8,276 research outputs found
Metamaterials for Ballistic Electrons
The paper presents a metamaterial for ballistic electrons, which consists of
a quantum barrier formed in a semiconductor with negative effective electron
mass. This barrier is the analogue of a metamaterial for electromagnetic waves
in media with negative electrical permittivity and magnetic permeability.
Besides applications similar to those of optical metamaterials, a nanosized
slab of a metamaterial for ballistic electrons, sandwiched between quantum
wells of positive effective mass materials, reveals unexpected conduction
properties, e.g. single or multiple room temperature negative differential
conductance regions at very low voltages and with considerable peak-to-valley
ratios, while the traversal time of ballistic electrons can be tuned to larger
or smaller values than in the absence of the metamaterial slab. Thus, slow and
fast electrons, analogous to slow and fast light, occur in metamaterials for
ballistic electrons
On-Site Wireless Power Generation
Conventional wireless power transfer systems consist of a microwave power
generator and a microwave power receiver separated by some distance. To realize
efficient power transfer, the system is typically brought to resonance, and the
coupled-antenna mode is optimized to reduce radiation into the surrounding
space. In this scheme, any modification of the receiver position or of its
electromagnetic properties results in the necessity of dynamically tuning the
whole system to restore the resonant matching condition. It implies poor
robustness to the receiver location and load impedance, as well as additional
energy consumption in the control network. In this study, we introduce a new
paradigm for wireless power delivery based on which the whole system, including
transmitter and receiver and the space in between, forms a unified microwave
power generator. In our proposed scenario the load itself becomes part of the
generator. Microwave oscillations are created directly at the receiver
location, eliminating the need for dynamical tuning of the system within the
range of the self-oscillation regime. The proposed concept has relevant
connections with the recent interest in parity-time symmetric systems, in which
balanced loss and gain distributions enable unusual electromagnetic responses.Comment: 10 pages, 13 figure
Full Hydrodynamic Model of Nonlinear Electromagnetic Response in Metallic Metamaterials
Applications of metallic metamaterials have generated significant interest in
recent years. Electromagnetic behavior of metamaterials in the optical range is
usually characterized by a local-linear response. In this article, we develop a
finite-difference time-domain (FDTD) solution of the hydrodynamic model that
describes a free electron gas in metals. Extending beyond the local-linear
response, the hydrodynamic model enables numerical investigation of nonlocal
and nonlinear interactions between electromagnetic waves and metallic
metamaterials. By explicitly imposing the current continuity constraint, the
proposed model is solved in a self-consistent manner. Charge, energy and
angular momentum conservation laws of high-order harmonic generation have been
demonstrated for the first time by the Maxwell-hydrodynamic FDTD model. The
model yields nonlinear optical responses for complex metallic metamaterials
irradiated by a variety of waveforms. Consequently, the multiphysics model
opens up unique opportunities for characterizing and designing nonlinear
nanodevices.Comment: 11 pages, 14 figure
Smart Table Based on Metasurface for Wireless Power Transfer
Metasurfaces have been investigated and its numerous exotic functionalities
and the potentials to arbitrarily control of the electromagnetic fields have
been extensively explored. However, only limited types of metasurface have
finally entered into real products. Here, we introduce a concept of a
metasurface-based smart table for wirelessly charging portable devices and
report its first prototype. The proposed metasurface can efficiently transform
evanescent fields into propagating waves which significantly improves the near
field coupling to charge a receiving device arbitrarily placed on its surface
wirelessly through magnetic resonance coupling. In this way, power transfer
efficiency of 80 is experimentally obtained when the receiver is placed at
any distances from the transmitter. The proposed concept enables a variety of
important applications in the fields of consumer electronics, electric
automobiles, implanted medical devices, etc. The further developed
metasurface-based smart table may serve as an ultimate 2-dimensional platform
and support charging multiple receivers.Comment: 8 pages, 7 figure
Negative index and mode coupling in all-dielectric metamaterials at terahertz frequencies
We report on the role of the coupling of the modes of Mie resonances in
all-dielectric metamaterials to ensure negative effective index at terahertz
frequencies. We study this role according to the lattice period and according
to the frequency overlapping of the modes of resonance. We show that negative
effective refractive index requires sufficiently strong mode coupling and that
for even more strong mode coupling, the first two modes of Mie resonances are
degenerated; the effective refractive index is then undeterminded. We also show
that adjusting the mode coupling leads to near-zero effective index, or even
null effective index. Further, we compare the mode coupling effect with
hybridization in metamaterials.Comment: 17pages, 10 figure
- …