Optical pulling force on nanoparticle clusters with gain due to Fano-like resonance

We demonstrate that,in a simple linearly-polarized plane wave,the optical pulling forces on nanoparticle clusters with gain can be induced by the Fano-like resonance.The numerical results based on the full-wave calculation show that the optical pulling forces can be attributed to the recoil forces for the nanoparticle clusters composed of dipolar nanoparticles with three different configurations.Interestingly,the recoil forces giving rise to optical pulling forces are exactly dominated by the coupling term between the electric and magnetic dipoles excited in the nanoparticle clusters,while other higherorder terms have a negligible contribution.In addition,the optical pulling force can be tailored by modulating the Fano-like resonance via either the particle size or the gain magnitude,offering an alternative freedom degree for optical manipulations of particle clusters.

Theoretical and experimental study of the pulling force of jet bits in radial drilling technology

Radial drilling technology, of which the jet bit is the key device, is a research focus in the field of oil drilling and production. This paper establishes mechanical equations for jet bits and analyzes the hydroseal of backward jets in bottom holes. Meanwhile this paper establishes a mechanical equation for a high pressure hose and analyzes the axial force distribution. Laboratory experiments indicate that the flow rate, the angle between the backward nozzle axis and the jet bit axis, and the hole diameter are the major influencing factors; the generation of the pulling force is mainly due to the inlet pressure of the jet bit; the backward jets can significantly increase not only the pulling force but also the stability of jet bits. The pulling force would reach 8,376 N under experimental conditions, which can steadily pull the high-pressure hose forward.

Pulling force of acoustic-vortex beams on centered elastic spheres based on the annular transducer model

To solve the difficulty of generating an ideal Bessel beam,an simplified annular transducer model is proposed to study the axial acoustic radiation force(ARF)and the corresponding negative ARF(pulling force)exerted on centered elastic spheres for acoustic-vortex(AV)beams of arbitrary orders.Based on the theory of acoustic scattering,the axial distributions of the velocity potential and the ARF for AV beams of different orders generated by the annular transducers with different physical sizes are simulated.It is proved that the pulling force can be generated by AV beams of arbitrary orders with multiple axial regions.The pulling force is more likely to exert on the sphere with a smaller k0a(product of the wave number and the radius)for the AV beam with a bigger topological charge due to the strengthened off-axis acoustic scattering.The pulling force decreases with the increase of the axial distance for the sphere with a bigger k0a.More pulling force areas with wider axial regions can be formed by AV beams using a bigger-sized annular transducer.The theoretical results demonstrate the feasibility of generating the pulling force along the axes of AV beams using the experimentally applicable circular array of planar transducers,and suggest application potentials for multi-position stable object manipulations in biomedical engineering.

Graphene-tuned threshold gain to achieve optical pulling force on microparticle

We investigate optical force on a graphene-coated gain microparticle by adopting the Maxwell's stress tensor method.It is found that there exists a threshold gain in obtaining the Fano-profile optical force which indicates the reversal of optical pushing and pulling force. And giant pushing/pulling force can be achieved if the gain value of the material is in the proximity of the threshold gain. Our results show that the threshold gain is more sensitive to the relaxation time than to the Fermi energy of the graphene. We further study the optical force on larger microparticle to demonstrate the pulling force occurring at octupole resonance with small gain value and then it will appear at quadrupole resonance by increasing gain value. Our work provides an in-depth insight into the interaction between light and gain material and gives the additional degree of freedom to optical manipulation of microparticle.

Dielectric or plasmonic Mie object at air–liquid interface: The transferred and the traveling momenta of photon

Considering the inhomogeneous or heterogeneous background, we have demonstrated that if the background and the half-immersed object are both non-absorbing, the transferred photon momentum to the pulled object can be considered as the one of Minkowski exactly at the interface. In contrast, the presence of loss inside matter, either in the half-immersed object or in the background, causes optical pushing of the object. Our analysis suggests that for half-immersed plasmonic or lossy dielectric, the transferred momentum of photon can mathematically be modeled as the type of Minkowski and also of Abraham. However, according to a final critical analysis, the idea of Abraham momentum transfer has been rejected. Hence,an obvious question arises: whence the Abraham momentum? It is demonstrated that though the transferred momentum to a half-immersed Mie object(lossy or lossless) can better be considered as the Minkowski momentum, Lorentz force analysis suggests that the momentum of a photon traveling through the continuous background, however, can be modeled as the type of Abraham. Finally, as an interesting sidewalk, a machine learning based system has been developed to predict the time-averaged force within a very short time avoiding time-consuming full wave simulation.

On Determining the Optimal Lifting Law of the Walking Propulsion Device Foot of an Underwater Robot from the Bottom

The problem of lifting the foot of the walking propulsion device of an underwater mobile robot is considered,taking into account the additional"compression""force acting on it.A mathematical model has been developed for the detachment of a propulsion foot from the ground,based on Henry's laws establishing the concentration of dissolved air in a liquid,the law of gas expansion at a constant temperature,Darcy's law on fluid filtration,and the theorem on the motion of the center of mass of a solid body.The linearized model allows to obtain and analytical solutions.Based on the solution of the variat ional problem,optimal modes of lifting the foot of the walking propulsion of an underwater mobile robot are established.

Photon momentum transfer in inhomogeneous dielectric mixtures and induced tractor beams

The determination of optical force as a consequence of momentum transfer is inevitably subject to the use of the proper momentum density and stress tensor.It is imperative and valuable to consider the intrinsic scheme of photon momentum transfer,particularly when a particle is embedded in a complex dielectric environment.Typically,we consider a particle submerged in an inhomogeneous background composed of different dielectric materials,excluding coherent illumination or hydrodynamic effects.A ray-tracing method is adopted to capture the direct process of momentum transfer from the complex background medium,and this approach is validated using the modified Einstein–Laub method,which uses only the interior fields of the particle in the calculation.In this way,debates regarding the calculation of the force with different stress tensors using exterior fields can be avoided.Our suggested interpretation supports only the Minkowski approach for the optical momentum transfer to the embedded scatterer while rejecting Peierls’s and Abraham’s approaches,though the momentum of a stably moving photon in a continuous background medium should be considered to be of the Abraham type.Our interpretation also provides a novel method of realizing a tractor beam for the exertion of negative force that offers an alternative to the use of negative-index materials,optical gain,or highly non-paraxial or multiple-light interference.

Photonic tractor beams:a review

Usually,an unfocused light beam,such as a paraxial Gaussian beam,can exert a force on an object along the direction of light propagation,which is known as light pressure.Recently,however,it was found that an unfocused light beam can also exert an optical pulling force(OPF)on an object toward the source direction;the beam is accordingly named an optical tractor beam.In recent years,this intriguing force has attracted much attention and a huge amount of progress has been made both in theory and experiment.We briefly review recent progress achieved on this topic.We classify the mechanisms to achieve an OPF into four different kinds according to the dominant factors.The first one is tailoring the incident beam.The second one is engineering the object’s optical parameters.The third one is designing the structured material background,in which the light–matter interaction occurs,and the fourth one is utilizing the indirect photophoretic force,which is related to the thermal effect of light absorption.For all the methods,we analyze the basic principles and review the recent achievements.Finally,we also give a brief conclusion and an outlook on the future development of this field.

CNT@leather-based electronic bidirectional pressure sensor

The ability of perceiving external pressures and conducting corresponding signals is one of the important functions of flexible electronics,which has been widely studied in electronic skin,prosthetics,robotics,healthcare,human-machine interfaces,etc.Pressure sensor should not be limited to the detection of unidirectional pressure.Here,a leather-based electronic pressure sensor and corresponding arrays with bidirectional sensing capability are demonstrated.The sensor/arrays consisting of two pieces of stacked leather both modified with acidified carbon nanotubes(a-CNTs)can achieve multi-level response to pressure over a broad working range and sense pulling force opposite to pressure.With polyurethane mixed with ferriferrous oxide(Fe3O4)powder being applied to their upper surface,the resistive sensor/individual units of arrays can also detect the magnetic field because of the contactless pulling force generated by the magnetized Fe3O4.Being able to sense pressure,pulling force and magnetic field,the leather-based electronic bidirectional pressure sensor and corresponding arrays with good performance not only exhibit potential for mass production and their broad application prospects,but also provide a new insight for the development of flexible electronics.