Browsing by Author "Wu, Bin"

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Doping-driven topological polaritons in graphene/α-MoO3 heterostructures
(2022-09) Hu, Hai; Chen, Na; Teng, Hanchao; Yu, Renwen; Qu, Yunpeng; Sun, Jianzhe; Xue, Mengfei; Hu, Debo; Wu, Bin; Li, Chi; Chen, Jianing; Liu, Mengkun; Sun, Zhipei; Liu, Yunqi; Li, Peining; Fan, Shanhui; García de Abajo, F. Javier; Dai, Qing
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Control over charge carrier density provides an efficient way to trigger phase transitions and modulate the optoelectronic properties of materials. This approach can also be used to induce topological transitions in the optical response of photonic systems. Here we report a topological transition in the isofrequency dispersion contours of hybrid polaritons supported by a two-dimensional heterostructure consisting of graphene and α-phase molybdenum trioxide. By chemically changing the doping level of graphene, we observed that the topology of polariton isofrequency surfaces transforms from open to closed shapes as a result of doping-dependent polariton hybridization. Moreover, when the substrate was changed, the dispersion contour became dominated by flat profiles at the topological transition, thus supporting tunable diffractionless polariton propagation and providing local control over the optical contour topology. We achieved subwavelength focusing of polaritons down to 4.8% of the free-space light wavelength by using a 1.5-μm-wide silica substrate as an in-plane lens. Our findings could lead to on-chip applications in nanoimaging, optical sensing and manipulation of energy transfer at the nanoscale.
Materiaalihallinta toimitusketjun ydinyrityksessä
(2009) Wu, Bin
Helsinki University of Technology | Master's thesis
The main objective of this master's thesis is to investigate the challenge in materials management from the view of the core company. The main objective focuses on geographically spread units' effects and the challenges which they bring to the materials management. Hymat Oy is a medium-sized company which operates in the hydraulic business. The business areas of Hymat Oy include: OEM, system hydraulic and after-sale. Hymat Oy acts as a first tier supplier, or as a core company depending on the business area. In the literary analysis, the following subject of operative materials management was studied: the definition of logistics, the meaning of supply chain, demand forecasting, supply chain dynamics, and the methods of materials control. Strategic materials management was studied by investigating the supplier relationship management, the effect of the purchasing organization on material management, the classification of items using ABC-analysis, and Kraljic's purchasing portfolio and monitoring of the purchasing. In the company analysis the following subjects were studied: the current situation of Hymat Oy's materials management, the supply chain dynamics' impact on Hymat Oy's different business areas, and the current methods in forecasting and purchasing monitoring. The conclusion of my master's thesis presents recommendations and development ideas to Hymat Oy's materials management. The geographically spread units do not require any particular action on materials management, in the case of Hymat. In the future, Hymat should continue the utilization of ABC-analysis, and develop ABC-analysis reports, which fulfill the company's own requirement. Hymat should also take a more proactive role and establish a cross functional team in purchasing. With the preceding things, Hymat can get a better understanding of the supplier markets. Hymat could also use Kraljic's purchasing portfolio to establish a category strategy for the different item groups or items.
Physical Layer Authentication for Massive MIMO Systems with Hardware Impairments
(2020-03) Zhang, Pinchang; Taleb, Tarik; Jiang, Xiaohong; Wu, Bin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We study transmitter authentication in massive multiple-input multiple-output (MIMO) systems with non-ideal hardware for the fifth generation (5G) and beyond networks. A new channel-based authentication scheme is proposed by taking hardware impairments into account. Based on signal processing theory, we first formulate channel estimation under hardware impairments and determine error covariance matrix to assess the quantity caused by hardware impairments on authentication performance. With the help of hypothesis testing and matrix transformation theories, we are then able to derive exact expressions for the probabilities of false alarm and detection under different channel covariance matrix models. Extensive simulations are carried out to validate theoretical results and illustrate the efficiency of the proposed scheme. Impacts of system parameters on performance are revealed as well.
Tunable Planar Focusing Based on Hyperbolic Phonon Polaritons in alpha-MoO3
(2022-06-09) Qu, Yunpeng; Chen, Na; Teng, Hanchao; Hu, Hai; Sun, Jianzhe; Yu, Renwen; Hu, Debo; Xue, Mengfei; Li, Chi; Wu, Bin; Chen, Jianing; Sun, Zhipei; Liu, Mengkun; Liu, Yunqi; García de Abajo, F. Javier; Dai, Qing
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Manipulation of the propagation and energy-transport characteristics of sub-wavelength infrared (IR) light fields is critical for the application of nanophotonic devices in photocatalysis, biosensing, and thermal management. In this context, metamaterials are useful composite materials, although traditional metal-based structures are constrained by their weak mid-IR response, while their associated capabilities for optical propagation and focusing are limited by the size of attainable artificial optical structures and the poor performance of the available active means of control. Herein, a tunable planar focusing device operating in the mid-IR region is reported by exploiting highly oriented in-plane hyperbolic phonon polaritons in alpha-MoO3. Specifically, an unprecedented change of effective focal length of polariton waves from 0.7 to 7.4 mu m is demonstrated by the following three different means of control: the dimension of the device, the employed light frequency, and engineering of phonon-plasmon hybridization. The high confinement characteristics of phonon polaritons in alpha-MoO3 permit the focal length and focal spot size to be reduced to 1/15 and 1/33 of the incident wavelength, respectively. In particular, the anisotropic phonon polaritons supported in alpha-MoO3 are combined with tunable surface-plasmon polaritons in graphene to realize in situ and dynamical control of the focusing performance, thus paving the way for phonon-polariton-based planar nanophotonic applications.