44 research outputs found
Multi-parameter sensing using thickness shear mode (TSM) resonators – a feasibility analysis
Multi-parameter sensing is examined for thickness shear mode (TSM)
resonators that are in mechanical contact with thin films and half-spaces on
both sides. An expression for the frequency-dependent electrical admittance
of such a system is derived which delivers insight into the set of material
and geometry parameters accessible by measurement. Further analysis
addresses to the problem of accuracy of extracted parameters at a given
uncertainty of experiment. Crucial quantities are the sensitivities of
measurement quantities with respect to the searched parameters determined as
the first derivatives by using tentative material and geometry parameters.
These sensitivities form a Jacobian matrix which is used for the exemplary
study of a system consisting of a TSM resonator of AT-cut quartz coated by a
copper layer and a glycerol half-space on top. Resonant and anti-resonant
frequencies and bandwidths up to the 16th overtone are evaluated in
order to extract the full set of six material–geometry
parameters of this system as accurately as possible. One further outcome is that the number of
employed measurement values can be extremely reduced when making use of the
knowledge of the Jacobian matrix calculated before.</p
Complex loading and simulation of acoustic thickness shear mode resonator
During the last decades thickness shear mode resonators (TSM, QCM) have been object of comprehensive research. Many approaches were made to describe the behavior and physical effects when loaded. We present a physical model that describes the TSM in the full frequency range, including overtones for a large variety of loadings (e.g. gases, liquids or solid materials). By using an automated curve fit algorithm, absolute values for the loaded material (e.g. thickness, viscosity) can be extracted. The model has been validated with a large number of experiments including liquids with complex viscosities, biomolecule interactions, electrochemisty or vacuum deposition techniques. Additionally, the appearance of layer resonances have been predicted and verified. Layer resonances are remarkable because they appear at even-numbered overtones, which have been considered to be impossible
Magnetic-field-induced supercurrent enhancement in hybrid superconductor/magnetic metal structures
The dc transport properties of the (S/M)I(M/S) tunnel structure - proximity
coupled superconductor (S) and magnetic (M) layers separated by an insulator
(I) - in a parallel magnetic field have been investigated. We choose for the M
metal the one in which the effective magnetic interaction, whether it arises
from direct exchange interaction or due to configuration mixing, aligns spins
of the conducting electrons antiparallel to the localized spins of magnetic
ions. For tunnel structures under consideration, we predict that there are the
conditions when the destructive action of the internal and applied magnetic
fields on Cooper pairs is weakened and the increase of the applied magnetic
field causes the field-induced enhancement of the tunnel critical current. The
experimental realization of the novel interesting effect of the interplay
between superconducting and magnetic orders is also discussed.Comment: 6 pages 2 figure
Recommended from our members
The complexity of surface acoustic wave fields used for microfluidic applications
Using surface acoustic waves (SAW) for the agitation and manipulation of fluids and immersed particles or cells in lab-on-a-chip systems has been state of the art for several years. Basic tasks comprise fluid mixing, atomization of liquids as well as sorting and separation (or trapping) of particles and cells, e.g. in so-called acoustic tweezers. Even though the fundamental principles governing SAW excitation and propagation on anisotropic, piezoelectric substrates are well-investigated, the complexity of wave field effects including SAW diffraction, refraction and interference cannot be comprehensively simulated at this point of time with sufficient accuracy. However, the design of microfluidic actuators relies on a profound knowledge of SAW propagation, including superposition of multiple SAWs, to achieve the predestined functionality of the devices. Here, we present extensive experimental results of high-resolution analysis of the lateral distribution of the complex displacement amplitude, i.e. the wave field, alongside with the electrical S-parameters of the generating transducers. These measurements were carried out and are compared in setups utilizing travelling SAW (tSAW) excited by single interdigital transducer (IDT), standing SAW generated between two IDTs (1DsSAW, 1D acoustic tweezers) and between two pairs of IDTs (2DsSAW, 2D acoustic tweezers) with different angular alignment in respect to pure Rayleigh mode propagation directions and other practically relevant orientations. For these basic configurations, typically used to drive SAW-based microfluidics, the influence of common SAW phenomena including beam steering, coupling coefficient dispersion and diffraction on the resultant wave field is investigated. The results show how tailoring of the acoustic conditions, based on profound knowledge of the physical effects, can be achieved to finally realize a desired behavior of a SAW-based microacoustic-fluidic system. © 2020 Elsevier B.V
Measurements of critical current diffraction patterns in annular Josephson junctions
We report systematic measurements of the critical current versus magnetic
field patterns of annular Josephson junctions in a wide magnetic field range. A
modulation of the envelope of the pattern, which depends on the junction width,
is observed. The data are compared with theory and good agreement is found.Comment: 4 pages, 5 figure
Josephson Coupling and Fiske Dynamics in Ferromagnetic Tunnel Junctions
We report on the fabrication of Nb/AlO_x/Pd_{0.82}Ni_{0.18}/Nb
superconductor/insulator/ferromagnetic metal/superconductor (SIFS) Josephson
junctions with high critical current densities, large normal resistance times
area products, high quality factors, and very good spatial uniformity. For
these junctions a transition from 0- to \pi-coupling is observed for a
thickness d_F ~ 6 nm of the ferromagnetic Pd_{0.82}Ni_{0.18} interlayer. The
magnetic field dependence of the \pi-coupled junctions demonstrates good
spatial homogeneity of the tunneling barrier and ferromagnetic interlayer.
Magnetic characterization shows that the Pd_{0.82}Ni_{0.18} has an out-of-plane
anisotropy and large saturation magnetization, indicating negligible dead
layers at the interfaces. A careful analysis of Fiske modes provides
information on the junction quality factor and the relevant damping mechanisms
up to about 400 GHz. Whereas losses due to quasiparticle tunneling dominate at
low frequencies, the damping is dominated by the finite surface resistance of
the junction electrodes at high frequencies. High quality factors of up to 30
around 200 GHz have been achieved. Our analysis shows that the fabricated
junctions are promising for applications in superconducting quantum circuits or
quantum tunneling experiments.Comment: 15 pages, 9 figure
Proximity and Josephson effects in superconductor - antiferromagnetic Nb / \gamma-Fe50Mn50 heterostructures
We study the proximity effect in superconductor (S), antiferromagnetic (AF)
bilayers, and report the fabrication and measurement of the first trilayer
S/AF/S Josephson junctions. The disordered f.c.c. alloy \gamma-Fe50Mn50 was
used as the AF, and the S is Nb. Micron and sub-micron scale junctions were
measured, and the scaling of gives a coherence length in the AF of
2.4 nm, which correlates with the coherence length due to suppression of
in the bilayer samples. The diffusion constant for FeMn was found to be 1.7
\times 10 m s, and the density of states at the Fermi level was
also obtained. An exchange biased FeMn/Co bilayer confirms the AF nature of the
FeMn in this thickness regime.Comment: 6 pages, 5 figures, accepted for Phys. Rev.
Temperature dependence of giant magnetoresistance and magnetic properties in electrodeposited Co-Cu/Cu multilayers: The role of superparamagnetic regions
We have shown recently that both the magnetization and the magnetoresistance of electrodeposited Co-Cu/Cu multilayers can be decomposed by assuming the presence of both ferromagnetic (FM) and superparamagnetic (SPM) regions in the magnetic layers. In the present work, for two selected samples, one with a large SPM and another one with a large FM contribution to the giant magnetoresistance, low temperature magnetic and magnetoresistance measurements were performed in order to reveal the evolution of the FM and SPM terms with temperature. The average apparent magnetic moment of the SPM regions deduced from the two sets of data showed a good agreement. The role of electrochemical processes in the formation of the SPM regions is discussed. An attempt has also been made to elaborate on some models for the spatial distribution of the constituent elements (Co and Cu) leading to the occurrence of SPM regions. The results are discussed also in the framework of interacting SPM regions