Numerical calculations of effective elastic properties of two cellular structures

Young's moduli of regular two-dimensional truss-like and eye-shape-like structures are simulated by using the finite element method. The structures are the idealizations of soft polymeric materials used in the electret applications. In the simulations size of the representative smallest units are varied, which changes the dimensions of the cell-walls in the structures. A power-law expression with a quadratic as the exponential term is proposed for the effective Young's moduli of the systems as a function of the solid volume fraction. The data is divided into three regions with respect to the volume fraction; low, intermediate and high concentrations. The parameters of the proposed power-law expression in each region are later represented as a function of the structural parameters, unit-cell dimensions. The presented expression can be used to predict structure/property relationship in materials with similar cellular structures. It is observed that the structures with volume fractions of solid higher than 0.15 exhibit the importance of the cell-wall thickness contribution in the elastic properties. The cell-wall thickness is the most significant factor to predict the effective Young's modulus of regular cellular structures at high volume fractions of solid. At lower concentrations of solid, eye-like structure yields lower Young's modulus than the truss-like structure with the similar anisotropy. Comparison of the numerical results with those of experimental data of poly(propylene) show good aggreement regarding the influence of cell-wall thickness on elastic properties of thin cellular films.Comment: 7 figures and 2 table

Synchronization of organ pipes: experimental observations and modeling

We report measurements on the synchronization properties of organ pipes. First, we investigate influence of an external acoustical signal from a loudspeaker on the sound of an organ pipe. Second, the mutual influence of two pipes with different pitch is analyzed. In analogy to the externally driven, or mutually coupled self-sustained oscillators, one observes a frequency locking, which can be explained by synchronization theory. Further, we measure the dependence of the frequency of the signals emitted by two mutually detuned pipes with varying distance between the pipes. The spectrum shows a broad ``hump'' structure, not found for coupled oscillators. This indicates a complex coupling of the two organ pipes leading to nonlinear beat phenomena.Comment: 24 pages, 10 Figures, fully revised, 4 big figures separate in jpeg format. accepted for Journal of the Acoustical Society of Americ

Light valve technology for HDTV-state of the art

After an introduction, in which liquid crystal and electron beam addressed light-valve projectors are briefly reviewed, the main light-valve technologies are explained in some detail. Transmissive and reflective liquid-crystal light valves with various types of addressing are described first; the trend toward active-matrix addressing and high resolution is demonstrated. Commercial light-valve projectors with electro-optic and oil-film control layers are briefly introduced before more recently developed technologies such as metallised viscoelastic layers, deformable micromechanical mirrors, and polymer-encapsulated liquid crystals are discussed. Finally, in view of its importance for the field, some aspects of active-matrix addressing are briefly examined

Photothermal poling of nonlinear optical polymer films

Photothermal heating of a nonlinear optical polymer film with a focused laser beam leads to local temperatures above the glass transition so that the molecular dipoles orient in the electric field applied to the electrodes. Periodic switching of the field direction during movement of the sample yields gratings with alternating polarity which were studied with scanning electro-optical microscopy. The width and the depth of the poled stripes were probed with electro-optical and pyroelectrical techniques, respectively. Photothermal poling may be combined with other poling techniques in order to produce various dipole-orientation patterns for device applications

Deformation behavior of thin viscoelastic layers used in an active-matrix-addressed spatial light modulator

Thin viscoelastic layers with active-matrix addressing are proposed as high-resolution spatial light modulators (SLMs) for use in a reflective schlieren light valve. Light modulation is achieved by diffraction from the periodically deformed mirror electrode covering the SLM layer. A two-dimensional array of Si-MOS transistors will be employed for addressing the viscoelastic SLM. Orthogonal and diagonally offset arrangements of pixels with two grating periods each are suggested for this active matrix. For measuring the deformation behavior of viscoelastic layers with a reflective top electrode, a standard microscope interferometer was modified so that the phase-shift technique could be employed. The deformation profile is recorded by means of a CCD image sensor, while the temporal development of the deformation is detected with a photomultiplier tube. Qualitatively, the experimental results agree with previously obtained predictions from an extensive theoretical analysis of the SLMs time behavior and spatial-frequency response