Pravin Patel

Synthesis of precision AC waveforms using a SINIS Josephson junction array

A synthesizer of precision AC waveforms based on a SINIS Josephson junction array has been developed. The array is divided into 15 segments in a binary series and the segments are individually biased using a high speed bias source with a 100 ns rise time. The design considerations and accuracy limitations of the system are discussed and comparisons between the synthesizer and thermal converters are presented.

Development of a 60 Hz Power Standard Using SNS Programmable Josephson Voltage Standards

We are implementing a new standard for 60 Hz power measurements based on precision sinusoidal reference voltages from two independent programmable Josephson voltage standards (PJVS): one for voltage and one for current. The National Institute of Standards and Technology PJVS systems use series arrays of Josephson junctions to produce accurate quantum-based DC voltages. Using stepwise-approximation synthesis, the PJVS systems produce sinewaves with precisely calculable RMS voltage and spectral content. We present measurements and calculations that elucidate the sources of error in the RMS voltage that are intrinsic to the digital-synthesis technique and that are due to the finite rise times and transients that occur when switching between the discrete voltages. Our goal is to reduce all error sources and uncertainty contributions from the PJVS synthesized waveforms to a few parts in 10 7 so that the overall uncertainty in the AC-power standard is a few parts in 106

Characterization of a High-Resolution Analog-to-Digital Converter with an Ac Josephson Voltage Source

An alternating current (ac) Josephson voltage source (Williams, et. al., 2002) was employed to characterize the dynamic behavior of a high-resolution 28-bit (8 frac12-digit) integrating analog-to-digital converter (ADC) of a digital sampling voltmeter (DSV), which is widely used in ac metrology at the Physikalisch-Technische Bundesanstalt - PTB. Extensive measurements were carried out to validate previous mathematical models of the DSV (Ramm, et. al., 1999) when sampling ac signals. Some measurement methods and results thereof are presented

Achieving Sub-100-ns Switching of Programmable Josephson Arrays

The accuracy of voltage waveforms, generated using programmable Josephson junction arrays, is limited by the time taken to switch between quantized levels. Relevant parameters are the time constants within the array chip, the characteristics of the cables, and the bandwidth of the bias electronics. A drive system for a 1-V SINIS array with 8192 junctions has been optimized, and a cable scheme has been devised which compensates for cable reflections. The measurements of the arrays temporal response, made with this cable system, are compared to an RC model, both with 3- and 7-ns single time constants

Power quality propagation measurements in smart grids

The importance of Power Quality (PQ) to the operation and management of electrical power networks is described. A discussion is given on the propagation of PQ phenomena. Preparations for a measurement campaign using multiple GPS synchronised digitisers and associated transducers on an island operating with high renewable penetration (Smart Grid) are described. Results from this campaign will be used to formulate models for PQ propagation that can be used to plan and manage future Smart Grids.

Development of a compact 1.54 μm acetylene standard at NPL

A compact and simplified ¹³C₂H₂ optical frequency standard is currently under development at NPL. The standard uses an inexpensive, commercially available 20 mW DFB diode laser, which is stabilized to line P(16) of the nu₁ + nu₃ band at 1542 nm in an experimental arrangement which dispenses with the need for an enhancement cavity. Preliminary stability and reproducibility data will be presented.

A novel tunable high impedance surface electromagnetic band gap metamaterials for RF and microwave applications

This paper presents a novel varactor based electronically tunable high impedance surface electromagnetic band-gap (HIS-EBG) metamaterial. The proposed structure is based on two-layer mushroom-like HIS-EBG ground plane, in which by controlling the DC bias voltage on the varactors, the effective capacitance can be adjusted which alters the resonance frequency. To assess the electromagnetic (EM) wave suppression property the structure is incorporated, as the ground plane, in a microstrip transmission line and it is experimentally characterized over the 500 MHz-10 GHz frequency band. Numerical simulations of the transmission coefficient for the whole microstrip system were performed. Both the simulation and measurement results are compared.

Cryogenic current comparator bridge with dual SQUID detectors

The cryogenic current comparator (CCC) resistance ratio bridge provides a high accuracy over a wide range of practical resistance values. Its performance is critically dependent on the choice of detector used to achieve a voltage null in the bridge. The necessary combination of low input current and voltage noise is not widely available in commercial instruments. A SQUID is a competitive device as a voltage null detector when matched to the resistors being compared. This paper describes a CCC bridge for resistors in the range 1 Ω to 10 kΩ, as well as quantized Hall resistance plateaux, employing two SQUIDS, one for current balance and one for voltage balance.

Development and evaluation of compact acetylene frequency standards

This paper describes the development and evaluation of compact and simple acetylene-stabilized diode laser frequency standards in the 1.55 μm spectral region. A variety of spectroscopic configurations have been investigated, using bulk acetylene cells and an acetylene-filled hollow core photonic crystal fiber. Frequency stability and reproducibility data, obtained by heterodyne beat frequency comparison with cavity-enhanced standards, will be presented for sources including a distributed feedback diode laser and a digital supermode distributed Bragg reflector diode laser.