Magnetic microsystems
The major technological challenges in the field of magnetic microsystems are the processes and materials. The Laboratory for Microactuators runs a unique, fast flexible and reliable process to manufacture three dimensional solenoidal microcoils using an automatic wirebonder. We develop and provide coils for on-chip magnetic micro actuators, microtransformers and power handling, inductive sensors, micro nuclear magnetic resonance, micro energy harvesting, or magnetic levitation. We further focus on the processing of magnetic materials. We investigate for example the structuring and performance of multilayered amorphous metal films as well as of magnetic polymers. They are applied to guide the magnetic flux and enhance the field for example to maximize the coupling of a transformer.
Micro Nuclear Magnetic Resonance | Prof. Dr.-Ing. Wallrabe
The Micro-MR research efforts at the Laboratory for Microactuators are focused on the development of magnetic resonance imaging and spectroscopy systems for samples with sub-millimeter dimensions.
The most difficult problem in high resolution MRI/NMR at the microscale is the need for sufficient signal to noise ratios (SNR) One way to enhance the sensitivity for signal reception is the use of microcoils to closely conform to small samples.
We build truly three dimensional, geometrically perfect microcoils with inner diameters down to 100 µm perpendicular to the substrate using 25 µm insulated Au or Cu wire. We wind the coils directly on the sample containers, which helps to optimize the sensitivity by enhancing the filling factor. We have also demonstrated the first automatically fabricated microprobes for wireless transmission of the MR signal, thus allowing simultaneous "magic angle spinning” of the sample together with the detection coil. To demonstrate the versatility of this technology, we have adapted these inserts to various Larmor frequencies (194, 500 and 700 MHz) and we have tested several samples such as water, Drosophila pupae, adamantane solid and LiCl at different magic angle spinning speeds.
A flat alternative to the solenoidal MR coils is given by a coil pair in Helmholz configuration that provides an excellent homogenous field in its centre. In addition to the sensitivity, this also improves the handling. The slot between the two coils can be used to slip-in fluidic sample inserts which can be efficiently mass-produced as disposable material to avoid difficult cleaning procedures and cross contamination.
Microtransformers | Dr. Ali Moazenzadeh
The trend towards slim handheld electronic devices makes the miniaturization and integration of power converters a key technology. To address this issue, the Laboratory of Microactuators works on two different strategies to fabricate miniaturized transformers. The first approach focuses on the inductive element optimization and fabrication employing a highly accurate coil winding technology developed in our laboratory. Utilizing an automatic wirebonder as a means for the microcoils fabrication enables ultra-fast manufacturing of 3D micro solenoids with a high winding density and a high degree of flexibility.
Since we can wind the primary and secondary coils of the transformers directly and precisely on top of each other our transformers reach extremely high coupling factors. The second approach consists in integrating high performance magnetic cores. For this purpose, we developed two novel MEMS compatible microfabrication processes.
The magnetic cores are either fabricated from soft magnetic amorphous alloys or from soft magnetic powder-based composites. Applying such technologies, four different types of microtransformers were fabricated, with different geometry, core material, and functional frequency range. The manufactured prototypes are intended for chip-level power conversion or isolation within a 0.3–300 MHz frequency range.
Wireless power transmission | Fralett Suárez Sandoval
The use of wireless power transmission allows, in comparison to standard wire-based applications, the possibility of transferring power where wires are hard or unlikely to introduce. Reasons may range from safety to biocompatibility aspects through mechanical and electrical breakthrough stability. From the consumer point of view, the number of battery-hungry devices owned by everyone ineluctably increases the number of obsolete wall chargers generated each year, something that could be avoided if a common charging spot is made available. Although medical and consumer applications could in principle benefit from the use of wireless power transmission, the manufacturing materials, transmission distance and medium, as well as the required circuitry has been shown to differ in each case.
In our laboratory we look for a way to employ microfabricated magnetic devices along with the necessary electronic circuitry to design and fabricate a flexible wireless power transmission system intended for both medical and consumer applications. Here, the word flexibility has several meanings. First, it addresses the paramount characteristics of our targeted system, meaning that it is scalable in size and easy to adapt to a specific application, Next, it means shape flexibility, i.e., the system is made on a flexible substrate to adapt to a curved surface, and finally, it means power adaptivity, meaning that smaller and larger systems can be powered with one and the same system.