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A compact leaky-wave antenna using a planar spoof surface plasmon polariton structure
摘要： This article presents and validates a leaky-wave antenna by using the spoof surface plasmon polariton (SSPP) technique. By properly designing the proposed SSPP unit, the SSPP wave can be switched between the confinement and radiation modes. A large radiation efficiency can be achieved by properly designing the modulation depth, which ensures that a compact SSPP leaky-wave array can be realized by using a small number of SSPP radiation units. To verify the design, a prototype which consists of a SSPP feeding network and a 4 by 4 SSPP radiation units has been fabricated by using a low cost FR-4 substrate. A good agreement between simulated and measured results has been obtained. The proposed array antenna shows the promising capability of the SSPP technique for leaky-wave antenna applications.
关键词： dispersion curve,the spoof surface plasmon polariton (SSPP),SSPP antenna array,SSPP power divider
更新于2025-09-23 15:23:52
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Inverse Problem in the Theory of Surface Traveling Waves in Layered Media
摘要： The regularization method, in addition to efficiently resolving the issue with ill-posed problems in various applications, also substantially suppresses noise and error propagation. To achieve these goals, the article proposes a new “genetic algorithm” (GA) method, linked with Tikhonov’s regularization method (GA-TRM). The regular operator is introduced in the GA fitness functions to study the inverse problem of surface-wave dispersion. Experimental results have shown that, compared with the classical algorithm, the new algorithm improves inversion accuracy, reduces errors, and lowers inversion instability.
关键词： regularization method,inverse problems,surface waves,dispersion curve,genetic algorithm
更新于2025-09-23 15:21:21
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Estimation of power loss spectra in slightly flattened distorted Bragg fiber waveguide
摘要： Dispersion characteristic and fiber loss spectra of a Bragg fiber waveguide having slightly flattened distortion are estimated for sensing applications. The characteristic and optical power loss equations of waveguide are obtained by matching the fields at various boundaries under quarter wave stack conditions. It is found that the optimum power loss is inversely proportional to the ninth power of distortion coefficient. The obtained results show that optimum fiber loss decreases with decrease of refractive index of cladding layer ′ ′b (low refractive index layer) and increase of refractive index of cladding layer ′ ′a (high refractive index layer). Also, fiber losses are estimated with increase of the high and low refractive index cladding layer losses. This loss spectrum of fiber can be considered as sensing signal. Since obtained fiber losses in distorted Bragg fiber are higher than standard Bragg fiber therefore, the sensitivity of proposed structure is higher than the standard Bragg fiber. Also, the sensitivity increases with the increase of refractive index of core medium. These results would be helpful to design a novel highly sensitive sensor based on hollow core distorted Bragg fiber.
关键词： Power losses,Distorted Bragg fiber,Dispersion curve,Sensitivity
更新于2025-09-23 15:19:57
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Time-frequency analysis of laser-excited surface acoustic waves based on synchrosqueezing transform
摘要： Laser-excited surface acoustic wave (LSAW) techniques can realize the measurement of surface properties through dispersion curve inversion. In addition to the conventional phase spectrum method, time-frequency analysis can also be used as a calculation tool for the dispersion curve. An accurate time-frequency analysis method is important in precisely inverting the surface properties. In this paper, synchrosqueezing transform (SST) is applied to the analysis of LSAW. By comparing the processing results of the constructed LSAW signal, SST shows higher time-frequency resolution and robustness than other common time-frequency analysis algorithms. Finite element model is used to simulate the propagation of LSAW in the film/substrate structure. And SST is used to calculate the dispersion curve of SAW information extracted during the simulation. A fast algorithm is introduced, where the film thickness is initially estimated by calculating the midrange. Through inversion, the resulting film thickness error is only 1.20% from the theoretical value. Therefore, SST is an effective tool for analyzing LSAW and calculating its dispersion curve.
关键词： Synchrosqueezing transform,Surface acoustic wave,Surface properties,Dispersion curve
更新于2025-09-19 17:13:59
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Spatial distribution of the phononic crystal modes excited by a moving laser source
摘要： In this paper, we have presented the dispersion curve of Lamb waves in an aluminum plate with a periodic rectangular corrugation experimentally. A mode selection method was applied to generate Lamb waves in the region of the corrugated periodic structure using a moving continuous wave laser, and the signal can be detected at any point in the excitation region. The relationship between the phase velocity and the frequency is observed. It is found that the intensity distribution of the dispersion curves in the experimental results is related to the slope of the dispersion curves as well as the selection of the detection point. Vibrations at a series of locations were detected, re?ecting the change in energy that Lamb waves undergo in the process of propagation through the periodic structure, which is different from the existing method of single-point excitation and detection. The spatial distribution of the mode amplitude at the resonances points, in particular induced by the Bragg re?ection, has been studied.
关键词： dispersion curve,phononic crystal,Bragg reflection,laser ultrasonic method,Lamb waves
更新于2025-09-11 14:15:04
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DESIGN OF 2D METAL PHOTONIC CRYSTAL ARRAY OF DIRECTIONAL RADIATION IN MICROWAVE BAND
摘要： A 2D metal photonic crystal structure with a rectangular lattice is designed for directed wave propagation in the microwave frequency band. The dispersion curve of EPC is computed for designing the directed period array. In order to favor the computing, the rectangular period array is studied, which is di?erent from the reference that is designed in optical range and uses the dielectric rods and hexagonal structure to compose the period array. The computed dispersion curves are combined with the theory of ?nite thick period array for obtaining the directed wave propagation structure. The in?uence of the number of metal rods on the antenna directionality is investigated, and the simulation results are compared and analyzed. It is found that when the number of transverse metal rods increases, the directionality of the antenna is enhanced, and the radiant power of the sidelobe radiation can be reduced. Based on the simulation results, the actual 2D metal photonic crystal array is constructed for the measurement validation. According to measurement results, the antenna located in the center of the array can get good directionality at 3.1 GHz.
关键词： 2D metal photonic crystal,antenna directionality,microwave band,directional radiation,dispersion curve
更新于2025-09-10 09:29:36
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Sodium Doping Effect on Optical Permittivity, Band Gap Structure, Nonlinearity and Piezoelectric Properties of PZT Nano-colloids and Nanostructures
摘要： In this research, effects of sodium atoms doping on optical properties of lead zirconate titanate (PZT) nanoparticles (NPs) are studied and compared with undoped particles. Analyses show formations of PZT nanostructures with dimensions below 30 nm. X-ray diffraction patterns show that the particle size increases and the intensity of the preferred direction decreases as the doping sodium atoms are used in the structure. Analyzing absorption spectra of the colloidal solutions shows doped particles are better absorbers at violet-green region of spectra. Also, it has been concluded that PZT NPs only have indirect optical band gap that is narrower for doped particles. Optical permittivity of the ?lms has been compared using a numerical method and shows the prominent effect of doping on real and imaginary parts of permittivity. Also, z-scan experiments have been done to measure thermo-optical and nonlinear absorption coef?cients of the nano-colloids using continue wave Nd-YAG laser illumination. Finally, sodium doping effects on piezoelectric properties of the samples are investigated using a Michelson interferometer.
关键词： z-scan,Piezoelectric,Michelson interferometer,dispersion curve,PZT nanoparticles
更新于2025-09-04 15:30:14