The Nonlinear ME Effect of FeNiMoSiB/PZT-5A Composite Under Step Magnetic Field Excitation for Magnetic Field Sensing

Under a high-amplitude ac excitation field, the magnetostrictive/piezoelectric composite exhibits the nonlinear magnetoelectric (ME) effect. A weak dc/ac magnetic field can be measured by demodulating the odd harmonics generated by the composite structure due to the nonlinear ME effect. The ac excitation magnetic field created by an external signal source will introduce crosstalk noise. Here, a novel method for measuring the weak magnetic field via FeNiMoSiB/PZT-5A/FeNiMoSiB composite excited by step magnetic field is presented. The ME composite excited by the step magnetic field will vibrate at its natural frequency to significantly enhance the ME effect. In addition, the resonance frequency of the ME composite is not affected by the excitation signal, which reduces the noise introduced by the external excitation source. Due to the nonlinear ME effect, the induced ME voltage is modulated by a weak dc/ac magnetic field to be measured. The weak magnetic field signal can be recovered from the ME voltage by the lock-in demodulation method. The ME unit for sensing the magnetic field is designed based on the longitudinal free vibration model excited by a step magnetic field. In the experiment, the step magnetic fields generated by a 2-kHz bipolar square-wave signal are used to excite the ME composite. The sensitivity of 29.77 mV/Oe and linearity error of 0.22% are achieved in the dc magnetic field of −3 to 3 Oe. The sensitivity to 1–50-kHz ac magnetic field to be measured in the flat area is about 37.5 mV/Oe.