Designing Model and Optimization of the Permanent Magnet for Joule Balance NIM-2

TL;DR

This paper presents an analytical model for designing permanent magnet systems in watt and joule balances, aiding in the precise measurement of the Planck constant and the redefinition of the kilogram.

Contribution

It introduces a new analytical design model for permanent magnets in joule balances, guiding optimization and reducing misalignment effects.

Findings

The model effectively guides the design process.

Optimized magnet design improves measurement accuracy.

Misalignment has minimal impact on magnetic field quality.

Abstract

Permanent magnets with yokes are widely used in the watt and joule balances to measure the Planck constant for the forthcoming redefinition of the unit of mass, the kilogram. Recently, a permanent magnet system has been in consideration for a further practice of NIM-2, the generalized joule balance. In this paper, an analytical model to design the permanent magnet system is presented. The presented model can be solved to obtain the preliminary parameters and then is used as guidance for FEA software to optimize the parameters of such magnetic system. As an instance for the application of the designing model, the design of the permanent magnet system for NIM-2 is described and the special design of opening shape makes the misalignment of the top and middle yokes has little influence on the vertical component of the magnetic field.