Spatio-spectral decomposition of complex eigenmodes in subwavelength nanostructures through transmission matrix analysis

Exploiting multiple near-field optical eigenmodes is an effective means of designing, engineering, and extending the functionalities of optical devices. However, the near-field optical eigenmodes of subwavelength plasmonic nanostructures are often highly multiplexed in both spectral and spatial distributions, making it extremely difficult to extract individual eigenmodes. We propose a novel mode analysis method that can resolve individual eigenmodes of subwavelength nanostructures, which are superimposed in conventional methods. A transmission matrix is constructed for each excitation wavelength by obtaining the near-field distributions for various incident angles, and through singular value decomposition, near-field profiles and energy spectra of individual eigenmodes are effectively resolved. By applying transmission matrix analysis to conventional electromagnetic simulations, we clearly resolved a set of orthogonal eigenmodes of single- and double-slot nanoantennas with a slot width of 20 nm. In addition, transmission matrix analysis leads to solutions that can selectively excite specific eigenmodes of nanostructures, allowing selective use of individual eigenmodes.

On-chip light scattering imaging of the guanine platelet

A guanine platelet is a very thin optical component that plays a role in light reflection control in the narrow space within the body of a fish. However, the details of this light control mechanism have not been revealed to date. In this work, guanine micro-platelets floating in water are visualized via light projection near an image sensor. These guanine platelets demonstrate light scattering toward specific directions. By setting a thin water layer on top of the image sensor’s cover glass, each platelet in the water layer forms column- or bar-code-shaped images on the screen. The existence of nanohole gratings in these platelets was confirmed by high-resolution optical microscopy. Numerical electromagnetic simulations indicated that the nanohole gratings contributed to the formation of unique light projection spots.

A bolt loosening detection method based on patch antenna with overlapping sub-patch

Bolts are widely used in civil engineering, and the detection of bolt loosening is of great significance to ensure the safety of a structure. This paper introduces a new method for detecting bolt loosening using a customized detachable strain sensor based on a patch antenna. A patch antenna with overlapping sub-patch is proposed to measure the longitudinal elongation of the entire bolt shaft, indicating the loosening state of the bolt. When the bolt is fastened, the elongation of the bolt under tension will change the combined length of the underlying patch and the radiation sub-patch, consequently increasing or decreasing the resonant frequency of the antenna. The resonant frequency of the antenna can be measured by the vector network analyzer. Furthermore, with wireless interrogation of the strain sensor based on the patch antenna, the proposed method can also be used in the wireless detection of bolt loosening. The authors conducted a finite element analysis of the bolt and the electromagnetic simulations of the antenna. They designed the detection sensor and conducted a series of experimental tests to demonstrate how a bolt under different applied preloads can be effective and feasible under the proposed method.

Marlim R3D phase 3: The marine magnetotelluric regional model and associated data set

Synthetic data provided by earth models are essential to investigate several geologic problems. Marlim R3D (MR3D) is an open-source realistic earth modeling project for electromagnetic simulations of the postsalt reservoirs of the Brazilian offshore margin. In phase 3, we have conducted a 3D marine magnetotelluric (MMT) study with the finite-difference method to generate the synthetic magnetotelluric (MT) data set for the MR3D earth model. To that end, we upscaled the original controlled-source electromagnetic model to preserve all local-scale features, such as the thin-layer turbidite reservoirs, and to include several geologic regional features, such as the coastline, land topography, basement rocks representing the continental crust, and mantle rocks. Then, we simulated an MMT survey with 500 receivers evenly spaced at 1 km intervals along the rugged seafloor of the MR3D model. To accurately represent the MMT model with a 329 × 329 × 200 km volume, we have produced a mesh with 161 × 136 × 242 cells (approximately 5.3 million cells). We computed the full MT and tipper tensor at 25 periods in the time range of 1–10,000 s. The data set, the model, and companion material are freely distributed for research or commercial use under the Creative Commons License at the Zenodo platform.

Application of Deep Learning to Predict RF Heating of Cardiac Leads During Magnetic Resonance Imaging at 1.5 T and 3 T

Purpose: Predicting magnetic resonance imaging (MRI)-induced heating of elongated conductive implants such as leads in cardiovascular implantable electronic devices (CIEDs) is essential to assessing patient safety. Phantom experiments and electromagnetic simulations have been traditionally used to estimate radiofrequency (RF) heating of implants, but they are notably time-consuming. Recently, machine learning has shown promise for fast prediction of RF heating of orthopedic implants, when the position of the implant within the MRI RF coil was predetermined. Here we explored whether deep learning could be applied to predict RF heating of conductive leads with variable positions/orientations during MRI at 1.5 T and 3 T.Methods: Models of 600 cardiac leads with clinically relevant trajectories were generated and electromagnetic simulations were performed to calculate the maximum of 1g-averaged SAR at the tips of lead models during MRI at 1.5 T and 3 T. Deep learning algorithms were trained to predict the maximum SAR at the lead’s tip from the knowledge of coordinates of points along the lead’s trajectory.Results: Despite the large range of SAR values (~200 W/kg-~3300 W/kg), the RMSE of predicted vs ground truth SAR remained at 223W/kg and 206 W/kg, with the R2 scores of 0.89 and 0.85 on the testing set for 1.5 T and 3 T models, respectively.Conclusion: Machine learning shows promise for fast assessment of RF heating of lead-like implants with only the knowledge of the lead’s geometry and MRI RF coil features.

Electromagnetic Simulation of Signal Distribution of Various RF Endoluminal Loop Geometries with Coil Orientation: Towards a Reconfigurable Design

With the objective of improving MR endoluminal imaging of the colonic wall, electromagnetic simulations of different configurations of single-layer and double-layer, and double-turn endoluminal coil geometries were run. Indeed, during colon navigation, variations in coil orientation with respect to B0 are bound to occur, leading to impaired image acquisition due to a loss of signal uniformity. In this work, three typical coil orientations encountered during navigation were chosen and the resulting signal uniformity of the different geometries was investigated through the simulated B 1 x , y / I R t values. Sampling this quantity over a circle of radius r enabled us to calculate the coefficient of variation (= standard deviation/mean) for this given distance. This procedure was repeated for r ∈ 5 ; 15 mm, which represents the region of interest in the colon. Our results show that single-loop and double-layer geometries could provide complementary solutions for improved signal uniformity. Finally, using four microelectromechanical system switches, we proposed the design of a reconfigurable endoluminal coil able to switch between those two geometries while also ensuring the active decoupling of the endoluminal coil during the RF transmission of an MR experiment.

Electromagnetic Simulations and Measurements of the K-800 Superconducting Cyclotron RF Cavity at INFN-LNS

In this paper, a complete three-dimensional (3D) RF model of the cyclotron coaxial resonator—including the coaxial sliding shorts, the “Liner” vacuum chamber, the coupler, the trimmer, and the high RF voltage “Dee” structures—has been developed. An eigenmode analysis was used to simulate the tuning of the resonator in the operating frequency range of 15–48 MHz obtained by two movable sliding shorts and a trimmer. A driven analysis has been performed in order to compute the |S11| parameter (or impedance matching) of the cavity excited by a movable coaxial power coupler. The numerical simulations have been performed using the different peculiarities of two commercial tools, COMSOL Multiphysics and CST microwave studio. Experimental validation of the developed model is presented. The evidence of an unwanted electric field component, orthogonal to the accelerating field, was discovered and a mitigation is also proposed. The impact of the proposed modification was evaluated by using a 3D beam dynamics code under development in the framework of the Superconducting Cyclotron upgrade ongoing at INFN-LNS.