Nondestructive Thermal Wave Detection of Internal Micro-defects using Scanning Electron-induced Acoustic Microscope

The nondestructive instrument as the application of coupling phenomenon between the thermal wave by non-Fourier heat conduction and the thermal stress wave by elastic vibration has been proposed for more than twenty years. This technique is called scanning electron-induced acoustic microscope (SEAM). Our own-built SEAM has, so far, successfully provided some nondestructive observations of micro-defects such as the micro-voids of sintered materials, martensitic phase transformation, grain boundary without any chemical etching, and so on. Some defects of them were indeed confirmed by digging using focused-ion beam (FIB) fabrication to make certain of those beings. In order to fully understand this coupling phenomenon, this paper gives the simple one-dimensional computational model of the multi-physics to explore the detailed transportation mechanism. The cyclic chopping of electron beam with extremely high frequency yields the thermal wave according to non-Fourier heat conduction, which respects the thermal relaxation different from the ordinal diffusive heat transmission. The wavelength of the thermal wave, which may determine the essential SEAM resolution, decreases as increasing the thermal relaxation time of material and also the modulation frequency. The numerical summaries are qualitatively in agreement with some nondestructive observations with changing the blanking frequency.