Christine Ruffert

Development and Evaluation of an Active Magnetic Guide for Microsystems With an Integrated Air Gap Measurement System

An active magnetic levitation system based on repulsive magnetic forces was developed as a guide for a linear hybrid microstep motor. With this levitation system, the vertical force, which is typically an order of magnitude greater than the driving force, can be compensated. A capacitive measurement system provides measurement data to maintaining a constant air gap. This paper presents the design, fabrication, and first measurement results of the magnetic guide and the air gap measurement sensor

Fabrication of a Micro Coil for Magneto-Optical Data Storage

Magnetic Amplifying Magneto-Optical System (MAMMOS) is a technique to substantially increase the data storage density of optical recording by a double layer media approach: a bottom recording TbFeCo layer, and a top GbFeCo layer used for domain spreading when a supporting magnetic field is applied. Using MAMMOS technique, the micro coil is fabricated for magneto-optical data storage.

Write head with a micro coil for magneto-optical data storage

To increase storage capacity, an advanced magneto-optical recording technology using high numerical aperture (NA) optics (NA>0.8) in combination with a micro coil creating a local magnetizing field has been investigated. For data recording, a beam of blue laser light locally heats up the magneto-optical storage layer, which is then magnetized by the micro coil. The micro coil therefore needs to be located at a very small working distance (<50 /spl mu/m) from the disks, which requires the magnetic coil to be mounted between the lens and the disk. Furthermore, the substrate has to be transparent to allow the laser beam to pass through the center of the magnetizing coil. The microcoil that has been developed has proven capable of creating the magnetic field required for magneto-optical recording, could operate at the required recording frequencies, and promises sufficient heat dissipation.

Linear Synchronous Micro Motor With Further Miniaturized Dimensions

When developing linear micro motors, the synchronous drive scheme is well suited since it offers relatively high driving forces while keeping the design, fabrication, and assembly relatively simple. After the feasibility of the application of the synchronous drive scheme in a micro motor was proven, a smaller version of the motor was developed to investigate this drive scheme’s miniaturization potential. Apart from scaling down the motor dimensions, further optimizations were applied using the results of FEM simulations. The micro motor was fabricated, assembled, and successfully tested. The results demonstrate that the synchronous linear micro motor was successfully scaled down. Furthermore, the results indicate that even a further miniaturization seems feasible.Copyright

Investigations on the Separation of Platinum Nanoparticles With Magnetic Beads

The magnetic capture and manipulation of metallic nanoparticles can be interesting for many small-scale synthetic reactions, e.g., in the area of fine chemical production. Here, the separation of colloidal platinum nanoparticles from solution by means of magnetic beads is investigated. Therefore, magnetic beads functionalized with avidin are employed and a functionalization of the metal nanoparticles with biotin is performed. It is shown that the functionalized nanoparticles can be separated by the magnetic beads with common external magnetic field strengths. Furthermore, since a regain of the catalytic nanoparticles material is of inherent interest, several means of separation of the nanoparticles from the magnetic beads are investigated and compared.

Assembly Concept of a Magnetic Levitation System for a Linear Micro Actuator

Linear micro motors lend themselves to being fabricated in a hybrid fashion, i.e. fabricating stator and traveler on separate wafers. While such an approach provides substantial flexibility in fabricating the micro components, it requires to coming up with an appropriate guide system, as well as an assembly process for system integration. This process has to assure that the most critical dimension (typically the air gap between stator and traveler) is achieved. In general, such a challenge is best met by a self-alignment assembly process. The first generation of linear actuators used an assembly process where a ball guide consisting of ground V-grooves and 200 μm ruby balls was created. Both micro step motors and micro synchronous motors were equipped with such guides, which proved to be quite reliable. However, to further minimize friction, future linear micro motors will feature magnetic levitation bearings. This paper presents an assembly process for such micro motors.Copyright

Design and Technology of a Magnetic Levitation System for Linear Micro Actuators

A major drawback of magnetic linear micro actuators is the vertical attractive force between stator and traveler. In the case of a micro step motor, this force is typically one order of magnitude greater than the driving force itself. To compensate for this undesired vertical force and thus taking full advantage of the driving force available, a magnetic levitation system was developed and implemented as a guide. The electromagnetic field generated by the stator coils interacts with the field of permanent magnets positioned in the traveler. This way, the traveler is elevated. Since repulsive magnetic levitation systems are inherently unstable, a tribological guide was integrated on both sides of the magnetic levitation system. During motion, the combination of stationary coils in the stator and moving permanent magnets in the traveler lifts up the traveler, while the lateral tribological guide prevents the traveler from shifting sideways. Initial investigations proved the feasibility of this magnetic levitation concept (1). A complete linear micro step motor system with magnetic levitation guide consists of the micro step motor itself, the magnetic micro levitation system (including the lateral guides), and a capacitive air gap measurement system. The latter one detects the size of the air gap between stator and traveler of the micro actuator. An assembly consisting of the three components results in a linear micro actuator system with adjustable air gap. For achieving optimal working conditions of the linear micro step motor, the magnetic levitation system was designed for a nominal air gap of 8 μm at the micro step motor. While earlier work proved the feasibility of such a guide, it also indicated (i) that the levitation system has to be capable of correcting a pitch motion of the traveler and (ii) that an as high magnetic levitation force as possible is desirable. To address the first issue, the magnetic levitation system received four coils arranged in a square along the axis of motion of the micro step motor. This way, both pitch and roll may be controlled. For resolving the second issue, the number of coil layers was increased from two to four. The technology for such a four layer coil is quite challenging, particularly since every effort has to be made to minimize its building height. The challenges were resolved by creating a coil system where the lateral insulation between conductors consists of SU-8™ (a photosensitive epoxy by Micro Resist Technology), while the vertical insulation layers were formed by a thin, stress compensated Si3 N4 film. This way, a very compact coil with a high conductor-to-insulator ratio and thus a great current conducting capability could be realized. Due to the thin Si3 N4 insulation, it also features an excellent thermal conductivity.© 2007 ASME

Fabrication of Magnetic Layers for Electromagnetic Microactuators

For designing and fabricating magnetic microactuators, both soft and hard magnetic materials may be required. For soft magnetic materials, a high saturation flux density Bs and a great relative permeability µr is desirable; for forming efficient permanent magnets, hard magnetic materials require a high maximal energy product |BH|max. In the area of soft magnetic materials, investigations on NiFe81/19, NiFe45/55, and CoFe were carried out, while an example for a hard magnetic material providing a high energy product is SmCo. Since patterned thin-film magnets feature inferior magnetic properties compared to bulk magnets, a method of determining their magnetic properties was developed.