The magnetoelectric sensor has the advantages of high sensitivity, low noise and simple preparation process. It has great application prospects in weak magnetic field detection such as geomagnetic field, biomagnetic field and so on. What`s more, the resolution of detection for low-frequency AC magnetic field can reach pT magnitude [1]. Because the piezoelectric material will produce a continuous output only when it is in a periodic vibration. so it needs to use modulation technology when measuring the statics magnetic field. The modulation techniques commonly used today are AC modulation and electric field modulation [2, ~3].But now, a new modulation method will be introduced in this paper, that is what referred to as rotation modulation. As shown in Fig.1(a), the component of the measured direct current projection on the shaft is a sinusoidal signal whose frequency is equal to the frequency of rotation, thus, we can measure constant magnetic field directly. More exciting, we may apply the rotation to MEMS structure to achieve miniaturization and integration. The test platform shown in Fig.1(b) is consist of rotation system and measurement system. Rotation system inclueds a ultrasonic motor and a fixture used for installing the magnetoelectric sensor and induction coil providing DC bias. The measurement system is composed of Signal Generator, Regulated DC Power Supply, Spectrum Analyzer, Magnetic Shield Tube. The magnetoelectric sensor used in the experiment was composed of Metglas/PZT/Metglas, which top layer and bottom layer are composed of two-layers of magnetostrictive Metglas. In order to obtain the best bias magnetic field, we firstly design a series of experiments with linearly increasing bias DC field at 2Hz(because the maximum rotation frequency of ultrasonic motor is 2Hz). Fig.2(a) shows that the optimal DC bias is about 8Oe. Then our group has tested the ME output voltage of magnetoelectric sensor with 10Oe measured DC field providing by coil, and the four groups experiments had been processed under condition of statics or rotation at three different speeds shown in Fig.2(b). There are three spikes whose value far greater than other`s, and their position is just corresponding to the frequency of rotation. Fig.2(c) has shown almost linear change between ME voltage and the measured DC field. Thus, it can be conclued that the proposed modulation method is really effective. In these experiments, our team have used coils to ensure the DC bias can be controlled accurately. The next step we will use ferromagnet for bias. Using the proposed modulation method can realize high-precision DC magnetic field measurement like AC modulation and electric field modulation after enchancing ME out voltage through the selection of magnetic composite materials, the optimization of the rotating structure and the using of charge amplifier.
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