On the Localized Surface Plasmonic Resonances of AgPd Alloy Nanoparticles by Experiment and Theory

Ag/Pd multilayers and AgPd alloyed ultrathin films were deposited on Corning glass by magnetron sputtering. After being annealed in a furnace in air at 460 °C, self-assembled nanoparticles were formed. Localized surface plasmon resonances were observed only for the Ag-rich samples in the full range of the visible light spectrum. The resonance position was found to depend on the initial film thickness. In order to gain further physical insight, rigorous theoretical calculations were carried out via the rigid coupled-wave analysis method for the entire compositional range between Ag and Pd. Theoretical calculations were proven to be in suitable agreement with the experimental results.

Terahertz Sensor Study Based on Spoof Surface Plasmon Polaritons

The spoof surface plasmon polaritons (SSPPs) structure can be used as a sensor in THz region for the biosensing. The accuracy of resonance and amplitude for sensor is very important for biosensing. The momentum matching of SSPPs determines the resonance position and the gap distance determines the amplitude. For the biomolecular sensing, the sample is positioned between the prism base and the SSPPs structure. The momentum matching condition at the current study does not consider the effect of sample refractive index and the resonance position has a significant error. Here the correction is made to the momentum matching condition which considers the effect of the sample refractive index. A comparative study of surface plasmon resonance (SPR) sensing performance based on frequency and angle variations shows that the sensing sensitivity for frequency region is superior to that of angle region; in the meanwhile, as an application of biosensors, we have detected different types of brain lesions in the frequency range. Furthermore, the reflection amplitude is related to gap size between the prism and SSPPs. The relationship of gap size and reflection amplitude is studied. By using the relationship between gap size and reflection amplitude, the amplitudes at different frequencies or incident angles for different refractivities have the same reflection dips compared to the other published results. The simulation is performed and the results proved the theory.

On the accuracy of position of the linear secular resonance g − g5 in the proper elements’ space

ABSTRACT An in-depth analysis is presented of the accuracy of position of the linear secular resonance g − g5 in the phase space of proper elements, as determined by the recently introduced polynomial fit method. Different attempts to pinpoint the exact location of this resonance are described, leading to improvement in the accuracy of resonance position achieved via local adjustments of the new method and measured in comparison with the corresponding positions of selected asteroids. The resonant state and proper frequencies of the longitude of perihelion of these asteroids are determined, and compared to the catalogue values computed in the course of determination of their synthetic proper elements. The problem of cycle slips, affecting the computation of frequencies, is thoroughly examined and successfully explained, and the procedure of double filtering of the time series of proper values to remove the cycle slips proposed. The results of tests of the new approach have shown that the accuracy of newly determined frequencies is significantly improved with respect to the previously available values.

A Preliminary Prototype High-Speed Feedback Control of an Artificial Cochlear Sensory Epithelium Mimicking Function of Outer Hair Cells

A novel feedback control technique for the local oscillation amplitude in an artificial cochlear sensory epithelium that mimics the functions of the outer hair cells in the cochlea is successfully developed and can be implemented with a control time on the order of hundreds of milliseconds. The prototype artificial cochlear sensory epithelium was improved from that developed in our previous study to enable the instantaneous determination of the local resonance position based on the electrical output from a bimorph piezoelectric membrane. The device contains local patterned electrodes deposited with micro electro mechanical system (MEMS) technology that is used to detect the electrical output and oscillate the device by applying local electrical stimuli. The main feature of the present feedback control system is the principle that the resonance position is recognized by simultaneously measuring the local electrical outputs of all of the electrodes and comparing their magnitudes, which drastically reduces the feedback control time. In this way, it takes 0.8 s to control the local oscillation of the device, representing the speed of control with the order of one hundred times relative to that in the previous study using the mechanical automatic stage to scan the oscillation amplitude at each electrode. Furthermore, the intrinsic difficulties in the experiment such as the electrical measurement against the electromagnetic noise, adhesion of materials, and fatigue failure mechanism of the oscillation system are also shown and discussed in detail based on the many scientific aspects. The basic knowledge of the MEMS fabrication and the experimental measurement would provide useful suggestions for future research. The proposed preliminary prototype high-speed feedback control can aid in the future development of fully implantable cochlear implants with a wider dynamic range.

Contactless Excitation of Piezoelectric Device through Curvilinear shaped Electric Field Generator

Contactless excitation of piezoelectric (PZT) component through focused E-field has been investigated in this work. In the intended technique, E-field is focused to ground electrode from a curvilinear-shaped potential electrode so that maximum E-field can penetrate sufficiently through PZT component which is positioned inbetween the electrodes. Simulation analysis shows that the contactless energization of PZT component is due to electric resonance as well as piezo-electric resonance. The maximum vibration occurs across the PZT components when the E-field generator operating frequency (f0 ) matches with the mechanical resonance frequency (fm). The max output power across the contactless energized PZT component mainly rely on operating frequency, resonance, position & resistive load. The output power achieved across the contactless excited PZT component by focused E-field generator is higher than the output power achieved across the contactless excited PZT component by capacitor like E- field generator. The max output power of 9.9mW is obtained across PZT component at 1295 kHz resonance frequency (fr ) and 19.5 kΩ optimum loads with an input of 50 V and 8 mm electrode separation. By enactment of this excitation methods provide free actuation of PZT component so as to overcome the difficulties associated with the confined motion for different applications.

Impact of thermal oxidation on the structural and optical properties of porous silicon microcavity

We report the structural and optical characterization of one-dimensional porous silicon microcavities. These structures are based on a planar resonator formed by two high-reflectance mirrors separated by a thin active optical spacer. In order to simulate and predict the optical properties of the microcavity, the transfer matrix method is used. A strong correlation between the formation parameters and the reflectance spectra is introduced. The prepared microcavities are exposed to thermal oxidation. The resonance position of the microcavity exhibits a blueshift proportional to the degree of oxidation. Structural changes of the microcavities after oxidation are investigated and analyzed using X-ray diffraction and Raman spectroscopy. The observed shift of characteristic silicon peak is attributed to the reduction of silicon crystallites as the oxidation increases.

The merits of ion cyclotron resonance heating schemes for sawtooth control in tokamak plasmas

JET experiments have compared the efficacy of low- and high-field side ion cyclotron resonance heating (ICRH) as an actuator to deliberately minimise the sawtooth period. It is found that low-field side ICRH with low minority concentration is optimal for sawtooth control for two main reasons. Firstly, low-field side heating means that any toroidal phasing of the ICRH ($-90^{\circ }$, $+90^{\circ }$ or dipole) has a destabilising effect on the sawteeth, meaning that dipole phasing can be employed, since this is preferable due to less plasma wall interaction from Resonant Frequency (RF) sheaths. Secondly, the resonance position of the low-field side ICRH does not have to be very accurately placed to achieve sawtooth control, relaxing the requirement for real-time control of the RF frequency. These empirical observations have been confirmed by hybrid kinetic–magnetohydrodynamic modelling, and suggest that the ICRH antenna design for ITER is well positioned to provide a control actuator capable of having a significant effect on the sawtooth behaviour.