This paper presents a multi spot projection unit, used in a 3D volume measurement system employed in a heart failure monitoring device, observing the volume of a patient’s feet for symptoms of heart problems (peripheral edema - swelling of the extremities). The stereoscopic image acquisition requires a surface with enough optically detectable texture, usually not present on human skin, which can be resolved by projecting an infrared, static multi-spot optical pattern. The focus of this paper is on creating a very cost-effective, energy efficient, eye-safe projection system, realizing a strongly divergent (up to ±60°) spot pattern, using infrared LEDs and mass fabricable micro-optical elements. Two different setup were tested: a) an LED array combined with a microlens array, and b) a combination of a single LED with a microlens array and a computer generated hologram (CGH) that adds a pseudo-random spot multiplication. For approach a) the microlens array was optimized by ray-tracing. The CGH function for approach b) was found using a wave optical design algorithm (iterative Fourier-Transform Algorithm – IFTA). The micro-lens array master was fabricated by diamondturning, whereas electron-beam lithography was employed for the CGH-master. Both masters were replicated using hotembossing of PMMA. Installed in a prototype of the medical measurement device, the influence on the 3D reconstruction was measured. The proposed solutions allow installing a competitively priced product for automatic peripheral edema monitoring in chronically ill patient homes, which is of great interest for improving their quality of life and the efficiency of their treatment.
Hot embossing and injection molding belong to the established plastic molding processes in microengineering. Based on experimental findings, a variety of microstructures have been replicated using these processes. However, with increasing requirements regarding the embossing surface, and the simultaneous decrease of the structure size down into the nanorange, increasing know-how is needed to adapt hot embossing to industrial standards. To reach this objective, a German-Canadian cooperation project has been launched to study hot embossing theoretically by process simulation and experimentally. The present publication reports on the proceeding and present first results.
Molding of micro components from thermoplastic polymers has become a routinely used industrial production process. Besides the famous injection molding technology hot embossing is nearly unknown to most people in micro technology. Initially developed for first feasibility tests with microstructured moldinserts hot embossing has been developed during the last ten years to a flexible and successful replication technology for polymer MEMS: Material screening, rapid prototyping but even small series with far more than 10.000 components has lead to a first commercialization of the related machinery. But also high end applications, difficult to realize with other technologies, are requested to replicate complex
microstructures. This paper gives an overview about the development of this technique and presents some new developments.
Hot embossing allows directly integrating conduction paths made of gold in the channel structures required for applications in lab-on-chip systems. In experiments, ditch depths of more than 100 micrometers wide and 2-3 micrometers thick construction paths. It turned out to be of no relevance whether the inclination of the lateral walls was 45 degree(s) or 90 degree(s).
A huge market development is expected for modern drug discovery and genomic analysis when rapid parallel analysis of a large number of samples gets available at affordable costs. The state of the art shows that low cost devices can be fabricated in mass production by micromolding of polymers. In close collaboration, Greiner Bio-One and Forschungszentrum Karlsruhe have developed a single-use plastic microfluidic capillary electrophoresis (CE) array in the standardized microplate footprint. This paper presents the results of experiences which show that hot embossing with a mechanically micromachined molding tool is the appropriate technology for low cost mass fabrication. A subsequent sealing of the microchannels allows sub-microliter sample volumes in 96- channel multiplexed microstructures.
After the successful development of micro-optical components today the first commercial applications are arising. This induces the necessity of adapted production technologies. Hot embossing and injection molding are two techniques to fabricate micro-optical components characterized by lateral structure details below 1 micrometers , structure heights up to one millimeter and aspect ratios between 20 and 100. Injection molding is famous for its short cycle times which makes this method well suited for mass production.Very delicate microstructures and multilayer components can be fabricated e.g. within the framework of the LIGA-process by hot embossing. Examples for micro-optical components fabricate by molding as well as process equipment will be discussed.
Silicon can be subjected to plasmaless isotropic etching in mixtures of elemental bromine and fluorine. BrF<SUB>3</SUB> is generated in the etching process. This ensures a high etching rate on smooth surfaces. The addition of noble gases, e.g. xenon, allows extremely smooth surfaces to be etched. Thermally oxidized SiO<SUB>2</SUB> layers are applied as the etching mask. Among other applications, this technique can be used to manufacture microlenses. As a consequence of the complete isotropy of the etching process, spherical depressions of 100 to 500 micrometers in diameter are produced in the silicon when small circular holes of 5 to 50 micrometers are underetched in the SiO<SUB>2</SUB> mask. After removal of the SiO<SUB>2</SUB> mask the silicon sample can be used as a mold insert for plastic molding. The molded microlenses have been checked dimensionally and verified optically. The microlenses are planned for technical use in a miniaturized endoscope. This requires further processing of the silicon sample. As no hemispherical recesses but calotte shells are needed, the silicon surface must be machine prior to molding. This is done by microgrinding with variable-grain diamond tools on CNC high- precision machines. To generate adjusting devices, stoppers, and holding structures, the ground silicon sample and a mechanically microstructured perforated plate are combined in a modular multi-level mold insert. The microlenses molded by hot embossing or injection molding are separated mechanically. They can then be integrated in the endoscope with a holding unit manufactured independently.