Localized acoustic and electromagnetic waves, nondiffracting fields and other directed-radiation ... more Localized acoustic and electromagnetic waves, nondiffracting fields and other directed-radiation beams are of great current interest. We present a new category of nondiffracting acoustic X-like waves that propagate in solid anisotropic elastic materials. The nondiffracting X-like pulses are spectral generalizations of monochromatic Bessel-like beams, which provides novel insight into the actual preparation of such localized space-time fields. The nondiffracting pulses
Dellingr Phase 2 deliverable DO7gives an inventory of the Nordic HPC/Cloud resources that could p... more Dellingr Phase 2 deliverable DO7gives an inventory of the Nordic HPC/Cloud resources that could potentially be shared across Nordic borders.
This report focuses on the achievements of our customers. We have selected illustrative examples ... more This report focuses on the achievements of our customers. We have selected illustrative examples from, e.g., physics, chemistry, biosciences, economics and astronomy. This report can only show a small sample of the results produced by our customers: CSC has over 1500 users, who are involved in over 700 active projects.
... an the diffraction properties. In this paper we simu-late SAW diffraction through periodic an... more ... an the diffraction properties. In this paper we simu-late SAW diffraction through periodic and nonperiodic strue-tures in YZ-LiNb03 with e numerical technique based on the angular-spectrum representation. We also apply the ...
We have prepared an extensive optimization program for holographic optical systems. The program e... more We have prepared an extensive optimization program for holographic optical systems. The program employs damped least squares algorithm to simultaneously optimize the phase functions of several planar, curved, tilted or decentered holograms. We study the convergence of the damped least squares algorithm in the context of holographic systems, and compare the results to those obtained by the simpler wavefront matching technique. We also discuss the merits of different types of phase functions and demonstrate some limits to which holographic elements can improve system performance. As an example of an optical system containing an optimized holographic element, we consider a tilted spherical mirror used in conjunction with an aberration-correction hologram. Finally, we present a possible fabrication method of the hologram.
A recently introduced method of producing nondiffracting space-time fields from ordinary diffract... more A recently introduced method of producing nondiffracting space-time fields from ordinary diffracting solutions is here examined in the space-frequency domain. It is shown that in a 3D space the method leads to localized wavefields whose Fourier components are nondiffracting beams. Hence the nondiffracting pulses are spectral generalizations of the monochromatic conical waves, a property which provides novel insight into the
... Here we [l61 have substantial film thickness, therefore these pre-consider electrical loading... more ... Here we [l61 have substantial film thickness, therefore these pre-consider electrical loading alone. Figures 5 and 6 refer to calculations for 20-period SPVDT's on YZ-LiXbO3 with the width ,I of the tiide electrode varied from LjS to 3,518. ... 11972) [7] DP Morgan, iEEE %ns. ...
Localized acoustic and electromagnetic waves, nondiffracting fields and other directed-radiation ... more Localized acoustic and electromagnetic waves, nondiffracting fields and other directed-radiation beams are of great current interest. We present a new category of nondiffracting acoustic X-like waves that propagate in solid anisotropic elastic materials. The nondiffracting X-like pulses are spectral generalizations of monochromatic Bessel-like beams, which provides novel insight into the actual preparation of such localized space-time fields. The nondiffracting pulses obtained via a frequency synthesis of nondiffracting Besselian waves are illustrated with the help of broadband X-like waves. The nondiffracting acoustic pulses in anisotropic substrates offer potential acoustic device applications.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 1997
We adapt the angular spectrum of plane waves (ASPW) decomposition to numerical simulations of the... more We adapt the angular spectrum of plane waves (ASPW) decomposition to numerical simulations of the diffraction of surface-acoustic waves (SAWs) on anisotropic model substrate, such as YZ lithium niobate. We utilize the thin-element decomposition (TED) method, appropriately modified for an anisotropic substrate; we also introduce a novel "average-wavenumber" variation of this scheme; these are numerically found to be mutually consistent. We apply the TED method to simulate wave propagation both in infinite periodic structures of metallized gratings and also in finite gratings. We demonstrate that the ASPW provides a convenient and numerically fast tool for precise diffraction calculations in practical SAW devices which also display structural variations in the lateral direction, perpendicular to the principal direction of wave propagation. Additionally, we compare the present TED method to waveguide theory in an analysis of the role of SAW reflections from the electrodes.
Bulk acoustic wave (BAW) propagation is simulated by numerically solving an equation of motion wi... more Bulk acoustic wave (BAW) propagation is simulated by numerically solving an equation of motion with the FFT method. The effect of a point source disturbance is simulated for various anisotropic media; the result has been presented as a movie. A comparison of the numerical computations with the experimental imaging data shows excellent agreement. The elasticity of the materials is visualized by constructing their slowness and group-velocity surfaces. The motivation for this work is provided by recent acoustic wavefront imaging experiments by Wolfe and collaborators
We derive the nondiffracting X waves, first discussed within acoustics by Lu and Greenleaf [IEEE ... more We derive the nondiffracting X waves, first discussed within acoustics by Lu and Greenleaf [IEEE Trans. Ultrason. Ferroelec. Freq. Contr. 39, 19 (1992)], using the general mathematical formalism based on an angular spectrum of plane waves. This serves to provide a unified treatment of not only the fundamental zeroth-order X waves of Lu and Greenleaf, but also of the lesser-known higher-order derivative X waves, first discussed here in terms of a single, universal, angular spectrum. The characteristic crossed (letter-X-like) shape and the special properties of the X waves, as well as of their angular-spectrum representation, are discussed and illustrated in detail. Asymptotically, for increasing order, the appearance of the X waves is found to transform into a triangular wedgelike waveform.
Localized acoustic and electromagnetic waves, nondiffracting fields and other directed-radiation ... more Localized acoustic and electromagnetic waves, nondiffracting fields and other directed-radiation beams are of great current interest. We present a new category of nondiffracting acoustic X-like waves that propagate in solid anisotropic elastic materials. The nondiffracting X-like pulses are spectral generalizations of monochromatic Bessel-like beams, which provides novel insight into the actual preparation of such localized space-time fields. The nondiffracting pulses
Dellingr Phase 2 deliverable DO7gives an inventory of the Nordic HPC/Cloud resources that could p... more Dellingr Phase 2 deliverable DO7gives an inventory of the Nordic HPC/Cloud resources that could potentially be shared across Nordic borders.
This report focuses on the achievements of our customers. We have selected illustrative examples ... more This report focuses on the achievements of our customers. We have selected illustrative examples from, e.g., physics, chemistry, biosciences, economics and astronomy. This report can only show a small sample of the results produced by our customers: CSC has over 1500 users, who are involved in over 700 active projects.
... an the diffraction properties. In this paper we simu-late SAW diffraction through periodic an... more ... an the diffraction properties. In this paper we simu-late SAW diffraction through periodic and nonperiodic strue-tures in YZ-LiNb03 with e numerical technique based on the angular-spectrum representation. We also apply the ...
We have prepared an extensive optimization program for holographic optical systems. The program e... more We have prepared an extensive optimization program for holographic optical systems. The program employs damped least squares algorithm to simultaneously optimize the phase functions of several planar, curved, tilted or decentered holograms. We study the convergence of the damped least squares algorithm in the context of holographic systems, and compare the results to those obtained by the simpler wavefront matching technique. We also discuss the merits of different types of phase functions and demonstrate some limits to which holographic elements can improve system performance. As an example of an optical system containing an optimized holographic element, we consider a tilted spherical mirror used in conjunction with an aberration-correction hologram. Finally, we present a possible fabrication method of the hologram.
A recently introduced method of producing nondiffracting space-time fields from ordinary diffract... more A recently introduced method of producing nondiffracting space-time fields from ordinary diffracting solutions is here examined in the space-frequency domain. It is shown that in a 3D space the method leads to localized wavefields whose Fourier components are nondiffracting beams. Hence the nondiffracting pulses are spectral generalizations of the monochromatic conical waves, a property which provides novel insight into the
... Here we [l61 have substantial film thickness, therefore these pre-consider electrical loading... more ... Here we [l61 have substantial film thickness, therefore these pre-consider electrical loading alone. Figures 5 and 6 refer to calculations for 20-period SPVDT's on YZ-LiXbO3 with the width ,I of the tiide electrode varied from LjS to 3,518. ... 11972) [7] DP Morgan, iEEE %ns. ...
Localized acoustic and electromagnetic waves, nondiffracting fields and other directed-radiation ... more Localized acoustic and electromagnetic waves, nondiffracting fields and other directed-radiation beams are of great current interest. We present a new category of nondiffracting acoustic X-like waves that propagate in solid anisotropic elastic materials. The nondiffracting X-like pulses are spectral generalizations of monochromatic Bessel-like beams, which provides novel insight into the actual preparation of such localized space-time fields. The nondiffracting pulses obtained via a frequency synthesis of nondiffracting Besselian waves are illustrated with the help of broadband X-like waves. The nondiffracting acoustic pulses in anisotropic substrates offer potential acoustic device applications.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 1997
We adapt the angular spectrum of plane waves (ASPW) decomposition to numerical simulations of the... more We adapt the angular spectrum of plane waves (ASPW) decomposition to numerical simulations of the diffraction of surface-acoustic waves (SAWs) on anisotropic model substrate, such as YZ lithium niobate. We utilize the thin-element decomposition (TED) method, appropriately modified for an anisotropic substrate; we also introduce a novel "average-wavenumber" variation of this scheme; these are numerically found to be mutually consistent. We apply the TED method to simulate wave propagation both in infinite periodic structures of metallized gratings and also in finite gratings. We demonstrate that the ASPW provides a convenient and numerically fast tool for precise diffraction calculations in practical SAW devices which also display structural variations in the lateral direction, perpendicular to the principal direction of wave propagation. Additionally, we compare the present TED method to waveguide theory in an analysis of the role of SAW reflections from the electrodes.
Bulk acoustic wave (BAW) propagation is simulated by numerically solving an equation of motion wi... more Bulk acoustic wave (BAW) propagation is simulated by numerically solving an equation of motion with the FFT method. The effect of a point source disturbance is simulated for various anisotropic media; the result has been presented as a movie. A comparison of the numerical computations with the experimental imaging data shows excellent agreement. The elasticity of the materials is visualized by constructing their slowness and group-velocity surfaces. The motivation for this work is provided by recent acoustic wavefront imaging experiments by Wolfe and collaborators
We derive the nondiffracting X waves, first discussed within acoustics by Lu and Greenleaf [IEEE ... more We derive the nondiffracting X waves, first discussed within acoustics by Lu and Greenleaf [IEEE Trans. Ultrason. Ferroelec. Freq. Contr. 39, 19 (1992)], using the general mathematical formalism based on an angular spectrum of plane waves. This serves to provide a unified treatment of not only the fundamental zeroth-order X waves of Lu and Greenleaf, but also of the lesser-known higher-order derivative X waves, first discussed here in terms of a single, universal, angular spectrum. The characteristic crossed (letter-X-like) shape and the special properties of the X waves, as well as of their angular-spectrum representation, are discussed and illustrated in detail. Asymptotically, for increasing order, the appearance of the X waves is found to transform into a triangular wedgelike waveform.
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Papers by Juha Fagerholm