52 research outputs found
Electromagnetic Nonreciprocity in a Magnetized Plasma Circulator
Nonreciprocal transport of electromagnetic waves within magnetized plasma is
a powerful building block towards understanding and exploiting the properties
of more general topological systems. Much recent attention has been paid to the
theoretical issues of wave interaction within such a medium, but there is a
lack of experimental verification that such systems can be viable in a lab or
industrial setting. This work provides an experimental proof-of-concept by
demonstrating nonreciprocity in a unit component, a microwave plasma
circulator. We design an E-plane Y junction plasma circulator operating in the
range of 4 to 6 GHz using standardized waveguide specifications. From both
simulations and experiments, we observe wide band isolation for the power
transmission through the circulator. The performance and the frequency band of
the circulator can be easily tuned by changing the plasma density and the
magnetic field strength. By linking simulations and experimental results, we
estimate the plasma density for the device.Comment: Revision 2: Added a section to introduce the scattering matrix in a
nonreciprocal microwave systems with additional references. Fixed typo on
greek letters. Swapped fig 1 and 2 for clarity. Defined the technical terms
in Section II to avoid confusion. Updated the correct value for the minimum
normalized isolated power when a positive magnetic field was applie
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Rainbow Trapping with Long Oscillation Lifetimes in Gradient Magnetoinductive Metasurfaces
We report a gradient metasurface design at microwave bands as an elegant approach to realize the goal of “rainbow trapping” for the storage of waves involving wave localization and absorption phenomena. A longitudinally placed coplanar waveguide is loaded with gradient metasurfaces on both sides, where split-ring resonators (SRRs) are the basic cell. The same SRRs are arranged along the transverse direction to establish magnetoinductive channels. Waves of different frequencies are coupled to corresponding SRRs at different positions in metasurfaces. Resonant trapping with a long oscillation life time enhances the absorption caused by inherent losses of the materials, thereby suppressing reflections. Both simulations and measurements verify the existence of “rainbow trapping.” The proposed strategy enhances the interaction between waves and matter, opening an avenue for further component designs, including absorptive filters, multiplexers, and buffers
Waveform Selectivity at the Same Frequency
Electromagnetic properties depend on the composition of materials, i.e.
either angstrom scales of molecules or, for metamaterials, subwavelength
periodic structures. Each material behaves differently in accordance with the
frequency of an incoming electromagnetic wave due to the frequency dispersion
or the resonance of the periodic structures. This indicates that if the
frequency is fixed, the material always responds in the same manner unless it
has nonlinearity. However, such nonlinearity is controlled by the magnitude of
the incoming wave or other bias. Therefore, it is difficult to distinguish
different incoming waves at the same frequency. Here we present a new concept
of circuit-based metasurfaces to selectively absorb or transmit specific types
of waveforms even at the same frequency. The metasurfaces, integrated with
schottky diodes as well as either capacitors or inductors, selectively absorb
short or long pulses, respectively. The two types of the circuit elements are
then combined to absorb or transmit specific waveforms in between. This
waveform selectivity gives us another freedom to control electromagnetic waves
in various fields including wireless communications, as our simulation reveals
that the metasurfaces are capable of varying bit error rates in response to
waveforms
Microwave Components with MEMS Switches
RF MEMS switches with metal-metal contacts are being developed for microwave applications where broadband, high linearity performance is required. These switches provide less than 0.2 dB insertion loss through 40 GHz. This paper describes the integration of these switches into selected microwave components such as reconfigurable antenna elements, tunable filters, switched delay lines, and SPDT switches. Microwave and millimeter wave measured results from these circuits are presented
On-chip unidirectional waveguiding for surface acoustic waves along a defect line in a triangular lattice
The latest advances in topological physics have yielded a rich toolset to
design highly robust wave transfer systems, for overcoming issues like beam
steering and lateral diffraction in surface acoustic waves (SAWs). However,
presently used designs for topologically protected SAWs have been largely
limited to spin or valley-polarized phases, which rely on non-zero Berry
curvature effects. Here we propose and experimentally demonstrate a highly
robust SAW waveguide on lithium niobate (LiNbO3), based on a line defect within
a true triangular phononic lattice, which instead employs an intrinsic
chirality of phase vortices and maintains a zero Berry curvature. The guided
SAW mode spans a wide bandwidth and shows confinement in the lateral direction
with 3 dB attenuation within half of the unit-cell length. SAW routing around
sharp bends has been demonstrated in such waveguide, with less than ~4%
reflection per bend. The waveguide has also been found robust for defect lines
with different configurations. The fully on-chip system permits unidirectional
SAW modes that are tightly bound to the waveguide, which provides a compact
footprint ideal for miniaturization of practical applications and offers
insight into the possibility of manipulating highly focused SAW propagation
Switchable nonlinear metasurfaces for absorbing high power surface waves
We demonstrate a concept of a nonlinear metamaterial that provides power dependent absorption of incident surface waves. The metasurface includes nonlinear circuits which transform it from a low loss to high loss state when illuminated with high power waves. The proposed surface allows low power signals to propagate but strongly absorbs high power signals. It can potentially be used on enclosures for electric devices to protest against damage. We experimentally verify that the nonlinear metasurface has two distinct states controlled by the incoming signal power. We also demonstrate that it inhibits the propagation of large signals and dramatically decreases the field that is leaked through an opening in a conductive enclosure
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