Michael Kröner

Vibration harvesting in traffic tunnels to power wireless sensor nodes

Monitoring the traffic and the structural health of traffic tunnels requires numerous sensors. Powering these remote and partially embedded sensors from ambient energies will reduce maintenance costs, and improve the sensor network performance. This work reports on vibration levels detected in railway and road tunnels as a potential energy source for embedded sensors. The measurement results showed that the vibrations at any location in the road tunnel and at the wall in the railway tunnel are too small for useful vibration harvesting. In contrast, the railway sleeper features usable vibrations and sufficient mounting space. For this application site, a robust piezoelectric vibration harvester was designed and equipped with a power interface circuit. Within the field test, it is demonstrated that sufficient energy is harvested to supply a microcontroller with a radio frequency (RF) interface.

Planar multipole ion trap

We report on the realization of a chip-based multipole ion trap manufactured using microelectromechanical systems technology, requiring minimal manual alignment of the electrodes. It provides ion confinement in an almost field-free volume between two planes of radiofrequency electrodes, deposited on glass substrates, which allows for optical access to the trap. An analytical model of the effective trapping potential is presented and compared with numerical calculations. Stable trapping of argon ions is achieved, and a lifetime of 16 s is measured. Electrostatic charging of the chip surfaces is studied and found to agree with a numerical estimate.

The effect of a distinct diameter variation on the thermoelectric properties of individual Bi0.39Te0.61 nanowires

The reduction of the thermal conductivity induced by nano-patterning is one of the major approaches for tailoring thermoelectric material properties. In particular, the role of surface roughness and morphology is under debate. Here, we choose two individual bismuth telluride nanowires (NWs), one with a strong diameter variation between 190 nm and 320 nm (NW1) and the other of 187 nm diameter with smooth sidewalls (NW2). Both serve as model systems for which bulk properties are expected if surface properties do not contribute. We investigate the role of the diameter variation by means of a combined full-thermoelectrical, structural and chemical characterization. By transmission electron microscopy the structure, chemical composition and morphology were determined after the thermoelectrical investigation. The NWs showed an oriented growth along the direction and the same composition. The Seebeck coefficients of both NWs are comparable to each other. The electrical conductivity of both NWs exceeds the bulk value indicating the presence of a topological surface state. Whereas the thermal conductivity of NW2 compares to the bulk, the thermal conductivity of NW1 is about half of NW2 which is discussed with respect to its distinct diameter variation.

Novel Fabrication Process for Micro Thermoelectric Generators (μTEGs)

A cost effective bottom-up process for the fabrication of micro thermoelectric generators (μTEGs) was developed. It is based on a novel fabrication method involving a selectively sacrificial photoresist for the sequential galvanostatic electrodeposition of thermoelectric materials. The use of an industrial pick and placer (P&P) for dispensing the second photoresist allows for accurate and flexible μTEG designs. The process makes use of Ordyl® as a negative dry film photoresist template and sequential lamination steps for shaping all thermoelectric legs and contacts. All structures of the μTEG are generated in one photoresist multi-layer - this represents the most significant advantage of the process. The process uses a minimum of clean room processing for the preparation of pre-structured substrates for electrodeposition and therefore provides a cost-effective, highly flexible fabrication platform for research and development.

Fabrication Process for Micro Thermoelectric Generators (μTEGs)

An innovative micro thermoelectric generator (μTEG) fabrication process has been developed. Two selectively dissolvable photoresists and galvanostatic electrodeposition are used to grow p- and n-type thermoelectric materials as well as the upper and lower contacts of the μTEGs onto a single substrate. Two particular features of the process are the usage of a multilamination technique to create structures for legs and contacts, as well as an industrial pick and placer (P&P), which allows dispensing of a second, selectively dissolvable, photoresist to protect certain areas during material deposition. This allows sequential electrochemical deposition of two different thermoelectric materials on a single substrate, without further costly and time-consuming process steps. The process therefore provides a highly flexible fabrication platform for research and development.

Storage of protonated water clusters in a biplanar multipole rf trap

We present the storage properties of protonated water clusters H+(H2O)n (n=1-4) in an improved biplanar ion trap. The design is based on our recently reported realization of a biplanar multipole radiofrequency (rf) ion trap (Debatin et al 2008 Phys. Rev. A 77 033422). The new experimental setup is composed of the ion trap in tandem time-of-flight configuration for mass-selective ion loading and mass-selective detection of stored ions. Special attention is paid to the supersonic discharge cluster source and our improved realization of a biplanar multipole ion trap with a simplified electrode layout. The source performance is presented and mass-selective loading into our trap is demonstrated with H+(H2O)n clusters. We achieve stable trapping of H+(H2O)n clusters (n=1?4) with storage lifetimes of 3?12?s, which is comparable to former achievements with stable atomic Ar+ ions in the first trap generation. Collision-induced cluster dissociation during the loading process is observed.

Power management strategies in self-sufficient sensor nodes

Wireless sensor nodes, powered from energy harvesting generators using available ambient power sources, need a sophisticated power management to optimally budget the scarcely available energy. By that, the reliability, the functionality, and availability of these nodes are increased. The decisions of the power management can either be based on a simple energy income and storage level knowledge, or it additionally has empirical information about the past power income. In case the system comprises two energy storage units with different capacities for long and short term use, the commonly used power management algorithms do not offer satisfactory functionality. This report provides an overview over different concepts of power management strategies for. These offer an improved performance by better task management, storage organization, and power routing.

Simulation, Design and Test of a Novel Planar RF Micro Ion Trap

We present a novel planar multipole radio frequency (rf) ion trap built with microfabrication technologies on a transparent substrate. Simulations were performed using an analytical model of the effective potential to determine the trapping capabilities of different designs. Based upon these simulations an ion trap was designed, fabricated and successfully characterized in first experiments at ultra high vacuum conditions.

Zerstörungsfreie Haftfestigkeitscharakterisierung von Full-Wafer-Bondverbindungen (Non-destructive strength characterization of full-wafer-bonds)

Abstract Der vorliegende Beitrag beschreibt eine zerstörungsfreie Testmethode, um die Haftfestigkeit von Bondverbindungen zu bestimmen. Zu diesem Zweck wurde ein modifizierter Blistertest entwickelt, bei dem die Länge eines künstlich erzeugten Risses in Kombination mit dem dafür aufgewendeten Druck ein Maß für die Haftfestigkeit der Bondverbindung darstellt. Zur Geometriefindung wurden verschiedene Teststrukturen untersucht. Das druckunabhängige Verhältnis von Verdrängungsvolumen zu neu generierter Rissfläche bei wachsender Rissausbreitung ist hierbei der entscheidende Faktor, welcher für den zerstörungsfreien Charakter der Testmethode verantwortlich ist.