131 research outputs found
The Voltage-Current Characteristic of high T_c DC SQUID: theory, simulation, experiment
The analytical theory for the voltage-current characteristics of the large
inductance (L>100 pH) high-T_c DC SQUIDs that has been developed previously is
consistently compared with the computer simulations and the experiment. The
theoretical voltage modulation for symmetric junctions is shown to be in a good
agreement with the results of known computer simulations. It is shown that the
asymmetry of the junctions results in the increase of the voltage modulation if
the critical current is in excess of some threshold value (about 8 microAmps).
Below this value the asymmetry leads to the reduction of the voltage modulation
as compared to the symmetric case. The comparison with the experiment shows
that the asymmetry can explain a large portion of experimental values of the
voltage modulation which lie above the theoretical curve for symmetric DC
SQUID. It also explains experimental points which lie below the curve at small
critical currents. However, a significant portion of these values which lie
below the curve cannot be explained by the junction asymmetry.Comment: 22 pages, 14 figure
Effect of diamagnetic contribution of water on harmonics distribution in a dilute solution of iron oxide nanoparticles measured using high-Tc SQUID magnetometer
The magnetization curve of iron oxide nanoparticles in low-concentration solutions was investigated by a highly sensitive high-Tc superconducting quantum interference device (SQUID) magnetometer. The diamagnetic contribution of water that was used as the carrier liquid was observed in the measured magnetization curves in the high magnetic field region over 100 mT. The effect of the diamagnetic contribution of water on the generation of harmonics during the application of AC and DC magnetic fields was simulated on the basis of measured magnetization curves. Although the diamagnetic effect depends on concentration, a linear relation was observed between the detected harmonics and concentration in the simulated and measured results. The simulation results suggested that improvement could be expected in harmonics generation because of the diamagnetic effect when the iron concentration was lower than 72 ÎŒg/ml. The use of second harmonics with an appropriate bias of the DC magnetic field could be utilized for realization of a fast and highly sensitive detection of magnetic nanoparticles in a low-concentration solution
Nonperiodic Flux to Voltage Conversion of an Arithmetic Series Array of dc SQUIDs
A theoretical study on the voltage response function of a series array of
dc SQUIDs is presented in which the elementary dc SQUID loops vary in size and,
possibly, in orientation. Such series arrays of two-junction SQUIDs possess
voltage response functions vs. external magnetic field B that differ
substantially from those of corresponding regular series arrays with identical
loop-areas, while maintaining a large voltage swing as well as a low noise
level. Applications include the design of current amplifiers and quantum
interference filters.Comment: 3 pages, 3 figure
High-- RF SQUIDs with Large Inductance of Quantization Loop
Experimental data on signal and noise characteristics of high-- RF
SQUIDs with large inductance of quantization loop are presented. The SQUIDs
were produced by a thick--film HTS--technique of painting on the YBaCuO
substrate. For the first time, a steady quantum interference was observed in RF
SQUID with the inductance as large as nH, that is, 60 times higher
than the fluctuation inductance at the liquid nitrogen
temperature T=77 K. A new method is offered to evaluate the sensitivity of RF
SQUID with optimum inductance of the quantization loop.Comment: 12 pages, 4 figures, 1 tabl
Liquid phase immunoassay utilizing magnetic marker and high Tc superconducting quantum interference device
We have developed a liquid phase immunoassay system utilizing a magnetic marker and a superconducting quantum interference device (SQUID). In this system, the magnetic marker was used to detect the biological material called antigen. The magnetic marker was designed so as to generate a remanence, and the remanence field of the markers that bound to the antigens was measured with the SQUID. The measurement was performed in a solution that contained both the bound and free (or unbound) markers, i.e., without using the so-called bound/free (BF) separation process. The Brownian rotation of the free markers in the solution was used to distinguish the bound markers from the free ones. Using the system, we conducted the detection of biological material called IgE without BF separation. At present, we could detect the IgE down to 7 pg (or 39 amol
Magneto-Optical Relaxation Measurements of Functionalized Nanoparticles as a Novel Biosensor
Measurements of magneto-optical relaxation signals of magnetic nanoparticles functionalized with biomolecules are a novel biosensing tool. Upon transmission of a laser beam through a nanoparticle suspension in a pulsed magnetic field, the properties of the laser beam change. This can be detected by optical methods. Biomolecular binding events leading to aggregation of nanoparticles are ascertainable by calculating the relaxation time and from this, the hydrodynamic diameters of the involved particles from the optical signal. Interaction between insulin-like growth factor 1 (IGF-1) and its antibody was utilized for demonstration of the measurement setup applicability as an immunoassay. Furthermore, a formerly developed kinetic model was utilized in order to determine kinetic parameters of the interaction. Beside utilization of the method as an immunoassay it can be applied for the characterization of diverse magnetic nanoparticles regarding their size and size distribution
Noise properties of direct current SQUIDs with quasiplanar YBa2Cu3O7 Josephson junctions
We describe the noise performance of dc SQUIDs fabricated with quasiplanar rampâtype Josephson junctions on the basis of câaxisâoriented YBa2Cu3O7/PrBa2Cu3O7 thinâfilm heterostructures. The noise spectrum of the dc SQUIDs was measured with dcâ and acâbias schemes at different temperatures and showed values below 10â5 Ί0/Hz1/2 down to frequencies of about 1 Hz at 70 K. Up to now for the magnetic fluxnoise and the energy resolution obtained at 1 kHz and 77 K the best values were 2.5Ă10â6, Ί0/Hz1/2 and 3Ă10â31 J/Hz, respectively. A study of the white and 1/fnoises of the SQUIDs was performed. The influence of magnetic flux, bias current, high static magnetic fields, and aging on the SQUID noise were investigated. The junctions and devices do not degrade due to aging in air or thermal cycling
Switching between dynamic states in intermediate-length Josephson junctions
The appearance of zero-field steps (ZFSâs) in the current-voltage characteristics of intermediate-length overlap-geometry Josephson tunnel junctions described by a perturbed sine-Gordon equation (PSGE) is associated with the growth of parametrically excited instabilities of the McCumber background curve (MCB). A linear stability analysis of a McCumber solution of the PSGE in the asymptotic linear region of the MCB and in the absence of magnetic field yields a Hillâs equation which predicts how the number, locations, and widths of the instability regions depend on the junction parameters. A numerical integration of the PSGE in terms of truncated series of time-dependent Fourier spatial modes verifies that the parametrically excited instabilities of the MCB evolve into the fluxon oscillations characteristic of the ZFSâs. An approximate analysis of the Fourier mode equations in the presence of a small magnetic field yields a field-dependent Hillâs equation which predicts that the major effect of such a field is to reduce the widths of the instability regions. Experimental measurements on Nb-NbxOy-Pb junctions of intermediate length, performed at different operating temperatures in order to vary the junction parameters and for various magnetic field values, verify the physical existence of switching from the MCB to the ZFSâs. Good qualitative, and in many cases quantitative, agreement between analytic, numerical, and experimental results is obtained
SQUIDs in biomagnetism : A roadmap towards improved healthcare
This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 686865.Peer reviewedPublisher PD
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