Near-field Wave Research Articles

Label-free super-resolution imaging of adenoviruses by submerged microsphere optical nanoscopy

Because of the small sizes of most viruses (typically 5–150 nm), standard optical microscopes, which have an optical diffraction limit of 200 nm, are not generally suitable for their direct observation. Electron microscopes usually require specimens to be placed under vacuum conditions, thus making them unsuitable for imaging live biological specimens in liquid environments. Indirect optical imaging of viruses has been made possible by the use of fluorescence optical microscopy that relies on the stimulated emission of light from the fluorescing specimens when they are excited with light of a specific wavelength, a process known as labeling or self-fluorescent emissions from certain organic materials. In this paper, we describe direct white-light optical imaging of 75-nm adenoviruses by submerged microsphere optical nanoscopy (SMON) without the use of fluorescent labeling or staining. The mechanism involved in the imaging is presented. Theoretical calculations of the imaging planes and the magnification factors have been verified by experimental results, with good agreement between theory and experiment. Researchers have demonstrated a super-resolution imaging technique that allows the direct observation of adenoviruses of 75 nm in size without staining or the use of fluorescent labeling. The approach, reported by Lin Li and co-workers at the University of Manchester, UK, achieves imaging well beyond the diffraction limit by employing glass microspheres submerged in water. A 100-μm-diameter BaTiO3 microsphere is placed on the object being imaged, illuminated with white light. The microsphere captures near-field evanescent waves and converts them via frustrated total internal reflection into propagating far-field waves, which can be imaged by a conventional optical microscope. The researchers also used the method to image 100-nm-spaced periodic structure of a DVD Blu-Ray disk and 50 nm nanopores in a sample of anodic aluminium oxide.

A submicron broadband surface-plasmon-polariton unidirectional coupler

The manipulation of light propagation is a basic subject in optics and has many important applications. With the development of nano-optics, this area has been downscaled to wavelength or even subwavelength scales. One of the most efficient ways to control light propagation is to exploit interference effects. Here, by manipulating the interference between two nanogrooves on a metal surface, we realize a submicron broadband surface-plasmon-polariton (SPP) unidirectional coupler. More importantly, we find an anomalous bandwidth shrinking behavior in the proposed SPP unidirectional coupler as the groove separation is down to a subwavelength scale of one-quarter of the SPP wavelength. This abnormal behavior is well explained by considering the contribution of the near-field quasi-cylindrical waves in addition to the interference of propagating SPPs and the dispersion effects of individual grooves. Such near-field effects provide new opportunities for the design of ultracompact optical devices.

Subwavelength light focusing using random nanoparticles

Focusing beyond the diffraction limit is achieved by using elastic light scattering from a highly turbid medium to convert propagating far-field components into near-field wave vectors. This finding may open new avenues for the subwavelength control of light, with applications in nanolithography and the interconnection between nanoelectronics and nanophotonics.

Research on Wave Mode Conversion of Curved Beam Structures by the Wave Approach

A general wave approach for the vibration analysis of curved beam structures is presented. The analysis is based on wave propagation, transmission, and reflection, including the effects of both propagating and decaying near-field wave components. A matrix formulation is used that offers a systematic and concise method for tackling free and forced vibrations of complex curved beam structures. To illustrate the effectiveness of the approach, several numerical examples are presented. The predictions made using the wave approach are shown to be in excellent agreement with a conventional finite element analysis, with the advantage of reduced computational costs and good conditioning number of the characteristic equation. The developed wave approach is applied to investigate the free vibration, vibration transmission, and power flow of built-up structures consisting of curved beams, straight beams, and masses, with the aim for designing vibration isolation structure with high attenuation ability. Wave reflection and transmission in the infinite curved beam structure, as well as vibration and energy transmission in coupled finite curved beam structure are investigated. Numerical results show that wave mode conversion takes place for the reflected and transmitted wave propagating through a curved beam, and the power flow in the coupled curved beam structure shows energy attenuation and conversion by curved beam and the discontinuities. The investigation will shed some light on the designing of curved beam structures.

Sound radiation from a fluid-loaded infinite plate with a patch

This paper focuses on the solution to the vibro-acoustic response of a line-driven fluid-loaded plate with an elastic patch acting as a distributed inhomogeneity. The patch affects the plate's sound radiation by adding extra loading to the driving force and by scattering structural waves. When the driving force is located beneath the patch, the extra loading reduces the plate's supersonic velocity response and sound radiation. At some frequencies, however, the constructive superposition of scattered structural waves and near-field waves by the driving force outweighs the effect of patch loading and results in an increased sound radiation power. When the patch is located away from the driving force, wave scattering phenomena dominates the plate vibration and subsequent sound radiation. By examining the effect of the length and location of the patch on the sound power, it is possible to relate the changes in the sound power to the changes in supersonic velocity spectrum and velocity distribution contributed by the trapped modes in the patched area and interference between the scattered waves by the patch and the near- and far-field structural waves directly generated by the driving force.

Shielding effectiveness of an apertured rectangular cavity against the near-field electromagnetic waves

The shielding effectiveness of an apertured rectangular cavity against the near-field waves of both electric and magnetic dipoles is investigated theoretically by using an extended equivalent circuit method. Both electric and magnetic shielding effectivenesses are calculated as functions of distance between the dipoles and the enclosure. It is shown that the near-field shielding effectiveness is lower than the far-field (plane-wave) shielding effectiveness. Also, in the near-field region, the shielding effectiveness will reduce obviously with the decrease of the source-to-enclosure distance. Based on Bethe's small aperture coupling theory, analytical formulas are presented to describe the quantitative relation between the near-field and the far-field shielding effectivenesses. It is shown that the results from equivalent circuit method are in good agreement with the relation obtained from the Bethe's theory.

基于微悬臂梁的近场动态无损检测仿真

提供了一种用于近场无损检测研究的采用微悬臂梁进行接收超声波的动态检测技术,借助COMSOL Multiphysics有限元软件模拟了微悬臂梁传感器接收由超声换能器所产生的超声波的动态响应。在进行逐点扫描时，探针针尖恰好在微缺陷上方时，振幅达到其最大值。并与试验结果进行对比，验证了该模拟方法的可行性，有助于对微器件缺陷精确的定性、定量表征作更深一步的理论研究，为后续的实验设计提供了参考，对更加微小的缺陷的检测，可通过改变微悬臂梁厚度或采用更高阶次的悬臂梁以增加谐振频率来实现。 An ultrasonic near-field dynamic non-destructive detection method based on Microcantilever is proposed to receive ultrasonic wave, and dynamic response of the near-field scattering of waves from Ultrasonic transducer using microcantilever receiver can be known with FET software COMSOL Multiphysics. The receiver scans the surface point by point and approaches the defect, when the receiver is just ahead of the defect, and the amplitude shows its maximum peak-to-peak value. The changes in the amplitude come from the near-field surface wave interaction with the free boundary of the defect wall. By contrast with experimental results, feasibility of the simulation method is demonstrated, which will contribute to deeper theoretical research on defect location of the micro-components, affording the reference for the follow- up experimental design. Higher resolution is obtained by changing the thickness of the cantilever or adopting more higher order frequency in order to test nano-defects.

Simplified Method of Isolated Structure Collapse Capacity Part, (I): Ground Motion Intensity Measure

The equivalent velocity spectrum as a new ground motion intensity measure (IM) characterization parameter is proposed in this paper. 44 far field ground motions and 20 near-field high-speed pulse seismic waves were used for single-degree-freedom (SDOF) nonlinear time history analysis, respectively. The correlations between five IMs and maximum deformation for SDOF at various periods and different yield coefficients were analyzed. The results show that for the structures with medium-to-long period, the correlation coefficient average value of the proposed equivalent speed and maximum deformation is more than 0.6, and maximum of those is more than 0.9. The correlation coefficient average value by using the proposed equivalent speed under far field ground motions is more than those under near field ground motions. The P-delta effect on the correlation coefficients between proposed IM for the structures with medium-to-short period is significant

Frequency dependence and passive drains in fish-eye lenses

The Maxwell fish eye lens has previously been reported as being capable of the much sought after phenomenon of subwavelength imaging. The inclusion of a drain in this system is considered crucial to the imaging ability, although its role is the topic of much debate. This paper provides a numerical investigation into a practical implementation of a drain in such systems, and analyzes the strong frequency dependence of both the Maxwell fish eye lens and an alternative, the Mi\~nano lens. The imaging capability of these types of lens is questioned, and it is supported by simulations involving various configurations of drain arrays. Finally, a discussion of the near-field and evanescent wave contribution is given.

Analysis on the Energy Dissipation of the Composite Isolated Structure under the Near-Field Multi Pulse Ground Motion

In this paper, the near-field multi pulse earthquake wave is generated by means of combining the velocity pulse component and the broad-band component based on studying the characteristics of the near-field ground motion.. Then, have made a numerical analysis on the composite isolated structure’s dynamic response as well as a quantitative analysis towards its energy dissipation with the help of the energy equation. Study shows, by comprehensively making good use of the energy dissipation characteristic of the laminated rubber bearing and the viscous damper, the viscous damper can perfectly find its way of taking its energy dissipation advantage, thus , to reduce the displacement of the isolation layer, and then improve the force state of the structure , accordingly decrease the damage to the upper structure. All in all, it has made a great contribution to improving the security of the structure under the near-field multi pulse earthquake.

Modeling the generation of infrasound from earthquakes

Earthquakes can generate complex seismo-acoustic wavefields, consisting of seismic waves, epicenter-coupled infrasound, and secondary infrasound. We report on the development of a numerical seismo-acoustic model for the generation of infrasound from earthquakes. We model the generation of seismic waves using a 3D finite difference algorithm that accounts for the earthquake moment tensor, source time function, depth, and local geology. The resultant acceleration-time histories (on a 2D grid at the surface) provide the initial conditions for modeling the near-field infrasonic pressure wave using the Rayleigh integral. Finally, we propagate the near-field source pressure through the Ground-to-Space atmospheric model using a time-domain parabolic equation technique. The modeling is applied to an earthquake of MW 4.6, that occurred on January 3, 2011 in Circleville, Utah; the ensuing predictions are in good agreement with observations made at the Utah network of infrasonic arrays, which are unique and indicate that the signals recorded at 6 arrays are from the epicentral region. These results suggest that measured infrasound from the Circleville earthquake is consistent with the generation of infrasound from body waves in the epicentral region.

Near-Field Tsunami Edge Waves and Complex Earthquake Rupture

The effect of distributed coseismic slip on progressive, near-field edge waves is examined for continental shelf tsunamis. Detailed observations of edge waves are difficult to separate from the other tsunami phases that are observed on tide gauge records. In this study, analytic methods are used to compute tsunami edge waves distributed over a finite number of modes and for uniformly sloping bathymetry. Coseismic displacements from static elastic theory are introduced as initial conditions in calculating the evolution of progressive edge-waves. Both simple crack representations (constant stress drop) and stochastic slip models (heterogeneous stress drop) are tested on a fault with geometry similar to that of the M w = 8.8 2010 Chile earthquake. Crack-like ruptures that are beneath or that span the shoreline result in similar longshore patterns of maximum edge-wave amplitude. Ruptures located farther offshore result in reduced edge-wave excitation, consistent with previous studies. Introduction of stress-drop heterogeneity by way of stochastic slip models results in significantly more variability in longshore edge-wave patterns compared to crack-like ruptures for the same offshore source position. In some cases, regions of high slip that are spatially distinct will yield sub-events, in terms of tsunami generation. Constructive interference of both non-trapped and trapped waves can yield significantly larger tsunamis than those that produced by simple earthquake characterizations.

Non-contacting characterization of the electrical and mechanical properties of rocks at submillimeter scales

At the meso and macro-scale, the connection between the elastic and the electromagnetic properties of granular materials such as rocks is complicated and involves, among other things, the chemical, mineralogical, and geometric features of the grains and their host medium. In the previous work, we showed how to perform rapid near-field millimeter wave scanning to obtain high-spatial resolution maps of the spatially varying dielectric permittivity of heterogeneous materials, including rocks. Here, we extend this concept to laser ultrasound and map the spatially varying mechanical properties of materials with similar resolution.

A seismoacoustic study of the 2011 January 3 Circleville earthquake

SUMMARY Wereportonauniquesetofinfrasoundobservationsfromasingleearthquake,the2011January 3Circlevilleearthquake(Mw 4.7,depthof8km),whichwasrecordedbynineinfrasoundarrays inUtah.Basedonananalysisofthesignalarrivaltimesandbackazimuthsateacharray,wefind thattheinfrasoundarrivalsatsixarrayscanbeassociatedtothesamesourceandthatthesource location is consistent with the earthquake epicentre. Results of propagation modelling indicate that the lack of associated arrivals at the remaining three arrays is due to path effects. Based on these findings we form the working hypothesis that the infrasound is generated by body waves causing the epicentral region to pump the atmosphere, akin to a baffled piston. To test this hypothesis, we have developed a numerical seismoacoustic model to simulate the generation of epicentral infrasound from earthquakes. We model the generation of seismic waves using a 3-D finite difference algorithm that accounts for the earthquake moment tensor, source time function, depth and local geology. The resultant acceleration–time histories on a 2-D grid at the surface then provide the initial conditions for modelling the near-field infrasonic pressure wave using the Rayleigh integral. Finally, we propagate the near-field source pressure through the Ground-to-Space atmospheric model using a time-domain Parabolic Equation technique. By comparing the resultant predictions with the six epicentral infrasound observations from the 2011 January 3, Circleville earthquake, we show that the observations agree well with our predictions. The predicted and observed amplitudes are within a factor of 2 (on average, the synthetic amplitudes are a factor of 1.6 larger than the observed amplitudes). In addition, arrivalsarepredictedatallsixarrayswheresignalsareobserved,andimportantlynotpredicted at the remaining three arrays. Durations are typically predicted to within a factor of 2, and in some cases much better. These results suggest that measured infrasound from the Circleville earthquake is consistent with the generation of infrasound from body waves in the epicentral region.

Spectral scaling of the aftershocks of the Tocopilla 2007 earthquake in northern Chile

We study the scaling of spectral properties of a set of 68 aftershocks of the 2007 November 14 Tocopilla (M 7.8) earthquake in northern Chile. These are all subduction events with similar reverse faulting focal mechanism that were recorded by a homogenous network of continuously recording strong motion instruments. The seismic moment and the corner frequency are obtained assuming that the aftershocks satisfy an inverse omega-square spectral decay; radiated energy is computed integrating the square velocity spectrum corrected for attenuation at high frequencies and for the finite bandwidth effect. Using a graphical approach, we test the scaling of seismic spectrum, and the scale invariance of the apparent stress drop with the earthquake size. To test whether the Tocopilla aftershocks scale with a single parameter, we introduce a non-dimensional number, , that should be constant if earthquakes are self-similar. For the Tocopilla aftershocks, Cr varies by a factor of 2. More interestingly, Cr for the aftershocks is close to 2, the value that is expected for events that are approximately modelled by a circular crack. Thus, in spite of obvious differences in waveforms, the aftershocks of the Tocopilla earthquake are self-similar. The main shock is different because its records contain large near-field waves. Finally, we investigate the scaling of energy release rate, Gc, with the slip. We estimated Gc from our previous estimates of the source parameters, assuming a simple circular crack model. We find that Gc values scale with the slip, and are in good agreement with those found by Abercrombie and Rice for the Northridge aftershocks.

Analysis on the disaster mechanism of rock collapse of M4.4 reservoir-induced earthquake on January 17, 2010, at Dongjing reservoir in Guizhou Province, China

Dongjing reservoir with storage capacity of 955 million m3 and 150 m dam height had been set up in Guizhou province, southeastern China on May in 2005. After filling with water in August 20, 2009, the reservoir-induced earthquake in 20 km took place first in September 2009 at the 440 m water level. When the water level changes, the number of earthquakes is increased rapidly. On January 17, 2010, the largest M 4.4 earthquake with depth of 7 km has happen and month frequency achieved 21 events at the highest water level. M 4.4 earthquake caused rock collapse with the disaster of killed six people and nine injure. After our investigation and study, the reason of higher epicentral intensity of earthquake was the surface effect of near-field elastic wave transmission. The disaster of rock falls certainly depended on the very very shallow earthquake, the height of valley and fault. Comparing as same magnitude of natural earthquake, very shallow earthquake increased 1–2° of epicentral intensity I0, more than twice amplitude of S-wave at 200 m height of valley and the largest displacement on fault. The superposition of three factors has increased the epicentral intensity of earthquake and directly caused rock collapse with the disaster of killed six people and nine injure.

Microsphere based microscope with optical super-resolution capability

We experimentally demonstrated that the microsphere can discern the details of the object whose sizes are below the conventional diffractive limit and such super-resolution capability can be reinforced if semi-immersing the corresponding microspheres in liquid droplet, producing a sharper contrast and a comparatively smaller magnification factor. The microsphere is considered as a channel that connects the near-field evanescent wave and the transmission one in far field. A conjecture based on this is proposed to explain the mechanism of super-resolution and the corresponding phenomenon.

Verification of evanescent coupling from subwavelength grating pairs

Near-field evanescent wave coupling of various subwavelength grating pairs, using a 1.55 μm infrared semiconductor laser has been demonstrated for use as an optical MEMS sensor. Subwavelength grating pairs were fabricated on both glass and silicon substrates. When coupled together the effective grating period is not subwavelength and can exhibit several diffraction orders. The 1.55 μm infrared source was incident on the coupled pairs and the first-order output intensity was recorded and compared with the output intensity from simulated results. This demonstrated evanescent wave coupling concept can be applied to MEMS systems with nanometer gap separations (e.g., pressure sensors, biosensors, and accelerometers) to allow for subnanometer displacement detection.

The wave and vibratory power transmission in a finite L-shaped Mindlin plate with two simply supported opposite edges

In this paper, wave and vibratory power transmission in a finite L-shaped Mindlin plate with two simply supported opposite edges are investigated using the wave approach. The dynamic responses, active and reactive power flow in the finite plate are calculated by the Mindlin plate theory (MPT) and classic plate theory (CPT). To satisfy the boundary conditions and continuous conditions at the coupled junction of the finite L-shaped plate, the near-field and far-field waves are entirely contained in the wave approach. The in-plane longitudinal and shear waves are also considered. The results indicate that the vibratory power flow based on the MPT is different from that based on the CPT not only at high frequencies but also at low and medium frequencies. The influence of the plate thickness on the vibrational power flow is investigated. From the results it is seen that the shear and rotary inertia correction of the MPT can influence the active and reactive power at the junction of the L-shaped plate not only at high frequencies but also at low and medium frequencies. Furthermore, the effects of structural damping on the active and reactive power flow at the junction are also analyzed.

Fast ultrasound beam prediction for linear and regular two-dimensional arrays

Real-time beam predictions are highly desirable for the patient-specific computations required in ultrasound therapy guidance and treatment planning. To address the longstanding issue of the computational burden associated with calculating the acoustic field in large volumes, we use graphics processing unit (GPU) computing to accelerate the computation of monochromatic pressure fields for therapeutic ultrasound arrays. In our strategy, we start with acceleration of field computations for single rectangular pistons, and then we explore fast calculations for arrays of rectangular pistons. For single-piston calculations, we employ the fast near-field method (FNM) to accurately and efficiently estimate the complex near-field wave patterns for rectangular pistons in homogeneous media. The FNM is compared with the Rayleigh-Sommerfeld method (RSM) for the number of abscissas required in the respective numerical integrations to achieve 1%, 0.1%, and 0.01% accuracy in the field calculations. Next, algorithms are described for accelerated computation of beam patterns for two different ultrasound transducer arrays: regular 1-D linear arrays and regular 2-D linear arrays. For the array types considered, the algorithm is split into two parts: 1) the computation of the field from one piston, and 2) the computation of a piston-array beam pattern based on a pre-computed field from one piston. It is shown that the process of calculating an array beam pattern is equivalent to the convolution of the single-piston field with the complex weights associated with an array of pistons. Our results show that the algorithms for computing monochromatic fields from linear and regularly spaced arrays can benefit greatly from GPU computing hardware, exceeding the performance of an expensive CPU by more than 100 times using an inexpensive GPU board. For a single rectangular piston, the FNM method facilitates volumetric computations with 0.01% accuracy at rates better than 30 ns per field point. Furthermore, we demonstrate array calculation speeds of up to 11.5 X 10(9) field-points per piston per second (0.087 ns per field point per piston) for a 512-piston linear array. Beam volumes containing 256(3) field points are calculated within 1 s for 1-D and 2-D arrays containing 512 and 20(2) pistons, respectively, thus facilitating future real-time thermal dose predictions.