Eigenfrequency distributions in multimode cavities

Utilizing microwave irradiation, a fundamentally different method of the energy transfer, to the chemical process units can potentially be advantageous compared to the conventional heating, inter alia due to the selective nature of interaction of the microwaves with the matter. This doctoral dissertation addresses some of the aspects associated with the use of the microwave technology in a polyesterification plant. In this context, application of the microwave irradiation to a model polyestrerification reaction, using different types of the microwave applicators was studied. Influence of the microwave irradiation as an alternative form of heat for two selected separation techniques, which can potentially be used in a downstream recovery section in the polyesterification process (for the water purification and recovery unreacted dihydroxy alcohols), namely pervaporation and adsorption-desorption processes, were studied. The microwave-activated processes were compared with the conventionally heated ones focusing on possible reduction in the production time and energy consumption and increase in product quality. Study related to heating of the individual reagents of the polyesterification process in a multimode microwave oven showed that the heating time is several times shorter than with the conventional heating at the expense of a higher electric energy consumption. The results obtained for a model reaction system of adipic acid and neopentyl glycol under the conventional and microwave heating using the multimode microwave cavity did not show significant differences in terms of conversion and the end-product properties. Optimized (lower) usage of the microwave power during the process and effective scale up possibility compared to the multimode cavity were presented by applying the Internal Transmission Line (INTLI) microwave reactor to the studied reactor system (polyesterification reaction of maleic anhydride, phthalic anhydride and 1,2-propylene glycol). The INTLI allows for irradiation of the liquid phase from the inside of the reactor, thereby enabling better coupling of the microwave energy with the liquid mixture. For the selected process conditions, the total energy consumption of the INTLI reactor was up to a factor two lower. Comparison of desorption kinetics and desorption efficiencies for a model polar and non-polar molecules from 13X molecular sieves for two techniques, the microwave swing regeneration (MSR) and the temperature swing regeneration (TSR) showed that microwaves can help to overcome the heat transfer limitations by direct heating of the adsorbent. Significantly faster desorption processes were enabled under the microwave heating with the enhancement being more pronounced in the event of the polar compound. The MSR process runs faster even when the adsorbent temperature is quite lower than the gas temperature in TSR. It was verified that the microwaves do not affect the adsorption capacity of the molecular sieves after several consecutive adsorption-desorption cycles. Membrane pervaporation for dewatering of water/ethanol mixtures, using a hydrophilic membrane, were conducted under the microwave and conventional heating in a multimode microwave oven and a convection oven, respectively. Observations were made that at the conditions with higher water content in the feed, the water flux through the membrane was higher under the conventional heating. On contrary, with lower water in the feed, the opposite trend was found; the water flux through the membrane was higher under the microwave heating. Enhancement in the permeate flux under microwaves, compared to conventional heating, at higher ethanol concentrations in the feed can be explained on the basis of stronger coupling of microwaves with ethanol than water. Contrary to water, the dielectric loss of ethanol increases with increasing temperature; therefore, microwave dissipation is preponderant in the hot areas and can easily lead to local heating and the spatial temperature gradients.

Harmonic oscillators might be one of the most fundamental entities described by physics. Yet they stay relevant in recent research. The topological properties associated with exceptional points that can occur when two modes interact have generated much interest in recent years. Harmonic oscillators are also at the heart of new quantum technological applications: the long lifetime of high-Q resonators make them advantageous as quantum memories, and they are employed for narrowband processing of quantum signals, as in Josephson parametric amplifiers. The goal of this thesis is to explore different fundamental regimes of two coupled harmonic oscillators using cavity optomechanics as the experimen- tal platform. With consistent progress in attaining ever increasing Q factors, mechanical and electromagnetic resonators realize near-ideal harmonic oscillators. By parametrically modulating the nonlinear optomechanical interaction between them, an effective linear coupling is achieved, which is tunable in strength and in the relative frequencies of the two modes. Thus cavity optomechanics provides a framework with excellent control over system parameters for the study of two coupled harmonic modes. The specific optomechanical implementation employed are superconducting circuits with the vibrating top plate of a capacitor as the mechanical element. Multimode optomechanical circuits are realized, with two microwave modes interacting with one or two mechanical oscillators. The supplementary modes serve either as intermediaries in the relation of the two modes of interest, or as auxiliaries used to control a parameter of the system. Three main experimental results are achieved. First, an auxiliary microwave mode allows the engineering of the effective dissipation rate of a mechanical oscillator. The latter then acts as a reservoir for the main microwave mode with which it interacts. The microwave mode susceptibility can be tuned, resulting in an instability akin to that of a maser and in resonant amplification of incoming microwave signals with an added noise close to the quantum minimum. Second, we study the conditions for a nonreciprocal interaction between two microwave modes, when the information flows in one direction but not in the other. The two modes interact through two mechanical oscillators, leading to frequency conversion between the two cavities. Dissipation in the mechanical modes is essential to the scheme in two ways: it provides a reciprocal phase necessary for the interference and eliminates the unwanted signals. Third, level attraction between a microwave and a mechanical mode is demonstrated, where the eigenfrequencies of the system are drawn closer as the result of interaction, rather distancing themselves as in the more usual case of level repulsion. The phenomenon is theoretically connected to exceptional points, and a general classification of the possible regimes of interaction between two harmonic modes is exposed, including level repulsion and attraction as special cases.

Unwanted modes in cylindrical cavity resonators operating in the H01n mode may be suppressed by inserting a ring of lossy material in a groove cut at the junction between an end wall and the cylindrical wall. This groove does not affect the H01n mode but may suppress the others if the groove dimensions are correctly chosen. An analysis of the effectiveness of this method is given and is confirmed by measurements in the 3 cm band of wavelengths.

Many applications require the presence of a dielectric inside a microwave resonator. The paper presents an analysis based on the mode-matching technique of a dielectric-loaded cavity that has a configuration which is more generalised than that first proposed by Amman and Morris. The cavity consists of a wave guide of rectangular cross-section filled with dielectric for part of its length and also for part of its transverse dimension, with movable shorting plungers in the guide beyond both ends of the dielectric. Such a structure supports resonances at frequencies where a particular waveguide mode is above cutoff inside the dielectric, but is below cutoff outside. Frequency tuning is possible via the tunable plungers. Computed results for the resonant frequencies and unloaded Q-factors are presented for anumber of cavity configurations. Close corroboration of the predicted resonance frequency by experiment has been obtained. Furthermore, the performance of a Gunn-effect diode oscillator employing such a dielectric-loaded cutoff waveguide cavity as the frequency stabilising agent is investigated experimentally.

ABSTRACTMicrowave sintering of ceramics in multimode cavities, particularly the use of picket-fence arrangements, has recently received considerable attention. Various types of ceramics have been successfully sintered and, in some cases, a desirable and unique “microwave effect” has been observed.At present, various aspects of the sintering process such as sample sizes and shapes, types of insulations, and the desirability of including a process stimulus such as SiC rods are considered forms of art and highly dependent on human expertise. The simulation of realistic sintering experiments in a multimode cavity may provide a better understanding of critical parameters involved and allow for the development of guidelines towards the optimization of the sintering process.In this paper, we utilize the FDTD technique to model various geometrical arrangements and material compatibility aspects in multimode microwave cavities and to simulate realistic sintering experiments. The FDTD procedure starts with the simulation of a field distribution in multimode microwave cavities that resembles a set of measured data using liquid crystal sheets. Also included in the simulation is the waveguide feed as well as a dielectric loading plate placed at the base of the cavity. The FDTD simulation thus provides realistic representation of a typical sintering experiment. Aspects that have been successfully simulated include types of insulation, role of SiC rods on the uniformity of the resulting fields, problems that may result from presence of thermocouples, and the possible shielding effects that may result from excessive use of SiC. These results as well as others showing the electromagnetic fields and power-deposition patterns in multiple ceramic samples are presented.

Materials Science and Component Technology Directorate, Naval Research Laboratory,4555 Overlook Avenue S.W., Washington DC 20375-5343, U. S. A.'E-mail: imam@anvil.nr.navy.milKeywords: microwave processing, millimeter-wave processing, ceramics, materials, joining,coating, coating removal, rapid sinteringAbstract. An 83 GHz gyrotron-based, millimeter-wave beam system is being used in materialprocessing: in rapid sintering of oxides, ferrites, and metal-ceramic composites to retain very finegrain structure in the product for improved mechanical and electromagnetic properties; in joining ofceramic and ceramic composite materials (with unique advantages- localization of heating, permit-ting inexpensive fixturing and instrumentation and minimizing thermal damage to components; de-positing energy specifically in a narrow joint region through a guided wave effect), and in coatingdensification and coating removal where the high frequency and short wavelength permit significantenergy deposition in relatively thin coatings. In a related effort, we are using a low frequency mi-crowave system for low cost continuous production of nanophase metals. This process should pro-duce a range of nanophase metals, metal oxides and mixtures of these, in sizeable quantities and atlow cost. The results of various experiments in these areas will be discussed, as will the potential oflow and high frequency microwave processing of advanced materials.IntroductionThe authors have been investigating the use of microwave and millimeter-wave systems inmaterial processing. Such systems can have unique advantages or capabilities vs. conventionalmaterial processing. We have investigated the use of 2.45 GHz and 35 GHz cavity systems in rapidthermal processing of ceramics [1-6]. We are currently using two particular systems: an S-Band,2.45 GHz system for continuous production of nanophase oxides and metals, and an 83 GHz, mil-limeter-wave beam system for sintering, joining, coating and coating removal [7-13]. Presently, theS-Band system uses a waveguide or a resonant cavity, while the millimeter-wave system operates ina quasi-optical mode, with the millimeter-wave beam controlled by reflective optics.Typically, microwave processing is promoted on the basis of thermal efficiency or rapidheating via in-depth energy deposition. We have been exploring the use of the millimeter-wavesystem in very rapid sintering of nanophase materials, particularly ferrites. Here, the in-depthheating permits very rapid processing (<10 minute cycles) intended to preserve very fine grainstructure in the product. For small components, cycle times of less than 1 minute are possible.Theory suggests that the nature of the magnetic behavior of these ferrite materials is expected tochange dramatically at grain sizes comparable to the magnetic domain. In the case of other materi-als, the fine grain size obtained leads to excellent mechanical properties and the possibility of su-perplastic net shape forming- a possible processing route for ceramics is rapid sintering of powdercompacts to nanophase green parts, then consolidation to full density and simultaneous shaping viausing superplastic forming.We are also investigating the use of the millimeter-wave beam system in joining of ceram-ics, applying coatings to ceramics and metals, and removal of coatings from metals and composites.Here, the millimeter-wave beam system provides unique advantages. The heating effects can beconfined to an area as small as a square centimeter, permitting very localized thermal processing.

We demonstrate the manipulation of the translational motion of a polar molecule in its J = 0 rotational ground state by the microwave (MW) dipole force combined with a counter-rotating nozzle. A cold molecular beam of CH3CN seeded in Kr with a longitudinal velocity of about 100 m s−1 was created by a pulsed counter-rotating nozzle. The cold beam was then introduced into a cylindrical MW cavity, in which a standing wave, TM01p mode MW field, nearly resonant to the |J, K〉 = |1, 0〉 ← |0, 0〉 rotational transition of CH3CN was created. By choosing an appropriate MW frequency, we successfully observed focusing and deflection of the cold beam of CH3CN due to the lens effect of the MW standing wave. The present result indicates that the combination of a counter-rotating nozzle and an MW cavity will be a versatile method for making cold and ultracold ensembles of various polar molecules in their rotational ground state.

We investigated experimentally the short- and long-range correlations in the fluctuations of the resonance frequencies of flat, rectangular microwave cavities that contained antennas acting as pointlike perturbations. We demonstrate that their spectral properties exhibit the features typical for singular statistics. Hitherto, only the nearest-neighbor spacing distribution had been studied. In addition we considered statistical measures for the long-range correlations and analyzed power spectra. Thereby we could corroborate that the spectral properties change to semi-Poisson statistic with increasing microwave frequency. Furthermore, the experimental results are shown to be well described by a model applicable to billiards containing a zero-range perturbation [T. Tudorovskiy et al., New J. Phys. 12, 123021 (2010)NJOPFM1367-263010.1088/1367-2630/12/12/123021].

A wideband differentially-fed substrate integrated waveguide (SIW) back cavity antenna is proposed for operation at 34 GHz millimeter bands. A wide rectangular slot is etched on the top of SIW back cavity loading with three square patches. The rectangular cavity with four tuning vias is employed for two resonant cavity modes and wideband operation. The transition between standard rectangular waveguide (RWG) and SIW are inspired by the same technology. The simulation shows that the impedance matching of the antenna without and with the transition for return loss better than 10 dB is 26–46 GHz (55.6%) and 26.2–42 GHz (46.3%) with the achieved gain of 6.7–9.2 dBi and 6–7.5 dBi, respectively. The proposed antenna features the advantages of low-profile and wideband, suitable for the full Ka-band system applications.

The theoretical and experimental investigation of the microwave (MW) combination scattering on spin fluctuations (SF) in the yttrium iron garnet film under acoustic pump were pursued. MW frequency f≂3.5–4.1 GHz was well above spin wave spectrum at a preassigned magnetic field. At the external magnetic field range H0≂5–40 Oe one (or more) intensity peaks of MW scattering were observed. The positions of these peaks do not depend on MW and surface acoustic wave (SAW) amplitudes and frequencies and depend heavily on the magnetic field directions in a film plane. Because these phenomena were closely associated with the domain walls (DW) reorientation or at the domain structure transformations, e.g., at the flexural instability of DW, one may speculate that critical scattering of MW on SAW and SF was observed. Cross section for such scattering was calculated. In nonsaturated magnetic films the phenomena of MW scattering on SAW and spin fluctuations at high amplitudes of the MW and SAW were investigated as well. In the area of external magnetic fields H0≥250 Oe a stepped dependence of intensity of scattering MW was observed. There is no appropriate explanation of this effect now.

Values of the tensor permeability components of a magnetized ferrite at microwave frequencies may be determined from the frequency shift that a sample produces in a resonant cavity. In this paper mathematical expressions are obtained relating this frequency shift to the diagonal and off-diagonal permeability tensor values and to the cavity geometry and ferrite geometry for any TE, TM or TEM mode natural to the empty cavity. The cavities considered are axial and have generalized cross section. The expressions are valid for ferrite discs whose volume is small compared with the cavity volume; it is assumed that the ferrite sample does not perturb the fields outside the ferrite from their empty cavity values. The cross section of the ferrite disc is arbitrary in shape and is perpendicular to the axis of the cavity. Examples are given in which the frequency shifts in a circular coaxial cavity, circular cylindrical cavity and rectangular cavity containing thin ferrite discs are derived for general TE and TM modes. The TEM-type cavity is also considered.

The effects of a time-varying complex dielectric constant upon the resonant characteristics of a cylindrical microwave cavity are presented. The cavity resonance equations are developed to consider the influence of small periodic changes in resonant frequency, bandwidth, and cavity-coupling coefficient upon the microwave power density within the cavity as a function of the probing microwave frequency. Expressions are derived which enable the separate contributions of periodic changes in cavity power density to be extracted from measurements at several microwave frequencies. It is shown that for high-Q cavities, variations in the sampled microwave cavity fields are due predominantly to shifts in the cavity resonant frequency. By repetitively interrupting the mirror cavity of a 3.51-μ xenon laser with a mechanical chopping wheel, very small periodic changes are induced in the electron density and collision frequency of the xenon dc discharge due to changes in the laser field strength. The resultant changes in microwave power level within a cylindrical cavity enclosing the discharge are measured as a function of probing frequency and compared with theoretical values, yielding excellent agreement for high-Q cavity conditions. Where cavity loading severely degrades the Q, good agreement is obtained within the cavity half-power frequencies. A microwave-frequency compensation technique is employed which permits accurate direct measurement of small electron-number density changes (Δne/ne∼3×10-5) along the discharge-tube length.

Axions are a popular dark matter candidate which are often searched for in experiments known as ``haloscopes" which exploit a putative axion-photon coupling. These experiments typically rely on Transverse Magnetic (TM) modes in resonant cavities to capture and detect photons generated via axion conversion. We present a study of a resonant cavity design for application in haloscope searches, of particular use in the push to higher mass axion searches (above $\sim$60$\,\mu$eV). In particular, we take advantage of azimuthally varying TM$_{m10}$ modes which, whilst typically insensitive to axions due to field non-uniformity, can be made axion-sensitive (and frequency tunable) through strategic placement of dielectric wedges, becoming a type of resonator known as a Dielectric Boosted Axion Sensitivity (DBAS) resonator. Results from finite-element modelling are presented, and compared with a simple proof-of-concept experiment. The results show a significant increase in axion sensitivity for these DBAS resonators over their empty cavity counterparts, and high potential for application in high mass axion searches when benchmarked against simpler, more traditional designs relying on fundamental TM modes.

This paper presents a microstrip patch antenna with frequency of 2.47 GHz with substrate of FR4 Epoxy with relative permittivity of 4.4. Due to very low cost and excellent mechanical properties it is ideal for wide range of electronic component applications. Here we have cut four rectangular corners on the patch. We have first cut one corner then we found the return loss as -15.6db and gain as 5.679.To improve the return loss and gain we did two cuts on the patch and the return loss and gain were found to be -19.2db and 7.798 resp. Again we did three cuts and finally four cuts. The design is made in HFSS software. The results obtained for four rectangular cuts are return loss is -22.38db and gain obtained is 9.01. We found out that the return loss and the gain obtained for four cuts gave the best results. Keywords: HFSS software, microstrip patch antenna, stepped cuts, WBAN application, Return loss, Gain Cite this Article Adarshita Khan, Archana R. Tiwari. Design of Rectangular Microstrip Patch Antenna for WBAN Application. Journal of Microwave Engineering & Technologies . 2020; 7(1): 25–33p.

Electromagnetic cavities can be used to measure antenna efficiency. Enclosing an antenna within a conducting rectangular or spherical cavity can eliminate the radiation resistance from the impedance without changing the loss resistance of the antenna. The cavity size should avoid both the disturbance of the field near the antenna and the cavity's resonance. The efficiency of the antenna is calculated from the measurement of its input resistance inside the cavity and in free space. The paper uses the same approach to compute cell phone antenna efficiency. First, the size of the rectangular cavity is chosen and its resonant frequencies closest to the US cellular band (824-894 MHz) are determined. Then, a monopole antenna is placed inside the cavity in order to excite a coupling between the antenna and the cavity at those resonant frequencies. A simple model of a bar cell phone is then placed inside the cavity, and the changes in the coupling are analyzed. Finally, a cell phone with its antenna connected to a coaxial cable is placed in the cavity, and the input resistance is measured. Efficiency values measured from the cavity are compared to the values obtained by the radiation pattern integration method. The results show that if a cavity is chosen appropriately, it can effectively be used for measurement of cell phone antenna efficiency.