Magneto-mechanical coupling coefficient k When the permalloy thin strip is excited by an alternating magnetic field under a bias magnetic field, due to the magnetostrictive effect and the piezomagnetic effect, alternate conversion between magnetic energy and mechanical energy occurs in the thin strip. The conversion is called magneto-mechanical coupling. The magneto-mechanical coupling coefficient k is used to measure its size, and the k value is determined by the following method.
The core element in the acousto-magnetic tag is a thin strip of permalloy. According to the phenomenological theory, the magneto-mechanical coupling coefficient k is expressed as: In the above formula, fr is the resonance frequency and fa is the anti-resonance frequency. In the resonance curve drawn according to the acousto-magnetic label test, when the excitation signal frequency is 57.9kHz, the resonance curve reaches the maximum value, namely fr=57.9kHz; when the excitation signal frequency is 59.7kHz, the resonance curve reaches the minimum value, namely fa =59.7kHz.
Therefore, calculate the magneto-mechanical coupling coefficient k=0.251. Obviously, the acousto-magnetic tag has resonance points and anti-resonance points. Under the action of a small excitation magnetic field, it can generate a larger resonance signal, and the voltage difference between the two points is large, indicating that the tag has a large magneto-mechanical coupling coefficient. The sharp resonance curve indicates that the tag has a higher Q value, a narrower bandwidth and stronger selectivity. Therefore, if an appropriate bias magnetic field is set to work in an area with better characteristics, a higher resonance signal and stronger frequency stability can be obtained.