LOW PERMEABILITY REFERENCE-STANDARDS WITH IMPROVED HIGH MAGNETIC-FIELD STRENGTH PERFORMANCE

Commercial instruments for determining the relative magnetic permeabil ity of weakly magnetic materials require calibration. This is achieved using reference standards of known permeability. These materials suff er to some extent from the fact that their relative magnetic permeabil ity varies with the applied magnetic field strength. When used to cali brate instruments, this can introduce significant errors. The authors report on the development of a material which improves this situation. By uniformly dispersing iron particles in an acrylic matrix their sel f demagnetising properties are substantially retained and, consequentl y, the permeability changes due to applied field are significantly sma ller than for conventional materials. Furthermore, because the amount of iron added can be varied, the permeability can be tailored to the r equired value. This allows commercial instruments to be calibrated at various points of their ranges or at a particular value of interest. U sing this technique it was possible to make reference materials with p ermeabilities in the range 1.005 to 1.100.