Universität Stuttgart
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Item Open Access Reflection of high-frequency phonons at silicon-solid interfaces(1981) Marx, Dieter; Eisenmenger, WolfgangIn reflection experiments with phonons of frequencies above 280 GHz propagating along (110) directions we observed large deviations from the acoustic mismatch theory for silicon-metal, silicon-condensed gas, and silicon-liquid helium interfaces.Item Open Access Diffusive scattering of high-frequency phonons at free silicon surfaces(1983) Marx, Dieter; Eisenmenger, WolfgangComparing measurements of high-frequency phonon reflection at the uncovered and optically polished (100)-silicon surface, with calculations considering phonon focusing, reveal complete diffusive scattering with at most 4% specular reflection contribution. Two possible mechanisms causing diffusive scattering are discussed.Item Open Access Phonon detection by the fountain pressure in superfluid 4Helium films(1980) Eisenmenger, WolfgangThe importance of phonon focussing was first demonstrated by Taylor, Maris and Elbaum, who calculated the phonon intensities or different modes in single crystals from the detailed form of the angle or k-dependent sound velocity surfaces. The results of these calculations are well-confirmed by experiment. It is quite surprising that phonon focussing leads in several crystals to very narrow beams of phonon energy propagation especially for transverse modes, as recently calculated by Rosch and Weis, who presented their computer results in a very instructive form. From these theoretical results it appears worthwhile to devise methods by which the intensity distribution of incoherent phonons propagating in single crystals can be measured in detail or directly imaged.Item Open Access Nonequilibrium phonons(1980) Eisenmenger, WolfgangNonequilibrium phonon experiments with superconducting film tunneling junctions have demonstrated that phonon spectra produced by nonequilibrium quasiparticle distributions are well in accord with the predictions of theory. This is also demonstrated by the successful application of superconducting tunneling junctions for phonon absorption spectroscopy and recently also for phonon emission spectroscopy.Item Open Access Neuartige PVDF-Dünnschichtwandler für Ultraschallmessungen im GHz-Bereich(1985) Ambrosy, Anton; Holdik, Karl; Eisenmenger, WolfgangWegen seines hohen Piezoeffekts wird auch das Pol:ymer Polyvinylidenfluorid (PVDP) als Ultraschallwandler benutzt. Bisher war es jedoch nicht möglich PVDP-Wandler im GHz-Bereich zu verwenden, da für hochfrequente Anwendungen dünnere und ebenere Folien. als sie kommerziell angeboten werden, notwendig sind. Mit der nun folgenden Methode wurden nun erstmals PVDF-Dünnschichtwandler, die noch bei 24 GHz funktionieren, aus der Lösung hergestellt.Item Open Access Satellite phonon absorption lines above the 875 GHz resonance of interstitial oxygen in silicon(1987) Dittrich, Ehrenfried; Scheitler, Wolfgang; Eisenmenger, WolfgangAcoustic phonon spectroscopy with superconducting tunneling junctions as phonon generator and detector revealed a large number of sharp absorption lines between 875 GHz (oxygen resonance) and 1.35 THz for silicon doped with interstitial oxygen (Si:0i). The strength of these lines scales with the square of the oxygen concentration ranging from 1017 to 1018 cm-3. Under mechanical stress the lines show a frequency shift almost identical to the main oxygen resonance at 875 GHz as well as to the also observable isotope resonance. These satellite absorption lines are therefore discussed as 0i–0i neighbour interaction. This is supported by the influence of annealing.Item Open Access Polarization distributions in isotropic, stretched or annealed PVDF films(1988) Bihler, Eckardt; Holdik, Karl; Eisenmenger, WolfgangThe spatial distribution of the polarization in polyvinylidene fluoride (PVDF) films was measured at room temperature with the PPS (piezoelectric pressure step) method. In order to investigate the time development under external fields, a thin insulation polyethylene terephthalate (PET) film covering an evaporated aluminium electrode was inserted between the sample and the measuring electrode. The observed development of inhomogeneous and internal polarization zones is attributed to charge injection and charge trapping at the polarization zone boundaries. The polarization zone develops at a position where the critical field strength for dipole orientation in the crystallites is exceeded by the approach of injected homocharges (or without injection by the depletion of internal homocharges and the excess of heterocharges). The critical field for α-crystallites corresponds to an electric field phase transition at 1.2 MV/cm. The development of central polarization zones in PVDF containing β-crystallites indicates injection of charges with both signs and almost equal mobility. The results indicate that the β-crystallites determine the charge injection rate or the mobility or both.Item Open Access Analysis of the phonon spectrum emitted by superconducting Al-tunneling junctions at high quasiparticle injection rates(1981) Welte, Michael; Eisenmenger, WolfgangThe phonon spectrum emitted by superconducting Al-tunneling junctions is analyzed by experiments, in which two junctions of different energy gaps are used as phonon generator and detector. The energy gap of the Al-films is varied by the evaporation conditions. The experiments show clearly that the phonon spectrum and the quasiparticle distributions in the generator are strongly nonthermal and depend markedly on the primary tunneling injection. At high injection rates also significant consequences of gap reductions and instabilities are observed.Item Open Access Physikalisch-medizinische Aspekte selbstfokussierter elektromagnetisch erzeugter Stoßwellen(1988) Eisenmenger, WolfgangGegenüber schon länger bekannten Methoden der Stoßwellenerzeugung in Flüssigkeiten wie Unterwasserfunkenentladung, chemische Detonation, mechanischer Schlag oder der Fokussierung von piezoelektrisch erzeugten Druckwellen, wurde die elektromagnetische Stoßwellenerzeugung erst im Jahre 1959 eingeführt. Sie diente seinerzeit zur Erzeugung von ebenen Stoßwellen für physikalische Stoßfrontuntersuchungen. Da mit diesem Generator bereits ebene Stoßwellen mit Drucken bis zu 700 bar über einem Querschnitt von 50 mm Durchmesser erzeugt werden konnten, ist verständlich, daß bei geeigneter Fokussierung leicht höhere Fokusdrucke bei wesentlich geringeren Drucken am Stoßwellengenerator selbst zu realisieren sind. Diese Situation führte zur Entwicklung des Stoßwellenlithotriptors "Lithostar" mit Linsenfokussierung sowie zum Vorschlag eines selbstfokussierenden elektromagnetischen Stoßwellengenerators.Item Open Access Biological effects and physical characterization of shock waves by an XL-1 experimental lithotripter(1989) Brümmer, Franz; Staudenraus, Joachim; Nesper, Martina; Suhr, Dierk; Eisenmenger, Wolfgang; Hülser, Dieter F.Extracorporeal shock wave lithotripsy (ESWL) has become the clinical standard method for non-invasive disintegration not only of concrements in kidney and urinary tract but also of gallstones. Despite the widespread clinical use of ESWL, the mechanism of stone destruction is not yet really understood, but several possibilities (cavitation, shock wave reflection) are discussed. The final cause of various side effects is still under discussion. Nevertheless, during the last few years much effort was put into possible extensions of ESWL applications On the other hand , physical characterizations of shock waves are rarely reported and combined measurements of biological effects in vitro and physical characterization of the applied shock waves are not available. We, therefore, examined the influence of water temperature and gas content on the shock wave efficency in biological systems and determined several physical characteristics (pressure amplitudes, rise time etc.) of the shock waves under the same experimental conditions.