Now showing items 1-19 of 19

    • Anisotropy sensitivity of an acoustic lens with slit aperture 

      Atalar, Abdullah; Ishikawa, I.; Ogura, Y.; Tomita, K. (IEEE, 1993)
      A conventional spherical acoustic lens is modified by restricting its aperture in the form of a slit to provide directional sensitivity. The spacing between the two parallel absorbing sheets forming the slit is adjustable ...
    • Asymptotic wave-like modeling of dielectric lenses 

      Yurchenko V.B.; Itintas, A.A. (2007)
      We propose asymptotic wave-like approximations for the accurate modeling of dielectric lenses used in quasi-optical systems of millimeter, submillimeter, and infrared wave applications. For the comparison, we obtain an ...
    • Bi-angular lens for material characterization 

      Yaralioglu G.G.; Atalar, Abdullah; Koymen H. (IEEE, Piscataway, NJ, United States, 1994)
      In this paper a new lens design is proposed for characterization of layered materials. Lamb wave lens employs Lamb waves for this purpose since these waves propagate along interfaces. However, below cut-off angle, the ...
    • Camera sabotage discovery for video surveillance applications 

      Aksay, A.; Temizel, A.; Çetin, A.E. (2007)
      In the recent years, number of surveillance cameras deployed has increased significantly. However it is important that these cameras are functioning as intended and capturing meaningful data. Offenders resort to techniques ...
    • Camera tamper detection using wavelet analysis for video surveillance 

      Aksay, A.; Temizel, A.; Çetin, A. E. (2007)
      It is generally accepted that video surveillance system operators lose their concentration after a short period of time and may miss important events taking place. In addition, many surveillance systems are frequently left ...
    • Characterization and imaging with lamb wave lens at gigahertz frequencies 

      Bozkurt, A.; Yaralioglu, G.; Atalar, Abdullah; Koymen, H.; Kramer, K. (IEEE, 1994-10)
      Lamb wave lenses with conical refracting surfaces are fabricated for use at 400 MHz and 1 GHz. The conical surfaces are ground and polished with mechanical means and they are sufficiently smooth for the frequencies of ...
    • Characterization of layered materials by the Lamb wave lens 

      Atalar, Abdullah; Koymen, H.; Degertekin, L. (IEEE, 1990)
      The Lamb wave lens is a type of lens that can replace the conventional lens of an acoustic microscope for some applications. When it insonifies a layered solid structure, it excites a single mode in the structure, provided ...
    • Compact optical temporal processors 

      Mendlovic, D.; Melamed, O.; Ozaktas, H. M. (Optical Society of America, 1995)
      Optical signal processing can be done with time-lens devices. A temporal processor based on chirp-z transformers is suggested. This configuration is more compact than a conventional 4-f temporal processor. On the basis of ...
    • Electromagnetic wave focusing from sources inside a two-dimensional left-handed material superlens 

      Aydın, K.; Bulu, I.; Özbay, E. (Institute of Physics Publishing, 2006)
      Lenses made of negative index materials exhibit different focusing behaviours compared to positive index material lenses. Flat lens behaviour and imaging below the diffraction limit is possible with negative refractive ...
    • Fractional free space, fractional lenses, and fractional imaging systems 

      Sümbül, U.; Ozaktas, H. M. (OSA - The Optical Society, 2003)
      Continuum extensions of common dual pairs of operators are presented and consolidated, based on the fractional Fourier transform. In particular, the fractional chirp multiplication, fractional chirp convolution, and ...
    • Fresnel lamb wave and V-groove lenses with tunable mode selectivity 

      Yarahoglu, G. G.; Atalar, Abdullah; Koymen, H. (IEEE, 1995)
      The Lamb wave and V-groove lenses are distinguished by their high surface wave excitation efficiencies. However, due to the fixed incidence angle, a particular lens can only be used for materials having surface wave ...
    • A Lamb Wave Lens for Acoustic Microscopy 

      Atalar, Abdullah; Koymen H.; Degertekin F.L. (1992)
      In a conventional scanning acoustic microscope the excited leaky modes contributes significantly to the high contrast obtained in the images. However, all such modes exist simultaneously, and the interpretation of the ...
    • Negative refraction and subwavelength focusing using photonic crystals 

      Ozbay, E.; Aydin, K.; Alici, K. B.; Guven, K. (2005)
      We review certain novel optical properties of two-dimensional dielectric photonic crystals (PCs) which exhibit negative refraction behavior. We investigate two mechanisms which utilize the band structure of the PC and lead ...
    • New directional acoustic lens: V-groove lens 

      Bozkurt, A.; Yarahoglu, G.; Atalar, Abdullah; Koymen, H. (IEEE, 1993)
      A new directional acoustic lens is introduced. The geometry is very similar to the line-focus lens except the lens cavity, which is shaped as a groove with flat-bottom V cross section. The slanted planar edges of the groove ...
    • Physical optics modeling of 2D dielectric lenses 

      Yurchenko, V. B.; Altintas, A. (Optical Society of America, 2009-01-27)
      We propose an advanced physical optics formulation for the accurate modeling of dielectric lenses used in quasi-optical systems of millimeter, submillimeter, and infrared wave applications. For comparison, we obtain an ...
    • Relationships among ray optical, Gaussian beam, and fractional Fourier transform descriptions of first-order optical systems 

      Ozaktas, H. M.; Erden, M. F. (Elsevier BV * North-Holland, 1997-11-01)
      Although wave optics is the standard method of analyzing systems composed of a sequence of lenses separated by arbitrary distances, it is often easier and more intuitive to ascertain the function and properties of such ...
    • Scaling of diffractive and refractive lenses for optical computing and interconnections 

      Ozaktas, H. M.; Urey, H.; Lohmann, A. W. (Optical Society of America, 1994-06-10)
      We discuss both numerically and analytically how the space-bandwidth product and the information density of lenses scale as functions of their diameter and f-number over many orders of magnitude. This information may be ...
    • Simulating a wavelength-size 2-D lens with an accurate numerical method 

      Boriskin, A. V.; Nosich, A. I.; Altintas, A. (IEEE Computer Society, 2001)
      The effect of a localized light source directivity improvement due to an arbitrarily shaped dielectric cylinder taken as a 2-D model of a dielectric lens is studied. The source is simulated by the field of a complex ...
    • Verification of impedance matching at the surface of left-handed materials 

      Aydın, K.; Bulu, I.; Özbay, E. (Wiley, 2006)
      Impedance matching at the surface of left-handed materials (LHM) is required for certain applications including a perfect lens. In this study, we present the experimental and theoretical verification of an impedance-matched ...