Simultaneous Excitation Research Articles

Microparticle focusing and micromixing with two-dimensional acoustic waves

Acoustofluidics has recently been popularized as a crucial element of lab-on-a-chip (LoC) platforms to efficiently manipulate microparticles and continuous matter alike. In this study, a three-dimensional (3D) numerical model is proposed to simulate the focusing of polystyrene microparticles with three diameters and micromixing of dilute species using two orthogonally oriented standing waves, contrasting them with one-dimensional (1D) waves. The limiting velocity method is modified to explore the 3D acoustic streaming in a symmetric microchannel. In contrast to 1D standing acoustic waves, the simultaneous excitation of two orthogonal waves generates an acoustic streaming velocity field that does not counteract the radiation force. The obtained results show that the focusing efficiency of 5-μm particles reaches 97% with two dimensional (2D) standing acoustic waves, which was unachievable using 1D waves. Moreover, by reducing the flow rate to 1 μL min−1, the focusing of critical microparticle diameter peaked at 94%, indicating an approximately 9% improvement over a flow rate of 2.5 μL min−1. Increasing the viscosity of the background fluid resulted in 16% better 2D focusing with a single vortex compared to other cases, and higher amplitudes did not change focusing efficiency with a single vortex, while reducing efficiency in other cases. Finally, using 2D acoustic waves remarkably improved the mixing efficiency of dilute species, underscoring the advantage of 2D acoustic waves over their 1D counterpart. The proposed numerical model can play a meaningful role in cutting fabrication costs of next-generation LoC devices by identifying the most crucial parameters influencing acoustofluidic matter transport.

Triple Differential Cross Sections for the Simultaneous Ionization and Excitation of He by Electron and Positron Impact

Triple Differential Cross Sections for the Simultaneous Ionization and Excitation of He by Electron and Positron Impact

Wavelength and polarisation dependence of pump-induced loss in Ti:sapphire

We use pump beam wavelength and polarisation to demonstrate that the phenomenon of pump-induced loss in Ti:sapphire is linked to simultaneous excitation of two separate absorption bands: the Ti3+ pump band and the parasitic 400 nm residual absorption. We find that the degree of pump-induced loss is linked to the relative absorption strengths of the residual absorption band and the Ti3+ pump band at the wavelength(s) of excitation.

Manipulation of high-frequency spin waves in ferromagnetic thin films via magnetic torques induced by ultrafast demagnetization

Spin-based technologies demand the effective excitation and control of high-frequency spin waves in order to increase the operational speed of magnonic logic circuits. An available option for the high-frequency spin wave is the perpendicular standing spin waves (PSSWs) in ferromagnetic thin films. However, the practical utilization of a PSSW is still challenging due to a few unsolved critical issues such as its relatively low amplitude and simultaneous excitation of other PSSW modes. Here, efficient excitation and control of a first-order PSSW mode are demonstrated in Ni80Fe20 thin films using a double-laser-pulse scheme. Based upon our experimental and theoretical investigations, it is found that the precession amplitudes of the Kittel and PSSW modes show strong dependence on equivalent torques (i.e., the averaged torques during fast relaxation process after the second pulse excitation) applied to these two modes. Thus, selective excitation and amplification of the first-order PSSW mode can be realized by manipulating the equivalent torque, i.e., introducing a second laser pulse with an appropriate arrival time and laser fluence. Moreover, the spectral tuning of this single PSSW mode can be achieved by proportionately adjusting the laser fluence of two pump pulses. These findings may pave the way for the realization and construction of future high-performance spintronic devices.

Tamm and surface plasmon hybrid modes in anisotropic graphene-photonic-crystal structure for hemoglobin detection

We propose Tamm plasmon (TP) and surface plasmon (SP) hybrid modes for hemoglobin (Hb) detection in anisotropic graphene-photonic-crystal (GPC) structures. The proposed GPC sensor shows polarization-dependent responses due to the in-plane anisotropic property. The reflection profiles of the proposed sensor exhibit two reflectivity minima due to the simultaneous excitation of TP and SP modes. When used to detect Hb, the TP mode offers a greater figure-of-merit (FoM) than the SP mode. Using a Fourier mode spectral analysis, we observe energy coupling from the TP to the SP mode when the incident light’s polarization changes, providing an option to enhance the sensor’s sensitivity. We propose a double dips method (DDM) to detect Hb based on the simultaneous excitation of TP and SP modes. Using DDM, the proposed sensor offers a maximum sensitivity of 314.5 degrees/RIU and a FoM of 1746 RIU−1 when the Hb level is 189 g/L. The proposed anisotropic GPC sensor offers possible applications for highly sensitive bio-molecule detection with high FoM.

Magnification factor for pile internal forces of pile‐supported wharves under bi‐directional ground motions

AbstractIn order to determine the pile internal forces of wharf under simultaneous seismic excitation in orthogonal horizontal directions with ease, the total internal forces can be obtained by multiplying the pile forces of two‐dimensional model under transverse earthquake loading with a magnification factor. The factors were computed from the seismic response of wharves having various aspect ratios (length to width) and eccentricity ratios when subjected to 30 pairs of bi‐directional earthquake records. Mean magnification factors and their corresponding dispersion are presented for all ground motion ensembles. The influence of aspect ratio and eccentricity ratio is evaluated and discussed. It is concluded that the magnification factor can be expressed as the function of aspect ratio and eccentricity ratio, and follows lognormal distribution. The proposed equation of magnification factor can be an alternative for internal force analysis of wharves under bi‐directional ground motion.

Acoustic and optical plasmons excitation in double-channel AlGaN/GaN HEMT under asymmetric boundaries

We have simulatively studied the electrical excitation of acoustic and optical plasmons in double-channel AlGaN/GaN high electron mobility transistors (HEMT) under asymmetric boundaries. By solving the self-consistent hydrodynamic model with Maxwell’s equations, it is found that the drift plasmons are excited in the bilayer 2DEGs under asymmetric boundaries. The oscillation intensity in a bilayer system is much stronger than that in a monolayer 2DEG system because of the simultaneous excitation of the fundamental and the second harmonic components. The fundamental component always corresponds to the acoustic plasmon, while the optical plasmon can be excited when it is resonant with the second harmonic of the acoustic plasmon. Because of the out-of-phase properties of the acoustic plasmons, their radiated power is limited by the current cancellation. On the other hand, as the optical plasmons are excited, the radiated powers are much higher than those of the single channel HEMT due to the in-phase currents generated in the double layers. The effects of different parameters such as gate lengths, 2DEG spacings, and electron concentrations on plasmon excitations and THz emissions of double-channel HEMTs are analyzed in detail. The numerical results provide a more powerful terahertz radiation mechanism in double-channel HEMT compared with the Dyakonov–Shur instability in traditional single-channel HEMT.

Enhanced terahertz frequency mixing in all-dielectric metamaterial with multiple surface plasmon polaritons resonances

Nonlinear metamaterials hold a promising platform for generating terahertz (THz) waves. In this paper, we present an all-dielectric metamaterial with multiple surface plasmon polariton (SPP) resonances for enhanced THz frequency mixing. The metamaterial is composed of graphene ribbons, a dielectric layer, and a one-dimensional photonic crystal, displaying the multiple absorptions with simultaneous excitation of three SPP resonances. Taking advantage of SPP resonances with high Q factor and strong localized field at the input frequency, the third-order nonlinear processes are remarkably enhanced, including third-harmonic generation and four-wave mixing, producing a variety of frequencies in the THz range. The proposed efficient nonlinear metamaterials offer promising applications for THz frequency synthesis.

Frequency-adjustable OAM antenna with co-divergent beams for IoT applications

A frequency-tunable Orbital Angular Momentum (OAM)-generating antenna array system is introduced for the first time to provide high-data-rate and secure communication for Internet of Things (IoT) infrastructures and devices. Propagation of simultaneous OAM modes brings about the high-data-rate and frequency tunability leads to interference suppression for secure communication. Regarding the design evolution of the proposed structure, the novel Multiple-Input-Multiple-Output (MIMO) antenna consisting of two input ports creates a 2 × 2 UCA, resulting in two 2 × 2 sub-UCA. Feeding each 2 × 2 sub-array with [0°, 90°, 180°, 270°] phase gradients in clockwise and counterclockwise states gives rise to dual-mode OAM-carrying waves with simultaneous excitation capability. It should be mentioned that each MIMO element owns frequency tunability, resulting in a frequency-adjustable dual-mode OAM antenna array. A prototypes of the suggested MIMO antenna as well as the OAM array are fabricated and measured. Changing the applied DC-voltage to the varactor diodes embedded in capacitive stubs of the antenna elements shifts the operating frequency in the MIMO antenna and consequently in the OAM array. Concerning the unique radiation characteristics of the OAM antenna, vortex beams having helical phase fronts are observed, confirming the generation of expected OAM waves. Therefore, it is asserted that the introduced structure, for the first time, proposes new features of frequency-tunability, and co-divergent simultaneous OAM propagation using the MIMO-UCA technique to provide high-data-rate and secure communication in IoT applications.

Resolvent-based motion-to-wake modelling of wind turbine wakes under dynamic rotor motion

We propose a linearized deterministic model for predicting coherent structures in the wake of a floating offshore wind turbine subject to platform motions. The model's motion-to-wake predictive capability is achieved through two building blocks: a motion-to-forcing (M2F) part and a forcing-to-wake (F2W) part. The M2F model provides a unified framework to parameterize the effects of arbitrary floating wind turbine motions as unsteady loads of a fixed actuator disk, requiring only the radial distribution of the aerodynamics force coefficient on the blade as input. The F2W model is derived based on a bi-global resolvent model obtained from the linearized Navier–Stokes equations, using the time-averaged wake of a fixed wind turbine as input. In addition to its capability of predicting sensitive frequency ranges, the model excels linear stability analysis by providing spatial modes of the wake response in a motion-specific and phase-resolved manner. The model successfully predicts the wake pulsing mode induced by surge, as well as the similarity and difference of the wake meandering modes caused by sway and yaw. Large-eddy simulations under different inflow turbulence intensities (TIs) and length scales are further conducted to analyse the wake meandering triggered by the simultaneous excitation of free-stream turbulence and sway motion. The results show distinct frequency signatures for the wake dynamics induced by ambient turbulence and sway motion. The inflow TI is found to have a stabilizing effect on the wake, reducing the motion-induced wake responses. Such a stabilizing effect is captured satisfactorily with the proposed model, provided that the effective viscosity is calibrated properly using the data from the fixed turbine wake under the corresponding turbulent inflow.

Amygdalar Excitation of Hippocampal Interneurons Can Lead to Emotion-driven Overgeneralization of Context.

Context is central to cognition: Detailed contextual representations enable flexible adjustment of behavior via comparison of the current situation with prior experience. Emotional experiences can greatly enhance contextual memory. However, sufficiently intense emotional signals can have the opposite effect, leading to weaker or less specific memories. How can emotional signals have such intensity-dependent effects? A plausible mechanistic account has emerged from recent anatomical data on the impact of the amygdala on the hippocampus in primates. In hippocampal CA3, the amygdala formed potent synapses on pyramidal neurons, calretinin (CR) interneurons, as well as parvalbumin (PV) interneurons. CR interneurons are known to disinhibit pyramidal neuron dendrites, whereas PV neurons provide strong perisomatic inhibition. This potentially counterintuitive connectivity, enabling amygdala to both enhance and inhibit CA3 activity, may provide a mechanism that can boost or suppress memory in an intensity-dependent way. To investigate this possibility, we simulated this connectivity pattern in a spiking network model. Our simulations revealed that moderate amygdala input can enrich CA3 representations of context through disinhibition via CR interneurons, but strong amygdalar input can impoverish CA3 activity through simultaneous excitation and feedforward inhibition via PV interneurons. Our model revealed an elegant circuit mechanism that mediates an affective "inverted U" phenomenonv: There is an optimal level of amygdalar input that enriches hippocampal context representations, but on either side of this zone, representations are impoverished. This circuit mechanism helps explain why excessive emotional arousal can disrupt contextual memory and lead to overgeneralization, as seen in severe anxiety and posttraumatic stress disorder.

Surface Acoustic Waves (SAW) Sensors: Tone-Burst Sensing for Lab-on-a-Chip Devices.

The article presents the design concept of a surface acoustic wave (SAW)-based lab-on-a-chip sensor with multifrequency and multidirectional sensitivity. The conventional SAW sensors use delay lines that suffer from multiple signal losses such as insertion, reflection, transmission losses, etc. Most delay lines are designed to transmit and receive continuous signal at a fixed frequency. Thus, the delay lines are limited to only a few features, like frequency shift and change in wave velocity, during the signal analysis. These facts lead to limited sensitivity and a lack of opportunity to utilize the multi-directional variability of the sensing platform at different frequencies. Motivated by these facts, a guided wave sensing platform that utilizes simultaneous tone burst-based excitation in multiple directions is proposed in this article. The design incorporates a five-count tone burst signal for the omnidirectional actuation. This helps the acquisition of sensitive long part of the coda wave (CW) signals from multiple directions, which is hypothesized to enhance sensitivity through improved signal analysis. In this article, the design methodology and implementation of unique tone burst interdigitated electrodes (TB-IDT) are presented. Sensing using TB-IDT enables accessing multiple frequencies simultaneously. This results in a wider frequency spectrum and allows better scope for the detection of different target analytes. The novel design process utilized guided wave analysis of the substrate, and selective directional focused interdigitated electrodes (F-IDT) were implemented. The article demonstrates computational simulation along with experimental results with validation of multifrequency and multidirectional sensing capability.

Quantum-interference-induced magnon blockade and antibunching in a hybrid quantum system

In this work, we study the phenomena of quantum-interference-assisted magnon blockade and magnon antibunching in a weakly interacting hybrid ferromagnet-superconductor system. The magnon excitations in two yttrium iron garnet spheres are indirectly coupled to a superconducting qubit through microwave cavity modes of two mutually perpendicular cavities. We find that when one of the magnon modes is driven by a weak microwave field, the destructive interference between more than two distinct transition pathways restricts the simultaneous excitation of two magnons. We analyze the magnon correlations in the driven magnon mode for the case of zero detunings as well as finite detunings of the magnon modes and the qubit. We show that the magnon antibunching can be tuned by changing the magnon-qubit coupling strength ratio and the driving detuning. Our work proposes a possible scheme that has a significant role in the construction of single magnon generating devices.

Optimal experiment design for multivariable system identification using simultaneous excitation

Having an accurate model of a system is essential for many applications today, especially those related to advanced process control (APC). When executing an industrial delivery project of APC, often significant time is spent performing experiments on the real process to identify a model. By designing higher quality experiments the time needed on site carrying out experiments can be reduced, saving both resources and engineering efforts. This paper investigates optimal input design to minimize the time needed to identify a linear time-invariant multi-variable system fulfilling certain requirements on the model accuracy. This is an extension of previous work which focused on sequential excitation on one input signal at the time. Here, however, the effects of using combined simultaneous and sequential excitation is investigated. The resulting non-convex optimization problem is relaxed using binary decision variables. An important feature of the approach is that the experiment is carried out in closed-loop using a model predictive controller with zone constraints to further guarantee that the output constraints are not violated. Simulation results indicate that there are many cases where using combined simultaneous and sequential excitation outperforms the previous sequential approach.

Фототераностика тяжелых дисплазий и преинвазивного рака шейки матки

Due to the high prevalence of pre-cancerous cervical diseases and cervical cancer, the search, pathogenetic reasoning and evaluation of the efficacy of new approaches to the diagnosis and treatment of these pathologies, including those aimed at fertility preservation, are extremely relevant. Objective. To study the clinical efficacy and safety of phototheranostics as a method of diagnosis and treatment of severe dysplasia and pre-invasive cervical cancer. Patients and methods. An open-label, retrospective-prospective, randomized, comparative, clinical trial involving 94 reproductive-aged patients with morphologically confirmed severe cervical intraepithelial neoplasia (CIN) and pre-invasive cervical cancer was conducted. All patients were divided into two groups: group 1 (comparison) included 49 patients who underwent cervical conization with curettage of the remaining cervical canal; group 2 (study) included 45 patients who underwent phototheranostics: photodynamic therapy (PDT) with simultaneous laser-induced fluorescence excitation. Results. After the first course of phototheranostics, most women in the study group had normal cytological results, which were observed 6, 9, and 12 months after treatment. In these periods, all patients who underwent phototheranostics had a normal colposcopic picture, while in the comparison group, some patients showed signs of cervical lesions. Morphological confirmation of the complete therapeutic effect was considered to be elimination of human papillomavirus (HPV) and normalization of the proliferative activity of the epithelial layer (assessed by the levels of Ki-67 and phosphohistone markers) during phototheranostics. Conclusion. The study demonstrated the high clinical efficacy of phototheranostics in the treatment of CIN and pre-invasive cervical cancer: 85–88% of women achieved the desired therapeutic effect after the first session of phototheranostics, and after the second session, all patients in the study group had complete regression of cervical mucosal lesions. In the study group, higher pregnancy rates and favourable outcomes in patients planning pregnancy confirmed that the use of PDT contributes to fertility preservation in women treated for CIN and pre-invasive cervical cancer, which is associated with the preservation of anatomo-functional characteristics of the cervix when using phototheranostics. Key words: PDT, HPV, photodynamic therapy, fluorescence diagnosis, cervical dysplasia, photosensitizers, pre-invasive cervical cancer, phototheranostics, pregnancy after PDT

Multiple Bloch surface wave excitation with gratings

We study the coupling of a finite number of Bloch Surface Waves (BSWs) propagating in different directions at the surface of a dielectric multilayer. These surface waves arise from a set of diffraction orders associated to a grating on the bottom surface of the substrate that is illuminated by a normally incident beam. Simultaneous excitation of multiple BSWs is possible with a set of diffraction orders having the same radial spatial frequency. Using rigorous electromagnetic theory, we design gratings for simultaneous excitation of two, four and six BSWs propagating in directions separated by π, π/2 and π/3 azimuthal intervals, respectively.

High speed surface acoustic wave and laterally excited bulk wave resonator based on single-crystal non-polar AlN film

One approach to extend the acoustic applications of aluminum nitride (AlN) in the GHz frequency range is to take advantage of the piezoelectric performance and high acoustic velocity (∼11 350 m/s) along the c-axis of this material. In particular, in the case of high-frequency micro-electromechanical systems, it should be possible to simplify the construction of resonators by using a-plane AlN-based structures. In the work described in this Letter, a single-crystalline a-plane AlN layer on an r-plane sapphire substrate is obtained by combining sputtering and high-temperature annealing. Based on this non-polar AlN, a resonator with only planar interdigital transducer electrodes is fabricated. Experiments on this resonator reveal simultaneous excitation of an anisotropic Rayleigh surface acoustic wave (SAW) at 2.38 GHz and a laterally excited bulk acoustic wave (LBAW) at 4.00 GHz. It is found that the Rayleigh SAW exhibits outstanding performance, with a quality factor as high as 2458 and great stability under variations in temperature. The LBAW at 4.00 GHz is excited by pure planar interdigitated electrodes without the need for any cavity or bottom electrode structure, thus demonstrating a promising approach to the construction of high-frequency resonators with a relatively simple structure.

Dielectric light-trapping nanostructure for enhanced light absorption in organic solar cells

Dielectric scatterers where Mie resonances can be excited in both electric and magnetic modes have emerged as a promising candidate for efficient light trapping (LT) in thin-film solar cells. We present that light absorption in organic solar cells (OSCs) can be significantly enhanced by a front-sided incorporation of a core–shell nanostructure consisting of a high-refractive-index dielectric nanosphere array conformally coated with a low-refractive-index dielectric layer. Strong forward light scattering of the all-dielectric LT structure enables the absorption in an organic semiconductor to be remarkably boosted over a broad range of wavelengths, which is attributed to interference of a simultaneous excitation of the electric and magnetic dipole resonant modes. The OSC with the LT structure shows the short-circuit current density (Jsc) of 28.23 mA/cm2, which is 10% higher than that of a flat OSC. We also explore how the LT structure affects scattering cross-sections, spectral multipole resonances, and far-field radiation patterns. The approach described in this work could offer the possibility for the improvement of characteristic performances of various applications, such as other thin-film solar cells, photodiodes, light-emitting diodes, and absorbers.

Revealing defect-bound excitons in WS2 monolayer at room temperature by exploiting the transverse electric polarized wave supported by a Si3N4/Ag heterostructure

Abstract Two-dimensional (2D) transition metal dichalcogenide (TMDC) monolayers are promising materials for light-emitting devices due to their excellent electric and optical properties. However, defects are inevitably introduced in the fabrication of TMDC monolayers, significantly influencing their emission properties. Although photoluminescence (PL) is considered as an effective tool for investigating the defects in TMDC monolayers. However, the PL from the defect-bound excitons is revealed only at low temperatures. Here, we show that the PL from the defect-bound excitons in a WS2 monolayer can be effectively revealed at room temperature by exploiting the transverse electric polarized wave supported by a Si3N4/Ag heterostructure. It is revealed that the defect-bound excitons in all possible positions of the WS2 monolayer can be effectively excited by the TE wave with significantly enhanced in-plane electric field localized on the surface of the Si3N4 layer. In addition, the emission from defect-bound excitons can propagate to the collection point with small attenuation. More importantly, the exciton dynamics in the WS2 monolayer can be modified by the Si3N4/Ag heterostructure, allowing the simultaneous excitation of neutral excitons, charge excitons (trions), and defect-bound excitons in the WS2 monolayer attached on the Si3N4/Ag heterostructure. We inspect the PL spectra obtained at different positions and find that the relative intensity of defect-bound excitons depends on the collection position. We also examine the dependences of the PL intensity and bandwidth on the excitation power for the three types of excitons. It is found that they exhibit different behaviors from those observed in the optical measurements by using the traditional excitation method. Our findings suggest a new way for exciting and studying the dynamics of multi-excitons at room temperature and indicate the potential applications of the TE wave in probing the defects in TMDC monolayers.

Self-routing dual color nanosource based on the co-excitation via coupling between nano cavities

Optical nano sources play important roles in optical communications, photonic integrated circuits, and quantum information. However, integratable, multi-color and directionally controllable nanoscale optical sources remain a challenge. This work presents a design of a two-channel upconversion nanosource based on phase coupling between metal-dielectric-metal (MDM) cavities. The resonant cavities embedded with upconversion nanoparticles (UCNPs) couple with each other by phase modulation in the bus waveguide, which enables simultaneous excitation and fluorescence enhancement of the UCNPs in cavities. Benefiting from inherent ability of MDM structure, the emitted light can be manipulated directionally for subsequent multi-channel applications. In addition, the relevant optical properties can be accurately described by a theoretical model. The excitation field strength in cavities was found to be sensitive to the coupling phase, and the derived theoretical model can predict the optimal coupling distance for an efficient dual-channel upconversion nano-emitter. This nano-emitter combines the unique fluorescence advantages of UCNPs with the easy preparation of MDM nanocavities for easy integration and nanoscale optical control, promising major applications in photonic chips, optical sensors, and complex energy optoelectronic devices.