Perpendicular Excitation Research Articles

Experimental study on damping characteristics of the particle dampers with damping rod and soft inside wall

In the perpendicular simple sinusoidal excitation, the damping characteristics of the soft-wall particle damper with a damping rod were experimentally investigated by controlling the acceleration amplitude and vibration frequency of the damper motion and measuring the force and acceleration signals. The experimental results show that the loss power of the damper increases monotonically with the rise of the excitation acceleration amplitude, and the effective mass shows the change of “gentle decrease-critical point-decrease”. As the driving frequency rises, the loss power progressively decreases, and the effective mass does not change significantly. By analyzing the damping characteristics of different dampers, it shows that the damping effectiveness of the soft inside wall particle damper with a damping rod is obviously better.

A New Technique for Connecting a Dual Excitation Synchronous Generator to the Power Grid

Due to an increasing demand for electric power and changes in the typology of loads, stability has become a major concern in power systems. As the system stability is directly related to the response of the connected generator, recent research has focused on enhancing generators’ stability and improving their response to load variations. This study focuses on adding another excitation winding on to the q-axis, perpendicular to the conventional excitation winding on the d-axis, to control both active and reactive power. This paper studies and compares the performance of the dual excitation synchronous generator (DESG) to conventional synchronous generators. The mathematical equations are derived, and a mathematical model is then developed. The experimental tests have been conducted using a laboratory model consisting of a two-phase synchronous generator driven by a DC motor with different loads. The obtained results and radial diagrams for the different loading types are presented and evaluated. Therefore, a new approach has been designed to connect the DESG directly to the power grid without any electronic components using a special coupling that works in one direction. Two perpendicular excitation coils, d and q, were formed from the existing coils, and the tests were carried out on all loads, ensuring that the revolving angle (i.e., the stability angle φ) was fixed. The results show that the proposed method offers significant cost savings, potentially amounting to 15–20% of the unit price. The experimental results confirm that the DESG significantly improves the generator stability by maintaining a constant rotor angle δ, which requires using an automatic angle regulator (AAR) in addition to the conventional automatic voltage regulator (AVR).

Dynamical Behaviors of a Mass Submitted to the Action of Perpendicular Spring and Excitations with Phase Shift

Dynamical Behaviors of a Mass Submitted to the Action of Perpendicular Spring and Excitations with Phase Shift

Magnetic Field Alignment and Optical Anisotropy of MoS2 Nanosheets Dispersed in a Liquid Crystal Polymer.

Molybdenum disulfide (MoS2) nanosheets exhibit anisotropic optical and electronic properties, stemming from their shape and electronic structure. Unveiling this anisotropy for study and usage in materials and devices requires the ability to control the orientation of dispersed nanosheets, but to date this has proved a challenging proposition. Here, we demonstrate magnetic field driven alignment of MoS2 nanosheets in a liquid crystal (LC) polymer and unveil the optical properties of the resulting anisotropic assembly. Nanosheet optical anisotropy is observed spectroscopically by Raman and direction-dependent photoluminescence (PL) measurements. Resulting data indicate significantly lower PL emission due to optical excitation with electric field oscillation out of plane, parallel to the MoS2 c-axis, than that associated with perpendicular excitation, with the dichroic ratio Iperp/Ipar = 3. The approach developed here provides a useful route to elucidate anisotropic optical properties of MoS2 nanosheets and to utilize such properties in new materials and devices.

Excitation modalities for enhanced micro and nanoparticle imaging in a smartphone coupled 3D printed fluorescent microscope.

Smartphone fluorescent microscopes (SFM) offer many functional characteristics similar to their benchtop counterparts at a fraction of the cost and have been shown to work for biomarker detection in many biomedical applications. However, imaging and quantification of bioparticles in the sub-micron and nanometer range remains challenging as it requires aggressive robustness and high-performance metrics of the building blocks of SFM. Here, we explored multiple excitation modalities and their performance on the imaging capability of an SFM. Employing spatial positional variations of the excitation source with respect to the imaging sample plane (i.e., parallel, perpendicular, oblique), we developed three distinct SFM variants. These SFM variants were tested using green-fluorescent beads of four different sizes (8.3, 2, 1, 0.8 μm). Optimal excitation voltage range was determined by imaging these beads at multiple excitation voltages to optimize for no data loss and acceptable noise levels for each SFM variant. The SFM with parallel excitation was able to only image 8.3 μm beads while the SFM variants with perpendicular and oblique excitation were able to image all four bead sizes. Relative performance of the SFM variants was quantified by calculating signal difference to noise ratio (SDNR) and contrast to noise ratio (CNR) from the captured images. SFM with oblique excitation generated the highest SDNR and CNR values, whereas, for power consumption, SFM with perpendicular excitation generated the best results. This study sheds light on significant findings related to performance of SFM systems and their potential utility in biomedical applications involving sub-micron imaging. Similarly, findings of this study are translatable to benchtop microscopy instruments as well as to enhance their imaging performance metrics.

DFT study on electronic and optical properties of graphene under an external electric field

The paper investigates the electronic and optical properties of graphene, under the external electric field (Eext) according to perpendicular direction, using density functional theory (DFT). Applying the Eext to the graphene sheet modifies its electronic and optical properties, including the band gap energy, total density of states (TDOS), absorption coefficient, dielectric function, and refractive index. Graphene’s band gap is opened by the application of Eext to its structure. As a result of the effect of Eext on graphene layer, its absorption coefficient increases in the ultraviolet (UV) range and decreases in the visible range. We found that the electronic and optical properties of graphene material, can be altered by a perpendicular excitation applied to its structure.

Magnetic skyrmion shape manipulation by perpendicular magnetic anisotropy excitation within geometrically confined nanostructures

Magnetic skyrmions are promising features of spintronic devices including race-track memory and nano-oscillators. Skyrmion shape can act as an additional degree of freedom along with other properties including topological charge, polarity and helicity etc. Skyrmion excitation associated with shape deformation is significant for microwave devices. By means of micromagnetic simulation study, we report skyrmion excitation within nanodiscs by dynamically modulated perpendicular magnetic anisotropy (PMA). At higher resonance frequencies, skyrmion shows shape deformation into regular polygons including elliptic, trigon, tetragon, up to decagon, characterized as n = 2, 3, 4 …, 10, respectively. We build a phase diagram showing that regular polygon shape deformation occurs within a PMA amplitude window with minimum and maximum limits depending on resonance frequency and disc radius. Further analysis reveals that with increase in disc radius, modes with higher n appear, however, skyrmion is distorted into irregular shape, with no specific polygon-like pattern, even for smaller PMA. With a semi-quantitative analysis, we relate n for different modes to resonance frequency, disc size and PMA magnitude. These findings can assist in getting fundamental physics underlying skyrmion deformation and can help in designing energy-efficient microwave generator/detector and nano-oscillator where skyrmion dynamics are very important.

Dependence of non-reciprocity in spin wave excitation on antenna configuration

The dependence of nonreciprocity of excitation of magnetostatic surface waves on antenna width was investigated experimentally and theoretically. The nonreciprocity was successfully modified by changing the excitation antenna width. The nonreciprocity ratio, which was defined as the spin wave intensity under negative bias field divided by that under positive bias field, was found to decrease with increasing antenna width. Micromagnetic simulations revealed that this decrease in the nonreciprocity ratio originates from the rapid decrease in the in-plane excitation field compared to the perpendicular excitation field with reducing the antenna width.

Parent bending effects on nonadiabatic transition dynamics: Isotopomer-resolved imaging of photodissociation of CF3Br at two source temperatures.

Nonadiabatic transition between electronic states plays a critical role in the photodissociation of the CX3Y (X = H and F; Y = Cl, Br, and I) system, and the transition probability was considered to be closely related to the X-C-Y bending motion. Hereby the effect of F-C-Br bending vibration on the nonadiabatic transition dynamics is studied by time-sliced ion velocity imaging of Br(2P1/2,3/2) isotopomers produced from the photodissociation of title molecules at two source temperatures, 298 K and 473 K, respectively. At the photolysis wavelength 234 nm, the anisotropy parameter (β) of the Br(2P3/2) products decreases from 1.3 at 298 K to 0.9 at 473 K, while the β of Br(2P1/2) remains at almost 2 at two temperatures, indicating the significant effect of bending excitation on the ground channel. Two nonadiabatic dissociation pathways are suggested in the Br(2P3/2) channel. One of them is the parallel excitation from the ground state to the 3 Q 0 state in C3V symmetry, and then transition to the 1 Q 1 state via conical intersection, and the other is the perpendicular excitation to the 3A' state in Cs symmetry and then decomposition along this state in the presence of the avoided crossing between 3A' and 4A' states. Closely related to the F-C-Br bending vibration of CF3Br is the latter transition.

Polarization-dependent fluorescence of CdSe/ZnS quantum dots coupling to a single gold-silver alloy nanotube

The fluorescence intensities of CdSe/ZnS quantum dots on a silver nanowire and a gold-silver alloy nanotube with different molar ratios of gold and silver are investigated under excitation with different polarization angles. The ratio of the fluorescence intensity of perpendicular and parallel polarization excitations is measured to be 4.05 for a silver nanowire and decreases to 1.30, 1.10 and 1.07 for nanotube with Au:Ag molar ratios of 1:4.0, 1:2.5 and 1:1.5, respectively. The numerical simulation results show that the aforementioned experimental phenomena can be attributed to the variation in the distribution of the surface plasmon electromagnetic field under perpendicular polarized light excitation. The electromagnetic field is primarily distributed on the outer surface of the silver nanowire, while the field partially penetrates the interior of the silver nanotube and becomes completely concentrated at the interior of the gold nanotube. This research also found that the productivity and robustness of the chemical synthesis of the alloy nanotubes can be greatly improved by using a microwave reactor.

Polarization-dependent plasmon mode mapping of Ag nanowires based on two-photon excitation fluorescence of quantum dots

We show that the plasmon modes of Ag nanowires can be imaged by coating them with a layer of quantum dots (QDs), held off the nanowire surface by a nanoscale dielectric spacer layer. Parallel or perpendicular excitation polarization modulates the intensity maps of two-photon excitation fluorescence (TPEF), which exhibit Fabry–Pérot cavity modes at the excitation or fluorescence wavelength. We attribute this phenomenon to the QDs excited by propagating surface plasmon polaritons or localized surface plasmon modes. The results of the TPEF intensity maps are well explained by theoretical simulations, and the energy transfer process is also discussed.

Chiral metamaterial-based microwave sensors

A significant resonance shift is found in both reflection and transmission coefficients from both parallel and perpendicular excitations in a helical structure. The responses from the perpendicular excitation show better sensitivity than those from the parallel excitation at 480 MHz-560 MHz for 0.2 circumference difference. Additional electromagnetic properties of a helical structure, such as chirality, optical rotatory dispersion and circular dichroism can also further combine to enhance the sensing performance.

Flow control with perpendicular acoustic forcing on NACA 2415 aerofoil at low Reynolds numbers

In this study, the effect of perpendicular acoustic excitation on laminar separation bubble, aerodynamic characteristics and stall characteristics over a NACA 2415 aerofoil was investigated experimentally at low Reynolds numbers at varying angles of attack. Extensive experiments such as force and pressure measurements, flow visualization via smoke-wire technique and velocity measurement via hot-wire system were conducted. The experimental results showed that when acoustic excitation of a certain frequency was applied, the length of the laminar separation bubble was shortened owing to the energy added to the flow by acoustic excitation. Because of the shortened laminar separation bubble, coefficient of lift was increased. Furthermore, at the stall angles the separated flow was forced to reattach to the surface of the aerofoil by acoustic forcing, so the stall angle and maximum coefficient of lift were increased, and drag coefficient was decreased.

Highly Sensitive Detection of the Lattice Distortion in Single Bent ZnO Nanowires by Second-Harmonic Generation Microscopy

Nanogenerators based on ZnO nanowires (NWs) realize the energy conversion at nanoscale, which are ascribed to the piezoelectric property caused by the lattice distortion of the ZnO NWs. The lattice distortion can significantly tune the electronic and optical properties, and requires a sensitive and convenient measurement. However, high-resolution transmission electron microscopy (HRTEM) technique provides a limited sensitivity of 0.01 nm on the variation of the lattice spacing and requires vacuum conditions. Here we demonstrate a highly-sensitive detection of the lattice distortion in single bent ZnO NWs by second-harmonic generation (SHG) microscopy. As the curvature of the single bent ZnO NW increases to 21 mm-1 (<4% bending distortion), it shows a significant decrease (~70%) in the SHG intensity ratio between perpendicular and parallel excitation polarization with respect to c-axis of ZnO NWs. Importantly, the extraordinary non-axisymmetrical SHG polarimetric patterns are also observed, indicating the twisting distortion around c-axis of ZnO NWs. Thus, SHG microscopy provides a sensitive all-optical and non-invasive method for in situ detecting the lattice distortion under various circumstances.

SAR reduction using a single SRR superstrate for a dual-band antenna

ABSTRACTA dual-band microstrip antenna operating at GSM 900 and GSM 1800 MHz is designed initially. Then a single split ring resonator (SRR) structure is used as a superstrate for this dual-band antenna. A circular current is induced in the SRR due to the perpendicular plane wave excitation, which in turn leads to an electric excitation coupled to the magnetic resonance. It also exhibits higher order excitations at 0.9 and 1.8 GHz which ultimately resulted in specific absorption rate (SAR) reduction of human head at both the designed frequencies of the antenna. The antenna and the SRR superstrate are printed on a 1.6 mm thick FR-4 substrate of dimension 59.6 × 49.6 mm2. Analysis of the SRR using the classic waveguide theory approach is discussed. Radiation pattern of the antenna in the presence of SRR superstrate and human head is also discussed. Prototype of the antenna along with the SRR superstrate is fabricated and measured for return loss and radiation pattern. Measurement results fairly agree with the simulated results. A human head phantom is utilized in the calculation of SAR.

Barometric Calibration of Luminescent Oxygen Probes

The invention of the Phosphorescence Quenching Method for the measurement of oxygen concentration in blood and tissue revolutionized physiological studies of oxygen transport in living organisms. Since the pioneering publication by Vanderkooi and Wilson in 1987, many researchers have contributed to the measurement of oxygen in the microcirculation, oxygen imaging in tissues and microvessels and to the development of new extracellular and intracellular phosphorescent probes. However, there is a problem of congruency in data from different laboratories, because of inter‐laboratory variability of the calibration coefficients in the Stern ‐ Volmer equation. Published data (9 sources) for a common oxygen probe Pd‐porphyrin + BSA have CV = 9.6%, due to differences in the calibration techniques used. These are methods for the formation of oxygen standards via chemical titration, calibrated gas mixtures and an oxygen electrode. Each method in turn also needs calibration. We have designed a barometric method for calibration of oxygen probes by using a regulated vacuum chamber and manometer to set multiple PO2 standards. The method is fast, accurate and can be applied to biological fluids sampled during or after an experiment. Calibration over the full physiological PO2 range (1–120 mmHg) takes about 15 min and requires 1–2 mg of probe.A sample of probe solution was placed on a cotton membrane inside an evacuated vial. The vial was fixed in a thermostated (37±0.1 °C) well with the membrane in a mid‐plane position, at the intersection of the perpendicular excitation and emission optical pathways. The probe was excited by a brief light pulse (1μs duration, 410 nm) from a high power diode. The emitted phosphorescence (620–750 nm) was detected by a Hamamatsu Photosensor module and recorded by a computer at 500 kS/s with 12‐bit resolution. The excitation flash rate was 100 s−1 and 1000 decay curves were collected for 10 s for each PO2. Standard PO2's in a vial were created by a vacuum pump, equipped with a regulator and a pressure filter and was set by a precision digital manometer (PO2 error 0.1 mmHg). The necessary correction was made for atmospheric pressure. When the pressure was changed to a higher or lower PO2 standard, the probe in the membrane equilibrated with the air in the vial with a time constant of 1.5 s, so a 10 s time interval was used before starting data acquisition. Recorded phosphorescence decay curves were analyzed with non‐linear fitting to two different models of decays to determine the exponential decay constants. It turned out that, even in the absence of oxygen gradients and at PO2= 0, the phosphorescence decay of conjugated Pd‐porphyrin was heterogeneous, and it was fitted well by a heterogeneous model. Application of a monoexponential model was possible only for the initial segment of the decay curve or for its tail. This property did not introduce a distortion in the PO2 measurement, if there is no “fitting delay.” A heterogeneous model fit the entire curve and was not sensitive to a delay. Thus, for consistency the experimental and calibration decay curves must be processed by exactly the same procedure. The equation of translation between data obtained with different calibration coefficients was derived for an accurate comparison of results from different laboratories.

Temperature-Dependence of High-Gain Operation in GaAs Photoconductive Semiconductor Switch at 1.6 $\mu \text{J}$ Excitation

This letter reports the temperature-dependence of high-gain operation in semi-insulating GaAs photoconductive semiconductor switches at 1.6 μJ laser diode excitation. Under the excitation of two different spot patterns, the electric field threshold for high-gain operation is investigated by varying the temperature. In addition, the switching characteristics dependence on temperature are also studied under the perpendicular spot excitation.

Polarized SERS on linear arrays of silver half-shells: SERS re-radiation modulated by local density of optical states

This work investigates polarization effects in surface-enhanced Raman scattering (SERS) on a particular kind of hybrid colloidal plasmonic-photonic crystal consisting in linear arrays of polystyrene colloids coated by a silver film forming caps (half-shells). The polarization of Raman scattering of adsorbed molecules is found to be imposed by the linear morphology of the plasmonic nanostructures, independent of the incident polarization. Specifically, it is demonstrated that the electric field component parallel to the linear plasmonic nanostructures brings the main contribution to the SERS enhancement for both parallel and perpendicular excitation. The stronger plasmon resonance, polarized along the chain of metal half-shells, is the one that determines the polarization of the SERS scattering, even if this resonance is not directly excited by the incident laser, but only re-radiated photons couple to it. The observed dependences indicate a strong contribution of the second part of the E4 enhancement, related to the enhancement at the frequency of the Raman scattered photons. FDTD electromagnetic simulations, taking into account both the excitation enhancement at the location of the scatterer and the enhancement of the scattering (re-radiation) by local density of optical states (LDOS) effects, support the experimental results. The presented results emphasize the practical importance of knowing and controlling the excitation/detection conditions in SERS experiments with nanostructures possessing well-defined and oriented morphological features. The LDOS approach employed here for the theoretical analysis, despite not being common for this purpose, proves its potential for becoming a useful ingredient in the analysis of plasmon-enhanced spectroscopies.

Polarizing polymer solar cells based on the self-organization of a liquid crystalline polymer

We manufactured polarizing polymer solar cells (PSCs) utilizing a liquid crystalline polymer (i.e., poly(2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT)) as an electron donor material and a material that selectively absorbs polarized light. The oriented PBTTT films prepared using a self-organization process exhibited a high dichroic ratio of ca. 6.35 at the absorption peak. The polarizing PSCs based on oriented PBTTT–PC71BM photoactive layers exhibit an anisotropic photovoltaic effect under polarized illumination along the two orthogonal axes. The polarizing PSCs have a larger power conversion efficiency under parallel-polarized illumination than that of isotropic PV devices under unpolarized illumination. Based on picosecond fluorescent spectra, the parallel excitation produces a slower ground state recovery and a longer exciton lifetime than perpendicular excitation for PBTTT molecules in a uniaxially oriented arrangement.

Multi-view second-harmonic generation imaging of mouse tail tendon via reflective micro-prisms.

Here we experimentally show that second-harmonic generation (SHG) imaging is not sensitive to collagen fibers oriented parallel to the direction of laser propagation and, as a consequence, can potentially miss important structural information. As an alternative approach, we demonstrate the use of reflective micro-prisms to enable multi-view SHG imaging of mouse tail tendon by redirecting the focused excitation and collection of subsequent emission. Our approach data corroborates the theoretical treatment on vanishing and nonvanishing orientations, where fibers along the laser direction are largely transparent by SHG. In strong contrast, the two-photon excited fluorescence of dye-labeled collagen fibers is isotropic and is not subject to this constraint. We utilized Pearson correlation to quantify differences in fluorescent and backward detected SHG images of the tendon fiber structure, where the SHG and TPEF were highly statistically correlated (0.6-0.8) for perpendicular excitation but were uncorrelated for excitation parallel to the fiber axis. The results suggest that improved imaging of 3D collagen structure is possible with multi-view SHG microscopy.