Open Microwave Cavity Research Articles

Machine learning-enabled thickness estimation of thin coatings on carbon fibre composites using microwaves

Accurate thickness measurement of thin coatings (typically 50–500 μm) on carbon fibre-reinforced polymer composites is a major challenge in the manufacturing and maintenance processes of modern aircraft. Different from the conventional material-dependent technique for prediction, a machine learning-enabled strategy with an artificial neural network configuration is used with no requirement of prior knowledge of the type of coating or substrate under test. In the test, an open microwave cavity resonator sensor is directly placed on a coated composite, and any variation of the coating material, coating thickness and conductivity of the composite alters the resonance frequency. Principal component analysis is employed in the signal pre-processing for the dimensionality reduction of the raw measurement data. In terms of the root-mean-square error, the maximum value for the calibration approach is approximately 15 μm and that for the machine learning-based approach is 12 μm. The sensor system developed enables real-time on-site assessment of coated composite structures and thus offers a new approach for non-destructive evaluation 4.0 with improved efficiency, accuracy and automation.

Two‐Magnon Non‐Locality and Coherence Induced by an Open Microwave Cavity: Generation and Robustness

The generation and robustness of two-magnon non-locality and coherence dynamics induced by an open microwave field cavity are investigated in this work. The studied system consists of a two-sublattice ferrimagnet coupled to a microwave field within an open cavity through its magnetic field component. The robustness of the two-magnons non-locality dynamics is analyzed using various non-locality and coherence measures (namely, uncertainty-induced non-locality [UIN], maximal Bell function, and log-negativity entanglement [L-NE]) in the presence of the spontaneous emission and the electromagnetic-wave dissipation. It is shown that photon-magnon couplings, two-magnon couplings, and dissipation all have an impact on the dynamical aspect of two-magnon non-locality and coherence. This work reveals that the two-magnon non-locality and coherence can be generated. For an initial maximal correlated two-magnon state, the initial UIN non-locality is shown to be more resilient than the maximum Bell function and log-negativity. The amplitudes of the two-magnon non-locality quantifiers decline as a result of the two-magnon coupling. The Bell non-locality and L-NE are reduced via spontaneous emission and dissipation, but the two-magnon UIN-coherence is preserved. These findings contribute to a better understanding of such dynamics and may shed light on measurement estimation in open quantum systems.

Dynamics of two magnons coupled to an open microwave cavity: local quantum Fisher- and local skew-information coherence

Dynamics of two magnons coupled to an open microwave cavity: local quantum Fisher- and local skew-information coherence

Two-Magnon Non-Locality and Coherence Induced by an Open Microwave Cavity: Generating and Robustness

Two-Magnon Non-Locality and Coherence Induced by an Open Microwave Cavity: Generating and Robustness

Open microwave cavity for use in a Purcell enhancement cooling scheme.

A microwave cavity is described which can be used to cool lepton plasmas for potential use in synthesis of antihydrogen. The cooling scheme is an incarnation of the Purcell effect: when plasmas are coupled to a microwave cavity, the plasma cooling rate is resonantly enhanced through increased spontaneous emission of cyclotron radiation. The cavity forms a three electrode section of a Penning-Malmberg trap and has a bulged cylindrical geometry with open ends aligned with the magnetic trapping axis. This allows plasmas to be injected and removed from the cavity without the need for moving parts while maintaining high quality factors for resonant modes. The cavity includes unique surface preparations for adjusting the cavity quality factor and achieving anti-static shielding using thin layers of nichrome and colloidal graphite, respectively. Geometric design considerations for a cavity with strong cooling power and low equilibrium plasma temperatures are discussed. Cavities of this weak-bulge design will be applicable to many situations where an open geometry is required.

Resonance Widths in Open Microwave Cavities Studied by Harmonic Inversion

From the measurement of a reflection spectrum of an open microwave cavity, the poles of the scattering matrix in the complex plane have been determined. The resonances have been extracted by means of the harmonic inversion method. By this, it became possible to resolve the resonances in a regime where the linewidths exceed the mean level spacing up to a factor of 10, a value inaccessible in experiments up to now. The obtained experimental distributions of linewidths were found to be in perfect agreement with predictions from random matrix theory when wall absorption and fluctuations caused by couplings to additional channels are considered.

Localized Modes in a Finite-Size Open Disordered Microwave Cavity

We present measurements of the spatial intensity distribution of localized modes in a two-dimensional open microwave cavity randomly filled with cylindrical dielectric scatterers. We show that each of these modes displays a range of localization lengths, and we successfully relate the largest value to the measured leakage rate at the boundary. These results constitute unambiguous signatures of the existence of strongly localized electromagnetic modes in two-dimensional open random media.

Electromagnetic Response of High-Frequency Gravitational Waves by Coupling Open Resonant Cavity

We present a new detecting scheme of high-frequency gravitational waves (HFGWs) in the GHz band, the scheme consists of a high-quality-fact or open microwave cavity, a static magnetic field passing through the cavity and an electromagnetic (EM) normal mode stored in the cavity It is found that under the resonant condition first-and second-order perturbation EM effects have almost the same detecting sensitivity to the HFGWs in the GHz band (h ∼ 10−26, ν ∼ 5 GHz), but the former contains more information from the HFGWs. We also provide a very brief review for possible improving way of the sensitivity This scheme would be highly complementary to other schemes of detecting the HFGWs.

Direct Observation of Localized Modes in an Open Disordered Microwave Cavity

We present measurements of the spatial intensity distribution of localized modes in a two-dimensional open microwave cavity randomly filled with cylindrical dielectric scatterers. The robustness of these modes with respect to a modification of the boundaries of the scattering region is successfully established. From a comparison with numerically calculated modes, we can extract precise values of the localization length which are in agreement with the measured spectral widths. These results constitute unambiguous signatures of the existence of strongly localized electromagnetic modes in two-dimensional open random media.

Nodal domains in open microwave systems

Nodal domains are studied both for real psiR and imaginary part psiI of the wave functions of an open microwave cavity and found to show the same behavior as wave functions in closed billiards. In addition we investigate the variation of the number of nodal domains and the signed area correlation by changing the global phase phig according to psiR+ipsiI=eiphig(psiR'+ipsiI'). This variation can be qualitatively, and the correlation quantitatively explained in terms of the phase rigidity characterizing the openness of the billiard.

Universal transport properties of open microwave cavities with and without time-reversal symmetry

We measure the transmission through asymmetric and reflection-symmetric chaotic microwave cavities in dependence on the number of attached waveguides. Ferrite cylinders are placed inside the cavities to break time-reversal symmetry. The phase-breaking properties of the ferrite and its range of applicability are discussed in detail. We use the random matrix theory accounting for absorption effects to calculate the universal distribution of transmission coefficients T and their energy derivatives dT/depsilon. Using the absorption strength as a fitting parameter, we find good agreement between universal transmission fluctuations predicted by the theory and the experimental data.

Wave function scarring in open quantum dots: A microwave-billiard analog study

We study the wave functions and transmission properties of an open microwave cavity in the frequency range of 1--17 GHz. The transmission of microwaves between the input and output antennas of the cavity is found to exhibit large fluctuations as a function of frequency, while the cavity wave functions are found to reveal the presence of periodically recurring scars, in close correspondence with specific peaks in the Fourier transform of the transmission fluctuations. This work, therefore, provides strong support for the results of recent studies of open quantum dots, which have revealed the presence of measurable transport results associated with specific wave function scars.

Open microwave cavities

We study resonances in an open quantum system and in a microwave cavity connected to a waveguide. In both cases, interferences via the continuum of decay channels take place. They cause resonance trapping, which is a separation of time-scales. It appears if the coupling strength gets large enough. The reorganisation of the system is accompanied by an essential biorthogonality of the resonance states.

Observation of resonance trapping in an open microwave cavity

The coupling of a quantum mechanical system to open decay channels has been theoretically studied in numerous works, mainly in the context of nuclear physics but also in atomic, molecular, and mesoscopic physics. Theory predicts that with increasing coupling strength to the channels the resonance widths of all states should first increase but finally decrease again for most of the states. In this Letter, the first direct experimental verification of this effect, known as resonance trapping, is presented. In the experiment a microwave Sinai cavity with an attached waveguide with variable slit width was used.

Observation of Nonquasistatic Plasma Surface Waves

Surface waves have been launched from a waveguide onto a glass-clad plasma column of moderate size (2πR≈λ0) in order to test the validity of quasistatic analysis when the small-column condition (2πR≈λ0) is not satisfied. Resonances were observed in an open microwave cavity, and dispersion of both the circularly symmetric surface wave and the dipole surface wave has been determined from experimental data. The two waves exhibit regions of backward-wave and forward-wave propagation. The observed positive slope of the dipole mode dispersion curve near ω/kz=c is contrary to the predictions of quasistatic analysis and is shown to agree quantitatively with the results of a more rigorous analysis.