arXiv subjects

Darine Haddad

Publications and source records attributed to Darine Haddad.

8 recordsLinked to original sources

arXiv2024

Flexures for Kibble balances: Minimizing the effects of anelastic relaxation

We studied the anelastic aftereffect of a flexure being used in a Kibble balance, where the flexure is subjected to a large excursion in velocity mode after which a high-precision force comparison is performed. We investigated the effect of a constant and a sinusoidal excursion on the force comparison. We explored theoretically and experimentally a simple erasing procedure, i.e., bending the flexure in the opposite direction for a given amplitude and time. We found that the erasing procedure reduced the time-dependent force by about 30%. The investigation was performed with an analytical model and verified experimentally with our new Kibble balance at the National Institute of Standards and Technology employing flexures made from precipitation-hardened Copper Beryllium alloy C17200. Our experimental determination of the modulus defect of the flexure yields 1.2E-4. This result is about a factor of two higher than previously reported from experiments. We additionally found a static shift of the flexure's internal equilibrium after a change in the stress and strain state. These static shifts, although measurable, are small and deemed uncritical for our Kibble balance application at present. During this investigation, we discovered magic flexures that promise to have very little anelastic relaxation. In these magic flexures, the mechanism causing anelastic relaxation is compensated for by properly shaping and loading a flexure with a non-constant cross-section in the region of bending.

physics.class-ph↗

arXiv2022

Calculation of magnetic forces and torques on the Kibble coil

Analytically the forces and torques on a coil in a field of magnetic flux density can be calculated one of two ways. The line integral can be conducted along the coil's wire, summing up the differential force contribution. For each differential line segment, the force is obtained as a cross product with the magnetic flux density. Alternatively, the coil's energy in the field is the current times the flux threading the coil. Hence, the energy is obtained by executing a surface integral over the coil's open surface. Here, a dot product of the differential surface element with the magnetic flux density is executed under the integral sign. The forces and torques can then be obtained from the negative derivative of the energy with respect to the appropriate coordinate. For yoke-based Kibble balances, the latter method is much simpler since most of the flux is contained in the inner yoke of the magnet and can be written as a simple equation. Here, we use this method to provide simple equations and their results for finding the torques and forces that act on a coil in a yoke-based magnet system. We further introduce a simple method that allows the calculation of the position and orientation difference between the coil and the magnet from three measurements.

physics.ins-det↗

arXiv2022

Conception of an enhanced mechanism for a new Kibble balance directly traceable to the quantum SI

The ``Quantum Electro-Mechanical Metrology Suite'' (QEMMS) is being designed and built at the National Institute of Standards and Technology. It includes a Kibble balance, a Graphene quantum Hall resistance array and a Josephson voltage system, so that it is a new primary standard for the unit of mass, the kilogram, directly traceable to the International System of Units (SI) based on quantum constants. We are targeting a measurement range of 10 g to 200 g and optimize the design for a relative combined uncertainty of $2\times 10^{-8}$ for masses of 100 g. QEMMS will be developed as an open hardware and software design. In this article, we explain the design of the moving and weighing mechanism in the QEMMS.

physics.ins-det↗

arXiv2021

Resolution of the paradox of the diamagnetic effect on the Kibble coil

Employing very simple electro-mechanical principles known from classical physics, the Kibble balance establishes a very precise and absolute link between quantum electrical standards and macroscopic mass or force measurements. The success of the Kibble balance, in both determining fundamental constants ($h$, $N_A$, $e$) and realizing a quasi-quantum mass in the 2019 newly revised International System of Units, relies on the perfection of Maxwell's equations and the symmetry they describe between Lorentz's force and Faraday's induction, a principle and a symmetry stunningly demonstrated in the weighing and velocity modes of Kibble balances to within $1\times10^{-8}$, with nothing but imperfect wires and magnets. However, recent advances in the understanding of the current effect in Kibble balances reveal a troubling paradox. A diamagnetic effect, a force that does not cancel between mass-on and mass-off measurement, is challenging balance maker's assumptions of symmetry at levels that are almost two orders of magnitude larger than the reported uncertainties. The diamagnetic effect, if it exists, shows up in weighing mode without a readily apparent reciprocal effect in the velocity mode, begging questions about systematic errors at the very foundation of the new measurement system. The hypothetical force is caused by the coil current changing the magnetic field, producing an unaccounted force that is systematically modulated with the weighing current. Here we show that this diamagnetic force exists, but the additional force does not change the equivalence between weighing and velocity measurements. We reveal the unexpected way that symmetry is preserved and show that for typical materials and geometries the total relative effect on the measurement is $\approx 1\times10^{-9}$.

physics.ins-det↗

arXiv2019

Magnet system for the Quantum Electro-Mechanical Metrology Suite

The design of the permanent magnet system for the new Quantum Electro-Mechanical Metrology Suite (QEMMS) is described. The QEMMS, developed at the National Institute of Standards and Technology (NIST), consists of a Kibble balance, a programmable Josephson voltage standard, and a quantum Hall resistance standard. It will be used to measure masses up to $100\,\mathrm{g}$ with relative uncertainties below $2\times 10^{-8}$. The magnet system is based on the design of the NIST-4 magnet system with significant changes to adopt to a smaller Kibble balance and to overcome known practical limitations. Analytical models are provided to describe the coil-current effect and model the forces required to split the magnet in two parts to install the coil. Both models are compared to simulation results obtained with finite element analysis and measurement results. Other aspects, such as the coil design and flatness of $Bl$ profile are considered.

physics.ins-det↗

arXiv2019

The Performance of the KIBB-g1 Tabletop Kibble Balance at NIST

A tabletop-sized Kibble balance (KIBB-g1) designed to directly realize mass at the gram-level range with uncertainties on the order of parts in 10$^6$ has been developed at the National Institute of Standards and Technology (NIST). The masses of a nominally 5\,g and 1\,g weight were determined with 1-$σ$ standard uncertainties of 9.0\,$\upmu$g and 6.7\,$\upmu$g, respectively. The corresponding relative uncertainties are $1.8\times 10^{-6}$ and $6.3\times 10^{-6}$. The construction of the instrument, capabilities, and full uncertainty budgets are presented in this manuscript.

physics.ins-det↗

arXiv2014

Construction, Measurement, Shimming, and Performance of the NIST-4 Magnet System

The magnet system is one of the key elements of a watt balance. For the new watt balance currently under construction at the National Institute of Standards and Technology, a permanent magnet system was chosen. We describe the detailed construction of the magnet system, first measurements of the field profile, and shimming techniques that were used to achieve a flat field profile. The relative change of the radial magnetic flux density is less than $10^{-4}$ over a range of 5 cm. We further characterize the most important aspects of the magnet and give order of magnitude estimates for several systematic effects that originate from the magnet system.

physics.ins-det↗

arXiv2014

Determination of the Planck constant using a watt balance with a superconducting magnet system at the National Institute of Standards and Technology

For the past two years, measurements have been performed with a watt balance at the National Institute of Standards and Technology (NIST) to determine the Planck constant. A detailed analysis of these measurements and their uncertainties has led to the value $h=6.626\,069\,79(30)\times 10^{-34}\,$J$\,$s. The relative standard uncertainty is $ 45\times 10^{-9}$. This result is $141\times 10^{-9}$ fractionally higher than $h_{90}$. Here $h_{90}$ is the conventional value of the Planck constant given by $h_{90}\equiv 4 /( K_{\mathrm{J-90}}^2R_{\mathrm{K-90}})$, where $K_{\mathrm{J-90}}$ and $R_{\mathrm{K-90}}$ denote the conventional values of the Josephson and von Klitzing constants, respectively.

physics.class-ph↗