Verification of the electromagnetic deep-penetration effect in the real world

The deep penetration of electromagnetic waves into lossy media can be obtained by properly generating inhomogeneous waves. In this work, for the very first time, we demonstrate the physical implementation and the practical relevance of this phenomenon. A thorough numerical investigation of the deep-penetration effects has been performed by designing and comparing three distinct practical radiators, emitting either homogeneous or inhomogeneous waves. As concerns the latter kind, a typical Menzel microstrip antenna is first used to radiate improper leaky waves. Then, a completely new approach based on an optimized 3-D horn TEM antenna applied to a lossy prism is described, which may find applications even at optical frequencies. The effectiveness of the proposed radiators is measured using different algorithms to consider distinct aspects of the propagation in lossy media. We finally demonstrate that the deep penetration is possible, by extending the ideal and theoretical evidence to practical relevance, and discuss both achievements and limits obtained through numerical simulations on the designed antennas.

Orientational characteristics of magnetization precession excitation on the interference grating formed by femtosecond laser.

The subject of investigation in this work is the excitation of magnetization precession in magnetic film on the surface of which is formed the temperature relief which is formed by interference picture formatted by preliminary divided ray from femtosecond laser. It is mentioned the discovered in experiment the dependence of excitation efficiency from the orientation of magnetic field applied in the plane of film. The main aim of this work is the theoretical interpretation of observed orientation dependence. The realized in experiment scheme “pump-probe” is described. The whole geometry of task is proposed. This geometry includes in oneself the magnetic film with formed in its surface interference picture and applied in the plane of film the constant field. It is shown that by the thermal expansion in the film the elastic waves two types are excited; the surface Rayleigh waves and leaky longitudinal waves. The projections of wave-vectors of propagating waves to plane of film are normal to the strips of interference picture. The orientation of field may change from to longitudinal to transverse from the same strips. The components of deformation tensor of Rayleigh and leaky waves are determined. The precession of magnetization in the coordinate system connected with field is investigated. By using the apparatus of crossing matrixes it is found the components of deformation tensor are determined. In the frame of linear approach in this system the task about excitation of magnetization precession by elastic deformations by Rayleigh and leaky waves is solved. The dynamical component of magnetization precession which ensures the light polarization rotation which passes along the normal to the plane of film is found. It is shown that the angle of rotation is straight proportional to the tensor deformation components with the summarization with the resonance character of precession magnetization dependence from the value of magnetic field. The dependence of polarization rotation from orientation of field which is applied in the plane of film is found. It is shown that by the orientation of field along and across the interference stripes the rotation of polarization plane is absent. Between these extreme orientations the dependence has appearance as two maxima divided by deep minimum. The received results are compared with data of experiment. It is found the quality and in some cases quantity correlation. The recommendations for further development of work are proposed.

Microwave synthesis of Bessel, Bessel–Gauss, and Gaussian beams: a fully vectorial electromagnetic approach

Bessel, Bessel-Gauss, and Gaussian beams have widely been investigated in optics in the paraxial approximation, under the frame of a scalar wave theory. Such approximations can hardly be applied in the microwave/millimeter-wave range, where the vectorial nature of the electromagnetic fields cannot be neglected, and experimental realizations for some of these beams appeared only recently. In this work, we discuss the generation of Bessel, Bessel-Gauss, and Gaussian beams through a fully vectorial electromagnetic approach. The field derivation of all these beams is first illustrated and numerical evaluations are then reported to compare their different propagation and diffractive behaviors. Finally, an innovative approach for realizing such solutions with planar microwave devices exploiting leaky waves is demonstrated through accurate numerical simulations.

Mode Analysis of Pt/LGS Surface Acoustic Wave Devices

Platinum (Pt) gratings on langasite (LGS) substrates are a widely used structures in high temperature surface acoustic wave (SAW) devices. Multiple modes can be excited in Pt/LGS SAW devices owing to the heavy weight of the Pt electrode and leaky waves in the LGS substrate. In this work, we report on a detailed mode analysis of Pt/LGS SAW devices, where three commonly used LGS cuts are considered. A three-dimensional (3D) finite element method (FEM) numerical model was developed, and the simulation and experiment results were compared. The experiment and simulation results showed that there are two modes excited in the Pt/LGS SAW devices with Euler angle (0°, 138.5°, 27°) and (0°, 138.5°, 117°), which are Rayleigh-type SAW and SH-type leaky wave, respectively. Only the Rayleigh-type mode was observed in the Pt/LGS SAW devices with Euler angle (0°, 138.5°, 72°). It was found that the acoustic velocities are dependent on the wavelength, which is attributed to the change of wave penetration depth in interdigital transducers (IDTs) and the velocity dispersion can be modulated by the thickness of the Pt electrode. We also demonstrated that addition of an Al2O3 passivation layer has no effect on the wave modes, but can increase the resonant frequencies. This paper provides a better understanding of the acoustic modes of Pt/LGS SAW devices, as well as useful guidance for device design. It is believed that the Rayleigh-type SAW and SH-type leaky waves are potentially useful for dual-mode sensing applications in harsh environments, to achieve multi-parameter monitoring or temperature-compensation on a single chip.