative magnitude and phase between the two microwave stimuli at the input ports of each line allows for tuning the degree and type of polarization of the microwave excitation at the center of the cross resonator. The third (output) port is used to measure the transmitted signal, which is crucial to work at low temperatures, where reflections along lengthy coaxial lines mask the signal reflected by the resonator. Electron paramagnetic resonance spectra recorded at low temperature in an S=5/2 molecular magnet system show that 82% fidelity circular polarization of the microwaves is achieved over the central area of the resonator.     

High-pressure apparatus for dielectric measurements in high frequency

The present article describes an experimental apparatus for the measurement of low-loss dielectric material under conditions of high pressures (maximum pressure 1500 bars) and high frequencies (1-15 MHz.) The measurements of these losses are based on the classical method of the Q-meter with a general Radio type 1690-A sample holder, located in a high-pressure bomb. All the manual operations made on the holder during the measurements are controlled by dc motors. The first results have shown that the dielectric losses of polyethylene (PE) vary with the pressure. This apparatus will later be used in the measurement of the dielectric losses of the insulating materials used for submarine telecommunication cables.     

Fabrication and properties of rf niobium-on-sapphire superconducting resonators

Niobium-on-sapphire resonators have been constructed as sensor elements for accelerometers in gravitational wave antennae. In their present form the resonators constitute small simple sensor elements for a wide range of applications where displacements take place, such as seismometry, gravimetry, thermal expansion measurements, as well as gravitational wave antennae. Radio-frequency losses in the niobium-sapphire interface have been observed. These limit the resonator Q to less than 10(5) and show a strong power dependence. Several methods of fabrication of the niobium-on-sapphire circuits have been investigated. Complete details for construction are given. An accelerometer based on these resonators is described in an accompanying paper.     

Imaging vibrations of electromechanical few layer graphene resonators with a moving vacuum enclosure

Imaging the vibrations of nanomechanical resonators means measuring their flexural mode shapes from the dependence of their frequency response on in-plane position. Applied to two-dimensional resonators, this technique provides a wealth of information on the mechanical properties of atomically-thin membranes. We present a simple and robust system to image the vibrations of few layer graphene (FLG) resonators at room temperature and in vacuum with an in-plane displacement precision of ≈0.20 μm. It consists of a sturdy vacuum enclosure mounted on a three-axis micropositioning stage and designed for free space optical measurements of vibrations. The system is equipped with ultraflexible radio frequency transmission lines to electrically actuate resonators. With it we characterize the lowest frequency mode of FLG resonators by measuring its frequency response as a function of position on the membrane and by extracting its effective mass. We use the background noise of the undriven vibrational spectrum to calibrate in-plane displacement. Finally, we measure the first three vibration modes of a resonator whose membrane is partially folded and find that folds locally suppress vibrations.     

Noninvasive beam-wave spectrometric instrumentation for measuring dielectric constant at microwave frequencies

From the characteristics of the reflected Gaussian beam-wave for oblique incidence, measured with a spectrometer arrangement, the dielectric properties of a selectively exposed region of a dielectric slab are ascertained at microwave frequencies. For this purpose, a focused (Gaussian) microwave beam is launched from a suitable applicator to irradiate obliquely a selected protion of the test dielectric and the complex reflection coefficient is measured and analyzed. Further, the magnitude of the angular shift involved in the direction of the reflected beam is also used to calculate the dielectric constant. Application of this method to noninvasive measurements of dielectric properties of selective partial-bodies of commercial dielectrics and biological substances is discussed.     

Temperature-stable parallel-plate dielectric cell for broadband liquid impedance measurements

A liquid impedance cell for broadband impedance measurements up to 110 MHz is presented. The design incorporates temperature control and minimizes parasitic capacitance and inductance. The cell is simple to fabricate and uses chemically resistant materials, stainless steel, and Teflon. This dielectric cell can be used in a variety of liquid measurements, particularly those related to impedance measurements of biological objects in solution. Temperature control is illustrated in measurements of the permittivity of deionized water from 5 to 55 °C. Numerical fitting procedures employed on the relaxation curves indicate good agreement with previous studies on beta-lactoglobulin and hen lysozyme. Titration capability is demonstrated through dielectric titration of hen lysozyme and beta-lactoglobulin.     

A set of measuring microwave resonators

An universal set of broadband high-Q measuring resonators operating in a frequency band of 0.6–180 GHz is described. The resonators may be used for physical investigations, measuring parameters of different media, and in spectroscopy, holography, radio-astronomy, communication engineering, and physical electronics. The microwave resonators with a mechanical frequency tuning range of 1/2 octave and higher and a loaded Q-factor of no less than 10⁵ are created, and there is a possibility of electronic frequency adjustments in them.     

Determination of the composition of biodiesel-diesel blends using the dielectric constant

There are many methods used to measure the composition of biodiesel in diesel. However, standard methods are limited by high cost and limited precision. Here is proposed a low-cost sensor to determine biodiesel in binary blends of biodiesel/diesel, using the dielectric constant. The concentrations were varied from 0–9% at frequencies from 100–2000 Hz. The correlation curves between the dielectric constant and the biodiesel/diesel concentration included an adjustment factor of 0.992. Moreover, the values of the dielectric constant obtained for each blend were statistically distinct, yielding precise measurements.     

Imaging conductive materials with high frequency electrical capacitance tomography

Electrical capacitance tomography (ECT) is known as an imaging technique for dielectric permittivity imaging. A novel ECT sensor model at a high excitation frequency is proposed to examine the capability of the ECT system to image both conductivity and permittivity contrasts. The proposed model uses a complex impedance forward model for the ECT system. This new model indicates that in higher excitation frequency both conductive and dielectric imaging may be feasible. Normally, capacitance tomography is designed for the measurements of imaginary part and resistance tomography is used to take the measurements of real part. The drawback of a typical capacitance tomography at a low excitation frequency, such as 200 kHz is that it cannot be used to measure the conductive phase of a conductive/dielectric mixed fluid, e.g. the gas/water flow. By increasing the excitation frequency, the capacitive impedance of the conductive material decreases and dielectric phenomena of the conductive fluid dominates so that it is possible to use capacitance tomography to characterise the dielectric/conductive flows. This paper presents a development of capacitance tomography with a high excitation frequency in measuring the gas/liquid mixture i.e. gas/water and gas/oil multiphase distributions. Both theoretical and experimental results are presented to verify this feasibility study.     

四通道二维光子晶体解波分复用系统

利用光子晶体环形腔缺陷模与线缺陷波导之间的共振耦合原理,设计了一种由主波导、环形腔和60°弯波导组成的四通道二维三角晶格光子晶体解波分复用系统。通过平面波展开法计算线缺陷波导的能带结构;利用时域有限差分法(FTDT)计算了不同频率的光波在该系统中的传输特性。最后,分析了影响输出效率和品质因子的因素并对该系统进行了改进。分析表明:改变环形腔内介质柱的半径可调节谐振频率,而在主波导末端增加反射介质柱以及改变耦合区域中介质柱的形状可提高各通道的谐振频率光波的透射率。计算结果显示:该系统较好地实现了4个波长的解波分复用,透射率均达90%以上。另外,该系统结构简单,便于加工制造,且体积小,有利于大规模集成。     

Use of a Dielectric as a Sensitive Element of an X-Ray Detector

An X-ray detector with a dielectric (KU1 optical glass) used as a sensitive element is described. Operation of the detector is based on the discovered effect of electric-field generation in a dielectric under exposure to radiation. The measurements were taken at the Angara-5-1 facility, at which the radiation source is megaampere Z-pinch plasma. It is shown that when the radiation power incident on the detector is approximately 1 MW/cm², the detector response is a few volts with a time resolution of 1–2 ns. This effect is thought to be caused by “hot” electrons induced by radiation in the dielectric. The estimates for these experimental conditions are presented.     

截止波导介质腔介电常数测量理论与方法研究

本文提出了用截止波导介质谐振腔测量微波材料相对介电常数和微波损耗的方法.利用开波导法给出了腔中TE0ml谐振模的电磁场,导出了利用此模测量介电常数和微波损耗的公式;通过测量频率和谐振曲线,就能算出材料的复介电常数,并对谐振模TE0ml进行了讨论;比较了这种测量方法与原有的短路金属板介质谐振腔法的优劣,结果表明采用截止波导介质谐振腔测量材料的微波损耗时更有优越性.     

谐振管内非线性驻波的间断Galerkin方法*

基于伪一维瞬态可压缩Navier-Stokes方程和理想气体状态方程,并结合保持强稳定性的三阶Runge-Kutta格式和斜率限制器技术,构建一种整体轴向谐振激励下求解变截面谐振管内非线性驻波的间断Galerkin方法。分别对直圆柱形、指数形以及圆锥形谐振管内的非线性驻波进行数值仿真计算,通过与现有数值仿真结果对比,验证了本方法的正确性,并重现了已有试验中非线性驻波压力波形中的第二峰值。在直圆柱形和指数形谐振管内研究间断Galerkin方法的两种网格加密方式对于不同形状下谐振管内非线性驻波仿真计算的数值精度、消除数值振荡和准确捕捉激波的不同作用,以及不同CFL数对于数值精度的影响。在指数形谐振管内,通过与有限体积法不同网格数目下的数值仿真结果和计算时间对比,验证了本方法具有耗时短、效率高以及计算精度高的优点。在圆锥形谐振管内,研究不同流速下谐振管内压力和速度波形的变化,并发现随着流速的增加,谐振管小端处的压力幅值增加,大端处速度幅值也随之增加且速度波形中会产生激波。通过间断Galerkin方法分析研究几种谐振管内非线性驻波的各种物理属性,为谐振管形状优化提供了重要参考,也为实现谐振管内非线性驻波的工程应用奠定了良好的基础。     

声子晶体软支撑石墨烯谐振器设计与特性研究

航空、航天等领域对高性能传感器提出了系列迫切需求,石墨烯因其优异的机械电子学特性,有望进一步提高传感器性能,得到了广泛研究。石墨烯谐振器作为一种新的敏感单元,因其极薄的厚度而具有非常高的传感灵敏度。但目前,室温下石墨烯谐振器的抗干扰能力和稳定性普遍较差,室温下石墨烯谐振器品质因数较低成为制约石墨烯谐振器性能提升和应用的一个关键因素,提高石墨烯谐振器品质因数成为亟待研究的问题。本文通过建立石墨烯谐振器的能量耗散稀释理论模型,分析石墨烯谐振器能量耗散分布特性;在理论模型指导下,提出一种基于声子晶体软支撑结构的石墨烯谐振器能量耗散抑制新机制,开展石墨烯声子晶体谐振器优化设计、制备与特性测试分析研究,从而为提高石墨烯谐振器品质因数提供一种新的技术手段。     

Problems in the theory and design of electromagnetic flowmeters for dielectric liquids. Part 3a. Modelling of zero drift due to flux linkage between coil and electrode cables

This paper investigates theoretically the magnitudes of zero offsets and zero drifts originating from magnetic flux linkage between the coils of the electromagnet and the loop formed by the electrode cables in an electromagnetic flowmeter for dielectric liquids. The dependence of such zero offsets on liquid properties, frequency of operation, etc. is explained. The paper gives the results of measurements of the effective electrical conductivity and permittivity of dielectric liquids BP180 and Castrol OX-9 (and mixtures of these) in the frequency range 1 Hz–1 kHz. These are used to predict the zero offsets expected in metering these liquids using phase sensitive detection with the flowmeter tube described in Part 1 of the paper. Precautions needed in flowmeter design to minimise instrument zero offsets and zero drifts are explained. The electromagnetic flowmeter theory was developed at Cranfield and the determination of the electrical properties of the dielectric liquids was carried out at QinetiQ.     

Hemispherical dielectric permittivity cell

A three-terminal dielectric cell based on a hemispherical design is constructed for low-temperature measurements of dielectric permittivity. The cell has a small sample volume, is geometrically stable, and shows no frequency dependence of capacitance. Measurements on test samples are presented showing both cell constant stability data and the linearity of measured capacitance with dielectric constant.