87 research outputs found
Channel Estimation for Diffusive MIMO Molecular Communications
In diffusion-based communication, as for molecular systems, the achievable
data rate is very low due to the slow nature of diffusion and the existence of
severe inter-symbol interference (ISI). Multiple-input multiple-output (MIMO)
technique can be used to improve the data rate. Knowledge of channel impulse
response (CIR) is essential for equalization and detection in MIMO systems.
This paper presents a training-based CIR estimation for diffusive MIMO (D-MIMO)
channels. Maximum likelihood and least-squares estimators are derived, and the
training sequences are designed to minimize the corresponding Cram\'er-Rao
bound. Sub-optimal estimators are compared to Cram\'er-Rao bound to validate
their performance.Comment: 5 pages, 5 figures, EuCNC 201
Diffusive MIMO Molecular Communications: Channel Estimation, Equalization and Detection
In diffusion-based communication, as for molecular systems, the achievable
data rate is low due to the stochastic nature of diffusion which exhibits a
severe inter-symbol-interference (ISI). Multiple-Input Multiple-Output (MIMO)
multiplexing improves the data rate at the expense of an inter-link
interference (ILI). This paper investigates training-based channel estimation
schemes for diffusive MIMO (D-MIMO) systems and corresponding equalization
methods. Maximum likelihood and least-squares estimators of mean channel are
derived, and the training sequence is designed to minimize the mean square
error (MSE). Numerical validations in terms of MSE are compared with Cramer-Rao
bound derived herein. Equalization is based on decision feedback equalizer
(DFE) structure as this is effective in mitigating diffusive ISI/ILI.
Zero-forcing, minimum MSE and least-squares criteria have been paired to DFE,
and their performances are evaluated in terms of bit error probability. Since
D-MIMO systems are severely affected by the ILI because of short transmitters
inter-distance, D-MIMO time interleaving is exploited as countermeasure to
mitigate the ILI with remarkable performance improvements. The feasibility of a
block-type communication including training and data equalization is explored
for D-MIMO, and system-level performances are numerically derived.Comment: Accepted paper at IEEE transaction on Communicatio
Analysis of cross-ply laminates with piezoelectric fiber-reinforced composite actuators using four-variable refined plate theory
This study presents an analytical solution for cross-ply composite laminates integrated with a piezoelectric fiber-reinforced composite (PFRC) actuator subjected to electromechanical loading using the four-variable refined plate theory. This theory predicts parabolic variation of transverse shear stresses and satisfies the zero traction on the plate surfaces without using the shear correction factor. Using the principle of minimum potential energy, the governing equations for simply supported rectangular plates are extracted and the Navier method is adopted for solution of the equations. The comparison of obtained results with other common plate theories and the exact solution indicates that besides the simplicity of the presented formulation, it is very accurate in analysis of laminated composite plates integrated with PFRC. Also the effects of the thickness ratio, aspect ratio, number of layers, staking sequence and amount of electrostatic loading on the displacements and stresses are investigated and the obtained findings are reported
Experimental study on the energy absorption capability of circular corrugated tubes under lateral loading and axial loading
A new type of energy absorber called an expansion joint (i.e. a corrugated tube) is examined in this research. Several experiments are performed on three types of thin-walled specimen, namely circular tubes, preformed corrugated tubes and complete corrugated tubes, to investigate the energy absorption of steel specimens under different conditions for quasi-static lateral loading and axial loading. For this purpose, some steel specimens were compressed between two rigid platens in the axial direction, and the other specimens were laterally compressed. The preformed corrugated tubes and the complete corrugated tubes were produced by the hydroforming method. In each geometrical group of specimens, several tubes, which have different wall thicknesses, different inner diameters and different lengths and which are either empty or filled with polyurethane foam, were tested. Experiments show that, for a lateral load, the specific absorbed energies of the complete corrugated tubes are higher than those of the corresponding preformed corrugated tubes and circular tubes with the same characteristics. Tests show that, under lateral loading, a complete corrugated tube with a thicker wall and a smaller diameter is the optimum energy absorber system. Therefore, when a circular tube transforms into the corrugated tube, a better energy absorber system with a higher capability is achieved under lateral loading. Also, experiments show that, under axial loading, simple circular tubes with no forming process have higher specific absorbed energies than corrugated tubes do. Corrugated specimens have more controllable plastic deformation and a more regular deformation mode than simple tubes have. Tests under axial loading illustrate that, when the preformed corrugated tubes are filled with polyurethane foam, the specific absorbed energy increases by up to 74%. A comparison of the results on empty and filled specimens shows that, in some cases, the specific absorbed energies of corrugated tubes under lateral loading are higher than the specific absorbed energies of circular tubes under axial loading. This means that, by shaping the circular tubes into preformed corrugated tubes and complete corrugated tubes via the hydroforming process, a new thin-walled structure with a high specific absorbed energy during the lateral compression process is introduced
Shaping THz emission spectra by using sub-wavelength nanopatterned spintronic THz emitters
We show in theory and experiment that in periodically patterned spintronic
THz emitters (STE), charge dynamics can modify the emission spectrum in a
well-controlled way. Characterization of sub-wavelength patterned STE at
frequencies up to 30 THz shows that the STE's emission spectrum systematically
changes with emitter size. The spectral intensity exhibits significant
reductions at frequencies below 4 THz, accompanied by pronounced dips at around
15 THz and 24 THz. While reducing the STE size enhances the modulation of all
features, it does not alter the dip frequencies. The effect originates from the
charging of the structure's edges by THz currents, causing a backflow that
interferes with the primary current pulse. An analytical model quantitatively
reproduces these results and agrees well with control experiments. Our findings
enable a detailed investigation of the charge dynamics in STE and provide
additional means for controlled shaping of STE emission spectra by nano
patterning.Comment: 7 pages, 4 figure
Antenna-coupled spintronic terahertz emitters driven by a 1550 nm femtosecond laser oscillator
We demonstrate antenna-coupled spintronic terahertz (THz) emitters excited by 1550 nm, 90 fs laser pulses. Antennas are employed to optimize THz outcoupling and frequency coverage of ferromagnetic/nonmagnetic metallic spintronic structures. We directly compare the antenna-coupled devices to those without antennas. Using a 200 μm H-dipole antenna and an ErAs:InGaAs photoconductive receiver, we obtain a 2.42-fold larger THz peak-peak signal, a bandwidth of 4.5 THz, and an increase in the peak dynamic range (DNR) from 53 dB to 65 dB. A 25 μm slotline antenna offered 5 dB larger peak DNR and a bandwidth of 5 THz. For all measurements, we use a comparatively low laser power of 45 mW from a commercial fiber-coupled system that is frequently employed in table-top THz time-domain systems.
This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through Project Nos. 290319996/TRR173, 318612841, and 278381540/PR1413/3-1 (REPHCON) and project B02 of the SFB/TRR227 Ultrafast Spin Dynamics. We further acknowledge CST for the EM Simulation solver
Free vibration analysis of FG plate with piezoelectric layers on elastic foundation using refined shear deformation theory
This study presents an analytical solution for free vibration analysis of functionally graded (FG) core integrated with piezoelectric layers and resting on elastic foundation. The four-variable refined plate theory is utilized which predicts parabolic variation of transverse shear stresses across the plate thickness, satisfies the zero traction on the plate surfaces and does not need the shear correction factor. Using both Hamilton's principle and Maxwell equation, the Equations of motions for simply supported rectangular plates resting on elastic foundation are obtained and the Navier method is adopted for solution of equations. Natural frequencies for different examples are obtained and they are compared with other common plate theories. It can be concluded that besides the simplicity of the presented formulation, this theory which does not need for shear correction factor, is very accurate in analysis of plates integrated with piezoelectric layers resting on elastic foundation and is comparable to other theories (the first order shear deformation theory (FSDT) and third order shear deformation theory). Also effects of power law index, thickness ratio and foundation parameter, on the natural frequency of plates have been investigated
Time-domain observation of ballistic orbital-angular-momentum currents with giant relaxation length in tungsten
The emerging field of orbitronics exploits the electron orbital momentum
. Compared to spin-polarized electrons, may allow
magnetic-information transfera with significantly higher density over longer
distances in more materials. However, direct experimental observation of
currents, their extended propagation lengths and their conversion
into charge currents has remained challenging. Here, we optically trigger
ultrafast angular-momentum transport in Ni|W|SiO thin-film stacks. The
resulting terahertz charge-current bursts exhibit a marked delay and width that
grow linearly with W thickness. We consistently ascribe these observations to a
ballistic current from Ni through W with giant decay length (~80
nm) and low velocity (~0.1 nm/fs). At the W/SiO interface, the
flow is efficiently converted into a charge current by the inverse orbital
Rashba-Edelstein effect, consistent with ab-initio calculations. Our findings
establish orbitronic materials with long-distance ballistic
transport as possible candidates for future ultrafast devices and an approach
to discriminate Hall- and Rashba-Edelstein-like conversion processes
Time-domain observation of ballistic orbital-angular-momentum currents with giant relaxation length in tungsten
The emerging field of orbitronics exploits the electron orbital momentum L. Compared to spin-polarized electrons, L may allow the transfer of magnetic information with considerably higher density over longer distances in more materials. However, direct experimental observation of L currents, their extended propagation lengths and their conversion into charge currents has remained challenging. Here, we optically trigger ultrafast angular-momentum transport in Ni|W|SiO2 thin-film stacks. The resulting terahertz charge-current bursts exhibit a marked delay and width that grow linearly with the W thickness. We consistently ascribe these observations to a ballistic L current from Ni through W with a giant decay length (~80 nm) and low velocity (~0.1 nm fs−1). At the W/SiO2 interface, the L flow is efficiently converted into a charge current by the inverse orbital Rashba–Edelstein effect, consistent with ab initio calculations. Our findings establish orbitronic materials with long-distance ballistic L transport as possible candidates for future ultrafast devices and an approach to discriminate Hall-like and Rashba–Edelstein-like conversion processes
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