Showing papers on "Resonance published in 2014"
TL;DR: In this article, the authors used interactions between highly excited atoms to make an optical transistor that can be activated by a single photon, which can then be used to make a single-photon transistor.
Abstract: Researchers have used interactions between highly excited atoms to make an optical transistor that can be activated by a single photon.
271 citations
TL;DR: The results show that it is possible to directly manipulate atomic-scale magnetic structures with the electric field of light on a sub-picosecond time scale.
Abstract: Multiferroics have attracted strong interest for potential applications where electric fields control magnetic order. The ultimate speed of control via magnetoelectric coupling, however, remains largely unexplored. Here, we report an experiment in which we drove spin dynamics in multiferroic TbMnO3 with an intense few-cycle terahertz (THz) light pulse tuned to resonance with an electromagnon, an electric-dipole active spin excitation. We observed the resulting spin motion using time-resolved resonant soft x-ray diffraction. Our results show that it is possible to directly manipulate atomic-scale magnetic structures with the electric field of light on a sub-picosecond time scale.
256 citations
TL;DR: An engineered defect in the crystal structure is used to localize optical and mechanical resonances in the band gap of the planar crystal, creating an artificial crystal structure that has a full phononic band gap for microwave X-band phonons and a two-dimensional pseudo-band gap for near-infrared photons.
Abstract: We present the fabrication and characterization of an artificial crystal structure formed from a thin film of silicon that has a full phononic band gap for microwave X-band phonons and a two-dimensional pseudo-band gap for near-infrared photons. An engineered defect in the crystal structure is used to localize optical and mechanical resonances in the band gap of the planar crystal. Two-tone optical spectroscopy is used to characterize the cavity system, showing a large coupling (g_0/2π≈220 kHz) between the fundamental optical cavity resonance at ω_o/2π=195 THz and colocalized mechanical resonances at frequency ω_m/2π≈9.3 GHz.
234 citations
TL;DR: In this paper, the authors investigate the nature of the coupling between the particles by looking at rectangular arrays and show that square, hexagonal, and honeycomb arrays show similar surface lattice resonances.
Abstract: Arrays of metallic particles may exhibit optical collective excitations known as surface lattice resonances (SLRs). These SLRs occur near the diffraction edge of the array and can be sharper than the plasmon resonance associated with the isolated single particle response. We have fabricated and modeled arrays of silver nanoparticles of different geometries. We show that square, hexagonal, and honeycomb arrays show similar SLRs; no one geometry shows a clear advantage over the others in terms of resonance linewidth. We investigate the nature of the coupling between the particles by looking at rectangular arrays. Our results combine experiment and modeling based on a simple coupled-dipole model.
167 citations
TL;DR: In this paper, the nitrogen-vacancy (NV) centers were created by shallow ion implantation followed by a slow, nanometer-by-nanometer removal of diamond material using oxidative etching in air.
Abstract: We present nanoscale nuclear magnetic resonance (NMR) measurements performed with nitrogen-vacancy (NV) centers located down to about 2 nm from the diamond surface. NV centers were created by shallow ion implantation followed by a slow, nanometer-by-nanometer removal of diamond material using oxidative etching in air. The close proximity of NV centers to the surface yielded large 1H NMR signals of up to 3.4 μT-rms, corresponding to ∼330 statistically polarized or ∼10 fully polarized proton spins in a (1.8 nm)3 detection volume.
165 citations
TL;DR: It is proposed that the observed small spin relaxation time in graphene is due to resonant scattering by local magnetic moments, which can come from a variety of sources, and specifically considers hydrogen adatoms, which are also resonant scatterers.
Abstract: We propose that the observed small (100 ps) spin relaxation time in graphene is due to resonant scattering by local magnetic moments. At resonances, magnetic moments behave as spin hot spots: the spin-flip scattering rates are as large as the spin-conserving ones, as long as the exchange interaction is greater than the resonance width. Smearing of the resonance peaks by the presence of electron-hole puddles gives quantitative agreement with experiment, for about 1 ppm of local moments. Although magnetic moments can come from a variety of sources, we specifically consider hydrogen adatoms, which are also resonant scatterers. The same mechanism would also work in the presence of a strong local spin-orbit interaction, but this would require heavy adatoms on graphene or a much greater coverage density of light adatoms. To make our mechanism more transparent, we also introduce toy atomic chain models for resonant scattering of electrons in the presence of a local magnetic moment and Rashba spin-orbit interaction.
144 citations
TL;DR: The transmission spectra of the plasmonic structure can be well modulated to form transmission window with the position and the full width at half maximum (FWHM) can be tuned freely, which is useful for the applications in sensors, nonlinear and slow-light devices.
Abstract: In this paper, an asymmetric plasmonic structure composed of a MIM (metal-insulator-metal) waveguide and a rectangular cavity is reported, which can support double Fano resonances originating from two different mechanisms. One of Fano resonance originates from the interference between a horizontal and a vertical resonance in the rectangular cavity. And the other is induced by the asymmetry of the plasmonic structure. Just because the double Fano resonances originate from two different mechanisms, each Fano resonance can be well tuned independently by changing the parameters of the rectangular cavity. And during the tuning process, the FOMs (figure of merit) of both the Fano resonances can keep unchanged almost with large values, both larger than 650. Such, the transmission spectra of the plasmonic structure can be well modulated to form transmission window with the position and the full width at half maximum (FWHM) can be tuned freely, which is useful for the applications in sensors, nonlinear and slow-light devices.
139 citations
TL;DR: In this paper, the authors synthesize colloidal nanocrystals of CsxWO3, a tungsten bronze in which electronic charge carriers are introduced by interstitial doping.
Abstract: Localized surface plasmon resonance phenomena have recently been investigated in unconventional plasmonic materials such as metal oxide and chalcogenide semiconductors doped with high concentrations of free carriers. We synthesize colloidal nanocrystals of CsxWO3, a tungsten bronze in which electronic charge carriers are introduced by interstitial doping. By using varying ratios of oleylamine to oleic acid, we synthesize three distinct shapes of these nanocrystals—hexagonal prisms, truncated cubes, and pseudospheres—which exhibit strongly shape-dependent absorption features in the near-infrared region. We rationalize these differences by noting that lower symmetry shapes correlate with sharper plasmon resonance features and more distinct resonance peaks. The plasmon peak positions also shift systematically with size and with the dielectric constant of the surrounding media, reminiscent of typical properties of plasmonic metal nanoparticles.
136 citations
TL;DR: In this paper, the authors investigated the fundamental mechanism of optical resonance in deep gratings by considering the excitation of magnetic polaritons (MPs) and showed that when the kinetic inductance is large, the maximum resonance wavelength can be more than twice that predicted by the cavity mode.
Abstract: Recently, it has been shown that convex cavities or 2D grating structures can enhance thermal emission for energy conversion systems. The mechanisms, however, cannot be well explained by either the conventional cavity resonance modes or surface plasmon polaritons. The present study elucidates the fundamental mechanism by considering the excitation of magnetic polaritons (MPs) in deep gratings. Rigorous coupled-wave analysis (RCWA) is employed to calculate the radiative properties by solving Maxwell's equations numerically. The LC-circuit model is employed to predict the resonance conditions. The current and field distributions further confirm the excitation of magnetic resonances. It is shown that MPs and cavity modes agree with each other when the kinetic inductance is negligibly small. However, when the kinetic inductance is sufficiently large, the maximum resonance wavelength can be more than twice that predicted by the cavity mode. Furthermore, different materials are considered and the frequency range is extended from the near-infrared to the microwave region to illustrate the scalability of the MPs. This study clarifies one of the underlying mechanisms of optical resonance in deep gratings and will benefit the design of wavelength-selective thermal emitters.
125 citations
TL;DR: In a homogeneously broadened atomic sample there is no overt Lorentz-Lorenz local field shift of the resonance, nor a collective Lamb shift, but the addition of inhomogeneous broadening restores the usual mean-field phenomenology.
Abstract: We study the collective response of a dense atomic sample to light essentially exactly using classical-electrodynamics simulations. In a homogeneously broadened atomic sample there is no overt Lorentz-Lorenz local field shift of the resonance, nor a collective Lamb shift. However, the addition of inhomogeneous broadening restores the usual mean-field phenomenology.
110 citations
TL;DR: In this paper, the second-mode axisymmetric disturbance waves were identified as the dominant wave within the resulting wavepacket, which consisted of a wide range of disturbance frequencies and wavenumbers, and the response of flow to the large-amplitude pulse disturbances indicated the presence of a fundamental resonance mechanism.
Abstract: Direct numerical simulations were performed to investigate wavepackets in a sharp cone boundary layer at Mach 6. In order to understand the natural transition process in hypersonic cone boundary layers, the flow was forced by a short-duration (localized) pulse. The pulse disturbance developed into a three-dimensional wavepacket, which consisted of a wide range of disturbance frequencies and wavenumbers. First, the linear development of the wavepacket was studied by forcing the flow with a low-amplitude pulse (0.001 % of the free-stream velocity). The dominant waves within the resulting wavepacket were identified as the second-mode axisymmetric disturbance waves. In addition, weaker first-mode oblique disturbance waves were also observed on the lateral sides of the wavepacket. In order to investigate the nonlinear transition regime, large-amplitude pulse disturbances (0.5 % of the free-stream velocity) were introduced. The response of the flow to the large-amplitude pulse disturbances indicated the presence of a fundamental resonance mechanism. Lower secondary peaks in the disturbance wave spectrum were identified at approximately half the frequency of the high-amplitude frequency band, suggesting the possibility of a subharmonic resonance mechanism. However, the spectrum also indicated that the fundamental resonance was much stronger than the subharmonic resonance. A secondary stability investigation using controlled disturbances confirmed that fundamental resonance is indeed a dominant mechanism compared to subharmonic resonance. Furthermore, strong peaks in the disturbance wave spectrum were also observed for low-azimuthal-wavenumber second-mode oblique waves, hinting at a possible oblique breakdown mechanism. Thus, the wavepacket simulations indicate that the second-mode fundamental resonance and oblique breakdown mechanisms are the strongest for the investigated flow. Hence, both mechanisms are likely to be relevant in the natural transition process for a cone boundary layer at Mach 6.
TL;DR: In this article, a Feshbach resonance based on the polariton spinor interactions in a semiconductor microcavity was demonstrated, where the energy of two interacting free particles came into resonance with a molecular bound state.
Abstract: Feshbach resonances provide a powerful tool for engineering interactions in ultracold atomic gases. The strong exciton–photon coupling in semiconductor microcavities facilitates the demonstration of a polaritonic Feshbach resonance with promising implications for manipulating polariton quantum fluids. A Feshbach resonance occurs when the energy of two interacting free particles comes into resonance with a molecular bound state. When approaching this resonance, marked changes in the interaction strength between the particles can arise. Feshbach resonances provide a powerful tool for controlling the interactions in ultracold atomic gases, which can be switched from repulsive to attractive1,2,3,4, and have allowed a range of many-body quantum physics effects to be explored5,6. Here we demonstrate a Feshbach resonance based on the polariton spinor interactions in a semiconductor microcavity. By tuning the energy of two polaritons with anti-parallel spins across the biexciton bound state energy, we show an enhancement of attractive interactions and a prompt change to repulsive interactions. A mean-field two-channel model quantitatively reproduces the experimental results. This observation paves the way for a new tool for tuning polariton interactions and to move forward into quantum correlated polariton physics.
TL;DR: Numerical results indicate that a temperature sensitivity as high as 4 nm/K can be achieved and that the most sensitive range of the sensor can be tuned by changing the volume ratios of ethanol and chloroform.
Abstract: We propose a temperature sensor design based on surface plasmon resonances (SPRs) supported by filling the holes of a six-hole photonic crystal fiber (PCF) with a silver nanowire. A liquid mixture (ethanol and chloroform) with a large thermo-optic coefficient is filled into the PCF holes as sensing medium. The filled silver nanowires can support resonance peaks and the peak will shift when temperature variations induce changes in the refractive indices of the mixture. By measuring the peak shift, the temperature change can be detected. The resonance peak is extremely sensitive to temperature because the refractive index of the filled mixture is close to that of the PCF material. Our numerical results indicate that a temperature sensitivity as high as 4 nm/K can be achieved and that the most sensitive range of the sensor can be tuned by changing the volume ratios of ethanol and chloroform. Moreover, the maximal sensitivity is relatively stable with random filled nanowires, which will be very convenient for the sensor fabrication.
TL;DR: In this article, the electromagnetic parameters of FeNi@C-paraffin composites were measured at 0.03-18 GHz and 0.78 dB at 13.78 GHz, respectively.
Abstract: Flower-like FeNi@C nanocomposites self-assembled by FeNi nanosheets and flocculent carbon were synthesized by the hydrothermal method. The electromagnetic parameters of FeNi@C–paraffin composites were measured at 0.03–18 GHz. Dual dielectric relaxations were observed in the composite system due to the cooperative consequence of the FeNi–C interfaces and dielectric carbon. The strong magnetic loss is from the coexistence of natural resonance and exchange resonance. For the 2.0 mm thickness layer, an optimal reflection loss (RL) of −46.7 dB is observed at 3.17 GHz, whereas the absorbent with a thickness of 1.3 mm has an RL of −32.78 dB at 13.78 GHz. The excellent microwave absorption abilities result from the synergy of dielectric and magnetic losses and quarter-wavelength cancellation.
TL;DR: A novel metamaterial structure that sustains extremely sharp resonances in the terahertz domain is reported that can sustain quality factors that are more than one order of magnitude larger than those of conventional split ring arrangements.
Abstract: We report on a novel metamaterial structure that sustains extremely sharp resonances in the terahertz domain. This system involves two conductively coupled split ring resonators that together exhibit a novel resonance, in broad analogy to the antiphase mode of the so-called Huygens coupled pendulum. Even though this resonance is in principle forbidden in each individual symmetric split ring, our experiments show that this new coupled mode can sustain quality factors that are more than one order of magnitude larger than those of conventional split ring arrangements. Because of the universality of the metamaterial response, the design principle we present here can be applied across the entire electromagnetic spectrum and to various metamaterial resonators.
TL;DR: The concluding result from an Ives-Stilwell-type time dilation experiment using 7Li+ ions confined at a velocity of β=v/c=0.338 in the storage ring ESR at Darmstadt is verified and interpreted within Lorentz invariance violating test theories.
Abstract: We present the concluding result from an Ives-Stilwell-type time dilation experiment using 7Li+ ions confined at a velocity of β=v/c=0.338 in the storage ring ESR at Darmstadt. A Λ-type three-level system within the hyperfine structure of the 7Li+3S1 →3P2 line is driven by two laser beams aligned parallel and antiparallel relative to the ion beam. The lasers' Doppler shifted frequencies required for resonance are measured with an accuracy of <4×10(-9) using optical-optical double resonance spectroscopy. This allows us to verify the special relativity relation between the time dilation factor γ and the velocity β, γ√1-β2=1 to within ±2.3×10(-9) at this velocity. The result, which is singled out by a high boost velocity β, is also interpreted within Lorentz invariance violating test theories.
TL;DR: In this paper, the amplitude and phase of the transmitted SAW during magnetic field sweeps showed a clear resonant behavior at a field close to the one calculated to give a precession frequency equal to the SAW frequency.
Abstract: Surface acoustic waves (SAW) were generated on a thin layer of the ferromagnetic semiconductor (Ga,Mn)(As,P). The out-of-plane uniaxial magnetic anisotropy of this dilute magnetic semiconductor is very sensitive to the strain of the layer, making it an ideal test material for the dynamic control of magnetization via magnetostriction. The amplitude and phase of the transmitted SAW during magnetic field sweeps showed a clear resonant behavior at a field close to the one calculated to give a precession frequency equal to the SAW frequency. A resonance was observed from 5 to 85 K, just below the Curie temperature of the layer. A full analytical treatment of the coupled magnetization/acoustic dynamics showed that the magnetostrictive coupling modifies the elastic constants of the material and accordingly the wave-vector solution to the elastic wave equation. The shape and position of the resonance were well reproduced by the calculations, in particular the fact that velocity (phase) variations resonated at lower fields than the acoustic attenuation variations. We suggest one reinterpret SAW-driven ferromagnetic resonance as a form of resonant, dynamic, delta-E effect, a concept usually reserved for static magnetoelastic phenomena.
TL;DR: A nanoassembly supporting the hybridization of an electric and magnetic plasmonic mode in Fano resonance conditions is investigated, able to generate an intense and localized magnetic hot-spot in the near-infrared spectral region.
Abstract: The possibility to develop nanosystems with appreciable magnetic response at optical frequencies has been a matter of intense study in the past few years. This aim was strongly hindered by the saturation of the magnetic response of "natural" materials beyond the THz regime. Recently, in order to overcome such limitation, it has been considered to enhance the magnetic fields through the induction of displacement currents triggered by plasmonic resonances. Here we investigate a nanoassembly supporting the hybridization of an electric and magnetic plasmonic mode in Fano resonance conditions. Taking advantage of the enhancement properties owned by such interferential resonance, we have been able to generate an intense and localized magnetic hot-spot in the near-infrared spectral region.
TL;DR: In this article, the spin Hall angle of Pt in Co75Fe25/Pt bilayer films was experimentally investigated by means of the spintorque ferromagnetic resonance and the modulation of damping measurements.
Abstract: The spin Hall angle of Pt in Co75Fe25/Pt bilayer films was experimentally investigated by means of the spin-torque ferromagnetic resonance and the modulation of damping measurements. By comparing the present results with the Ni80Fe20/Pt system, we found that the ferromagnetic layer underneath the Pt one greatly affects the estimation of the spin Hall angle. We also discuss the spin diffusion length of Pt and the ferromagnetic thickness dependence of the Gilbert damping coefficient.
TL;DR: In this paper, the authors presented theoretical examination and experimental demonstration of locally resonant (LR) phononic plates consisting of a periodic array of beam-like resonators attached to a thin homogeneous plate.
Abstract: We present theoretical examination and experimental demonstration of locally resonant (LR) phononic plates consisting of a periodic array of beam-like resonators attached to a thin homogeneous plate. Such phononic plates feature unique wave physics due to the coexistence of localized resonance and structural periodicity. We demonstrate that a low-frequency complete band gap for flexural plate waves can be created in the proposed structure owing to the interaction between the localized resonant modes of the beam-like resonators and the flexural wave modes of the host plate. We show that the location and width of the complete band gap can be dramatically tuned by changing the properties of the beam-like resonators. To understand the opening mechanism and evolution behaviour of the complete band gap, some approximate but explicit models are provided and discussed. We further perform experimental measurements of a specimen fabricated by an array of double-stacked aluminum beam-like resonators attached to a thin aluminum plate with 5 cm structure periodicity. The experimental results evidence a complete band gap extending from 465 to 860 Hz, matching well with our theoretical prediction. The LR phononic plates proposed in this work can find potential applications in attenuation of low-frequency mechanical vibrations and insulation of low-frequency audible sound.
TL;DR: In this article, the authors present a system which allows to tune the coupling between a superconducting resonator and a transmission line, which allows capture, storage and on-demand release of microwaves at a tunable rate.
Abstract: We present a system which allows to tune the coupling between a superconducting resonator and a transmission line. This storage resonator is addressed through a second, coupling resonator, which is frequency-tunable and controlled by a magnetic flux applied to a superconducting quantum interference device. We experimentally demonstrate that the lifetime of the storage resonator can be tuned by more than three orders of magnitude. A field can be stored for 18 μs when the coupling resonator is tuned off resonance and it can be released in 14 ns when the coupling resonator is tuned on resonance. The device allows capture, storage, and on-demand release of microwaves at a tunable rate.
TL;DR: It is demonstrated that small Au nanorods with a high aspect ratio develop a strong longitudinal SPR, with intensity comparable to that in Ag rods, as soon as the resonance energy drops below the onset of the interband transitions due to the geometry.
Abstract: It is known that the surface-plasmon resonance (SPR) in small spherical Au nanoparticles of about 2 nm is strongly damped. We demonstrate that small Au nanorods with a high aspect ratio develop a strong longitudinal SPR, with intensity comparable to that in Ag rods, as soon as the resonance energy drops below the onset of the interband transitions due to the geometry. We present ab initio calculations of time-dependent density-functional theory of rods with lengths of up to 7 nm. By changing the length and width, not only the energy but also the character of the resonance in Au rods can be tuned. Moreover, the aspect ratio alone is not sufficient to predict the character of the spectrum; the absolute size matters.
TL;DR: In this paper, the authors report on experimental measurement of air damping effects in high frequency nanomembrane resonators made of atomically thin molybdenum disulfide (MoS2) drumhead structures.
Abstract: We report on experimental measurement of air damping effects in high frequency nanomembrane resonators made of atomically thin molybdenum disulfide (MoS2) drumhead structures. Circular MoS2 nanomembranes with thickness of monolayer, few-layer, and multi-layer up to ∼70 nm (∼100 layers) exhibit intriguing pressure dependence of resonance characteristics. In completely covered drumheads, where there is no immediate equilibrium between the drum cavity and environment, resonance frequencies and quality (Q) factors strongly depend on environmental pressure due to bulging of the nanomembranes. In incompletely covered drumheads, strong frequency shifts due to compressing-cavity stiffening occur above ∼200 Torr. The pressure-dependent Q factors are limited by free molecule flow (FMF) damping, and all the mono-, bi-, and tri-layer devices exhibit lower FMF damping than thicker, conventional devices do.
TL;DR: Numerical simulations show a sharp resonance-derived spectral profile that is additionally shaped by a neighboring Rayleigh anomaly, and it is shown numerically that the narrow bandwidth is predominantly due to the low refractive-index contrast between the waveguide film and the substrate.
Abstract: We design and fabricate efficient, narrow-band, transmission color filters whose operating principle resides in a narrow-band guided-mode resonance associated with a surface-plasmon resonance. The fundamental device consists of an aluminum grating over a 200-nm-thick aluminum oxide film on a glass substrate. Numerical simulations show a sharp resonance-derived spectral profile that is additionally shaped by a neighboring Rayleigh anomaly. Besides the Rayleigh effect, we show numerically that the narrow bandwidth is predominantly due to the low refractive-index contrast between the waveguide film and the substrate. Red, green, and blue filters are fabricated using ultraviolet holographic lithography followed by a lift-off process. The experimental spectral efficiency in transmission exceeds 80% with full-width-at-half-maximum linewidths near 20 nm. We provide color images of the zero-order transmitted spectra, and illustrate the pure colors associated with the modal resonance extracted as side-coupled output light.
TL;DR: This work provides a general method for decoding the effect of biophysical parameters on linear membrane resonance and phase by tracking trajectories, parametrized by the relevant biophysical parameter, in pre-constructed attribute diagrams.
Abstract: Many neuron types exhibit preferred frequency responses in their voltage amplitude (resonance) or phase shift to subthreshold oscillatory currents, but the effect of biophysical parameters on these properties is not well understood. We propose a general framework to analyze the role of different ionic currents and their interactions in shaping the properties of impedance amplitude and phase in linearized biophysical models and demonstrate this approach in a two-dimensional linear model with two effective conductances g L and g 1. We compute the key attributes of impedance and phase (resonance frequency and amplitude, zero-phase frequency, selectivity, etc.) in the g L ???g 1 parameter space. Using these attribute diagrams we identify two basic mechanisms for the generation of resonance: an increase in the resonance amplitude as g 1 increases while the overall impedance is decreased, and an increase in the maximal impedance, without any change in the input resistance, as the ionic current time constant increases. We use the attribute diagrams to analyze resonance and phase of the linearization of two biophysical models that include resonant (I h or slow potassium) and amplifying currents (persistent sodium). In the absence of amplifying currents, the two models behave similarly as the conductances of the resonant currents is increased whereas, with the amplifying current present, the two models have qualitatively opposite responses. This work provides a general method for decoding the effect of biophysical parameters on linear membrane resonance and phase by tracking trajectories, parametrized by the relevant biophysical parameter, in pre-constructed attribute diagrams.
TL;DR: This paper proposes a novel resonator structure for efficiency and transferred power improvements: a transmitter that consists of two strongly coupled resonators that behave as a single resonator with enhanced performances.
Abstract: This paper proposes a novel resonator structure for efficiency and transferred power improvements: a transmitter (a receiver) that consists of two strongly coupled resonators. The two strongly coupled resonators are embedded within a transmitter device (a receiver device) and behave as a single resonator with enhanced performances. Unlike the conventional four-coil system, the first and the fourth resonators are also designed to have high loaded-Q and maximum cross couplings. Therefore, the first and the fourth resonators also take part in the coupled resonance with opposite-side resonators. This provides additional energy exchange path. The exact design guidelines are provided for each different resonance topology from analytical derivation. It is analyzed and experimentally demonstrated that the efficiency and the transferred power are increased by the proposed two-resonator technique. For a 30 cm × 25 cm parallel-resonant transmitter and an 18 cm × 16 cm parallel-resonant receiver at 13-cm distance, the efficiency and the transferred power with the proposed technique are 65.2% and 17.2 W, respectively, whereas those values without the proposed technique are only 37.3% and 6.2 W.
TL;DR: Hedman and Nicholson as mentioned in this paper used the same tools to confirm that several of the waves in Saturn's rings were likely generated by resonances with fundamental sectoral normal modes inside Saturn itself.
Abstract: In a previous paper (Hedman and Nicholson 2013), we developed tools that allowed us to confirm that several of the waves in Saturn's rings were likely generated by resonances with fundamental sectoral normal modes inside Saturn itself. Here we use these same tools to examine eight additional waves that are probably generated by structures inside the planet. One of these waves appears to be generated by a resonance with a fundamental sectoral normal mode with azimuthal harmonic number m=10. If this attribution is correct, then the m=10 mode must have a larger amplitude than the modes with m=5-9, since the latter do not appear to generate strong waves. We also identify five waves with pattern speeds between 807 degrees/day and 834 degrees/day. Since these pattern speeds are close to the planet's rotation rate, they probably are due to persistent gravitational anomalies within the planet. These waves are all found in regions of enhanced optical depth known as plateaux, but surprisingly the surface mass densities they yield are comparable to the surface mass densities of the background C ring. Finally, one wave appears to be a one-armed spiral pattern whose rotation rate suggests it is generated by a resonance with a structure inside Saturn, but the nature of this perturbing structure remains unclear. Strangely, the resonant radius for this wave seems to be drifting inwards at an average rate of 0.8 km/year over the last thirty years, implying that the relevant planetary oscillation frequency has been steadily increasing.
TL;DR: In this article, the authors explored a new paradigm through the employment of parametric resonance, which is not limited due to linear damping, therefore, the power output can potentially build up to higher levels.
Abstract: In the arena of vibration energy harvesting, the key technical challenges continue to be low power density and narrow operational frequency bandwidth. While the convention has relied upon the activation of the fundamental mode of resonance through direct excitation, this article explores a new paradigm through the employment of parametric resonance. Unlike the former, oscillatory amplitude growth is not limited due to linear damping. Therefore, the power output can potentially build up to higher levels. Additionally, it is the onset of non-linearity that eventually limits parametric resonance; hence, this approach can also potentially broaden the operating frequency range. Theoretical prediction and numerical modelling have suggested an order higher in oscillatory amplitude growth. An experimental macro-sized electromagnetic prototype (practical volume of ~1800 cm3) when driven into parametric resonance, has demonstrated around 50% increase in half power band and an order of magnitude higher peak power density normalised against input acceleration squared (293 mW cm23 m22 s4 with 171.5 mW at 0.57 m s22) in contrast to the same prototype directly driven at fundamental resonance (36.5 mW cm23 m22 s4 with 27.75 mW at 0.65 m s22). This figure suggests promising potentials while comparing with current state-of-the-art macro-sized counterparts, such as Perpetuum’s PMG-17 (119 mW cm23 m22 s4).
TL;DR: In this article, the integration of auto-parametric resonance, as a form of resonant amplification of the base excitation, to further minimise this activation criterion and realize the profitable regions of parametric resonance at even lower input acceleration levels.
Abstract: Parametric resonance, as a resonant amplification phenomenon, is a superior mechanical amplifier than direct resonance and has already been demonstrated to possess the potential to offer over an order of magnitude higher power output for vibration energy harvesting than the conventional direct excitation. However, unlike directly excited systems, parametric resonance has a minimum threshold amplitude that must be attained prior to its activation. The authors have previously presented the addition of initial spring designs to minimise this threshold, through non-resonant direct amplification of the base excitation that is subsequently fed into the parametric resonator. This paper explores the integration of auto-parametric resonance, as a form of resonant amplification of the base excitation, to further minimise this activation criterion and realise the profitable regions of parametric resonance at even lower input acceleration levels. Numerical and experimental results have demonstrated in excess of an order of magnitude reduction in the initiation threshold amplitude for an auto-parametric resonator (∼0.6 ms−2) as well as several folds lower for a parametric resonator with a non-resonant base amplifier (∼4.0 ms−2), as oppose to a sole parametric resonator without any threshold reduction mechanisms (10's ms−2). Therefore, the superior power performance of parametric resonance over direct resonance has been activated and demonstrated at much lower input levels.