9,254 research outputs found
Realization of the farad from the dc quantum Hall effect with digitally-assisted impedance bridges
A new traceability chain for the derivation of the farad from dc quantum Hall
effect has been implemented at INRIM. Main components of the chain are two new
coaxial transformer bridges: a resistance ratio bridge, and a quadrature
bridge, both operating at 1541 Hz. The bridges are energized and controlled
with a polyphase direct-digital-synthesizer, which permits to achieve both main
and auxiliary equilibria in an automated way; the bridges and do not include
any variable inductive divider or variable impedance box. The relative
uncertainty in the realization of the farad, at the level of 1000 pF, is
estimated to be 64E-9. A first verification of the realization is given by a
comparison with the maintained national capacitance standard, where an
agreement between measurements within their relative combined uncertainty of
420E-9 is obtained.Comment: 15 pages, 11 figures, 3 table
Compact nonlinear model of an implantable electrode array for spinal cord stimulation (SCS)
We describe the construction of a model of the electrode-electrolyte interface and surrounding electrolyte in the case of a platinum-electrode array intended for spinal-cord stimulation (SCS) application. We show that a finite, two dimensional, resistor array provides a satisfactory model of the bulk electrolyte, and we identify the complexity required of that resistor array. The electrode-electrolyte interface is modelled in a fashion suitable for commonly-available, compact simulators using a nonlinear extension of the model of Franks et al. that incorporates diodes and a memristor. The electrode-electrolyte interface model accounts for the nonlinear current-overpotential characteristic and diffusion-limiting effects. We characterise a commercial, implantable, electrode array, fit the model to it, and show that the model successfully predicts subtle operational characteristics
Performance of a Low Noise Front-end ASIC for Si/CdTe Detectors in Compton Gamma-ray Telescope
Compton telescopes based on semiconductor technologies are being developed to
explore the gamma-ray universe in an energy band 0.1--20 MeV, which is not well
covered by the present or near-future gamma-ray telescopes. The key feature of
such Compton telescopes is the high energy resolution that is crucial for high
angular resolution and high background rejection capability. The energy
resolution around 1 keV is required to approach physical limit of the angular
resolution due to Doppler broadening. We have developed a low noise front-end
ASIC (Application-Specific Integrated Circuit), VA32TA, to realize this goal
for the readout of Double-sided Silicon Strip Detector (DSSD) and Cadmium
Telluride (CdTe) pixel detector which are essential elements of the
semiconductor Compton telescope. We report on the design and test results of
the VA32TA. We have reached an energy resolution of 1.3 keV (FWHM) for 60 keV
and 122 keV at 0 degree C with a DSSD and 1.7 keV (FWHM) with a CdTe detector.Comment: 6 pages, 7 figures, IEEE style file, to appear in IEEE Trans. Nucl.
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Static flux bias of a flux qubit using persistent current trapping
Qubits based on the magnetic flux degree of freedom require a flux bias,
whose stability and precision strongly affect the qubit performance, up to a
point of forbidding the qubit operation. Moreover, in the perspective of
multiqubit systems, it must be possible to flux-bias each qubit independently,
hence avoiding the traditional use of externally generated magnetic fields in
favour of on-chip techniques that minimize cross-couplings. The solution
discussed in this paper exploits a persistent current, trapped in a
superconducting circuit integrated on chip that can be inductively coupled with
an individual qubit. The circuit does not make use of resistive elements that
can be detrimental for the qubit coherence. The trapping procedure allows to
control and change stepwise the amount of stored current; after that, the
circuit can be completely disconnected from the external sources. We show in a
practical case how this works and how to drive the bias circuit at the required
value.Comment: 5 figures submitted to Superconductor Science and Technolog
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