Standing Wave Model Research Articles

Bit Error Performance of APD and SPAD Receivers in Optical Wireless Communication

This review concentrates on the state-of-the-art hardware-oriented receiver aspects for optical wireless communication (OWC), and points to the importance of BER performance analysis and modeling in presence of non-perpendicular light incidence. Receivers in OWC networks for 6G applications have to work for strongly different light incidence angles, to allow the formation of connections to locally separated transceivers without the need for rotation units and accurate adjustment. In turn, and in combination with fully integrated optical receivers, reduction of cost and increased comfort can be achieved. Fully integrated [bipolar] complementary metal-oxide-semiconductor ([Bi]CMOS) receivers with on-chip avalanche photodiodes (APDs) and single-photon avalanche diodes (SPADs) are presented and their performance in optical wireless communication is summarized. Impressive data rates up to 2 Gbit/s and free-space transmission distances up to 27 m at bit error ratios (BER) below 10−9 are reached with linear-mode APD receivers. The importance of optical interference in the isolation and passivation stack on top of the integrated photodiodes is illuminated. To be able to predict the dependence of the BER of single-photon avalanche diode (SPAD) receivers on the light incidence angle, a model, which includes a model for the photon detection probability and a standing-wave model for the isolation and passivation stack, is extended. The dependence of the BER on the light incidence angle onto the photodiodes is investigated by electromagnetic simulation for optical transmission of the layers on top of the photodiode, device simulation for the avalanche triggering probability and BER modeling with MATLAB. It is found that incidence angles up to 30° have moderate influence on the BER and that the BER degrades significantly for incidence angles larger than 50°.

Semi-analytical approach for refractive index sensors based on reflective metasurfaces

We present a semi-analytical approach for the analysis and design of refractive index sensors based on metal–insulator–metal (MIM) metasurfaces. While numerical methods require extensive calculations for all values of geometrical parameters, the semi-analytical approach provides straightforward guidelines for a design of optimal metasurfaces with maximized sensitivity. Semi-analytical formulas for refractive index sensitivities are derived from equations of the temporal coupled mode theory and standing-wave resonance model. They require three numerically calculated parameters (resonant frequency and radiative and non-radiative decay rates of the resonant mode), obtained by the fitting of reflectance spectra. Generality of the presented approach allows us to consider the operation of metasurface sensors in three different interrogation methods: spectral (frequency), intensity (reflectance), and phase. Validity of the proposed approach is confirmed by a good agreement with numerical results. Starting from semi-analytical formulas, we derive working frequencies of metasurface based sensors, prove that the critical coupling with equal decay rates of the resonant mode is the optimal working regime, and demonstrate that optimal MIM metasurfaces should have periods as large as possible with the thickness of MIM cavities determined by the critical coupling condition.

Comparing spontaneous and stimulus frequency otoacoustic emissions in mice with tectorial membrane defects

The global standing-wave model for generation of spontaneous otoacoustic emissions (SOAEs) suggests that they are amplitude-stabilized standing waves and that the spacing between SOAEs corresponds to the interval over which the phase changes by one cycle as determined from the phase-gradient delays of stimulus frequency otoacoustic emissions (SFOAEs). Because data characterizing the relationship between spontaneous and evoked emissions in nonhuman mammals are limited, we examined SOAEs and SFOAEs in tectorial membrane (TM) mutants and their controls. Computations indicate that the spacing between adjacent SOAEs is predicted by the SFOAE phase-gradient delays for TM mutants lacking Ceacam16, where SOAE frequencies are greater than ~20 kHz and the mutants retain near-normal hearing when young. Mice with a missense mutation in Tecta (TectaY1870C/+), as well as mice lacking Otoancorin (Otoa−/−), were also examined. Although these mutants exhibit hearing loss, they generate SOAEs with average frequencies of 11 kHz in TectaY1870C/+ and 6 kHz in Otoa−/−. In these animals, the spacing between adjacent SOAEs is larger than predicted by the SFOAE phase delays. It is also demonstrated that mice do not exhibit the strong frequency-dependence in signal coding that characterizes species with good low-frequency hearing. In fact, a transition occurs near the apical end of the mouse cochlea rather than at the mid-point along the cochlear partition. Hence, disagreements with the standing-wave model are not easily explained by a transition in tuning ratios between apical and basal regions of the cochlea, especially for SOAEs generated in TectaY1870C/+mice.

A Transmission-Line-Based Cochlear Standing Wave Model To Elucidate Mechanism of Human Auditory System.

How do people hear sounds? As a counterpart of Prof. G. V. Békésy's traveling wave theory, we have proposed resonance theory of outer hair cells and cochlear standing wave theory, respectively. Based on these proposals, this paper develops a transmission-line-based cochlear standing wave model. Since the macroscopic cochlear model is designed as it looks like, various auditory physiology can be explained. Transient analyses with pure-tone excitation and Gaussian pulse excitation are carried out, and Prof. D. Kemp's otoacoustic emission (OAE) is demonstrated successfully.Clinical relevance-Our new model has a great potential to explain auditory physiology including structural inner disorders, hearing loss, and even tinnitus.

Vibrational properties of LaNiO3 films in the ultrathin regime

Collective rotations and tilts of oxygen polyhedra play a crucial role in the physical properties of complex oxides such as magnetism and conductivity. Such rotations can be tuned by preparing thin films in which dimensionality, strain, and interface effects come into play. However, little is known of the tilt and rotational distortions in films a few unit cells thick including the question of if coherent tilt patterns survive at all in this ultrathin limit. Here, a series of films of perovskite LaNiO3 is studied and it is shown that the phonon mode related to oxygen octahedral tilts can be followed by Raman spectroscopy down to a film thickness of three pseudocubic perovskite unit cells (∼1.2 nm). To push the limits of resolution to the ultrathin regime, a statistical analysis method is introduced to separate the Raman signals of the film and substrate. Most interestingly, these analyses reveal a pronounced hardening of the tilt vibrational mode in the thinnest films. A comparison between the experimental results, first principles simulations of the atomic structure, and the standing wave model, which accounts for size effects on the phononic properties, reveals that in the ultrathin regime, the Raman spectra are a hybrid entity of both the bulk and surface phononic behavior. These results showcase Raman spectroscopy as a powerful tool to probe the behavior of perovskite films down to the ultrathin limit.

Optimization of vehicle horn placement based on a one-dimensional standing-wave model

Vehicle horns must satisfy sound pressure level regulations in each country. Therefore, it is essential to optimize the horn location inside the front grille of the vehicle to maximize sound transmission through the grille opening and adhere to sound pressure level regulations. This study developed a computational method to determine optimal horn locations during early stages of vehicle development to reduce the number of trials during later stages. Therefore, an analytical model based on a one-dimensional standing-wave model was established using parameters obtained in the early stages. Subsequently, spectral changes were predicted for the transfer characteristics based on the horn location (i.e., from the horn to the exterior of the front grille). The analytical model was validated by comparing computed spectral images with those obtained experimentally from sample commercial vehicles. Image correlations between the analytical model and experimental results were greater than 80%. The high correlation suggests that the analytical model sufficiently represented the sound propagation phenomena, including transmission from the front grille. Finally, the model results established the optimal horn placement, which was validated using a commercial vehicle as a case study. The placement obtained by the proposed analytical model was in good agreement with that of the commercial vehicle.

Far-infrared bands in plasmonic metal-insulator-metal absorbers optimized for long-wave infrared

ABSTRACTMetal–insulator–metal (MIM) resonant absorbers comprise a conducting ground plane, a dielectric of thickness t, and thin separated metal top-surface structures of dimension l. The fundamental resonance wavelength is predicted by an analytic standing-wave model based on t, l, and the dielectric refractive index spectrum. For the dielectrics SiO2, AlN, and TiO2, values for l of a few microns give fundamental resonances in the 8-12 μm long-wave infrared (LWIR) wavelength region. Agreement with theory is better for t/l exceeding 0.1. Harmonics at shorter wavelengths were already known, but we show that there are additional resonances in the far-infrared 20 - 50 μm wavelength range in MIM structures designed to have LWIR fundamental resonances. These new resonances are consistent with the model if far-IR dispersion features in the index spectrum are considered. LWIR fundamental absorptions are experimentally shown to be optimized for a ratio t/l of 0.1 to 0.3 for SiO2- and AlN-based MIM absorbers, respectively, with TiO2-based MIM optimized at an intermediate ratio.

Edge-dependent reflection and inherited fine structure of higher-order plasmons in graphene nanoribbons

We investigate higher-order plasmons in graphene nanoribbons, and we present how electronic edge states and wave-function fine structure influence the graphene plasmons. Based on nearest-neighbor tight-binding calculations, we find that a standing-wave model based on nonlocal bulk plasmon dispersion is surprisingly accurate for armchair ribbons of widths even down to a few nanometers, and we determine the corresponding phase shift upon edge reflection and an effective ribbon width. Wider zigzag ribbons exhibit a similar phase shift, whereas the standing-wave model describes few-nanometer zigzag ribbons less satisfactorily, to a large extent because of their edge states. We directly confirm that also the larger broadening of plasmons for zigzag ribbons is due to their edge states. Furthermore, we report a prominent fine structure in the induced charges of the ribbon plasmons, which for armchair ribbons follows the electronic wave-function oscillations induced by intervalley coupling. Interestingly, the wave-function fine structure is also found in our analogous density-functional theory calculations, and both these and tight-binding numerical calculations are explained quite well with analytical Dirac theory for graphene ribbons.

Design optimization and resonance modes of a plasmonic sensor based on a rectangular resonator

In this paper, we propose a plasmonic nanosensor based on a metal/insulator/metal plasmonic waveguide with a rectangular resonator. The proposed nanosensor can be used for mechanical strain and thermal stress sensing. We investigated the plasmonic resonance modes based on a standing wave model in the rectangular resonator. In addition, the plasmonic resonances of the rectangular resonator were numerically investigated using the finite-difference time-domain method. The bonding and anti-bonding modes of the plasmonic resonator can be expressed using the mechanical model of coupled harmonic oscillators.

Acoustic standing wave modulation of capacitively coupled plasmas

This work presents a concept of using acoustic standing waves to modulate plasmas. A 1D self-consistent fluid model combined with an acoustic standing wave model has been established to investigate the strong coupling effects between acoustic standing waves and capacitively coupled argon plasmas. The modulation effects are revealed by comparing the spatiotemporal distributions of electron density and excited species number density with and without the acoustic standing waves in one acoustic period, as well as the electric field, the electron temperature, the ionization and excitation rates, and the power density in one radio-frequency period. Under the nonlinear acoustic standing waves, the plasmas oscillate in between the electrodes, which indicates a strong modulation effect beyond conventional regimes. This modulation effect is primarily attributed to the neutral flux friction to the plasma species and secondarily to the variation of the neutral gas density. A pulsed excited species flux with a maximum value up to twice of the minimum can be achieved at the electrodes as a result of the acoustic standing wave modulation. The distributions of the ionization and excitation rates in one RF period are significantly influenced by the acoustic standing waves, due to the variation of the neutral gas density and electron temperature. This study initiates the effort to understand the mechanisms and characteristics of plasma discharges in a high-intensity acoustic standing wave field. Using acoustic waves to modulate plasmas has the potential to create many new applications and promote plasma-materials interactions.

Molecular dynamics simulations of acoustic absorption by a carbon nanotube

Acoustic absorption by a carbon nanotube (CNT) was studied using molecular dynamics (MD) simulations in a molecular domain containing a monatomic gas driven by a time-varying periodic force to simulate acoustic wave propagation. Attenuation of the sound wave and the characteristics of the sound field due to interactions with the CNT were studied by evaluating the behavior of various acoustic parameters and comparing the behavior with that of the domain without the CNT present. A standing wave model was developed for the CNT-containing system to predict sound attenuation by the CNT and the results were verified against estimates of attenuation using the thermodynamic concept of exergy. This study demonstrates acoustic absorption effects of a CNT in a thermostatted MD simulation, quantifies the acoustic losses induced by the CNT, and illustrates their effects on the CNT. Overall, a platform was developed for MD simulations that can model acoustic damping induced by nanostructured materials such as CNTs, which can be used for further understanding of nanoscale acoustic loss mechanisms associated with molecular interactions between acoustic waves and nanomaterials.

Localized surface plasmon polariton resonance in holographically structured Al-doped ZnO

In this paper, we studied the localized surface plasmon polariton (SPP) resonance in hole arrays in transparent conducting aluminum-doped zinc oxide (AZO). CMOS-compatible fabrication process was demonstrated for the AZO devices. The localized SPP resonance was observed and confirmed by electromagnetic simulations. Using a standing wave model, the observed SPP was dominated by the standing-wave resonance along (1,1) direction in square lattices. This research lays the groundwork for a fabrication technique that can contribute to the core technology of future integrated photonics through its extension into tunable conductive materials.

Modeling dynamic properties of spontaneous otoacoustic emissions: Low-frequency biasing and entrainment

Spontaneous otoacoustic emissions (SOAE) are sounds generated inside the living cochlea and are regarded as by-products of the active mechanism present in the peripheral auditory system. There is still debate whether these emissions are the product of local oscillators located at various positions along the cochlea (local oscillator model) or if they result from standing waves due to a global collective phenomenon that involves different aspects of the cochlea (global standing wave model). This paper uses a global standing wave cochlear model to predict various features of SOAEs. This involves a state-space formulation with a spatially distributed set of nonlinear active micromechanical elements coupled via cochlear fluid coupling. Simulation results have been compared with available experimental data and demonstrate two interesting nonlinear features of the cochlea: first, nonlinear properties of SOAEs modulated by external low-frequency bias tones are easily predicted and can be used to investigate the plausibility of different nonlinear functions incorporated in the micromechanical elements. Second, entrainment patterns can be obtained when the model is stimulated by a swept-tone: results show distinct areas of beating and others of entrainment between the external stimulus and the SOAE, which depend on the level and instantaneous frequency of the sweep.

Measurement of spatial and temporal evolution of electromagnetic fields in a 100 MHz plasma source using B dot and double dipole probes

Very high frequency plasma sources are often accompanied by plasma density nonuniformities associated with a standing-wave effect. Electron density measurements using a plasma absorption probe show density nonuniformities that can be larger than predicted by a standing wave model. These structures have been associated with harmonics of the electric fields in the plasma. The authors present the first time and phase-resolved measurements of the spatial structure of the electromagnetic waves in a 100 MHz plasma source using argon at 40 mTorr employing a B dot probe. The authors show that the harmonic structure is related to a current reversal and subsequent circulation that appears when the sheath collapses during the radio frequency cycle. The circulation is driven by inward traveling waves that are electromagnetic in nature, not plasma waves traveling at the electron thermal velocity. Double dipole probe measurements were used to validate the B dot probe electric field measurements derived from the time derivative of Βθ which is derived from the B dot probe signal.

Optical responses of magnetic-vortex resonance in double-disk metamaterial variations

Optical toroidal resonance in structural variations of the double-disk metamaterial, in viewpoint of an equivalent LC-circuit model, is numerically studied to optimize its geometrically-dependent optical characteristics, such as the enhancement capability of local-field confinement and the extinction coefficient. Responses of high-order magnetic vortex resonances (i.e., the double- and triple-fold vortex modes), in addition to the fundamental toroidal dipole, are excited in accordance with a standing-wave model of oscillating current. The induced strengths for these vortex responses are sensitive, in different manners, to the incident angle of the light, though their frequencies are angularly independent. • Toroidal resonance was studied in accordance with an LC-circuit model. • The fundamental and high-order H -vortex resonances were evaluated. • The toroidal response is promising for trapping and energy harvesting.

Six-dimensional standing-wave braneworld with normal matter as source

A six dimensional standing-wave braneworld model has been constructed. It consists in an anisotropic 4-brane generated by standing gravitational waves whose source is normal matter. In this model the compact (on-brane) dimension is assumed to be sufficiently small in order to describe our universe (hybrid compactification). The bulk geometry is non-static, unlike most of the braneworld models in the literature. The principal feature of this model is the fact that the source is not a phantom like scalar field, as the original standing-wave model that was proposed in five dimensions and its six dimensional extension recently proposed in the literature. Here it was obtained a solution in the presence of normal matter what assures that the model is stable. Also our model is the first standing wave brane model in the literature which can be applied successfully to the hierarchy problem. Additionally, we have shown that the zero-mode for the scalar and fermionic fields are localized around the brane. Particularly for the scalar field we show that it is localized on the brane, regardless the warp factor is decreasing or increasing. This is in contrast to the case of the local string-like defect where the scalar field is localized for a decreasing warp factor only.

An experimental analysis of a vibrating guitar string using high-speed photography

We use high-speed photography (1200 frames/s) to investigate the vibrational motion of a plucked guitar string over several cycles. We investigate the vibrational pattern for plucking the string at two different locations along the string's length, and with different initial amplitudes. The vibrational patterns are then compared to a standing wave model of the string vibrations. We find excellent agreement between the observed vibrational patterns and the model for small-initial-amplitude displacement of the string. For larger amplitude displacements, the qualitative behavior of the string's vibrational pattern differs significantly from the small-amplitude displacement. This behavior may be due to the presence of inharmonicity, as suggested by its incorporation into the model calculations.

Efficient standing-wave model for DFB lasers by nonlinear carrier approximation

A nonlinear approximation scheme is proposed to describe the time-dependent longitudinal carrier distribution with a view toward finding the efficient solution scheme of the previously proposed standing-wave model for simulation of DFB lasers. It shows its advantage over the existing linear scheme in terms of the modal accuracy in cases where the optical power is large enough to trigger the saturation effect. The validity of this improved scheme is demonstrated through comparisons made on the static and dynamic performances of \(\lambda /4\)-phase shifted DFB lasers.

Lithographically Patterned Electrodeposition of Gold, Silver, and Nickel Nanoring Arrays with Widely Tunable Near-Infrared Plasmonic Resonances

A novel low-cost nanoring array fabrication method that combines the process of lithographically patterned nanoscale electrodeposition (LPNE) with colloidal lithography is described. Nanoring array fabrication was accomplished in three steps: (i) a thin (70 nm) sacrificial nickel or silver film was first vapor-deposited onto a plasma-etched packed colloidal monolayer; (ii) the polymer colloids were removed from the surface, a thin film of positive photoresist was applied, and a backside exposure of the photoresist was used to create a nanohole electrode array; (iii) this array of nanoscale cylindrical electrodes was then used for the electrodeposition of gold, silver, or nickel nanorings. Removal of the photoresist and sacrificial metal film yielded a nanoring array in which all of the nanoring dimensions were set independently: the inter-ring spacing was fixed by the colloidal radius, the radius of the nanorings was controlled by the plasma etching process, and the width of the nanorings was controlled by the electrodeposition process. A combination of scanning electron microscopy (SEM) measurements and Fourier transform near-infrared (FT-NIR) absorption spectroscopy were used to characterize the nanoring arrays. Nanoring arrays with radii from 200 to 400 nm exhibited a single strong NIR plasmonic resonance with an absorption maximum wavelength that varied linearly from 1.25 to 3.33 μm as predicted by a simple standing wave model linear antenna theory. This simple yet versatile nanoring array fabrication method was also used to electrodeposit concentric double gold nanoring arrays that exhibited multiple NIR plasmonic resonances.

Mold level stabilization using a standing wave model in continuous casting

In continuous steel casting plants, it is very important to stabilize the molten steel level in the mold for quality of the final products and productivity. Standing waves in the mold cause periodic molten steel level fluctuations, which can deteriorate the product quality and productivity. Nevertheless, there has not been any effective countermeasure for them, because they are different from other disturbances in the sense that they are not changes in the flow rate of the molten steel and hence should not be controlled by manipulating the mass flow. This paper proposes a standing wave model and a mold stabilization technique that can prevent harmful influence of standing waves. This technique can prevent interactions between the mold level control and the standing waves in the mold by removing standing wave components from the original mold level signal. On-line experimental results have shown good performance and this technique has been in practical use in a continuous steel casting process in JFE.