Strain sensitivity of highly magnetostrictive amorphous films for use in microstrain sensors

Strain sensitivity of amorphous ${\mathrm{(Fe}}_{\mathrm{90}}{\mathrm{Co}}_{\mathrm{10}}{\mathrm{)}}_{\mathrm{78}}{\mathrm{Si}}_{\mathrm{12}}{\mathrm{B}}_{\mathrm{10}}$ sputtered film was studied in detail, so as to examine the potential of film for highly sensitive microstrain gauges. The film exhibited the figure of merit $\mathrm{F=(\Delta \mu /\mu )/\epsilon }$ (change in film permeability μ per unit strain ε) of ${\text{1.2×10}}^5,$ the value of which is comparable to that of amorphous ribbons. Reflecting the large value of F, the high-frequency impedance of the film was also subjected to change due to strain: the change in impedance of 46% was observed at 100 MHz applying a strain of ${\text{300×10}}^{\text{−6}}.$ It is also demonstrated that utilizing the strain-dependent impedance, a small strain of ${\text{0.2×10}}^{\text{−6}}$ can be detected with the film.