Subwavelength asymmetric Au–VO_2 nanodisk dimer for switchable directional scattering

We propose an asymmetric Au–VOnanodisk dimer for realizing a switchable directional scattering. Specifically, the directional scattering can be triggered on/off through controlling the phase transition of the VOnanodisk from metallic to semiconductor state. More strikingly, an obvious directional scattering with the directivity of ～40 dB is achieved under the metallic state of VOnanodisk. This tunable directional scattering is further explained with an interference model where the Au and VOnanodisks are treated as two weakly interacting electric dipoles. The phase transition controlled scattering patterns of asymmetric Au–VOnanodisk dimer are then well interpreted from the phase difference between these two dipoles.

Switchable directional scattering based on spoof core-shell plasmonic structures

Manipulating directional electromagnetic scattering plays a crucial role in the realization of exotic optical phenomenon.Here,we show that the spoof plasmonic structure is able to achieve the switching of directional scattering direction on a subwavelength scale by inserting a perfect electric conductor(PEC)cylinder into the hollow of the spoof plasmonic structure.Based on the modal analysis,it is found that the electromagnetic response of the core-shell structure not only is well excited,but also exhibits the directional scattering by interference between the electric and magnetic dipolar resonances.We also discuss the influence of PEC cylinder radius on the performance of the directional scattering.Finally,the active tunable directional scattering is realized by switching between the two states.This work provides a feasible pathway to the subwavelength manipulation of electromagnetic wave.Moreover,it offers a simple method to switch the directional scattering direction.The proposed design approach can be easily applied to digital electromagnetic wave communication and associated applications.

High frequency S wave envelope synthesis using a multiple non-isotropic scattering model: application to aftershocks from the 2008 Wenchuan earthquake

Based on the formulation of a multiple non-isotropic scattering process, a characteristic source time is introduced to define the initial impulse width of energy density at the source. An analytical expression of the initial intensity spectral density of a seismic wave is incorporated into the integral equation of seismic wave energy density. And, a recursive formula of Green＇s function is derived to obtain the higher order Green＇s function, which is included to describe the stronger non-isotropic scattering process. Then, the effect of the scattering pattern on the energy density envelope is investigated by the modified scattering theory. Significant differences arc found in the decay of the energy density envelopes with distances using different scattering patterns. The envelope synthesized by the forward dominated scattering pattern is larger than the results obtained by the isotropic and backward dominated scattering pattern. Different scattering patterns are also used to fit the observation data from the aftershocks of the 2008 Wenchuan earthquake. It is concluded that the envelopes synthesized by the forward scattering pattern can match the data better than the isotropic and backward dominated scattering cases, and a new interpretation of the coda wave is given. Finally, using the forward dominated scattering pattern, the envelope broadening of the observed data is reproduced.

Superscattering-enhanced narrow band forward scattering antenna

We present a narrow band forward scattering optical antenna which is based on the excitation of distinctive whispering gallery modes（WGMs）. The antenna is composed of three coaxial cylinder layers： a dielectric layer is sandwiched between a metallic core and cladding. Owing to the destructive interference between the scattering of the outer metallic cladding and the WGM in the backward direction, the power flow in the forward direction is increased. Simulation and analysis show that in proper geometry conditions, the cavity can be tuned into a superscattering state. At this state, both the zeroth and the first order of WGM are excited and contribute to the total scattering. It is shown that the power ratio（power towards backward divided by power towards forward） can be enhanced to about 27 times larger than that for a non-resonant position by the superscattering. Owing to the confinement of the cladding to WGMs, the wavelength range of effective forward scattering is considerably narrow（about 15 nm）.

Experimental researches on underwater target scattering properties in non-incident direction

In the bistatic case, theoretical analysis and experimental researches on underwater acoustic scattering properties of some submarine model are made in this paper. When sourcet target and receiver have complicated triangular configuration, the relationships among target strength, incidence angle and bistatic angle are obtained. The validity of this theory is verified by theoretical calculations and tank experiments. The research results can be directly used in bistatic or multistatic underwater acoustic detection systems.

Broadband transverse displacement sensing of silicon hollow nanodisk under focused radial polarization illumination in the near-infrared region

Broadband transverse displacement sensing by exploiting the interaction of a focused radially polarized beam with a silicon hollow nanodisk is proposed.The multipolar decomposition analysis indicates that the interference between a longitudinal total electric dipole(TED)moment and a lateral magnetic dipole(MD)moment is dominant in the far-field transverse scattering in the near-infrared region.Within a broadband wavelength range with the width of 155 nm,the longitudinal TED is almost in phase with the lateral MD,and then broadband position sensing based on the sensitivity of scattering directivity to transverse displacement can be achieved.

Application of the direct blast adaptive suppression method to the forward scattered broadband signals

The basic principles of target detection by forward acoustic scattering are presented.A direct blast suppression approach based on adaptive filtering(DBS-AF) is proposed to suppress the direct blast.The DBS-AF technique is extended to the linear frequency modulation(LFM) signal,where the envelope of the signal is regarded as a 'general waveform' and imported into the adaptive filter.Application of the DBS-AF method to the data collected from a lake trial yields an output detection curve,in which the direct blast is mapped to the background while the acoustic field aberration is represented by the peak value fluctuation.The inhibitory effect in single hydrophone is approximately- 5 dB,and is then enhanced by exploiting the mean value removal approach as a preprocessing technique.The direct blast is further suppressed to a level of-10 dB by making full use of multichannel receptions.The main factors affecting the algorithm performance are as follows:the fluctuation degree of the receptions during the weighting vector training period and the power ratio of the forward scattered wave to the direct blast when the target is present.

APPLICATION OF THE FACTORIZATION METHOD TO RECOVER CUTS WITH OBLIQUE DERIVATIVE BOUNDARY CONDITION

Direct and inverse problems for the scattering of cracks with mixed oblique derivative boundary conditions from the incident plane wave are considered,which describe the scattering phenomenons such as the scattering of tidal waves by spits or reefs.The solvability of the direct scattering problem is proven by using the boundary integral equation method.In order to show the equivalent boundary integral system is Fredholm of index zero,some relationships concerning the tangential potential operator is used.Due to the mixed oblique derivative boundary conditions,we cannot employ the factorization method in a usual manner to reconstruct the cracks.An alternative technique is used in the theoretical analysis such that the far field operator can be factorized in an appropriate form and fulfills the range identity theorem.Finally,we present some numerical examples to demonstrate the feasibility and effectiveness of the factorization method.

Harmonic generation at air–soil interface by femtosecond laser filament

We observe the third-harmonic generation and second-harmonic generation together with element fluorescence from the interaction of a femtosecond laser filament with a rough surface sample（sandy soil） in non-phasematched directions. The harmonics prove to originate from the phase-matched surface harmonics and air filament, then scatter in non-phase-matched directions due to the rough surface. These harmonics occurr when the sample is in the region before and after the laser filament, where the laser intensity is not high enough to excite the element fluorescence. The observed harmonics are related to the element spectroscopy, which will benefit the understanding of the interaction of the laser filament with a solid and be helpful for the application on filament induced breakdown spectroscopy.