Coaxial Cavity Resonator Research Articles

Design of a compact quarter wave coaxial cavity resonator for plasma ignition applications

Atmospheric and higher pressure RF and microwave plasma sources have numerous applications including material processing and spectroscopy. More recently, advantages in using such discharges for combustion ignition are being investigated. A particularly simple and compact microwave discharge generating device is the quarter wave coaxial cavity resonator (QWCCR). This paper presents a new, compacted design of such a device. A simple approximate analysis of the quality factor, Q, which is a measure of the resonant electromagnetic potential step-up capability is given, and compared to experimentally measured quality factors showing reasonable agreement. Analytic results indicate that the foreshortened folded cavity quality factors are comparable to tapered coaxial cavity designs.

Research on Field Distribution of TM<SUB>310</SUB> Mode in Cylindrical Coaxial Cavity Resonator with Coupling of Waveguide Hole

摘要: 该文研究了采用TM310高阶模同轴谐振腔与波导孔耦合构成的多注速调管输出回路。从理论上阐述了调节该输出腔的外观品质因数的原理和方法，并利用三维电磁场软件CST进行了模拟验证，得到TM310模场分布均匀的，具有较低外观品质因数的同轴输出腔。 关键词: 多注速调管;孔耦合;高阶模TM310;场分布;外观品质因数

Research on Field Distribution of TM<SUB><I>s</I>10</SUB> Mode in Cylindrical Coaxial Cavity Resonator with Inductive Tuning

摘要: 圆柱型同轴谐振腔中的横磁模TMs10的电场分量沿圆周方向呈周期性均匀分布，电感调谐的圆柱型谐振腔的圆周边界不再规则，腔内场分布的均匀性遭到破坏。为了能准确描述场分布的情况，该文建立了不规则圆周边界的同轴谐振腔的物理模型，通过理论分析得出了边界发生变化时同轴谐振腔中电场分布的变化规律。并通过三维电磁场软件进行了数值模拟，模拟结果与理论分析所得结论一致。 关键词: 多注速调管; 同轴谐振腔; 场分布; 高阶模; 复杂边界

固定频率后同轴谐振腔尺寸与TMn10模式阶数的可调性

固定频率后同轴谐振腔尺寸与TMn10模式阶数的可调性

Electromagnetic design of a novel microwave internal combustion engine ignition source, the quarter wave coaxial cavity igniter

New ignition sources are needed to operate the next generation of lean high-efficiency internal combustion engines. A significant environmental and economic benefit could be obtained from these lean engines. Towards this goal, the quarter wave coaxial cavity resonator (QWCCR), igniter was examined. A brief overview of the QWCCR's history is presented, followed by an electromagnetic analysis of the resonator. Microwave and radio-frequency gas breakdown at atmospheric and higher conditions are reviewed briefly. The presented analysis focuses on geometric and material parameter relations compared with performance characteristics, such as resonator quality factor and developed tip electric field which initiates a single-electrode high-pressure microwave gas breakdown. Conductor surface losses, dielectric losses, and radiation losses of the device are considered in the analysis, for which parameters of a prototype QWCCR were chosen for construction and evaluation of a resonator. Improved designs allowed successful integration of a QWCCR into a Briggs and Stratton engine. Given the capability of precise control, high power, and high energy delivery, and the opportunity for further optimization, the QWCCR has the potential to deliver more energy per ignition than a conventional spark plug and thus should be considered for application as a lean ignition source.

Development and research of a coaxial microwave plasma thruster

An overview of the research on a coaxial microwave plasma thruster at Northwestern Polytechnic University is presented. Emphasis is put on the development and research on key components of the thruster system, a microthrust balance, plasma plume diagnostics, and a numerical simulation of the plasma flow field inside the thruster cavity. The developed thruster cavity is chosen from a coaxial resonant cavity with concentrated capacitance, which can operate well in atmosphere and vacuum conditions. The development of a microwave source shows that a magnetron powered by a switch power supply has advantages in the power level and efficiency, but a solid state microwave source synthesized from the arsenide field effect transistor is superior in weight and volume. Through elimination of the effect of large gravity and resistance force induced by a gas pipe line and a microwave transmitting line on the microthrust, 15 mN and 340 s in the performance of the microwave plasma thruster at 70 W and with helium gas are measured. Diagnosing experiment shows that the plasma plume density is in the range of (1-7.2)x10(16)m(3). Numerical simulation of the plasma flow field inside the coaxial thruster cavity shows that there is a good match between the microwave power and gas flow rate.

Experimental investigation of coaxial side branch resonators

Digital particle image velocimetry is employed to investigate acoustically-coupled flow past a coaxial deep cavity (side branch) resonator mounted in a duct. The emphasis is on the effect of the separation between the coaxial side branches on the interaction between separated shear layers that form across the side branch openings. Various resonator geometries are characterized in terms of patterns of instantaneous and time-averaged flow velocity, vorticity, and streamline topology at several phases of the acoustic cycle. In addition, phase-averaged images of the flow in conjunction with unsteady pressure measurements are evaluated in order to provide insight into the mechanisms of acoustic power generation. Generally speaking, the acoustic source undergoes a significant transformation as the distance between the coaxial side branches changes. As the distance between the side branches decreases, interaction between the associated oscillating shear layers results in substantial changes in the spatial structure of the acoustic source region.

High-throughput characterization of local conductivity of Nd 0.9Ca 0.1Ba 2Cu 3O 7− δ thin film by the low-temperature scanning microwave microscope

We developed a scanning microwave microscope (SμM) designed for high-throughput electric-property screening as well as for rapid construction of electronic phase diagrams at low temperatures. As a sensor probe, we used a high- Q λ/4 coaxial cavity resonator to which a thin needle with ball-tip end was attached. The sensor module was mounted on the low-temperature XYZ stage, which allowed us to map out the change of resonance frequency and quality factor due to the local tip-sample interaction at low temperatures. From the measurements of combinatorial thin films, such as Ti 1− x Co x O 2− δ and Nd 0.9Ca 0.1Ba 2Cu 3O 7− δ (NCBCO), it was demonstrated that this SμM system has enough performance for the high-throughput characterization of sample conductance under variable temperature conditions.

Development of Variable Temperature Scanning Microwave Microscope for High Throughput Materials Characterization

AbstractWe developed a variable-temperature scanning microwave microscope (VT-SμM) that can perform high-throughput materials characterization in the temperature range between 4K and room temperature. As a sensor probe we used a high-Q coaxial cavity resonator, which was mounted on the low-temperature stage to allow variable-temperature measurements. We carried out systematic studies on the thermal degradation of the conducting polymers using the combinatorial libraries of polyaniline and polythiophene thin films, which showed rapid decrease of conductivity above 300C and 250C, respectively. The low-temperature performance of the VT-SμM was demonstrated by the measurement of composition-spread Nd1-xSrxMnO3 thin film, for which we succeeded in detecting the clear metal-insulator transition at 100K. We also propose a simple and easy method for the quantitative analysis of conductive thin films, by using the standard composition-spread thin films of Ti1-xNbxO2.

Singlet oxygen production and quenching mechanisms in travelling microwave discharges

Experimental and theoretical studies of singlet oxygen excitation in travelling microwave (TMW) discharges are presented. Singlet oxygen O2(a1Δg) concentrations and atomic oxygen mole fraction have been measured for different pressures, input powers and distances from the MW resonator. It was shown that a steady-state TMW discharge with a coaxial cavity resonator could provide a maximal O2(a1Δg) yield of 22% for 2 Torr of pure oxygen and 27–30% for He : O2 = 1 : 1 mixture. The two-dimensional (r, z) model developed for calculations of plasma-chemical kinetics, heat and mass transfer was used for simulation of processes in the TMW discharge under study. Effects of gas pressure, gas flow rate and input power are studied and compared with experimental measurements of O2(a1Δg) concentrations and atomic oxygen mole fractions.

Filter technologies for wireless base stations

Phenomenal growth in the telecommunication industry in recent years has brought significant advances in filter technology as new communication systems emerged, demanding more stringent filter characteristics. In particular, the growth of the wireless communication industry has spurred tremendous activity in the area of microwave filter miniaturization and has been responsible for many advances made in this field. The filters that are currently being used in wireless base stations can be divided into two main categories: coaxial cavity resonator filters and dielectric resonator (DR) filters. While coaxial cavity filters have limited quality factor (Q) values, they offer the lowest cost design and are still being widely employed, particularly in wide bandwidth applications. With increased demands for high performance wireless systems, dielectric resonator filters are emerging as the baseline design for wireless base stations. Over the next five years, dielectric resonator filters are expected to have a significant share of the overall wireless base station filter market. High-temperature superconductor (HTS) filters are also expected to have a share of this market, particularly for systems, which have very stringent requirements for out-of-band interference. In this article, we begin by reviewing the main filter requirements, highlighting the technologies that are being currently employed. Emerging filter technologies that have the potential to replace the existing technologies are then described.

Accurate Design of Coaxial Cavity Resonator Filters

Quarter wavelength coaxial line cavities are commonly used structures in constructing diplexer and band pass filters at the Very and Ultra High Frequencies (V-UHF). Despite its wide use of this structure, design rules of selecting geometrical details concerning the input/output feeding points are determined in each case experimentally, which is a tiresome process. In order to achieve an accurate and reliable design and to avoid cut and paste to achieve fine tuning of resonance at the desired frequency and matching at the input/output lines a field analysis is implemented to develop accurate design rules. In this context the effect of feeding structure geometrical details as well as inner-outer conductor gaps are examined. Furthermore, in order to achieve an additional control of the filter bandwidth the use of a tapered coaxial line is also examined and computed. The performance of various structures is examined and design curves are provided to ease the work of designer.

Improved surface imaging with a near-field scanning microwave microscope using a tunable resonator

We report a microwave surface imaging technique using a near-field scanning microwave microscope with a tunable resonance cavity. By tuning the resonance cavity, we could demonstrate improved sensitivity and spatial resolution of the topographic image of YBa2Cu3Oy thin films on MgO substrates. By measuring the shift of resonant frequency and the change of quality factor, we obtained near-field scanning microwave images with a spatial resolution better than 4 μm at an operating frequency of f=1–1.5 GHz. The principal of operation could be explained by the perturbation theory of a coaxial resonant cavity, considering the radius of the probe tip, the sample–tip distance, and the impedance matching.

Broadband coaxial cavity resonator for complex permittivity measurements of liquids

A novel cavity perturbation technique using coaxial cavity resonators for the measurement of complex permittivity of liquids is presented. The method employs two types of resonators (Resonator I and Resonator II). Resonator I operates in the frequency range 600 MHz-7 GHz and resonator II operates in the frequency range 4 GHz-14 GHz. The introduction of the capillary tube filled with the sample liquid into the coaxial resonator causes shifts in the resonance frequency and loaded Q-factor of the resonator. The shifts in the resonance frequency and loaded Q-factor are used to determine the real and imaginary parts of the complex permittivity of the sample liquid, respectively. Using this technique, the dielectric parameters of water and nitrobenzene are measured. The results are compared with those obtained using other standard methods. The sources of errors are analyzed.

Complex permittivity measurement of liquids with coaxial cavity resonators using a perturbation technique

Open ended coaxial cavity resonators for measuring the complex permittivity of liquids are presented. Measurements are based on the cavity perturbation technique. The first resonator operates in the frequency range 0.6-7 GHz, while a second resonator operates in the frequency range 5-14 GHz. The complex permittivity of water is measured. Results are compared with those obtained using other methods.

Theoretical and Experimental Studies of Photothermal Dielectric Spectroscopic Microscope

A new photothermal technique is proposed. This is based on the temperature characteristic of the dielectric constant of light-irradiated material. When a dielectric material is illuminated with chopped light, alternating variation of capacitance is caused by the heat produced due to light absorption, and this variation is detectable with sufficient dynamic range and sensitivity. First, quantitative derivations are presented for the alternating capacitance variation in terms of the optical, thermal, dielectric and geometric parameters of the system. Next, some fundamental experiments on the photothermal dielectric spectroscopic microscope (PTDSM) to confirm the validity of this theoretically predicted photothermal dielectric signal are performed, and it is shown that the observed signals agree with the theoretical ones very well. Finally, a highly sensitive PTDSM using the coaxial cavity resonator with operating frequency of microwave range is developed. Using this microscope, the temperature characteristics of the dielectric materials for microwave application are successfully measured.

Development of a microwave moisture sensor for aggregates

An instantaneous method for measuring the moisture content in an aggregate such as sand is developed using a microwave coaxial cavity resonator with an outer slot antenna. We measure the attenuation of the resonant peak of the cavity resonator, which is related to the moisture content of the aggregate. The resonator is movable so that the moisture can be measured at the several positions in a pile of the aggregate. The standard deviation in the measured moisture content is 0.08%, which is better than our previous result.

Microwave Measurements of Low Pulp Concentration in Papermaking Process

A method of microwave measurements of low pulp concentrations in the papermaking process is developed using a coaxial cavity resonator with an inner slot antenna. We measure the attenuation of the resonant peak of the cavity resonator which is related to the pulp concentration. The pulp concentration up to 10.1% is measured, and then the linear relationship between the attenuation and low pulp concentrations down to 0.6% is determined. By this method, a low pulp concentration can be measured within the standard deviation of 0.03% by linear approximation.

Microwave Measurements of Moisture Content of Aggregate

An instantaneous method for measuring the moisture content in aggregate such as sand is developed using a microwave open-ended coaxial cavity resonator. We measure the attenuation and frequency shift of resonant peaks of the cavity resonator, which are related to the moisture content of the sand. The standard deviations in the attenuation and frequency shift are 0.30% and 0.14% in the percentage of moisture, respectively. The frequency shift measurement is better than the attenuation measurement to calculate the moisture content.

Development of Microwave Caliper for Sheet Materials

A microwave caliper used for performing noncontact measurements of the thickness of dry sheet materials is developed using a microwave coaxial cavity resonator. Since the coaxial cavity is open-ended on one side, even a thick sheet material can be measured. High resolution of thickness is obtained due to a strong electric field on the open circuit plane of the cavity. The fringing electric field distribution of the open-ended coaxial cavity, which has been difficult to observe, is monitored as a thermal distribution by a thermography. The frequency shift of a resonance peak is found to be closely related to the dielectric constant.