Measuring magnetic properties from very soft to very hard magnetic materials. Luc Van Bockstal Metis Instruments Leuven, Belgium

Transcription

1 Measuring magnetic properties from very soft to very hard magnetic materials Luc Van Bockstal Metis Instruments Leuven, Belgium

2 Topics Metis Instruments Magnetic measurements for ac and transient fields AC hysteresis meter Low coercivity material Pulsed hysteresis meter High coercivity material Conclusions

3 Metis Instruments in a nutshell : History Founded May 25th 1998 Spin-off of the KULeuven, Belgium Research group: Solid State Physics & Magnetism Technology base: Design and construction of pulsed field research equipment SME

4 Measurement techniques AC and transient induced voltages is a issue Pick up loop Simple technique for ac and transient signal: U = - d Ø / d t Derived sensors B = Ø / S H = B / µ 0 in non-magnetic material and H t = H t m = Ø / K in Helmholz coil pair

5 CASE 1 : the HyMAC an AC hysteresis meter Measurement of: Core losses of transformer steel Cutting effects of magnetic materials Permeability of new magnetic materials Or..vibrations due to magnetostriction Constraints Closed magnetic circuit toroid Epstein yoke

6 Case 2 : the HyMPulse a high field hysteresis meter Issues Accurately measure Remanence Coercivity > 1800 ka/m Segment shape Temperature C Constraints for a hysteresis meter Closed magnetic circuit (conventional type) Open magnetic circuit (new type) Power / energy High Field hysteresis meter Using pulsed fields For testing really hard magnetic materials industrial

7 System Set-up Magnetiser Solenoid Coil with measurement probe Heating unit DAQ Computer with DAQ software Closed circuit cooler (not displayed)

8 Measurement principle Measurement using pulsed field Magnetic field of magnet is reversed

9 Measurement principle During magnetisation pulse: Measurement of magnet moment m of sample and external applied field H e Calculation of M(H) M = m / V H = H e N M B / µ 0 = H + M

10 Measurement probe M-Sensor (Patent granted): Elimination of background signals Position- and Geometryindependent Related to Helmholtz H field -Sensor: Induktive Measurement of H extern

11 Probe uniformity map M B i Sensitivity colour plot Scale : % H e

12 HyMpulse Innovation for measuring properties of advanced permanent magnets any material: NdFeB, hard-ferrites, SmCo any geometry: segment, cylinder, disk

13 Advantages Measurement insensitive to magnet shape (patent pending): 1 probe fits all No pole shoes per magnet geometry Measurements of segments, bars, discs, etc with 1 probe

14 Advantages Fields up to 7+ Tesla: No physical constraints on applied field HcJ over 1800 ka/m easily measurable Possible to measure full demagnetization curves of Ferrites, NdFeB & SmCo

15 Eddy Current Correction Eddy-current Pulsed field / field ramps induces eddycurrents Eddy-current correction A: use very slow ramp rate B: compare pulses with different ramp rate C: use small samples D:

16 Eddy Current Correction Correction using proprietary technology Patent procedure started Performance check of technology via comparative measurements: Different magnet dimensions Even on the biggest samples (30 x 40 mm) the values correspond HH-Measurements correspond

17 Eddy Current Correction Without correction After correction

18 Measurement procedure Calibration shot Measurement of magnetic environment Only once per magnetic field Entry of measurement data (date, operator, material ) Fixation of sample External heating until desired temperature Temperature shielding Measurement of hysteresis curve Charge magnetiser Measurement of M(t), B ext (t) with ½ sinus impulse Visualisation and data storage Demagnetizing of magnet for easy handling

19 User interface 28 kj

20 offline data viewing Metis Results Viewer German, English, French, Dutch, Mouseclick on color: load / delete measurement Color = customisable Can be downloaded from our website

21 Repeatability Statistical analysis Br < 1% (4 sigma) HcB < 1% HcJ < 1% Comparison: HHcoil: < 0.5%

22 Measurement accuracy Comparative measurements with leading magnet supplier: Calibration of HyMPulse with known magnet Measurements on multiple unknown magnets : Br-values differ less than 0.01 T (less than 1%) HcJ-values differ less than 1% Check with HelmHoltz coil + Fluxmeter Working point differs less than 0.01 T Delivery of certification Certified to deliver same results as IEC60404-x Certification verified with set of calibrated magnets

23 Measurement F(Temperature) Specifications: 20 C to 180 C Heating principle: Sample holder in separate heating unit Temperature control via PID controller Application of high temperature resistive material

24 Measurement at 20 & 150 C

25 Demag factor (N) Calculation of M(H) M = m / V H = H e N M B / µ 0 = H + M Calculation of N-factor is necessary : 2D-3D FEM: 1 time per Geometry Via analytical way for simple geometries (eg brick,) Extruded shape???

26 Typical specifications Coil diameter and maximum field determine necessary field Magnet volume determines accuracy Parameters for 7 T external field: Bigger diameters at lower fields for ferrites Sample diagonal [mm] Min Volume [mm³] Energy [kj]

27 Thank You! Metis Instruments & Equipment Kapeldreef Leuven Belgium Voice: Fax: