Transmission Coefficient Curves Research Articles

Wave energy conversion by an array of oscillating water columns deployed along a long-flexible floating breakwater

Large-scale spatial configurations combining Wave Energy Converters (WECs) and coastal attenuating-wave facilities have the potential to exploit marine renewable energy sustainably. In this study, an integrated concept of multiple Oscillating Water Columns (OWCs) and a very long floating breakwater is introduced. Associated energy extraction, gap resonance and hydroelastic interaction problems are examined. A coupled numerical simulation methodology consisting of a Finite Volume Method (FVM)based solver and a Finite Element Method (FEM) solver, is developed to investigate the strong fluid and structure coupled problem. The fluid-structure information is matched in real-time and the flexible modes of the floating breakwater are obtained by imposing a restrained beam inside the pontoon. The accurate time-domain model is validated against both simulated and measured data. Extensive parametric studies indicate that the energy conversion has a conflict with the wave attenuation in terms of determining the along-shore number of OWCs. The highest energy conversion in medium-period and long-period waves are observed in the OWCs near the end and middle locations, respectively. Besides, the constructive resonant gap effect between OWCs and the breakwater can amplify the peaks of energy conversion efficiency, leads to a sudden collapse in transmission coefficient curves. With an increased sidewall draft, OWCs closer to oblique incident direction generate stronger piston-type and sloshing oscillations. Additionally, compared with a rigid breakwater, the elastic deformation of the breakwater plays a destructive role in wave energy conversion, which is attributed to the out-of-phase interference of multi-mode radiated waves.

Simulation and Comparative Study of Resonant Tunneling Diode

This paper studies and investigates the effect of physical and electrical parameters on double, triple and six barrier resonant tunneling diodes (RTD). The materials used for quantum well and barriers are Gallium arsenide (GaAs) and Aluminium gallium arsenide (AlGaAs), respectively. The parameters that were reasoned and studied include conduction band, current density, transmission coefficient and resonance energy. The above parameters were studied by changing bias voltage, temperature, barrier width and doping concentration. From the simulations performed it is observed that for double barrier RTD the peak current density is observed at 0.2 V and the valley current density is observed at 0.3 V, whereas for a triple barrier RTD the peak current density is observed at 0.015 V and the valley current density is observed at 0.06 V. The value of transmission coefficient for double barrier RTD decreases especially after bias applied is more than resonant bias (0.2 V). The effect of increasing bias leads to a decrease in the resonance level in the conduction band. The width of resonance energy decreases with the increase in barrier width. With increase in number of barrier the number of resonance level increases which leads to an increasing peaks in the transmission coefficient curve. The effect of increasing temperature leads to higher current and more resonance energy. With the thickening of barrier width, less transmission of electrons occurs leading to a reduced current density. When the barriers are increased the negative differential region (NDR) is achieved at low voltages.
 HIGHLIGHTS
 
 This paper studies and investigates the effect of physical and electrical parameters on double, triple and six barrier resonant tunneling diodes (RTD)
 The parameters include conduction band, current density, transmission coefficient, and resonance energy
 The parameters were studied by changing bias voltage, temperature, barrier width, and doping concentration
 It is observed that for double barrier RTD the peak current density is observed at 0.2 V and the valley current density is observed at 0.3 V
 For a triple barrier RTD the peak current density is observed at 0.015 V and the valley current density is observed at 0.06 V
 
 GRAPHICAL ABSTRACT

Analysis of electromagnetic transmission characteristics of square loop frequency selective fabrics with different layers

Nine square loop frequency selective fabrics (FSFs) with different layers were designed, prepared, and tested in this paper. Then the electromagnetic transmission characteristics were analyzed in detail. The test results reveal that the transmission characteristics of single-layer FSFs are basically identical in two electromagnetic wave polarization modes and keep good frequency selective characteristics as the incidence angle increases. For FSFs with the same frequency selective surface (FSS) layers, the increase of FSS layer number may exert influence on the electromagnetic transmission characteristics, but the influence mode and extent are inconsistent for two kinds of FSFs. For FSFs with complementary FSS layers, the transmission coefficient curves of the double-layer sample are the combination of two single-layer FSFs, with three resonance phenomena at 7.63, 10.75, and 12.38 GHz. However, three-layer FSFs with complementary FSS layers show poor frequency selective characteristics, mainly presenting full shielding characteristics. An equivalent circuit model of multi-layer FSF is built to explore the electromagnetic transmission mechanism; many factors, such as the fabric type, structure, conductive unit type, and size, would nonlinearly affect the electromagnetic transmission characteristics. The work can provide reference value for the study of diverse multi-layer FSFs and variant electromagnetic characteristics.

Continuous and elastically consistent viscoelastic reflection and transmission coefficient curves for plane inhomogeneousPandSwaves

SUMMARYFor inhomogeneous plane waves in dissipative media, correctly selecting the vertical slowness (q) is the key requirement to obtain physically acceptable reflection/transmission (R/T) coefficients (e.g. both continuous curves as a function of incidence angle, and consistency with the elastic coefficients at very low attenuation). Based on the fundamental branch-cut theory, the continuity criterion ensures the continuity of the R/T coefficient curves. The elastic consistence is obtained due to the definition of the mixed principal values and the consistent assumptions of time dependence of the harmonic plane wave, the Z-direction of the spatial coordinate system and the particle motion (polarization) vectors. The elastic consistence of R/T coefficients is checked by both elastic models with zero dissipation factor (1/Q) and the equal-Q model in which the Q values of the incident wave and the R/T waves are non-zero but equal for the P and S waves on both sides of the interface. In particular, the previously reported 180° phase difference between the viscoelastic coefficients with arbitrarily small attenuation but the same ratio of Q across the interface and the corresponding elastic coefficients is circumvented by introducing the mixed principal value. The continuity criterion is implemented directly in the complex vertical slowness squared (q2) plane in which the branch-cut is defined. Furthermore, the loci of q2 and several ‘critical angles’ defined for anelastic waves are clearly investigated and clarified. The loci of q2 are expressed as a function of the incidence angle and the incident wave inhomogeneity parameter D. The plots of wave inhomogeneity parameter (D and/or attenuation angle γ) versus incidence angle are calculated from the slowness vectors. The resultant D values, especially their equality for all vertically propagating R/T waves, are examined using the complex Snell's law to provide extra support to the correctness of the slowness vectors and thus of the R/T coefficients. It is worth noting that phase angle of the R/T waves from an inhomogeneous incident wave may exhibit rapid changes at vertical incidence because near-vertical reflection is still the dominant application of the exploration seismic method. To the best of our knowledge, this research is the first time it has been possible to obtain continuous and elastically consistent viscoelastic R/T coefficients.

Optimization of sound transmission loss of open acoustic barriers with respect to unit cell topology

Open acoustic barriers exhibit excellent sound transmission reduction property at a certain frequency/frequencies which highly depends on the configuration of its unit cell. Design of unit cell configuration for minimum sound transmission at predefined objective frequency remains an open question. This paper aims at providing an automatic design method for open acoustic barriers with multi-material unit cell. Firstly, a wave finite element method is developed to calculate the sound transmission through an infinite array of periodic scatterers. As the unit cell contains infinite fluid domain, the application of Floquet-Bloch theorem to the boundaries of perfectly match layers (PML) is necessary and has been resolved in this paper. This wave finite element method with the implementation of PML is validated by comparing to analytical solution of sound transmission through an array of steel cylinders. Then a genetic algorithm is employed to optimize the sound transmission loss with respect to material distribution of a bi-material unit cell. Finally, the effectiveness of this inverse design is demonstrated by examples with different predefined frequencies. Corresponding unit cell typologies are obtained and the dips of sound power transmission coefficient curve are successfully tuned to objective frequencies.

A Conformal Metamaterial with Wide DNG Region for C and X Microwave Bands

In this paper, a novel shaped and conformal, 14.8 mm × 14.8 mm sized unit cell on a flexible substrate, showing DNG phenomena at C (4–8 GHz) and X band (8.8–10.5 GHz, 11.2–11.6 GHz) is designed. The metamaterial offers 6.1 GHz of whole DNG region, transmission coefficient with stopband of 8.6 GHz ranging from 2 to 16 GHz and a broad 10 GHz NRI region from 2 to 12 GHz. The 1 × 2, 2 × 2, and 4 × 4 array formations of designed metamaterial too maintains DNG characteristics. Measured and simulated transmission coefficient curve of the designed unit cell are in good agreement.

A modified rhombus shaped flexible wideband double negative (DNG) metamaterial for S, C, X, and Ku band applications

AbstractIn this paper a wideband, flexible, and novel structured double negative (DNG) metamaterial is designed for S, C, X, and Ku microwave applications. The 12 mm × 12 mm sized metamaterial is fabricated on a flexible FR4 substrate with thickness 0.25 mm. The metamaterial shows a total wide DNG region of 8.2 GHz (3.8–4.3 GHz and 6.8–14.5 GHz). The transmission coefficient of the unit cell has a total band gap bandwidth of 8.3 GHz from frequency range 2 to 16 GHz. The designed metamaterial also exhibits an extra-large and continuous negative refractive index (NRI) bandwidth of 13 GHz (2–15 GHz). The stop band regions along with DNG and NRI regions individually cover S, C, X, and Ku microwave regions. The complete analysis is done using CST microwave studio. The simulated and measured transmission coefficient curves of the proposed metamaterial are in good agreement. The structure is simple, cost effective, flexible, light weight, and wideband covering S, C, X, and Ku microwave spectra.

Design of a slotted chipless RFID humidity sensor tag

This paper proposes a chipless Radio-Frequency Identification (RFID) sensor tag for low-cost and long-term humidity monitoring. The slotted scatterer structure are fabricated on FR4 substrate by grooving etching. The encoding unit stores the ID information by the combination of the different length slots. Si nanowires are deposited on the surface of the slots to form the sensing unit. Based on the principle of radar electromagnetic backscattering, the test system measures the transmission coefficient curve to obtain the ID and humidity information of the tag. The test results show that the proposed chipless sensor tag achieves good hysteresis and consistence performances and the maximum error is not exceed 10%.

Acoustic metamaterial panel for both fluid passage and broadband soundproofing in the audible frequency range

We present the design, including an experimental demonstration, of an acoustic metamaterial panel aimed at reducing incoming broadband noise in the audible frequency range while allowing an incoming fluid to pass through the holes formed in the panel. The noise reduction performance of the proposed acoustic metamaterial panel is attributed to an array of annular cavities enclosing the fluid passage holes. The acoustic behavior of the acoustic metamaterial panel is theoretically analyzed by the transfer matrix method, and an equivalent acoustic impedance of each annular cavity is included with its effective length in the derived transfer matrix. The effective bulk modulus for the acoustic metamaterial panel is then extracted from the transmission and reflection coefficients by using the retrieval method. It is shown that the frequency range of the negative effective bulk modulus coincides with the stop band of the acoustic metamaterial panel. The underlying physical mechanism for the negative effective bulk modulus is attributed to the out-of-phase motion of vibrating particles in adjacent annular cavities. A calculated transmission coefficient curve of the acoustic metamaterial panel is shown to be in good agreement with the measured one. The findings presented in this work should be useful in the design of a holey soundproof panel.

A rheological model for immersed corrugated elastic plates

The influence of surface imperfections on the propagation of guided waves in an immersed elastic plate can be interpreted by means of a rheological model. The corrugated surface is modeled by a very thin interface, similar to a Jones spring model, which replaces the continuity boundary conditions at the liquid – corrugated solid-plate interface. As the surrounding liquid is considered to be perfect, only one complex stiffness is used for the model of Jones. The selection of the plate guided mode and the test frequency are motivated by the detectability and non-interference with other modes. The spring stiffness is obtained by a best fit procedure, between the analytical solution and the results obtained by the finite elements method (FEM). One way ensuring the agreement of the two approaches, rheological and FEM, is to consider angular resonances provided by the transmission coefficients. Small changes in the parameters of the roughness keep the positions of the angular resonances of the plate practically unchanged, while at the same time large variations of the half width of the transmission coefficient curve is observed. The effect of corrugation parameters on the guided modes in the plate can be predicted by using the rheological model with the deduced spring complex stiffness.

Reflection and transmission coefficients of the SH0 mode in the adhesive structures with imperfect interface

Compared with body waves, ultrasonic guided waves can provide more local characteristic information about the interface in the defect detection of adhesive structures. In the paper, the expressions of the reflection and transmission coefficients of the lowest SH mode (SH0) in multilayered plate-like adhesive structure were deduced on the basis of wave propagation controlling equations and tangential stiffness coefficient KT was contained in the expressions. Then, the expressions were compared with the previous results to verify their applicability and correctness. Then, aluminum/epoxy resin/aluminum adhesive structures were used to explore the effects of the changes in incident angle, frequency-thickness product and tangential stiffness coefficient on SH wave propagation characteristics in adhesive structures with different interface quality (perfect, weak bonding, and slip/debonding interfaces). The results showed that the propagation mode of SH wave in adhesive structures was mainly determined by the incident angle, frequency, adhesive layer thickness and tangential stiffness coefficient. With the increase in the frequency-thickness product, multi-order resonance is generated in the reflection and transmission coefficient curves of SH wave under the perfect and weak bonding interfaces. If proper values of the incident angle of acoustic waves and frequency-thickness product are selected, the perfect, weak bonding, and slip/debonding interfaces can be differentiated from each other, but the slip and debonding interfaces cannot be distinguished from each other. The study provides theoretical contribution to the detection of multilayered plate-like adhesive structure by SH wave.

Wave propagation in water-immersed adhesive structure with the substrates of finite thickness

In previous theoretical studies on the adhesive structure, the substrate is mostly considered as a semi-infinite solid space and corresponding theoretical derivation is rarely related to the thickness of the substrate. In the paper, based on the transfer matrix method, we studied in the water-immersed trilaminar plate-like adhesive structure with the substrates of finite thickness and the perfect/sliding interfaces in the case of plane longitudinal wave incidence and deduced the expressions of reflection and transmission coefficients of longitudinal waves. In order to verify the accuracy and applicability of the deduced formula, this formula was firstly applied to the water-immersed steel–epoxy resin–steel adhesive structure with perfect interfaces and the calculated result was compared with the existing data. Taking the water-immersed aluminum–epoxy resin–aluminum adhesive structure with perfect/sliding interfaces as an example, the impacts of incident angle and frequency on the reflection and transmission characteristics of the longitudinal wave were then analyzed. Finally, the theoretical method was experimentally verified and the experimental results were well consistent with the numerical calculation results. The reflection and transmission coefficient curves of longitudinal wave showed the obvious resonance when the longitudinal wave was normally incident. Regardless of the substrate thickness, the frequency of acoustic waves or the incident angle, it can only confirm whether a sliding interface exists, but the interface to slide cannot be determined.

Scaling behavior in the transmission coefficient for a self-affine multi-barrier system using graphene

By means of a deposited or epitaxial graphene model, we study the transmission coefficient as a function of the incident electron's energy, for a multi-barrier system which is finitely self-affine (i.e., it is self-similar but with different scaling ratios in the x and energy axis) and has mirror symmetry with respect to the center of the structure. The main result is the scaling behavior in the transmission coefficient (which in fact resembles the form of the multi-barrier structure) and the appearance of a scaling relation between curves of different parameter values. This system is finitely self-affine as the number of scaled pieces is finite and the scaling is only made in the energy axis. In order to study the transmission properties of the proposed structure, we consider first different “generations” of its construction, we compute their transmission coefficient curves and then search for some resemblance of the geometric properties of the multi-barrier structure in the form of scaling relations between transmission curves. We find that not only such scaling relations exist, but they are surprisingly simple. In fact they are simple enough to write down a closed algebraic expression that describe them. We thought that this is due to the finite self-affinity property and that it could be used as a basic model to analyze more complicated multi-barrier profiles.

Optical Absorption of Blood Depends on Temperature during a 0.5 ms Laser Pulse at 586 nm

Optical properties are important parameters in port wine stain laser treatment models. In this study we investigated whether changes in blood optical properties occur during a 0.5 ms laser pulse. Blood from three volunteers was irradiated in vitro with laser pulses (radiant exposure 2-12 J cm-2, wavelength 586 nm, pulse length 0.5 ms). Reflection and transmission coefficients, measured using double integrating spheres, decreased slightly during the first part of the pulse. At 2.9 J cm-2 radiant exposure, the reflectance increased, independent of total radiant exposure of the pulse. This was caused by blood coagulation. A second sudden increase in reflection and a significant increase in transmission occurred near 6.3 J cm-2 and was accompanied by a "popping" sound, indicating rapid expansion of bubbles due to blood vaporization. A multilayered model of blood was used to fit calculated transmission coefficient curves to the measurements and determine temperature-dependent optical blood absorption. Heat diffusion was shown to be of minor importance. A 2.5-fold increase in absorption for temperatures increasing from 20 to 100 degrees C, accurately describes transmission coefficients measured up to 2.9 J cm-2.

Vibration propagation in frame structure

We consider propagation of longitudinal and transverse sound waves along T-shaped concrete frame structures which are combinations of walls and ceilings. The formulation of Morse [J. Acoust. Soc. Am. 22, 219 (1950)] and Muskat et al. [Geophysics V, 115 (1940)] is followed throughout, though not in detail. For the horizontal part of the structure, the boundary condition of the vanishing of the normal components of stresses over the bounding surfaces is used. Both a plane longitudinal wave and a transverse wave when incident on a solid/vacuum interface produce both a reflected longitudinal wave and a reflected transverse wave. For propagation along the vertical part of the structure, we use the boundary conditions that both the displacements and the stresses at the solid/solid interface shall be continuous. Transmission coefficients are plotted as functions of the incident frequencies and the angles of incidence. They are compared with the theoretical works of Cremer [Acustica 3, 317 (1953)] and Arenberg [J. Acoust. Soc. Am. 20, 1 (1948)] because no previous experimental work has been done for this type of structure. Comparison shows reasonable agreement on the shape of transmission coefficient curves.

Amplitudes of horizontally refracted Love waves

abstractLove-wave transmission and reflection are studied numerically for a vertical interface between two layered models. By a new method of approximation, the transmission and reflection coefficients can be computed for propagation directions differing from normal incidence. We consider the Love mode as a superposition of propagating plane SH waves in a surface layer and an inhomogeneous plane SH wave falling off with depth in the half-space below. The method is based on satisfying all boundary conditions on the vertical interface and computing the coupling between the interface stress displacement pattern and the transmitted/reflected Love modes. The computations are done rapidly on a small computer.The transmission coefficients change rapidly with period. For propagation from ocean to continent, they increase with decreasing periods in the interval 60 to 20 sec. The opposite trend is found for propagation from continent to ocean. The amplitude transmission coefficient curves show almost no dependence on the angle of incidence except for large angles. The fine structure of the curves is similar to that for plane SV waves incident on an interface between two homogeneous elastic media. Love-wave amplitude observations at OBS on the ocean bottom northwest of San Francisco and at BKS in Berkeley also show these trends as a function of period and of angle of incidence.