Abstract
This paper presents some current or potential applications in metrology based on the diamagnetism of pyrolytic carbon (PyC). The magnetic repulsion force acting between a piece of PyC subjected to a magnetic flux can be used as magnetic spring either to control the position of the sensitive sensor element or to detect changes of a physical quantity to be measured. The first part of this paper provides examples briefly described of devices based on the diamagnetism of PyC for measuring mechanical quantities. There are two main configurations for magnetic levitation: one, used for measuring acceleration or inclination for instance, is based on the levitation of a PyC tile above a magnet or set of magnets; In the other, used to measure forces caused for example by contact or buoyancy, it is the permanent magnet that is levitated at a stable height above a fixed PyC tile. The second part describes current work at the Laboratoire Commun de Métrologie (LCM-LNE/CNAM) on the development of new laser power sensors using either diamagnetic force changes by photothermal excitation of electrons or diamagnetic torsion spring.
Highlights
An object made from a diamagnetic material is repelled by a magnetic field
The tiltmeter is a horizontal pendulum type whose mass consists of a diamagnetic pyrolytic carbon (PyC) rod suspended in the potential well of a suitably shaped magnetic field provided by a permanent magnet
The optical power is proportional to the mass change which corresponds to a magnetic repulsion force change acting on the PyC tile irradiated by a laser beam
Summary
As a consequence of Earnshaw’s theorem [1,2], this property can be used to create a local minimum in the potential energy in magnetic fields and stabilize magnetic forces Note that it took about 160 years from discovery of diamagnetism to the first practical demonstration of levitation [3]. The elements displaying the strongest diamagnetism at ambient temperature are the naturally occurring element bismuth and the man-made material pyrolytic carbon. Oriented pyrolytic graphite (HOPG) composed of a stack along the z direction of layers parallel to a x–y plane, has interesting thermal, optical and electrical properties exploited for various applications, among them metrology Both its magnetic susceptibility and thermal conductivity are anisotropic.
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