Research On Rotating Modulated DC Magnetoelectric Sensor

Magnetoelectric sensors based on piezoelectric materials and magnetostrictive materials have the advantages of high sensitivity,high resolution,wide frequency range,etc.,but due to static leakage and drift of piezoelectric materials under static/quasi-static deformation,Magnetoelectric sensors are difficult to directly measure DC or ultra-low frequency magnetic fields.To this end,the magnetic field modulation and electric field modulation have been proposed internationally.These two methods can significantly improve the sensitivity,but require a large excitation current or excitation voltage.Therefore,this paper designs a rotary modulation method,which can measure DC magnetic field by the rotary drive of the motor under low-voltage power supply.It has broad application prospects in the fields of magnetic exploration,geomagnetic navigation and magnetic forensic diagnosis.Firstly,the principle of frequency modulation of magnetoelectric composites is theoretically analyzed.The rotational modulation method of long strip magnetoelectric sensor is designed.Mathematical model is established for this method,and the component of magnetic field on the sensitive axis of magnetoelectric composite during rotation process is analyzed,which is consistent with whose relationship of the magnetic field with rotational angle in the finite element simulation results.It proves that this method is feasible.Subsequently,a method of adaptive vibration noise cancellation based on NLMS algorithm is designed for the existing vibration noise during rotation process.Then,a PZT-5A1 piezoelectric fiber sheet of 50×16 ×0.3 mm and a Metglas 2605 SA1 magnetostrictive ribbon of 80 ×10×0.025 mm were selected as experimental materials.The symmetry magnetoelectric composite materials with 1~5 layers of Metglas were prepared by vacuuming,solidification and welding,and their frequency response,optimal bias magnetic field and magnetoelectric voltage coefficient were tested.According to experimental results,the influence of the number of Metglas layers on the magnetoelectric performance is analyzed.Subsequently,the magnetoelectric composite with optimal layer number for rotational modulation experiments is determined.Finally,the experimental test platform is built,including a non-magnetic rotating device and signal test device.Hereafter,we test DC and AC magnetic field at 1.5Hz,2Hz,and 2.5Hz rotational frequency,whose output signal spectrum is consistent with the theoretical analysis.The experimental results prove that the proposed rotational modulation method is feasible.Next,the magnetoelectric composite material of optimal layers is used as the signal sensor,and another piezoelectric fiber with the same size is used as the vibration noise sensor.The output signals of above two sensors are processed by the method of adaptive vibration noise cancellation.Processed result shows that such method can keep better linearity of magnetoelectric voltage amplitude and obvious cancellation of piezoelectric vibration noise.The RMS noise at 2.5Hz modulation is reduced to 7.2% of the unprocessed level.