Weder A.,Fraunhofer Institute for Photonic Microsystems
Proceedings - 2nd International Conference on Computational Intelligence, Communication Systems and Networks, CICSyN 2010 | Year: 2010
In the recent years, Wireless Body Sensor Networks (WBSNs) attracted much attention in the research community. The key to success for WBSNs is the utilization of highly efficient transceivers and the application of intelligent policies to handle the limited (energy) resources. Simulations are a frequently used tool to evaluate different policies and analyze the performance of wireless networks in different configurations. The nRF24L01 is an ultra-low-power transceiver for the 2.4 GHz frequency band which is very well suited to build simple but efficient WBSNs. This work presents a detailed simulation model of the nRF24L01 for MiXiM, a simulation framework for wireless networks. The implementation is focused on tracking the transceiver's energy consumption in operation. The presented simulation model is a valuable tool for network designers and implementers when working with the nRF24L01. © 2010 IEEE.
Riedel S.,Fraunhofer Institute for Photonic Microsystems |
Sundqvist J.,Lund University |
Gumprecht T.,Fraunhofer Institute for Integrated Systems and Device Technology
Thin Solid Films | Year: 2015
We demonstrate the deposition of SixNy thin films using octachlorotrisilane (Si3Cl8) and ammonia between 300 and 500 °C by an atomic layer deposition-like growth mechanism. Although there are chemical vapor deposition growth mechanisms present, which lead to an incomplete saturation, a step coverage > 80% in high aspect ratio (> 60:1) trenches could be achieved. The deposited films oxidize after contact with ambient air leading to substoichiometric N/Si ratios. Increasing the deposition temperature diminishes this oxidation. At temperatures > 390 °C a bulk N/Si ratio of ∼ 1.3 is achieved. The capacitance-voltage (C-V) measurements of these films yield a k value of ∼ 6 and a strong C-V hysteresis indicates significant charge trapping. © 2015 Elsevier B.V. All rights reserved.
Tress W.,TU Dresden |
Tress W.,Linkoping University |
Merten A.,TU Dresden |
Merten A.,Fraunhofer Institute for Photonic Microsystems |
And 5 more authors.
Advanced Energy Materials | Year: 2013
We investigate the role of the spatial absorption profile within bulk heterojunction small molecule solar cells comprising a 50 nm ZnPc:C60 active layer. Exploiting interference effects the absorption profile is varied by both the illumination wavelength and the thickness of an optical spacer layer adjacent to the reflecting electrode. The fill factor under 1 sun illumination is observed to change from 43 to 49% depending on the absorption profile which approximately equals the charge-carrier generation profile. It is shown by varying the mixing ratio between ZnPc and C60 that the importance of the generation profile is correlated with the imbalance of mobilities. Therefore, it is concluded that non-geminate recombination is the dominating loss mechanism in these devices. Numerical drift-diffusion simulations reproduce the experimental observations showing that charge carrier extraction is more efficient if charge carriers are generated close to the contact collecting the less mobile charge carrier type. Furthermore, this effect can explain the dependence of the internal quantum efficiency measured at short circuit on wavelength and implies that the spectral mismatch for a given solar simulator and device depends on the applied voltage. The spatial absorption profile in the bulk heterojunction of an organic solar cell is varied by employing different thicknesses of an optical spacer layer. The fill factor correlates with the profile and the imbalance in charge carrier mobilities. These results indicate that extraction of holes in competition with bimolecular recombination limits the device performance. Therefore, the spectral shape of the external quantum efficiency and, in turn, the spectral mismatch change with applied voltage. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Gruger H.,Fraunhofer Institute for Photonic Microsystems
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2015
Over the past decades zoom lenses have become an important type of objective. Due to their ability to dynamically change magnification or field angle they are being used in many fields of application. Most zoom lenses consist of a number of lenses or lens groups. The magnification can be changed by axial shifting some of these lens groups with a more or less complicated moving function. However, in principle it should be possible to construct zoom lenses that do not rely on the movement of some of its components. Instead, the change in magnification is achieved by changing the optical power of at least two lenses within the system (optical power zoom - OPZ). Moreover, for broadband applications it is highly favorable to use mirrors instead of lenses due to the absence of chromatic aberrations. Based on a "Schiefspiegler" approach an all-reflective OPZ objective with a zoom power of three consisting of four mirrors has been designed. Two mirrors are assumed to have a variable radius of curvature for changing optical power. During aberration correction special consideration has been given to the reduction of field curvature, since the optical power change strongly influences field curvature for different zoom positions. The simulation shows adequate image quality for photographic applications over the whole zooming range. For the realization of such an OPZ objective deformable mirrors with a comparatively large stroke are needed. Before starting a complex development of such devices three setups with different fixed focal lengths were built to prove and evaluate the concept for digital imaging. © 2015 SPIE.
Large public building complexes, such as exhibition halls, airports, shopping centers or museums, as well as hospitals and public authority buildings are sometimes like a maze. Arrows, maps and signs are supposed to make it clearer. But right when you enter the building for the first time, it is often very laborious and complicated to follow them through the maze of corridors, hallways, rooms and floors. Classic GPS-based navigation apps do not work in enclosed spaces, because the satellite signals are sometimes significantly disrupted by walls and ceilings. Researchers at the Fraunhofer Institute for Photonic Microsystems IPMS in Dresden, Germany have found a way to use smartphones for navigation inside buildings too. For this they rely on WLAN: With local radio networks, the researchers locate smartphones indoor to within about two meters. To determine the position, the software evaluates the signal strength of the WLAN spots. The app, which was originally developed for use in hospitals, is based on the Android mobile phone operating system. When starting the app, different targets can be selected – for example, examination rooms, patient rooms, cafeterias and restrooms or mobile inventory, such as beds and wheelchairs. As with navigation devices in cars, the user sees the building plan in a two-dimensional bird's-eye view. The target and current position are marked with dots and the shortest route is shown on the map. If the user moves, so does his position point. If the destination is outside the screen or on a different floor, arrows show the way. The hospital provides the material for the desired maps. Emergency evacuation plans can often be used as a template. "We can bring any large map sharply and without any annoying delays onto every screen," says Christian Scheibner from the Department of Wireless Microsystems of the IPMS. The app receives all the necessary data from the user's server. Thanks to open interfaces, the positioning and navigation algorithms as well as the graphical representations can be installed simply and straightforwardly in customers' applications. In the apps of trade fairs organizers, for example, which often lack maps, route planning or position determination. "Hospitals have caught up considerably in terms of wireless hot spots in recent years. For example, there are more and more medical devices which are equipped with WLAN and which can be used for indoor navigation" says the hardware and software developer Scheibner. The software works in all indoor areas where WLAN is available. The navigation destinations can be linked with other information. As a result, a user in a shopping mall, for example, will find his way directly and quickly to the rack with special deals. A demo system of the app is running successfully at the IPMS. "Interested parties can try it on site at the Institute at any time," says Scheibner. The technology was developed on behalf of an infrastructure outfitter for hospitals. They are being presented at the MEDICA international trade fair in Dusseldorf from November 16 to 19, 2015. Explore further: WLAN leads the way