Koen Vervaeke

Size dependence of microscopic Hall sensor detection limits

In this paper the magnetic field detection limits of microscopic Hall sensors are investigated as a function of their lateral size. Hall sensors fabricated from GaAs/AlGaAs heterostructures and silicon are experimentally investigated at different temperatures using Hall effect and noise spectrum measurements. At room temperature a clear size dependence of the detection limit is observed, whereas at low temperatures this dependence is found to disappear. The results are explained using the theory of noise in semiconductors.

Inline magnet inspection using fast high resolution MagCam magnetic field mapping and analysis

Driven by a clear industrial need for advanced inspection equipment for high-end permanent magnets for drives, sensors, medical applications, consumer electronics and other applications, we present a new magnetic measurement technology, called a ‘magnetic field camera’, a powerful and unique measurement platform for fast and accurate live inspection of both uniaxial and multipole permanent magnets. It is based on high resolution - high speed 2D mapping of the magnetic field distribution, using a patented semiconductor chip with an integrated 2D array of over 16000 microscopic Hall sensors. The measured magnetic field maps are analyzed by powerful data analysis software which uses advanced algorithms to extract unprecedented magnet information from the MagCam measurements. All these quantitative magnet properties can be tested against user-defined quality tolerances for immediate and automated pass/fail or classification analyses, all in real time. The system can be remotely operated using standard industrial communication protocols for integration in production lines. Its applications include inspection of incoming magnets, automated inline magnet quality control and research and development of magnets and magnetic systems and more.

Automated magnetic inspection of permanent magnet rotors

We report on the development of a magnetic inspection station for permanent magnet rotors, based on the established magnetic field camera technology, which uses high density two-dimensional Hall sensor arrays for fast high-resolution measurements of magnetic field distributions. The high speed of the system allows measuring the radial field distribution of a rotor in a few seconds with high axial (0.1mm) and angular (0.1°) spatial resolutions. The resulting 2D field distribution contains a lot of information about different important magnetic properties of the rotor, which are extracted using proprietary data analysis software. This analysis results in quantitative values for properties such as polarity identification, statistical analysis of the field distribution, north-south pole asymmetry, pole size measurement and analysis, pole peak uniformity, total magnetic flux, localized magnetization defects and localized material defects. It is argued that modern permanent magnet machines need innovative magnetic inspection solutions such as that described in this paper.

Large area magnetic field camera for inline motor magnet inspection

This paper reports on a further development of the award-winning [1] magnetic field camera technology [2-4] for advanced inspection of permanent magnets, into solutions for the inspection of large magnets, as used e.g. in electric drives. The innovation consists of combining multiple redesigned modular magnetic field camera sensor modules into a single large area magnetic field camera that can record the magnetic field distribution in a virtually unlimited area with high spatial resolution, at high speed, thanks to parallel read-out. The modular design of the system gives it a high degree of flexibility, allowing rearrangement of modules in various patterns and making multiple operation modes possible, such as direct 2D area magnetic field mapping or operating the system in line scan mode, requiring only a fast 1D scan to result in a quantitative 2D area magnetic image of large magnets. The resulting large area 2D magnetic field images can be analyzed in the same way as a single small area image, allowing high speed extraction of various quantitative key magnet characteristics that can be objectively used for quality control. Newly developed system software allows flexible measurement and data processing chains to be defined in a modular way, allowing both manual and automated magnet inspection tasks to be implemented in a straightforward way. However, in this paper the focus is on the hardware part. The development of the large area magnetic field camera system opens up new possibilities for fast and accurate inspection of large magnets, allowing the flexibility to perform automated inline magnet inspection in production lines, automated or manual quality control and R&D for a wide variety of magnetic systems.

Direct local observation of magnetic anisotropy in microscopic Ga1−xMnxAs dots

The effect of the patterning of a Ga1−xMnxAs (x=0.08) film into an array of microscopic dots on its magnetic properties is locally studied by means of scanning Hall probe microscopy. The measured stray field patterns indicate the presence of a single domain state with a uniform magnetization within the Ga1−xMnxAs dots. The magnetic anisotropy of the dot array is directly imaged, revealing a [100] easy axis in the as-grown sample and a [11¯0] easy axis orientation after annealing. In contrast to a temperature dependent anisotropy in the plain Ga1−xMnxAs film, no magnetic easy axis reorientation is observed within the experimentally accessible temperature range.

3-Axis magnetic field camera for ultrafast and high resolution inspection of permanent magnets

The current manuscript reports on a three-axis magnetic field camera system, capable of measuring the three components of the magnetic field distribution in a two-dimensional plane with high spatial resolution and at high speed. This new development, which is also commercially available, is illustrated by performing a full inspection of a rotary sensor magnet, whereby the complete vector magnetic field distribution is inspected, including the Bx, By and Bz components, as well as derived magnetic field components such as the full B-field and the distribution of the magnetic field vector direction (polar and azimuthal angles). Applications are found in R&D, production and quality control environments in different industries, such as sensor systems, permanent magnet motors, medical devices, automotive engineering, magnet manufacturing, consumer electronics and research institutes, where it can contribute to speed up R&D cycles, reduce time-to-market, quickly identify magnet quality issues and assure high quality products and high yield levels in the production line.

Industrial-scale motor cogging torque control for a high-volume motor manufacturing

Rare Earth Permanent Magnet (REPM) motor acoustics plays an increasingly important role in automotive mechatronic components and systems, due to more vehicle electrification and ever-increasing market demand. A large number of factors affect PM motor acoustic behavior. One of major contributing factors is the motor cogging torque. This paper reports industrial practice and control of motor cogging torque level which must meet a high-demanding technical specification. Since there exist a wide spectrum of motor slot and pole number combinations with varying permanent magnet structures, 9-slot and 6-pole Surface-mounted PM (SPM) topology has been investigated in great details. It is found that permanent magnet rotor field quality has a sensitive and significant impact on the RE SPM cogging torque level during the high-volume motor manufacturing. With right diagnosis and analysis tool, rigorous specifications of active materials in particular PM, and manufacturing process, the cogging torque level can be reduced and controlled.

6D magnetic field distribution measurements of permanent magnets with magnetic field camera scanner

We present state-of-the-art high resolution and fast 3D magnetic field mapping on permanent magnets of the (Bx, By, Bz) magnetic field vector components in 3D space, resulting in measurement data with 6 degrees of freedom. These measurements are performed using a high speed 3D magnetic field camera, featuring an integrated 2D Hall sensor array, mounted on a 3-axis mechanical scan stage with a scan range of 300 × 300 × 300mm3 with which measurement speeds of 120mm2/s are obtained with a spatial resolution of 0.1mm × 0.1mm. Volume 3D magnetic field distribution measurements of sensor magnets are performed and analyzed using powerful and versatile data analysis software for the data analysis and quality control of permanent magnets, both in R&D, incoming magnet inspection and production.