@article{AhnertAbelKolloscheetal.2011,
  author    = {Ahnert, Karsten and Abel, Markus and Kollosche, Matthias and Jorgensen, Per Jorgen and Kofod, Guggi},
  title     = {Soft capacitors for wave energy harvesting},
  series = {Journal of materials chemistry},
  volume    = {21},
  journal   = {Journal of materials chemistry},
  number    = {38},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {0959-9428},
  doi       = {10.1039/c1jm12454d},
  pages     = {14492 -- 14497},
  year      = {2011},
  abstract  = {Wave energy harvesting could be a substantial renewable energy source without impact on the global climate and ecology, yet practical attempts have struggled with the problems of wear and catastrophic failure. An innovative technology for ocean wave energy harvesting was recently proposed, based on the use of soft capacitors. This study presents a realistic theoretical and numerical model for the quantitative characterization of this harvesting method. Parameter regions with optimal behavior are found, and novel material descriptors are determined, which dramatically simplify analysis. The characteristics of currently available materials are evaluated, and found to merit a very conservative estimate of 10 years for raw material cost recovery.},
  language  = {en}
}
@article{KappelAbelGerhard2011,
  author    = {Kappel, Marcel and Abel, Markus and Gerhard, Reimund},
  title     = {Characterization and calibration of piezoelectric polymers in situ measurements of body vibrations},
  series = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques},
  volume    = {82},
  journal   = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques},
  number    = {7},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0034-6748},
  doi       = {10.1063/1.3607435},
  pages     = {6},
  year      = {2011},
  abstract  = {Piezoelectric polymers are known for their flexibility in applications, mainly due to their bending ability, robustness, and variable sensor geometry. It is an optimal material for minimal-invasive investigations in vibrational systems, e.g., for wood, where acoustical impedance matches particularly well. Many applications may be imagined, e. g., monitoring of buildings, vehicles, machinery, alarm systems, such that our investigations may have a large impact on technology. Longitudinal piezoelectricity converts mechanical vibrations normal to the polymer-film plane into an electrical signal, and the respective piezoelectric coefficient needs to be carefully determined in dependence on the relevant material parameters. In order to evaluate efficiency and durability for piezopolymers, we use polyvinylidene fluoride and measure the piezoelectric coefficient with respect to static pressure, amplitude of the dynamically applied force, and long-term stability. A known problem is the slow relaxation of the material towards equilibrium, if the external pressure changes; here, we demonstrate how to counter this problem with careful calibration. Since our focus is on acoustical measurements, we determine accurately the frequency response curve - for acoustics probably the most important characteristic. Eventually, we show that our piezopolymer transducers can be used as a calibrated acoustical sensors for body vibration measurements on a wooden musical instrument, where it is important to perform minimal-invasive measurements. A comparison with the simultaneously recorded airborne sound yields important insight of the mechanism of sound radiation in comparison with the sound propagating in the material. This is especially important for transient signals, where not only the long-living eigenmodes contribute to the sound radiation. Our analyses support that piezopolymer sensors can be employed as a general tool for the determination of the internal dynamics of vibrating systems.},
  language  = {en}
}