A Gold Bar Purity Testing Method Based on Vibration Characteristics

Abstract

Vibration characteristic of a structure is unique due to mainly its material and geometrical properties. Hence, a variation imposed on either one or both the parameters can cause a different vibration response. This fact can be used to develop an alternative approach in testing the purity of gold particularly when the gold bar (Au) is no longer isotropic material due to the presence of other metals. A fake gold bar is commonly made by filling inside of the bar with other material for example Tungsten or Wolfram (W) which has density nearly the same as gold but its price is cheaper. This can not be identified easily without performing a testing as it has the same appearance as the pure gold bar. The purpose of this research is to develop gold bar purity testing method by observing natural frequencies and Frequency Response Function (FRF) of vibration response. For early development, the vibration response of gold bar and fake one are investigated. For this, numerical calculations are used rather than measurements. The results show that the natural frequencies and frequency response function (FRF) are useful information to detect whether a metal bar is pure gold bar or containing other metals. Higher natural frequency orders are required when the volume of tungsten in the bar reduces as the gap of lower order natural frequencies of pure gold bar and the fake become small. Moreover, the excitation point at corner and central of area of gold bar are suggested to be chosen during purity testing