Development of Magnetostrictive Strument and Measurement

　　Development of Magnetostrictive Strument and Measurement
　　Rare-earth giant magnetostrictive material is a material with large magnetostriction, short response time, large magnetic - mechanical coupling coefficient, wide frequency band, low drive voltage, environmental protection and many other advantages. Therefore, it has broad application prospects, it will be a new concern to the people of another Rare Earth Functional Materials.For the current rapid development of magnetostrictive material applications, the measurement methods of magnetostrictive material parameters are constantly improving. Magnetostrictive parameter measurement use different ways in accordance with the principle of magnetostrictive, such as strain resistance , capacitors, optical lever, optical interferometry, displacement transfer method, etc. These measurement methods have variant merits and drawbacks.In practical applications, magnetostrictive materials are often virgulate. Ball Neodymium Magnets Therefore, the test magnetostrictive properties of the rod materials for the development and application of materials is of great significance. This topic is in rod magnetostrictive material developed a magnetostrictive measurement instruments. Apparatus include power structure, the excitation coil, micro-displacement sensor and output signal Digital Display SystemFor the magnetic field which beget magnetostriction , we used solenoid electromagnet as an incentive magnetic field. Design principle is simple, practical, compact, light weight, small size. in the production multi-storey solenoids of limited length and radius are used. Its length and radius ratio is l / r≥6, this will obtain the larger uniform distribution space of internal magnetic field intensity . In order to not stop the flexing materials, we design that the largest diameter of the sample has no contact with the coil skeleton, At the same time gap can not be too large, otherwise the magnetic field intensity surrounding material will be small. We made a water-cooling interlayer to prevent the coil heat which can influence measurements, cooling water flow in from the bottom and flow out from the top of the solenoid, from controling the flow velocity , the temperature of the matetials can be keeped at a stable value, so we can eliminate the influence of thermal expansion of materials. After test on non-ferromagnetism material Al stick, and sample has no thermal expansion phenomenon via water-cooled. Meanwhile, in order to avoid the impact of magnetic field on the sensor, the sensor will be placed outside solenoid where have no magnetic field, the locality is fixed on by electromagnetic simulation software Maxwell 2D. The result of simulation is the magnetic field uniformity and stability in the center of solenoid, the field gradually reduced forth from the solenoid and it become almost zero at the place 10 centimeters from the solenoid, so sensors is put in place at 11 cm. We add samples in the central location of solenoid and electrify the solenoid to generated magnetic field, the flexing of sample transfer through the Copper Rods to micro-displacement sensors, it will avoid the impact of the external magnetic field, and amplify the output signal of the displacement. The output signal of magnetic field and displacement display by two digital meters, they show directly the value of the magnetic field and the displacement values after calibration. Calibration of electromagnet is completed by Hall measurements and flux measurement methods, the http://www.chinamagnets.biz results in two ways are identical.In this paper, the magnetostrictive coefficient is measured by micro-displacement transmission methods.
　　Micro-displacement sensor is based on the principle of electromagnetic induction, two-stage differential transformer using the empirical formula as a reference to determine their skeleton structure size. In the paper, we use innovatively NE555 modulation circuit to generate pulse frequency, to provide the original coil vibrating voltage. In the part of signal measurement we use the differential rectifier circuit In order to identify the direction of movement and eliminate zero point residual voltage . This design improved sensitivity and stability, and linear relationship of displacement variation and voltage in the output displace between -3 ~ 3 mm was good. Via calibtating the sensor its output voltage transform into homologous displacement.We Select the magnetic material nickel rod which is known to measure its magnetostriction curve and compare with the experiment results record in the books, the two results are very close. The magnetostrictive characteristic curve of Giant magnetostrictive materials Terfenol-D is also measured, and then compare with the experiment results record in the journal, the two results are also very close. Then we explained the phenomenon of magnetostrictive hysteresis, and also compared this curve with the experiment results recorded in the books. At last, through the theoretical foundation of process of magnetization we find the relationship between magnetostriction and magnetization process, and worked out the theoretical characteristics model, finally calculated a theoretical magnetostrictive curve by Matlab software ,it is in good agreement with experimental curve.Experimental and theoretical results show that the measurement system work well on the test accuracy, stability, resolving power etc. .It achieved the desired results.With the development of researching on the ferromagnetic material characteristics the application of magnetostriction on the engineering technology is also developing. It is particularly essential to study on the measurement methods of magnetostriction and it can promote not only the study of the material,but also the application of magnetostrictive effect in the production and life .