Multiple off-axis acoustic vortices generated by dual coaxial vortex beams

As a kind of special acoustic field, the helical wavefront of an acoustic vortex（AV） beam is demonstrated to have a pressure zero with phase singularity at the center in the transverse plane. The orbital angular momentum of AVs can be applied to the field of particle manipulation, which attracts more and more attention in acoustic researches. In this paper,by using the simplified circular array of point sources, dual coaxial AV beams are excited by the even-and odd-numbered sources with the topological charges of l_E and l_O based on the phase-coded approach, and the composite acoustic field with an on-axis center-AV and multiple off-axis sub-AVs can be generated by the superimposition of the AV beams for｜l_E｜ ≠ ｜l_O｜. The generation of edge phase dislocation is theoretically derived and numerically analyzed for l_E=-l_O. The numbers and the topological charges as well as the locations of the center-AV and sub-AVs are demonstrated, which are proved to be determined by the topological charges of the coaxial AV beams. The proposed approach breaks through the limit of only one on-axis AV with a single topological charge along the beam axis, and also provides the feasibility of off-axis particle trapping with multiple AVs in object manipulation.

Helium-hydrogen synergistic effects on swelling in in-situ multiple-ion beams irradiated steels

The development of reliable fusion energy is one of the most important challenges in this century.The accelerated degradation of structural materials in fusion reactors caused by neutron irradiation would cause severe problems.Due to the lack of suitable fusion neutron testing facilities,we have to rely on ion irradiation experiments to test candidate materials in fusion reactors.Moreover,fusion neutron irradiation effects are accompanied by the simultaneous transmutation production of helium and hydrogen.One important method to study the He-H synergistic effects in materials is multiple simultaneous ion beams(MSIB)irradiation that has been studied for decades.To date,there is no convincing conclusion on these He-H synergistic effects among these experiments.Recently,a multiple ion beam in-situ transmission electron microscopy(TEM)analysis facility was developed in Xiamen University(XIAMEN facility),which is the first triple beam system and the only in-running in-situ irradiation facility with TEM in China.In this work,we conducted the first high-temperature triple simultaneous ion beams irradiation experiment with TEM observation using the XIAMEN facility.The responses to in-situ triple-ion beams irradiation in austenitic steel 304L SS and ferritic/martensitic steel CLF-1 were studied and compared with the results in dual-and single-ion beam(s)irradiated steels.Synergistic effects were observed in MSIB irradiated steels.Helium was found to be critical for cavity formation,while hydrogen has strong synergistic effect on increasing swelling.

Efficient manipulation of terahertz waves by multi-bit coding metasurfaces and further applications of such metasurfaces

Benefiting from the unprecedented superiority of coding metasurfaces at manipulating electromagnetic waves in the microwave band,in this paper,we use the Pancharatnam-Berry(PB)phase concept to propose a high-efficiency reflectivetype coding metasurface that can arbitrarily manipulate the scattering pattern of terahertz waves and implement many novel functionalities.By optimizing the coding sequences,we demonstrate that the designed 1-,2-,and 3-bit coding metasurfaces with specific coding sequences have the strong ability to control reflected terahertz waves.The two proposed1-bit coding metasurfaces demonstrate that the reflected terahertz beam can be redirected and arbitrarily controlled.For normally incident x-and y-polarized waves,a 10 d B radar cross-section(RCS)reduction can be achieved from 2.1 THz to5.2 THz using the designed 2-bit coding metasurface.Moreover,two kinds of orbital angular momentum(OAM)vortex beams with different moduli are generated by a coding metasurface using different coding sequences.Our research provides a new degree of freedom for the sophisticated manipulation of terahertz waves,and contributes to the development of metasurfaces towards practical applications.

Multiple Fan-Beam Antenna Array for Massive MIMO Applications

In this paper,a multiple fan-beam antenna array is proposed for massive multiple-input multipleoutput(MIMO)applications.The proposed array is based on vertical spatial filtering to reduce radio frequency complexity in a massive MIMO system.A microstrip line feeding network is utilized to achieve a specific phase distribution for multiple fan beams.A 64-element antenna array is designed and fabricated to validate the design strategy.The proposed antenna array uses 16 ports to excite 64 antenna elements,which is more cost effective than traditional massive MIMO systems.The measured results demonstrate that the proposed antenna array can achieve two fan beams at 7 in the vertical dimension,and the measured gain of every port exceeds 10 dBi at 2.6 GHz.

Optical SDMA for applying compressive sensing in WSN

In order to apply compressive sensing in wireless sensor network, inside the nodes cluster classified by the spatial correlation, we propose that a cluster head adopts free space optical communication with space division multiple access, and a sensor node uses a modulating retro-reflector for communication. Thus while a random sampling matrix is used to guide the establishment of links between head cluster and sensor nodes, the random linear projection is accomplished. To establish multiple links at the same time, an optical space division multiple access antenna is designed. It works in fixed beams switching mode and consists of optic lens with a large field of view（FOV）, fiber array on the focal plane which is used to realize virtual channels segmentation, direction of arrival sensor, optical matrix switch and controller. Based on the angles of nodes＇ laser beams, by dynamically changing the route, optical matrix switch actualizes the multi-beam full duplex tracking receiving and transmission. Due to the structure of fiber array, there will be several fade zones both in the focal plane and in lens＇ FOV. In order to lower the impact of fade zones and harmonize multibeam, a fiber array adjustment is designed. By theoretical, simulated and experimental study, the antenna＇s qualitative feasibility is validated.

Multiplicity Results for a Fourth-Order Boundary Value Problem

This paper deals with multiplicity results for nonlinear elastic equations of the type wheree∈L￣2(0,1),g:[0,1]×R×R→R is a bounded contimuous function.and the pair(α,β)satisfiesand

Development of massively parallel electron beam direct write lithography using active-matrix nanocrystalline-silicon electron emitter arrays

Nanoscale lithographic technologies have been intensively studied for the development of the next generation of semiconductor manufacturing practices.While mask-less/direct-write electron beam(EB)lithography methods serve as a candidate for the upcoming 10-nm node approaches and beyond,it remains difficult to achieve an appropriate level of throughput.Several innovative features of the multiple EB system that involve the use of a thermionic source have been proposed.However,a blanking array mechanism is required for the individual control of multiple beamlets whereby each beamlet is deflected onto a blanking object or passed through an array.This paper reviews the recent developments of our application studies on the development of a high-speed massively parallel electron beam direct write(MPEBDW)lithography.The emitter array used in our study includes nanocrystalline-Si(nc-Si)ballistic electron emitters.Electrons are drifted via multiple tunnelling cascade transport and are emitted as hot electrons.The transport mechanism allows one to quickly turn electron beamlets on or off.The emitter array is a micro-electro-mechanical system(MEMS)that is hetero-integrated with a separately fabricated active-matrix-driving complementary metal-oxide semiconductor(CMOS)large-scale integration(LSI)system that controls each emitter individually.The basic function of the LSI was confirmed to receive external writing bitmap data and generate driving signals for turning beamlets on or off.Each emitted beamlet(10×10μm^(2))is converged to 10×10 nm^(2) on a target via the reduction electron optic system under development.This paper presents an overview of the system and characteristic evaluations of the nc-Si emitter array.We examine beamlets and their electron emission characteristics via a 1:1 exposure test.