Characterization of magnetoelastic ribbons as vibration sensors based on the measured natural frequencies of a cantilever beam

Abstract

In the current work, magnetoelastic ribbons of metallic glass alloy known as Metglas 2826MB are fully characterized as vibration sensors. The characterization involves seven different sensor parameters such as the frequency response, linearity, signal to noise ratio (SNR), quality factor, stability, repeatability and sensitivity. Two experimental setups where used for the characterization process, one for the frequency response parameter (FR setup) and one for the rest of the parameters (NFR setup). The frequency response parameter was examined for two different states of the ribbon, the non-annealed and the annealed states, and better characteristics were revealed for the annealed state. In the NFR setup, a cantilever beam (CB) was used as a vibrating platform, with two annealed Metglas ribbons attached on its free end using a double-sided tape. The 2nd, 4th and 6th bending modes of the CB were used for the characterization process. Concerning linearity, the ribbons showed an extremely linear behavior, with an average value for the adjusted R-square being Ra2=0.99995. The SNR and Quality factor parameters were studied versus the DC magnetization field of the Metglas ribbons (bias field), and the results showed that the implementation of a DC magnetic field increased the strength of the detectable signal without reducing its quality. In particular, the improvement on the detectable signal for the 2nd, 4th and 6th bending modes was 151%, 41% and 27%, respectively. The ribbons stability was examined within a time period of 2 h, with the average percentage deviation from the mean frequency being as small as 0.005% and the average change of the frequency with time as small as Fa = (1.1 ± 0.4) × 10−4 Hz/min. As for the repeatability parameter, the ribbons were subjected to alternating biasing and showed an excellent behavior during repetition cycles, with the average percentage deviation from the reference state being 0.004%, 0.002% and 0.003% for the 1st, 2nd and 3rd cycle, respectively. The last parameter studied was the sensitivity of the ribbons in detecting the shift of the natural frequencies versus CB stiffness, when a crack is introduced. Each bending mode revealed a different value of sensitivity, with the 2nd mode having the lowest and the 6th mode having the highest. The average sensitivity value among the three modes was calculated to be Sa = (38 ± 1) × 10−3 Hz/(N m−1).