The Effect Of Magnetic Bias Fields On The Characteristics Of Rare Earth Magnetostrictive Transducer

With the development of science and technology, research and application about intelligent materials is getting more and more attention in many fields. Rare-earth giant magnetostrictive material is a new type of magnetic material, which can deform largely in magnetic field, it has been widely used in various transducers. Rare earth giant magnetostrictive transducer is a device which transforms electromagnetic energy into mechanical energy or sound energy. It is efficient in electromechanical conversion. However, the strain of Rare-earth giant magnetostrictive material, which happens under the magnetostrictive effect, only depends on the magnitude but not the direction of extra magnetic field. As a result, frequency doubling effects will appear in the transducer under the action of alternating current. Because the doubling effects degrade the performance and the conversion efficiency of the transducer, it is essential to apply a bias magnetic field to wipe out this doubling effects. This paper studies the effects of bias magnetic field on the performance of magnetostrictive transducer. The main content and relative results are as follows:(1)The effects of basic structure parameters of permanent magnets is studied.. The magnetostrictive transducer model is established and analyzed by using the finite element simulation software, COMSOL Multiphysics. Results show that, the magnetic field distribution and the output displacement of transducer are getting better as increasing of the magnet thickness. However, as the thickness increasing, the size of transducer is getting bigger and the cooling performance is getting worse. By comprehensive consideration of magnet field uniformity, intensity, output displacement and cooling performance, the permanent magnet thickness is set as 7 mm and the spacing is set as 2 mm.(2)The effects of the bias magnetic field on the output char acteristic of transducer are studied. A 90 mm cylindrical permanent magnet is evenly divided into 30 layers of 3 mm small circular ring permanent magnets. The influences of layer numbers and the uniformity on the strain and magnet field are analyzed. Results show that, the influence of the layer numbers is limited in a certain range. In this model, the strain changes slowly and gradually gets saturated while the number of permanent magnet is greater than 8 layer. The output displacement and magnetic strength both increase with uniformity, while the increase of displacement is approximately linear.(3)The effects of pre-stress and bias magnetic field coupling effects on the output characteristic of transducer are studied. The curve of strain versus pre-stress is obtained by parameter scan. With the increasing of pre-stress, magnetostrictive strain coefficient,?, is increasing linearly in certain range. Then, the bias magnetic field and pre-stress effects are considered at the same time. When the layer of magnets is two, the effect of pre-stress on displacement amplitude is small. As the layer number of permanent magnetic increasing, the variation of displacement amplitude versus pre-stress is a little different. However, it is also increasing slowly.This paper focus on the effects of bias magnetic field on the output performance of magnetostrictive transducer. The related conclusions can provide certain theoretical guidance for the application of magnetostrictive transducer.