Enhancement of structure-borne wave energy harvesting is investigated by exploiting metamaterial-based and metamaterial-inspired electroelastic systems. The concepts of wave focusing, localization, and funneling are leveraged to establish novel metamaterial energy harvester (MEH) configurations. The MEH systems transform the incoming structure-borne wave energy into electrical energy by coupling the metamaterial and electroelastic domains. The energy harvesting component of the work employs piezoelectric transduction due to the high power density and ease of application offered by piezoelectric materials. Therefore, in all MEH configurations studied in this work, the metamaterial system is combined with piezoelectric energy harvesting for enhanced electricity generation from waves propagating in elastic structures. Experiments are conducted to validate the dramatic performance enhancement in MEH systems as compared to using the same volume of piezoelectric patch in the absence of the metamaterial component. It is shown that MEH systems can be used for both broadband and tuned wave energy harvesting. The MEH concepts covered in this paper are (1) wave focusing using a metamaterial-inspired parabolic acoustic mirror (for broadband energy harvesting), (2) energy localization using an imperfection in a 2D lattice structure (for tuned energy harvesting), and (3) wave guiding using an acoustic funnel (for narrow-to-broadband energy harvesting). It is shown that MEH systems can boost the harvested power by more than an order of magnitude.
Superconducting NbN x thin films were deposited by plasma-enhanced atomic layer deposition (PEALD) using the metal organic precursor (tert-butylimido)-tris (diethylamino)-niobium (TBTDEN) and hydrogen plasma. The transition temperature T C and the resistivity of the NbN thin films were measured by four-point probe measurement. Their composition was analyzed by x-ray diffraction and Rutherford backscattering spectroscopy. The deposition process was optimized to obtain a low resistivity as well as a high superconducting transition temperature. A T C close to 10 K and a resistivity of 2.5 µ m as well as a critical current density of 8.9 × 10 5 A cm −2 were achieved. Originally, a high oxygen concentration was detected in the compound. By variation of the plasma parameters, the concentration could be reduced from 57 atom (at.)% to 11 at.%. Because of the excellent thickness control and conformality, such ALD films may be suited very well for applications in superconductor electronics and sensing devices.
Due to its high molecular specificity, Raman spectroscopy is a well-established analytical tool. Usually the inelastically scattered Raman light is spectrally dispersed by a spectrometer. Here, we present an alternative method, using an optical fiber as dispersive element. As the group velocity within the fiber is wavelength-dependent, different Raman bands arrive at different times at the detector. In combination with time-correlated single-photon counting, Raman spectra can be measured in the time domain. As detector we implemented a Superconducting Nanowire Single-Photon Detector (SNSPD), which possesses a timing accuracy of about 20 ps. Within this contribution we show first results of Raman spectra measured in the time domain using gradient index fibers of varying length.
We have developed a cryogenic measurement system for single-photon counting, which can be used in optical experiments requiring high time resolution in the picosecond range. The system utilizes niobium nitride superconducting nanowire single-photon detectors which are integrated in a time-correlated single-photon counting (TCSPC) setup. In this work, we describe details of the mechanical design, the electrical setup, and the cryogenic optical components. The performance of the complete system in TCSPC mode is tentatively benchmarked using 140 fs long laser pulses at a repetition frequency of 75 MHz. Due to the high temporal stability of these pulses, the measured time resolution of 35 ps (FWHM) is limited by the timing jitter of the measurement system. The result was cross-checked in a Coherent Anti-stokes Raman Scattering (CARS) setup, where scattered pulses from a β-barium borate crystal have been detected with the same time resolution.
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