140 research outputs found
Acoustic attenuation in magnetic insulator films: dynamical phase-field simulations
A magnon and a phonon are the quanta of spin wave and lattice wave,
respectively, and they can hybridize into a magnon polaron when their
frequencies and wavenumbers are equal. Guided by an analytically calculated
magnon polaron dispersion, we perform dynamical phase-field simulations to
investigate the effects of magnon polaron formation and magnetic damping on the
attenuation of a bulk acoustic wave in a magnetic insulator film. It is found
that a stronger magnon-phonon hybridization leads to a larger attenuation,
whereas the largest attenuation occurs under an intermediate magnetic damping
coefficient. The simulations also demonstrate a dynamic rotation of the
acoustic wave polarization by almost 90{\deg} and a dynamic magnetic-field
control of acoustic wave antennation, which have potential applications in
nonreciprocal acoustic devices.Comment: 5 figure
Ultra-wideband THz/IR Metamaterial Absorber based on Doped Silicon
Metamaterial-based absorbers have been extensively investigated in the
terahertz (THz) range with ever increasing performances. In this paper, we
propose an all-dielectric THz absorber based on doped silicon. The unit cell
consists of a silicon cross resonator with an internal cross-shaped air cavity.
Numerical results suggest that the proposed absorber can operate from THz to
mid-infrared, having an average power absorption of >95% between 0.6 and 10
THz. Experimental results using THz time-domain spectroscopy show a good
agreement with simulations. The underlying mechanisms for broadband absorptions
are attributed to the combined effects of multiple cavities modes formed by
silicon resonators and bulk absorption in the substrate, as confirmed by
simulated field patterns. This ultra-wideband absorption is polarization
insensitive and can operate across a wide range of the incident angle. The
proposed absorber can be readily integrated into silicon-based platforms and is
expected to be used in sensing, imaging, energy harvesting and wireless
communications systems.Comment: 6 pages, 5 figure
Achieving Covert Wireless Communications Using a Full-Duplex Receiver
Covert communications hide the transmission of a message from a watchful
adversary while ensuring a certain decoding performance at the receiver. In
this work, a wireless communication system under fading channels is considered
where covertness is achieved by using a full-duplex (FD) receiver. More
precisely, the receiver of covert information generates artificial noise with a
varying power causing uncertainty at the adversary, Willie, regarding the
statistics of the received signals. Given that Willie's optimal detector is a
threshold test on the received power, we derive a closed-form expression for
the optimal detection performance of Willie averaged over the fading channel
realizations. Furthermore, we provide guidelines for the optimal choice of
artificial noise power range, and the optimal transmission probability of
covert information to maximize the detection errors at Willie. Our analysis
shows that the transmission of artificial noise, although causes
self-interference, provides the opportunity of achieving covertness but its
transmit power levels need to be managed carefully. We also demonstrate that
the prior transmission probability of 0.5 is not always the best choice for
achieving the maximum possible covertness, when the covert transmission
probability and artificial noise power can be jointly optimized.Comment: 13 pages, 11 figures, Accepted for publication in IEEE Transactions
on Wireless Communication
Exploring regulatory fit between service relationships and appeals in co-production
Acknowledgements This work was supported by National Natural Science Foundation of China [grant numbers 72072135; 71872140; 71772141; 71632001] and āthe Fundamental Research Funds for the Central Universitiesā in UIBE [grant number 20QD16].Peer reviewedPostprin
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