Anomalous Features in Surface Impedance of Y-Ba-Cu-O Thin Films: Dependence on Frequency, RF and DC Fields

Two high-quality Y-Ba-Cu-O thin films on MgO substrates have been investigated using the coplanar resonator technique at 8 and 16 GHz. Both films exhibit an anomalous decrease in their surface impedance, Zs as a function of microwave field, Hrf. In zero dc field, Hrf-dependences of Rs and Xs for both the samples are uncorrelated, and only one of the quantities, Rs or Xs, displays anomalous behavior. Here, application of relatively weak (~5 mT) dc magnetic fields, Hdc can produce a correlated decrease of Rs(Hrf) and Xs(Hrf). The dependences of Zs on Hdc in both low and high microwave power regimes were found to be non-monotonic. The frequency dependence of Rs ~ fn, 1.7<n<2.5, remained the same upon the transition from low to high microwave power ranges. The consequences of the reported findings for microwave device applications are briefly discussedComment: 4 pages, 4 figures. Submitted to ASC'2000 Conference Proceeding

Dual feeding cavity resonator for efficiency enhancement in liquid heating applications

A new type of microwave resonator feeding topology is proposed to enhance the power delivered to a lossy sample for microwave heating applications. The method uses two input signals with equal phase and magnitude, instead of the usual one input. As a result, for the same total input power, the delivered power can be increased to twice the power than the case of the one input. A 2.45 GHz TM010 cylindrical cavity with dual input ports is used to heat a water sample with a total input power of 0.25 W. The efficacy of the proposed heating topology was verified by 3D electromagnetic simulation and heating measurements, including S-parameters, incident and reflected power, and thermal images. All measurement results support the increase in heating efficiency in the two port case, while using the same total amount of power as for the one port cas

Temperature correction for cylindrical cavity perturbation measurements

The need for accurate material property measurements using microwave cavities requires a form of compensation to correct for changes in temperature and other external influences. This paper details a method for temperature correcting microwave cavity perturbation measurements by monitoring two modes; one which is perturbed by the sample and one which is not (referred to as a nodal mode). The nodal modes used (TM310 and TE311 for an axial sample in a cylindrical cavity) are subject only to sample-independent influences. To demonstrate this technique, the bulk permittivity of a PTFE rod has been measured under varying temperature conditions. The results show that without correction, the measured temperature-dependent dielectric constant has large variations associated with the stepped and linear temperature ramping procedures. The corrected response mitigates systematic errors in the real part. However, the correction of the imaginary part requires careful consideration of the mode coupling strength. This paper demonstrates the importance of temperature correction in dynamic cavity perturbation experiments

A compact microwave microfluidic sensor using a re-entrant cavity

A miniaturized 2.4 GHz re-entrant cavity has been designed, manufactured and tested as a sensor for microfluidic compositional analysis. It has been fully evaluated experimentally with water and common solvents, namely methanol, ethanol, and chloroform, with excellent agreement with the expected behaviour predicted by the Debye model. The sensor’s performance has also been assessed for analysis of segmented flow using water and oil. The samples’ interaction with the electric field in the gap region has been maximized by aligning the sample tube parallel to the electric field in this region, and the small width of the gap (typically 1 mm) result in a highly localised complex permittivity measurement. The re-entrant cavity has simple mechanical geometry, small size, high quality factor, and due to the high concentration of electric field in the gap region, a very small mode volume. These factors combine to result in a highly sensitive, compact sensor for both pure liquids and liquid mixtures in capillary or microfluidic environment

A Laboratory Test Setup for in Situ Measurements of the Dielectric Properties of Catalyst Powder Samples under Reaction Conditions by Microwave Cavity Perturbation : Set up and Initial Tests

The catalytic behavior of zeolite catalysts for the ammonia-based selective catalytic reduction (SCR) of nitrogen oxides (NOX) depends strongly on the type of zeolite material. An essential precondition for SCR is a previous ammonia gas adsorption that occurs on acidic sites of the zeolite. In order to understand and develop SCR active materials, it is crucial to know the amount of sorbed ammonia under reaction conditions. To support classical temperature-programmed desorption (TPD) experiments, a correlation of the dielectric properties with the catalytic properties and the ammonia sorption under reaction conditions appears promising. In this work, a laboratory test setup, which enables direct measurements of the dielectric properties of catalytic powder samples under a defined gas atmosphere and temperature by microwave cavity perturbation, has been developed. Based on previous investigations and computational simulations, a resonator cavity and a heating system were designed, installed and characterized. The resonator cavity is designed to operate in its TM010 mode at 1.2 GHz. The first measurement of the ammonia loading of an H-ZSM-5 zeolite confirmed the operating performance of the test setup at constant temperatures of up to 300 °C. It showed how both real and imaginary parts of the relative complex permittivity are strongly correlated with the mass of stored ammonia

Continuous and scalable polymer capsule processing for inertial fusion energy target shell fabrication using droplet microfluidics

High specification, polymer capsules, to produce inertial fusion energy targets, were continuously fabricated using surfactant-free, inertial centralisation, and ultrafast polymerisation, in a scalable flow reactor. Laser-driven, inertial confinement fusion depends upon the interaction of high-energy lasers and hydrogen isotopes, contained within small, spherical and concentric target shells, causing a nuclear fusion reaction at ~150 M°C. Potentially, targets will be consumed at ~1 M per day per reactor, demanding a 5000x unit cost reduction to ~$0.20, and is a critical, key challenge. Experimentally, double emulsions were used as templates for capsule-shells, and were formed at 20 Hz, on a fluidic chip. Droplets were centralised in a dynamic flow, and their shapes both evaluated, and mathematically modeled, before subsequent shell solidification. The shells were photo-cured individually, on-the-fly, with precisely-actuated, millisecond-length (70 ms), uniform-intensity UV pulses, delivered through eight, radially orchestrated light-pipes. The near 100% yield rate of uniform shells had a minimum 99.0% concentricity and sphericity, and the solidification processing period was significantly reduced, over conventional batch methods. The data suggest the new possibility of a continuous, on-the-fly, IFE target fabrication process, employing sequential processing operations within a continuous enclosed duct system, which may include cryogenic fuel-filling, and shell curing, to produce ready-to-use IFE targets

Dual mode microwave microfluidic sensor for temperature variant liquid characterization

A dual mode, microstrip, microfluidic sensor was designed, built, and tested, which has the ability to measure a liquid's permittivity at 2.5 GHz and, simultaneously, compensate for temperature variations. The active liquid volume is small, only around 4.5 μL. The sensor comprises two quarter ring microstrip resonators, which are excited in parallel. The first of these is a microfluidic sensor whose resonant frequency and quality factor depend on the dielectric properties of a liquid sample. The second is used as a reference to adjust for changes in the ambient temperature. To validate this method, two liquids (water and chloroform) have been tested over a temperature range from 23 °C to 35 °C, with excellent compensation results

Phenomenological model of the non linear microwave response of a superconductor containing weak links

A phenomenological model is proposed which describes the effect of both dc and rf magnetic fields H on the microwave surface impedance, Zs=Rs+jXs, of a superconductor containing weak links. Two types of the weak links are considered; a weak link between two grains, shunted by another grain, and a nonshunted weak link. In both cases, the dependences of Rs and Xs on applied H were found to be anomalous. Under certain conditions, the values of Zs(H) can fall below the zero-field values. Comparison with experiment is performed, and very good qualitative and (in some cases) quantitative agreement is found