Mode Theory Research Articles

Modeling of Fiber Optic Acoustic Coupler for Ultrasonic Sensing

Abstract Fiber Bragg grating (FBG) sensors have been applied in the remote bonding configuration for structural health monitoring, in which ultrasonic modes are propagated along the optical fiber to the sensor. Recently coupling of the ultrasonic mode from optical fiber to optical fiber through an adhesive coupler has also been demonstrated. This paper develops a finite element (FE) model to describe the coupler behavior as a function of the fiber and coupler properties, for future optimization of couplers. The FE model is validated with previous experimental data. We also compare the FE model to three theoretical models (spring and damper frictional contact models and coupled mode theory). The results show that the FE model and spring well replicate the experimental results. Future work will use the resulting FE and spring models to derive solutions for the coupling coefficient as a function of the geometrical and material parameters of the coupler.

A Theoretical Study on Static Gas Pressure Measurement via Circular Non-Touch Mode Capacitive Pressure Sensor.

A circular non-touch mode capacitive pressure sensor can operate in both transverse and normal uniform loading modes, but the elastic behavior of its movable electrode plate is different under the two different loading modes, making its input-output analytical relationships between pressure and capacitance different. This suggests that when such a sensor operates, respectively, in transverse and normal uniform loading modes, the theory of its numerical design and calibration is different, in other words, the theory for the transverse uniform loading mode (available in the literature) cannot be used as the theory for the normal uniform loading mode (not yet available in the literature). In this paper, a circular non-touch mode capacitive pressure sensor operating in normal uniform loading mode is considered. The elastic behavior of the movable electrode plate of the sensor under normal uniform loading is analytically solved with the improved governing equations, and the improved analytical solution obtained can be used to mathematically describe the movable electrode plate with larger elastic deflections, in comparison with the existing two analytical solutions in the literature. This provides a larger technical space for developing the circular non-touch mode capacitive pressure sensors used for measuring the static gas pressure (belonging to normal uniform loading).

Exceptional point sensing via energy loss profile in a non-Hermitian system

The heightened sensitivity observed in non-Hermitian systems at exceptional points (EPs) has garnered significant attention. Typical EP sensor implementations rely on precise measurements of spectra and importantly, for real time sensing measurements, the EP condition ceases to hold as the perturbation increases over time, thereby preventing the use of high sensitivity at the EP point. In this work, we present an new approach to EP sensing which goes beyond these two traditional constraints. Firstly, instead of measuring the spectra, our scheme of EP based sensing is based on the observation of decay length of the optical mode in finite size gratings, which is validated via coupled mode theory as well as full wave electrodynamic simulations. Secondly, for larger perturbation strengths, the EP is spectrally shifted instead of being destroyed — this spectral shift of the EP is calibrated and using this look-up table, we propose continuous real time detection by varying the excitation laser wavelength. As a proof of principle of our technique, we present an application to the sensing of coronavirus particles, which shows unprecedented limit of detection. Furthermore, our analysis includes calculation of the signal-to-noise ratio, revealing that EP sensors offer advantage when classical technical noise dominates over fundamental noise. These findings will contribute to the expanding field of exceptional point based sensing technologies for real time applications beyond spectral measurements.

Germanium metasurface near-infrared high-q absorber with symmetry-protected bound states in the continuum

The all-dielectric germanium nanohole (GNH) metasurface with a sub-wavelength thickness supports simultaneous excitation of quasi bound state in the continuum (BIC) and super radiant mode. By selecting the different hole depths in a germanium slab, we present a trade-off metasurface between high Q-factor and high absorption in the photonic system. The presented device demonstrated absorption of super-radiant mode ∼98.5% and quasi-BIC ∼93% without back-metal reflector at the telecommunication wavelength. The numerical results, obtained by the finite difference time domain (FDTD) method are explained in the framework of temporal coupled mode theory (TCMT).

On the temperature dependence of the density of states of liquids at low energies

We report neutron-scattering measurements of the density of states (DOS) of water and liquid Fomblin in a wide range of temperatures. In the liquid phase, we confirm the presence of a universal low-energy linear scaling of the experimental DOS as a function of the frequency, g(ω)=a(T)ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g(\\omega )= a(T) \\omega $$\\end{document}, which persists at all temperatures. The low-frequency scaling of the DOS exhibits a sharp jump at the melting point of water, below which the standard Debye’s law, g(ω)∝ω2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g(\\omega ) \\propto \\omega ^2$$\\end{document}, is recovered. On the contrary, in Fomblin, we observe a continuous transition between the two exponents reflecting its glassy dynamics, which is confirmed by structure measurements. More importantly, in both systems, we find that the slope a(T) grows with temperature following an exponential Arrhenius-like form, a(T)∝exp(-⟨E⟩/T)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$a(T) \\propto \\exp (-\\langle E \\rangle /T)$$\\end{document}. We confirm this experimental trend using molecular dynamics simulations and show that the prediction of instantaneous normal mode (INM) theory for a(T) is in qualitative agreement with the experimental data.

Generalized Identity, Zero-Ground, and Necessity

AbstractThis paper offers a modification of Fabrice Correia’s and Alexander Skiles’ (Grounding, Essence, and Identity) definition of grounding in terms of generalized identity that extends it to zero-grounding. The definition promises (1) to improve our understanding of zero-grounding by capturing it within the framework of generalized identity, and (2) to unlock the theoretical potential of zero-grounding for Correia’s and Skiles’ account. The latter is demonstrated by arguing that the definition allows an essentialist theory of modality based on Correia’s and Skiles’ account to answer a recent explanatory challenge by Jessica Leech (From Essence to Necessity via Identity) by combining the following two ideas: (1) Some necessities are grounded in truths about zero-grounding, and (2) at least some identity-propositions are zero-grounded. Finally, some advantages of the zero-grounding approach over Correia’s and Skiles’ recent definition of necessity in terms of generalized identity and logical consequence are argued for.

RF Circuit Analysis of UWB Planar Log Periodic Antenna for 5G Communications Using Theory of Characteristic Modes

RF Circuit Analysis of UWB Planar Log Periodic Antenna for 5G Communications Using Theory of Characteristic Modes

Plasmonic induced transparency and slow light integrated device for graphene-based metamaterial

The terahertz excitation characteristics of a graphene-based band structure are studied. This structure has different planar band structures that can excite two bright modes and then it can achieve an excellent plasmonic induced transparency effect through the two bright modes. By analyzing the boundary conditions of the electromagnetic field, the dispersion relationship of this structure can be smoothly obtained. Furthermore, the internal loss factor in the matching coupled mode theory can be calculated. Meanwhile, the tuning performance of this simple structure is analyzed through the external voltage. The Fermi level regulated by voltage is also analyzed, and its influence on the entire tuning mechanism is studied. A detailed analysis is conducted on the slow light performance of this structure, and the influence of Fermi level on the slow light performance is explored. This investigation is expected to provide potential theoretical foundations for slow light, optical storage, and other fields.

Dual-narrowband terahertz metamaterial absorber based on all-metal vertical ring array for enhanced sensing application

In this paper, a novel design of a dual-narrowband metamaterial absorber (MMA) was proposed for using as a high-performance refractive index (RI) sensor in the terahertz (THz) region. The proposed MMA is based on a vertical-ring-shaped (VRS) structure gold film array. Through numerical simulation, it was found that the MMA can achieve high absorption levels of 99.8% and 94.6% at 1.723 THz and 2.457 THz, respectively, which are consistent with the values obtained using coupling mode theory (CMT). The MMA also exhibits high Q-factor values of about 27.35 and 102.38, respectively, which are close to the CMT values of 29.94 and 98.34. The dual-band strong absorption of the MMA is attributed to the guided modes of the critical coupling resonance, and the absorption properties can be adjusted by changing the geometrical parameters of the unit-cell structure. The proposed MMA has a narrowband and a higher Q-factor, making it suitable for RI sensing, with a sensitivity of about 1.66 and 1.88 THz RIU−1, and a figure-of-merit (FOM) of about 259.4 and 659.7 RIU−1, respectively. These findings open up new opportunities for the development of highly efficient MMAs, which have potential applications in biochemical sensing and detection in the THz region.

Application of Resonant Modal Theory to the Design of Dual-Band Wideband Dipole Antenna

Application of Resonant Modal Theory to the Design of Dual-Band Wideband Dipole Antenna

Four-state Fano resonance electro-optical modulator and sensor based on double borophene-dielectric grating structure

In this paper, we propose a borophene-based double-dielectric-grating structure (BDDGS) to realize the Fano resonance electro-optical modulator and sensor. The Fano resonance originated from the coupling of two resonance modes excited by the upper borophene grating (UBG) and the lower borophene grating (LBG). The coupling mode theory (CMT) is utilized to fit the Fano transmission spectrum. The calculated result fits well with the simulated spectrum. We found the Fano resonance wavelengths exhibit a blue shift with increasing the carrier density of the borophene layer. Further, we utilize this property to achieve a Four-state Fano resonance electro-optical modulator. The working wavelengths of the ON-ON (11), ON–OFF (10), OFF–ON (01), and OFF-OFF (00) states are 1.321 μm and 1.676 μm, respectively. The asymmetric Fano spectra exhibit high sensing sensitivity S=21THz/RIU and figure of merit FOM=3.9RIU−1. Moreover, our proposed structure possesses a slow-fast light effect with the maximum group index are 57.84 and −332.3, respectively. Although several Fano resonance and electro-optical modulators based on two- dimensional (2D) material, like graphene, black phosphorus, and transition metal dichalcogenides (TMDs) are previously reported, this paper designed a borophene-based metamaterial to achieve Fano resonance electro-optical modulator and sensor, because borophene possesses a series of excellent physical and chemical properties, for example, mechanical compliance, high carrier mobility, and optical transparency. Therefore, the proposed borophene-based metamaterial will be beneficial in the fields of high-performance plasmonic sensors, slow light, and electro-optical modulators in the near future.

Combining Sliding Mode and Fractional-Order Theory for Maximum Power Point Tracking Enhancement of Variable-Speed Wind Energy Conversion

The present study used the wind turbine as a model to focus on combining sliding mode and fractional-order theory for maximum power point tracking (MPPT) enhancement. The combination of sliding mode and fractional-order theory was implemented considering the nonlinearity of the studied model for studying the system’s response. The response of the wind turbine was evaluated after introducing disturbance to the output of the regulator. The results showed the excellent ability of the system to track the reference, regardless of any disturbances. There was no impact of any disturbance on the system or the system’s good follow-up. Moreover, the control scheme showed robustness as regards rejecting the disturbances.

Multi-frequency and multi-functional optical switch based on dual plasmon-induced transparency

Research into multi-frequency and multi-functional optical switches for complex applications is pioneering territory. By employing a single-layer structure comprising three distinct graphene strips, we successfully created a dual-PIT effect through the destructive interference among two bright modes and a dark mode. The numerical simulations were corroborated by coupled mode theory, reflecting a high degree of consistency between the theory and the simulations. Remarkably, the modulation of the Fermi level in graphene metamaterials through gate voltage enabled the realization of asynchronous optical switches capable of operating at six, five, four, and three frequencies. Notably, the six-frequency switch exhibited an impressive modulation depth of 88.54% and an insertion loss of just 0.15 dB, highlighting its superior performance. This study lays a solid foundation for future multi-frequency and multi-functional optical switch designs, offering significant implications and practical applications.

Reconfigurable terahertz stretchable spoof surface plasmon polariton waveguide for filter applications

In this paper, a reconfigurable terahertz spoof surface plasmon polariton (SPP) waveguide is proposed on a stretchable polydimethylsiloxane (PDMS) substrate. The SPP unit incorporates a folded stub and a conventional V-shaped SPP groove, enhancing the equivalent capacitance and consequently reducing the cutoff frequency. The cutoff frequency of the proposed SPP unit can be tuned from 285 to 390 GHz with stretchable factors of 1 ∼ 1.2, thereby achieving a reconfigurable operating frequency. The horizontal dimension of the proposed SPP waveguide can be tuned from 6.36 mm to 7.12 mm. Moreover, the SPP waveguide can generate transmission continuous phase shifts of −30°, −60°, −90°, and −120° with stretchable factors of 1.05, 1.1, 1.15, and 1.2, respectively, in the 150–190 GHz band. Applying the characteristic mode theory, a split ring resonator (SRR) functions as the equivalent magnetic dipole, which remains unaffected by stretchable deformation. When loaded with four SRR cells, the proposed SPP waveguide generates a tunable passband with a fixed notched frequency at 193 GHz. Another stretchable SPP resonator serves as the equivalent electric dipole, operating from 284 GHz to 256 GHz in 1∼1.2 stretchable states. By loading three SPP resonators, the SPP waveguide can achieve a passband for the initial state, and a tunable stopband is introduced under 1.1 and 1.2 stretchable states. The proposed stretchable method provides a promising solution for planar terahertz components and systems with reconfigurable functions.

Talbot-like pattern evolution in complex structured light from a unitary transformation

Astigmatic unitary transformations allow for the adiabatic connections of all feasible states of paraxial Gaussian beams on the same modal sphere, i.e., Hermite-Laguerre-Gaussian (HLG) modes. Here, we present a comprehensive investigation into the unitary modal evolution of complex structured Gaussian beams, comprised of HLG modes from disparate modal spheres, via astigmatic transformation. The non-synchronized higher-order geometric phases in cyclic transformations originate a Talbot-effect-like modal evolution in the superposition state of these HLG modes, resulting in pattern variations and revivals in transformations with specific geodesic loops. Using Ince-Gaussian modes as an illustrative example, we systematically analyze and experimentally corroborate the beamforming mechanism behind the pattern evolution. Our results outline a generic modal conversion theory of structured Gaussian beams via astigmatic unitary transformation, offering a new approach for shaping spatial modal structure. These findings may inspire a wide variety of applications based on structured light.

Inverse Design of a Dielectric Metasurface by the Spatial Coupled Mode Theory

Inverse Design of a Dielectric Metasurface by the Spatial Coupled Mode Theory

Optimizing Islamic Education Learning through Understanding Students' Learning Modalities in Improving Academic Achievement

This research aims to recognize student learning modalities and analyze the implications of learning modalities in optimizing PAI learning. By identifying them, students can determine learning styles, teachers can determine learning strategies and methods and parents can educate and treat children according to their learning styles. In this research, David Kolb's learning modality theory is used. He believes there are four learning styles: diverger style, assimilator style, converger style, and accommodator style. At the same time, Richard Bandler, John Grinder, and Michael Grinder put forward three learning styles: Visual, Auditory and kinesthetic. This paper uses the library research method, with a qualitative approach and data collection techniques, namely documentation, data taken in the form of primary data from articles, books and theses related to learning modalities and implications in PAI learning and secondary data from the Koran and interpretation. The conclusion is that the impact of learning modalities for optimizing PAI learning is that teachers can determine the learning curriculum, learning resources, learning materials, and suitable media for students, use varied methods, carry out assessment strategies and develop student potential. Schools also contribute to providing school facilities.

Spontaneous symmetry breaking of coupled Fabry–Pérot nanocavities

Ring cavities are quickly emerging as preferential platforms to investigate spontaneous symmetry breaking. However, research on handedness polarisation splitting within Kerr-coupled cavities is yet at a preliminary stage. Here, we observe experimentally spontaneous symmetry breaking in a non-Hermitian coupled Fabry‒Pérot nanocavity. In the experiment, horizontally polarised light is incident on the nanocavities, and symmetry breaking occurs when the power exceeds the symmetry breaking threshold of 8mW\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$8\\,{{\\mbox{mW}}}$$\\end{document}. We interpret such observation via nonlinear coupled mode theory, finding that an excitation power-dependent random splitting of right- or left-handed circular polarisations (RCP and LCP, respectively) emerges at the resonance peak. Further numerical simulations show that when the incident power is above the symmetry breaking threshold, the device exhibits spontaneous symmetry breaking characteristics: an additional polarisation component appears in the output field when the input field is monopolarised, and this is attributed to the imbalance of RCP and LCP. Our findings provide further understanding of spontaneous symmetry breaking in non-Hermitian systems and demonstrate the potential applications of the proposed device in optical signal processing.

Bimodal Absorber Frequencies Shift Induced by the Coupling of Bright and Dark Modes.

In this paper, we demonstrate that the absorption frequencies of the bimodal absorber shift with the coupling strength of the bright and dark modes. The coupling between the bright mode and the dark mode can acquire electromagnetically induced transparency, we obtain the analytical relationship between the absorbing frequencies, the resonant frequencies, losses of the bright mode and dark mode, and the coupling strength between two modes by combining the coupled mode theory with the interference theory. As the coupling strength between the bright mode and the dark mode decreases, the two absorption peaks gradually move closer to each other, inversely, they will move away from each other. The simulation employs three distinct metasurface structures with coupling of the bright and dark modes, thereby verifying the generality of the theoretical findings.

An MILP model based on a processing strategy of complex multisource constraints for the short-term peak shaving operation of large-scale cascaded hydropower plants

Hydropower with flexible regulation plays an important role in short-term peak shaving operations. However, short-term peak shaving operation is a challenging problem due to the large scale, the nonconvex and nonlinear characteristics, and the complex multisource tasks. This study proposes a mixed integer linear programming (MILP) model, termed MILPoPSC, based on a processing strategy for complex multisource constraints, tailored for short-term peak shaving in large-scale cascaded hydropower plants. The MILP model, designed to incorporate multisource tasks by abstracting them into constraints, ensures that task requirements are met. A novel multisource constraint transformation method is introduced to derive constraint expressions related to power flow, facilitating the unification of constrained variables. Additionally, a classification and integration method based on restriction mode and set theory is proposed to improve solving efficiency by integrating constrains of the same type. The proposed method was applied to 7 hydropower cascade plants in the Wujiang River. The results showed that the linearization method and the processing strategy of complex multisource constraints can successfully reduce the complexity of the MILP model without affecting the solution quality. This indicates that MILPoPSC has good practical value for the short-term peak shaving operation of large-scale cascaded hydropower plants in China.