Showing papers by "Morten Willatzen published in 2013"

Metadevices for the confinement of sound and broadband double-negativity behavior

Abstract: We show that the acoustic response of perforated and elastically filled rigid screens can give rise to a broad landscape of tunable devices. We begin presenting deep-subwavelength transmission properties of a structured plate and demonstrate the immediate relationship to truly bound surface modes. We extend our theoretical model to analyze structured metal-fluid-metal wave guides for the confinement of sound and present exact expressions for the dispersion relations which describe the hybridization of resonances. We discuss the validity of our analytical model by direct comparison to full-wave simulations and use this technique in the search for broadband response in composite structures where the effective mass density and bulk modulus are simultaneously negative and exhibiting weak influences by viscous losses.

An electromechanical model for a dielectric electroactive polymer generator

Abstract: Smart electroactive materials have attracted much of the scientific interest over the past few years, as they reflect a quite promising alternative to conservative approaches used nowadays in various transducer applications. Especially Dielectric ElectroActive Polymers (DEAPs), which are constantly gaining momentum due to their superior low-speed performance, light-weighted nature and higher energy density when compared with competing technologies. In this paper an electromechanical model for a DEAP generator is presented, accounting for both the visco-hyperelastic characteristics of the polymer material, as well as the later one's experimentally determined stretch-capacitance dependence. Apart from the visco-hyperelastic model validation via purely mechanical experiments, the model's electromechanical coupling is verified as well, via experiments conducted under all three distinct energy harvesting cycles; namely the Constant Charge (CC), Constant Voltage (CV) and Constant E-field (CE) cycles.

Spontaneous Emission Enhancement at Finite-length Metal Nanowires

Abstract: We study spontaneous emission enhancement of a two-level atomic emitter placed in a dielectric medium near a flnite-length cylindrical metal nanowire. We calculate the dependence of the Purcell factor and the normalized decay rate to a continuous spectrum on the nanowire radius for several emitter transition wavelengths and difierent orientations of the transition dipole moment. For a particular transition wavelength we calculate the dependence of these quantities as well as the fl-factor on the emitter distance from the nanowire and the nanowire radius. The obtained results demonstrate that the spontaneous emission characteristics exhibit signiflcant difierences as compared to the case of an inflnite wire.

Design optimization of a linear actuator

Abstract: The mechanical contacting of a dielectric elastomer actuator is investigated. The actuator is constructed by coiling the dielectric elastomer around two parallel metal rods, similar to a rubber band stretched by two index fingers. The goal of this paper is to design the geometry and the mechanical properties of a polymeric interlayer between the elastomer and the rods, gluing all materials together, so as to optimize the mechanical durability of the system. Finite element analysis is employed for the theoretical study which is linked up to experimental results performed by Danfoss PolyPower A/S.

Ultrasonic transducer with dielectric elastomer as active layer

Abstract: There is provided a new type of ultrasound transducer, where a Dielectric Elastomer (DE) material is used as the active layer (actuation and/or sensing). Such a transducer operates by applying a combination of a DC and an AC voltage signal to achieve frequencies above 100 kHz. The DE material is typically sandwiched between two planar electrodes.