Measuring magnetic properties from very soft to very hard magnetic materials

Luc Van BockstalMetis InstrumentsLeuven, Belgium

Topics

• Metis Instruments• Magnetic measurements for ac and

transient fields• AC hysteresis meter

– Low coercivity material

• Pulsed hysteresis meter– High coercivity material

• Conclusions

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

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 / µ0 in non-magnetic material and Ht = Ht

– m = Ø / K in Helmholz coil pair

CASE 1 : the HyMACan 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

Case 2 : the HyMPulsea high field hysteresis meter

• Issues– Accurately measure Remanence– Coercivity > 1800 kA/m– Segment shape– Temperature 20-150 °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’

HyMPulseSystem Set-up

• Magnetiser• Solenoid Coil with

measurement probe• Heating unit• DAQ• Computer with DAQ

software • Closed circuit cooler (not

displayed)

HyMPulseMeasurement principle

• Measurement using pulsed field

• Magnetic field of magnet is reversed

HyMPulseMeasurement principle

• During magnetisation pulse:– Measurement of

• magnet moment m of sample and

• external applied field He

– Calculation of M(H)• M = m / V• H = He – N M• B / µ0 = H + M

HyMPulseMeasurement probe

• M-Sensor (Patent granted):– Elimination of background

signals

– Position- and Geometry-independent

– Related to Helmholtz

• H field -Sensor:– Induktive

– Measurement of Hextern

HyMPulseProbe uniformity map

MBi

He

Sensitivity colour plot Scale : 99.5 – 100.5 %

HyMpulse

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

HyMPulseAdvantages

• 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

HyMPulseAdvantages

• 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

HyMPulseEddy Current Correction

• Eddy-current– Pulsed field / field ramps induces eddy-

currents

• Eddy-current correction– A: use very slow ramp rate– B: compare pulses with different ramp rate– C: use small samples– D: …

HyMPulseEddy 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

HyMPulseEddy Current Correction

Without correction

After correction

HyMPulseMeasurement 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), Bext(t) with ½ sinus impulse– Visualisation and data storage

• Demagnetizing of magnet for easy handling

HyMPulseUser interface

28 kJ

HyMPulse offline data viewingMetis Results Viewer

Mouseclick on color: load / delete measurement

Color = customisable

German, English, French, Dutch, …

Can be downloaded from our website www.metis.be

HyMPulseRepeatability

• Br < 1% (4 sigma)• HcB < 1%• HcJ < 1%

• Comparison: HHcoil: < 0.5%

Statistical analysis

HyMPulseMeasurement 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

HyMPulseMeasurement 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

HyMPulseMeasurement at 20°& 150°C

HyMPulseDemag factor (N)

• Calculation of M(H)– M = m / V– H = He – N M– B / µ0 = 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 ???

HyMPulseTypical 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]

25 600 850 1500 2860 2000 44

Thank You!

Metis Instruments & EquipmentKapeldreef 603001 LeuvenBelgiumVoice: +32 16 298 344Fax: +32 16 298 405Contact@metis.be