Investigation of the thermal effects in dynamically driven dielectric elastomer actuators

Dielectric elastomer actuators (DEAs) are compliant capacitors, which are able to transduce electrical into mechanical energy and vice versa. As they may be applied in different surrounding conditions and in applications with alternating excitations, it is necessary to investigate both, the thermal behavior and the in fluence of the temperature change during operation. Due to mechanical and electrical loss mechanisms during the energy transfer, the DEA is subjected to an intrinsic heating. In detail, the dielectric material, which has viscoelastic properties, shows a mechanical hysteresis under varying mechanical loads. This behavior leads to a viscoelastic loss of energy in the polymer layer, resulting in a heating of the structure. The non-ideal conduction of the electrode provokes a resistive loss when charging and discharging the electrode layer. Operation with frequencies in the kilohertz-range leads to remarkable local heat dissipation. The viscoelastic material behavior and the resistivity are assumed to be dependent on the temperature and/or on the strain of the material. By this, a back-coupling from the thermal field to the mechanical field or the electrical field is observed. In order to provide a thermal equilibrium, also the convective cooling { the structure is subjected to { has to be considered. Depending on the frequency and the type of electrical driving signal and mechanical load, viscoelastic and resistive heating provide different contributions during the dynamic process. In the present study we capture the described effects within our modeling approach. For a given dielectric elastomer actuator, numerical investigations are performed for a given electrical load

Combined Simulation of a Micro Permanent Magnetic Linear Contactless Displacement Sensor

The permanent magnetic linear contactless displacement (PLCD) sensor is a new type of displacement sensor operating on the magnetic inductive principle. It has many excellent properties and has already been used for many applications. In this article a Micro-PLCD sensor which can be used for microelectromechanical system (MEMS) measurements is designed and simulated with the CST EM STUDIO® software, including building a virtual model, magnetostatic calculations, low frequency calculations, steady current calculations and thermal calculations. The influence of some important parameters such as air gap dimension, working frequency, coil current and eddy currents etc. is studied in depth

The dielectric breakdown limit of silicone dielectric elastomer actuators

Soft silicone elastomers are used in a generation of dielectric elastomer actuators (DEAs) with improved actuation speed and durability compared to the commonly used, highly viscoelastic polyacrylate 3M VHB films. The maximum voltage-induced stretch of DEAs is ultimately limited by their dielectric breakdown field strength. We measure the dependence of dielectric breakdown field strength on thickness and stretch for a silicone elastomer, when voltage-induced deformation is prevented. The experimental results are combined with an analytic model of equi-biaxial actuation to show that accounting for variable dielectric field strength results in different values of optimal pre-stretch and thickness that maximize the DEA actuation

Individual Profiling of Circulating Tumor Cell Composition and Therapeutic Outcome in Patients with Hepatocellular Carcinoma

AbstractBACKGROUND AND AIMS: Circulating tumor cells (CTCs) have been proposed as a monitoring tool in patients with solid tumors. So far, automated approaches are challenged by the cellular heterogeneity of CTC, especially the epithelial-mesenchymal transition. Recently, Yu and colleagues showed that shifts in these cell populations correlated with response and progression, respectively, to chemotherapy in patients with breast cancer. In this study, we assessed which non-hematopoietic cell types were identifiable in the peripheral blood of hepatocellular carcinoma (HCC) patients and whether their distribution during treatment courses is associated with clinical characteristics. METHODS: Subsequent to few enrichment steps, cell suspensions were spun onto glass slides and further characterized using multi-immunofluorescence staining. All non-hematopoietic cells were counted and individual cell profiles were analyzed per patient and treatment. RESULTS:We detected a remarkable variation of cells with epithelial, mesenchymal, liver-specific, and mixed characteristics and different size ranges. The distribution of these subgroups varied significantly between different patient groups and was associated with therapeutic outcome. Kaplan-Meier logrank test showed that a change in the ratio of epithelial to mesenchymal cells was associated with longer median time to progression (1 vs 15 months; P = .03; hazard ratio = 0.18; 95%confidence interval = 0.01-2.75). CONCLUSIONS: Our data suggest that different CTC populations are identifiable in peripheral blood of HCC patients and, for the first time in HCC, that these individual cell type profiles may have distinct clinical implications. The further characterization and analysis of patients in this ongoing study seems to be warranted

Out of Plane High Aspect Ratio Micro Wires as Suspension Elements in Inertial Sensors

Micro- and nanowires with high aspect ratios, arranged as slim and tall standing metal pillars offer promising features for microsystems [1–7]. The goals are: - 1st fabrication of high aspect ratio out of plane metal wires next to low aspect ratio blocks, - 2nd multilayer material link of these metal structures (one wire + two metal blocks), - 3rd realization and characterization of an acceleration sensor applying these structures. The KNMF services refer to the fabrication of templates made by aligned X-ray lithography. The high aspect ratio templates provide vertical cylindrical holes with aspect ratios from 16 to 33 next to template openings with low aspect ratios (Fig. 1 d). The remaining process steps are to be processed at Technische Universität Darmstadt (TUD). Results from KNMF 2010-004-000365 proposal are shown in Tab. 1. Two main issues still remain before the MEMS can prove to work as an inertial sensor: a) The structures (columns) on the X-ray exposure mask are approximately 1 µm smaller than designed. Therefore, the vertical wire is less robust and buckles (Tab. 1 b, c). Hence, the mass load has to be reduced and the process steps in Fig. 1 g have to be designed for a better wire protection. The mass load reduction can be achieved by a reduced electroforming height in Fig. 1 f. The process steps can more efficiently protect the wire, if the seed layer is designed differently. The connection from the bottom circuit path to the top of the sacrificial SU-8 3005 layer currently runs at the outer edges of the mass block (Fig. 2 a). There, it has to be wet etched for an efficient removal of the sacrificial layer. This step can be omitted, if the connection from the circuit path to the seed layer runs at the inner edges of the mass block (Fig. 2 a). The inner connection offers enough flexibility for the movement of the metal blocks when measuring acceleration. b) The electrodeposition shows to be inhomogeneous due to the design of the circuit path layer. The circuit path layer shows substantial resistances and it delivers the electrodeposition current. A layer redesign including local thickening can solve this problem (Fig. 2 b). Both improvements shown in Fig. 2 have been successfully implemented in a similar UV lithography approach at TUD [2–4], [7] and are scheduled in the KNMF proposal 2012-008- 000970. Acknowledgements The aligned X-ray exposures in the KNMF proposal 2010-004-000365 done by F J Pantenburg and P Meyer are greatly acknowledged. References [1] P. F. Greiner, J. Eberhardt, and H. F. Schlaak, “Metallic Micro Nails MAde by direct LiG process - MiNiMAL,” in Proceedings of the 2nd KNMF User Meeting, Karlsruhe, 2010, p. 69. [2] P. F. Greiner and H. F. Schlaak, “High Aspect Ratio Metal Nano and Micro Pillars as Suspension Elements in MEMS,” in 9th International Workshop on High Aspect Ratio Micro Structure Technology, HsinChu, Taiwan, 2011, pp. 53–54. [3] F. Greiner, J. Eberhardt, and H. F. Schlaak, “Senkrechte metallische Nano- und Mikrodrähte mit hohem Aspektverhältnis als neuartige Federelemente in Mikrosystemen - Vertical High Aspect Ratio Nano and Micro Wires as Novel Suspension Elements in MEMS,” in Proceedings of the Mikrosystemtechnik Kongress 2011, Berlin, Offenbach, 2011, pp. 328–331. [4] F. Greiner and H. Schlaak, “High aspect ratio metal micro and nano pillars for minimal footprint MEMS suspension,” Microsystem Technologies, pp. 1–7, 2012. [5] J. J. Schneider, H. F. Schlaak, D. Pavlidis, F. Küppers, and W. Ensinger, “Elektromechanische Sensoren mit eindimensionalen Nanoobjekten - ELEMENT, FKZ 16SV5475,” Berlin, 18-Jun-2012. [6] F. Dassinger, M. Hottes, F. Greiner, H. F. Schlaak, and W. Ensinger, “Mikro-Nano-Integration für die Inertialsensorik,” Sensor Magazin, vol. 27, no. 3, p. 24, Sep-2012. [7] F. Greiner, S. Quednau, F. Dassinger, R. Sarwar, H. F. Schlaak, M. Guttmann, and P. Meyer, “Fabrication techniques of multiscale 3D-MEMS with vertical metal micro- and nanowire integration,” J. Micromech. Microeng., submitted, 2012