Dr. Craig S. Long Profile

Dr. Craig S. Long

at Council for Scientific and Industrial Research

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Author

Publications (6)

Proceedings Article | 18 September 2008 Paper

Intracavity mode competition between classes of flat-top beams

Igor Litvin, Philip Loveday, Craig Long, Nikolai Kazak, Vladimir Belyi, Andrew Forbes

Proceedings Volume 7062, 706210 (2008) https://doi.org/10.1117/12.793686

KEYWORDS: Mirrors, Diffractive optical elements, Resonators, Output couplers, Optical resonators, Wavefronts, Gaussian beams, Chemical elements, Deformable mirrors, Laser resonators

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Proceedings Article | 12 September 2008 Paper

Variable flattened Gaussian beam order selection by dynamic control of an intracavity diffractive mirror

Andrew Forbes, Craig Long, Igor Litvin, Philip Loveday, Vladimir Belyi, Nikolai Kazak

Proceedings Volume 7062, 706219 (2008) https://doi.org/10.1117/12.793698

KEYWORDS: Mirrors, Diffractive optical elements, Electrodes, Resonators, Gaussian beams, Deformable mirrors, Output couplers, Optical resonators, Chemical elements, Beam propagation method

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Proceedings Article | 19 March 2008 Paper

A piezoelectric deformable mirror for intra-cavity laser adaptive optics

Craig Long, Philip Loveday, Andrew Forbes

Proceedings Volume 6930, 69300Y (2008) https://doi.org/10.1117/12.776178

KEYWORDS: Mirrors, Zernike polynomials, Deformable mirrors, Electrodes, Diffractive optical elements, Finite element methods, Prototyping, Adaptive optics, Laser resonators, Output couplers

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Proceedings Article | 11 April 2007 Paper

A thermo-hydraulic wax actuation system for high force and large displacement applications

Craig Long, Philip Loveday

Proceedings Volume 6527, 652707 (2007) https://doi.org/10.1117/12.714737

KEYWORDS: Actuators, Silicon, Smart materials, Temperature metrology, Solids, Liquids, Contamination, Shape memory alloys, Solid state electronics, Microelectromechanical systems

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Proceedings Article | 10 April 2007 Paper

Time domain simulation of piezoelectric excitation of guided waves in rails using waveguide finite elements

Philip Loveday, Craig Long

Proceedings Volume 6529, 65290V (2007) https://doi.org/10.1117/12.714744

KEYWORDS: Waveguides, Wave propagation, Transducers, Finite element methods, 3D modeling, Waveguide modes, Fourier transforms, Dispersion, Matrices, Sensors

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Piezoelectric transducers are commonly used to excite waves in elastic waveguides such as pipes, rock bolts and rails. While it is possible to simulate the operation of these transducers attached to the waveguide, in the time domain, using conventional finite element methods available in commercial software, these models tend to be very large. An alternative method is to use specially formulated waveguide finite elements (sometimes called Semi-Analytical Finite Elements). Models using these elements require only a two-dimensional finite element mesh of the cross-section of the waveguide. The waveguide finite element model was combined with a conventional 3-D finite element model of the piezoelectric transducer to compute the frequency response of the waveguide. However, it is difficult to experimentally verify such a frequency domain model. Experiments are usually conducted by exciting a transducer, attached to the waveguide, with a short time signal such as a tone-burst and measuring the response at a position along the waveguide before reflections from the ends of the waveguide are encountered. The measured signals are a combination of all the modes that are excited in the waveguide and separating the individual modes of wave propagation is difficult if there are numerous modes present. Instead of converting the measured signals to the frequency domain we transform the modeled frequency responses to time domain signals in order to verify the models against experiment. The frequency response was computed at many frequency points and multiplied by the frequency spectrum of the excitation signal, before an inverse Fourier transform was used to transform from the frequency domain to the time domain. The time response of a rail, excited by a rectangular piezoelectric ceramic patch, was computed and found to compare favorably with measurements performed using a laser vibrometer. By using this approach it is possible to determine which modes of propagation dominate the response and to predict the signals that would be obtained at large distances, which cannot be measured in the lab, and would be computationally infeasible using conventional finite element modeling.

Proceedings Article | 26 July 2004 Paper

Ultrasonic motor resonator design using shape and topology optimization

Philip Loveday, Craig Long, Albert Groenwold

Proceedings Volume 5390, (2004) https://doi.org/10.1117/12.539791

KEYWORDS: Resonators, 3D modeling, Ultrasonics, Solids, Prototyping, Optimization (mathematics), Chemical elements, Manufacturing, Optical amplifiers, Finite element methods

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