The Experts below are selected from a list of 504 Experts worldwide ranked by ideXlab platform

Hoon Sohn - One of the best experts on this subject based on the ideXlab platform.

  • Accelerated damage visualization using binary search with fixed pitch-catch distance laser ultrasonic scanning
    Smart Materials and Structures, 2017
    Co-Authors: Byeongjin Park, Hoon Sohn
    Abstract:

    Laser ultrasonic scanning, especially full-field wave propagation imaging, is attractive for damage visualization thanks to its Noncontact Nature, sensitivity to local damage, and high spatial resolution. However, its practicality is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Inspired by binary search, an accelerated damage visualization technique is developed to visualize damage with a reduced scanning time. The pitch-catch distance between the excitation point and the sensing point is also fixed during scanning to maintain a high signal-to-noise ratio (SNR) of measured ultrasonic responses. The approximate damage boundary is identified by examining the interactions between ultrasonic waves and damage observed at the scanning points that are sparsely selected by a binary search algorithm. Here, a time-domain laser ultrasonic response is transformed into a spatial ultrasonic domain response using a basis pursuit approach so that the interactions between ultrasonic waves and damage, such as reflections and transmissions, can be better identified in the spatial ultrasonic domain. Then, the area inside the identified damage boundary is visualized as damage. The performance of the proposed damage visualization technique is validated excusing a numerical simulation performed on an aluminum plate with a notch and experiments performed on an aluminum plate with a crack and a wind turbine blade with delamination. The proposed damage visualization technique accelerates the damage visualization process in three aspects: (1) the number of measurements that is necessary for damage visualization is dramatically reduced by a binary search algorithm; (2) the number of averaging that is necessary to achieve a high SNR is reduced by maintaining the wave propagation distance short; and (3) with the proposed technique, the same damage can be identified with a lower spatial resolution than the spatial resolution required by full-field wave propagation imaging.

  • Accelerated damage visualization using binary search with fixed distance laser ultrasonic scanning
    Sensors and Smart Structures Technologies for Civil Mechanical and Aerospace Systems 2017, 2017
    Co-Authors: Byeongjin Park, Hoon Sohn
    Abstract:

    Laser ultrasonic scanning, especially full-field wave propagation imaging, is attractive for damage detection due to its Noncontact Nature, sensitivity to local damage, and high spatial resolution. However, its practicality is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Inspired by binary search, an accelerated laser scanning technique is developed to localize and visualize damage with reduced scanning points and scanning time. The distance between the excitation point and the sensing point during scanning is fixed in this technique to maintain a high signal-to-noise ratio for measured ultrasonic responses. First, the approximate damage boundary is identified by examining the interactions between the ultrasonic waves and damage at the sparse scanning points that are selected by the binary search algorithm. Here, a time-domain laser ultrasonic response is transformed into a spatial ultrasonic domain using a basis pursuit approach so that the interactions between the ultrasonic waves and damage, such as reflections and transmissions, can be better identified in the spatial ultrasonic domain. Then, the region inside the identified damage boundary is visualized as damage. The performance of the proposed accelerated laser scanning technique is validated through the experiment performed on an aluminum plate with a crack. The number of scanning points that is necessary for damage localization and visualization is dramatically reduced from N·M to 4log 2 N · log 2 M even for the worst case scenario. N and M represent the number of equally spaced scanning points in the x and y directions, respectively, which are required to obtain full-field wave propagation images of the target inspection region.

  • Reconstruction of laser ultrasonic wavefield images from reduced sparse measurements using compressed sensing aided super-resolution
    2017
    Co-Authors: Byeongjin Park, Hoon Sohn
    Abstract:

    Laser ultrasonic scanning is attractive for damage detection due to its Noncontact Nature, sensitivity to local damage, and high spatial resolution. However, its practicality is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Recently, compressed sensing (CS) and super-resolution (SR) are gaining popularity in the image recovery field. CS estimates unmeasured ultrasonic responses from measured responses, and SR recovers high spatial frequency information from low resolution images. Inspired by these techniques, a laser ultrasonic wavefield reconstruction technique is developed to localize and visualize damage with a reduced number of ultrasonic measurements. First, a low spatial resolution ultrasonic wavefield image for a given inspection region is reconstructed from reduced number of ultrasonic measurements using CS. Here, the ultrasonic waves are generated using a pulsed laser, and measured at a fixed sensing point using a laser Doppler vibrometer (LDV)....

  • Accelerated Noncontact laser ultrasonic scanning for damage detection using combined binary search and compressed sensing
    Mechanical Systems and Signal Processing, 2017
    Co-Authors: Byeongjin Park, Hoon Sohn, Peipei Liu
    Abstract:

    Abstract Laser ultrasonic scanning is attractive for damage detection due to its Noncontact Nature, sensitivity to local damage, and high spatial resolution. However, its practicality is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Inspired by binary search and compressed sensing, an accelerated laser scanning technique is developed to localize and visualize damage with reduced scanning points and scanning time. First, the approximate damage location is identified by examining the interactions between the ultrasonic waves and damage at the sparse scanning points that are selected by the binary search algorithm. Here, a time-domain laser ultrasonic response is transformed into a spatial ultrasonic domain using a basis pursuit approach so that the interactions between the ultrasonic waves and damage, such as reflections and transmissions, can be better identified in the spatial ultrasonic domain. Second, wavefield images around the damage are reconstructed from the previously selected scanning points using compressed sensing. The performance of the proposed accelerated laser scanning technique is validated using a numerical simulation performed on an aluminum plate with a notch and experiments performed on an aluminum plate with a crack and a carbon fiber-reinforced plastic plate with delamination. The number of scanning points that is necessary for damage localization and visualization is dramatically reduced from N · M to 2 log 2 N · log 2 M . N and M represent the number of equally spaced scanning points in the x and y directions, respectively, which are required to obtain full-field wave propagation images of the target inspection region. For example, the number of scanning points in the composite plate experiment is reduced by 97.1% (from 2601 points to 75 points).

Ramin Golestanian - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear dynamics of a rack-pinion-rack device powered by the Casimir force
    Physical Review E, 2010
    Co-Authors: Mirfaez Miri, Vahid Nekouie, Ramin Golestanian
    Abstract:

    Using the lateral Casimir force\char22{}a manifestation of the quantum fluctuations of the electromagnetic field between objects with corrugated surfaces\char22{}as the main force transduction mechanism, a nanomechanical device with rich dynamical behaviors is proposed. The device is made of two parallel racks that are moving in the same direction and a pinion in the middle that couples with both racks via the Noncontact lateral Casimir force. The built-in frustration in the device causes it to be very sensitive and react dramatically to minute changes in the geometrical parameters and initial conditions of the system. The Noncontact Nature of the proposed device could help with the ubiquitous wear problem in nanoscale mechanical systems.

  • A frustrated non-contact rack-pinion-rack device
    Journal of Physics: Conference Series, 2009
    Co-Authors: Mirfaez Miri, Ramin Golestanian
    Abstract:

    A design is proposed for a mechanical device made of a nanoscale pinion sandwiched without contact between two racks that exert opposing forces rooted in the quantum fluctuations of the electromagnetic field via the lateral Casimir force. The built-in frustration in the design of the system helps it to react dramatically to minute changes in the geometrical features, which suggests that it could act as a good sensor. The Noncontact Nature of this device could help solve the infamous wear problem in nanoscale mechanical devices.

  • A frustrated nanomechanical device powered by the lateral Casimir force
    Applied Physics Letters, 2008
    Co-Authors: Mirfaez Miri, Ramin Golestanian
    Abstract:

    The coupling between corrugated surfaces due to the lateral Casimir force is employed to propose a nanoscale mechanical device composed of two racks and a pinion. The Noncontact Nature of the interaction allows for the system to be made frustrated by choosing the two racks to move in the same direction and forcing the pinion to choose between two opposite directions. This leads to a rich and sensitive phase behavior, which makes the device potentially useful as a mechanical sensor or amplifier. The device could also be used to make a mechanical clock signal of tunable frequency.

Byeongjin Park - One of the best experts on this subject based on the ideXlab platform.

  • Accelerated damage visualization using binary search with fixed pitch-catch distance laser ultrasonic scanning
    Smart Materials and Structures, 2017
    Co-Authors: Byeongjin Park, Hoon Sohn
    Abstract:

    Laser ultrasonic scanning, especially full-field wave propagation imaging, is attractive for damage visualization thanks to its Noncontact Nature, sensitivity to local damage, and high spatial resolution. However, its practicality is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Inspired by binary search, an accelerated damage visualization technique is developed to visualize damage with a reduced scanning time. The pitch-catch distance between the excitation point and the sensing point is also fixed during scanning to maintain a high signal-to-noise ratio (SNR) of measured ultrasonic responses. The approximate damage boundary is identified by examining the interactions between ultrasonic waves and damage observed at the scanning points that are sparsely selected by a binary search algorithm. Here, a time-domain laser ultrasonic response is transformed into a spatial ultrasonic domain response using a basis pursuit approach so that the interactions between ultrasonic waves and damage, such as reflections and transmissions, can be better identified in the spatial ultrasonic domain. Then, the area inside the identified damage boundary is visualized as damage. The performance of the proposed damage visualization technique is validated excusing a numerical simulation performed on an aluminum plate with a notch and experiments performed on an aluminum plate with a crack and a wind turbine blade with delamination. The proposed damage visualization technique accelerates the damage visualization process in three aspects: (1) the number of measurements that is necessary for damage visualization is dramatically reduced by a binary search algorithm; (2) the number of averaging that is necessary to achieve a high SNR is reduced by maintaining the wave propagation distance short; and (3) with the proposed technique, the same damage can be identified with a lower spatial resolution than the spatial resolution required by full-field wave propagation imaging.

  • Accelerated damage visualization using binary search with fixed distance laser ultrasonic scanning
    Sensors and Smart Structures Technologies for Civil Mechanical and Aerospace Systems 2017, 2017
    Co-Authors: Byeongjin Park, Hoon Sohn
    Abstract:

    Laser ultrasonic scanning, especially full-field wave propagation imaging, is attractive for damage detection due to its Noncontact Nature, sensitivity to local damage, and high spatial resolution. However, its practicality is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Inspired by binary search, an accelerated laser scanning technique is developed to localize and visualize damage with reduced scanning points and scanning time. The distance between the excitation point and the sensing point during scanning is fixed in this technique to maintain a high signal-to-noise ratio for measured ultrasonic responses. First, the approximate damage boundary is identified by examining the interactions between the ultrasonic waves and damage at the sparse scanning points that are selected by the binary search algorithm. Here, a time-domain laser ultrasonic response is transformed into a spatial ultrasonic domain using a basis pursuit approach so that the interactions between the ultrasonic waves and damage, such as reflections and transmissions, can be better identified in the spatial ultrasonic domain. Then, the region inside the identified damage boundary is visualized as damage. The performance of the proposed accelerated laser scanning technique is validated through the experiment performed on an aluminum plate with a crack. The number of scanning points that is necessary for damage localization and visualization is dramatically reduced from N·M to 4log 2 N · log 2 M even for the worst case scenario. N and M represent the number of equally spaced scanning points in the x and y directions, respectively, which are required to obtain full-field wave propagation images of the target inspection region.

  • Reconstruction of laser ultrasonic wavefield images from reduced sparse measurements using compressed sensing aided super-resolution
    2017
    Co-Authors: Byeongjin Park, Hoon Sohn
    Abstract:

    Laser ultrasonic scanning is attractive for damage detection due to its Noncontact Nature, sensitivity to local damage, and high spatial resolution. However, its practicality is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Recently, compressed sensing (CS) and super-resolution (SR) are gaining popularity in the image recovery field. CS estimates unmeasured ultrasonic responses from measured responses, and SR recovers high spatial frequency information from low resolution images. Inspired by these techniques, a laser ultrasonic wavefield reconstruction technique is developed to localize and visualize damage with a reduced number of ultrasonic measurements. First, a low spatial resolution ultrasonic wavefield image for a given inspection region is reconstructed from reduced number of ultrasonic measurements using CS. Here, the ultrasonic waves are generated using a pulsed laser, and measured at a fixed sensing point using a laser Doppler vibrometer (LDV)....

  • Accelerated Noncontact laser ultrasonic scanning for damage detection using combined binary search and compressed sensing
    Mechanical Systems and Signal Processing, 2017
    Co-Authors: Byeongjin Park, Hoon Sohn, Peipei Liu
    Abstract:

    Abstract Laser ultrasonic scanning is attractive for damage detection due to its Noncontact Nature, sensitivity to local damage, and high spatial resolution. However, its practicality is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Inspired by binary search and compressed sensing, an accelerated laser scanning technique is developed to localize and visualize damage with reduced scanning points and scanning time. First, the approximate damage location is identified by examining the interactions between the ultrasonic waves and damage at the sparse scanning points that are selected by the binary search algorithm. Here, a time-domain laser ultrasonic response is transformed into a spatial ultrasonic domain using a basis pursuit approach so that the interactions between the ultrasonic waves and damage, such as reflections and transmissions, can be better identified in the spatial ultrasonic domain. Second, wavefield images around the damage are reconstructed from the previously selected scanning points using compressed sensing. The performance of the proposed accelerated laser scanning technique is validated using a numerical simulation performed on an aluminum plate with a notch and experiments performed on an aluminum plate with a crack and a carbon fiber-reinforced plastic plate with delamination. The number of scanning points that is necessary for damage localization and visualization is dramatically reduced from N · M to 2 log 2 N · log 2 M . N and M represent the number of equally spaced scanning points in the x and y directions, respectively, which are required to obtain full-field wave propagation images of the target inspection region. For example, the number of scanning points in the composite plate experiment is reduced by 97.1% (from 2601 points to 75 points).

Mirfaez Miri - One of the best experts on this subject based on the ideXlab platform.

  • Nonlinear dynamics of a rack-pinion-rack device powered by the Casimir force
    Physical Review E, 2010
    Co-Authors: Mirfaez Miri, Vahid Nekouie, Ramin Golestanian
    Abstract:

    Using the lateral Casimir force\char22{}a manifestation of the quantum fluctuations of the electromagnetic field between objects with corrugated surfaces\char22{}as the main force transduction mechanism, a nanomechanical device with rich dynamical behaviors is proposed. The device is made of two parallel racks that are moving in the same direction and a pinion in the middle that couples with both racks via the Noncontact lateral Casimir force. The built-in frustration in the device causes it to be very sensitive and react dramatically to minute changes in the geometrical parameters and initial conditions of the system. The Noncontact Nature of the proposed device could help with the ubiquitous wear problem in nanoscale mechanical systems.

  • A frustrated non-contact rack-pinion-rack device
    Journal of Physics: Conference Series, 2009
    Co-Authors: Mirfaez Miri, Ramin Golestanian
    Abstract:

    A design is proposed for a mechanical device made of a nanoscale pinion sandwiched without contact between two racks that exert opposing forces rooted in the quantum fluctuations of the electromagnetic field via the lateral Casimir force. The built-in frustration in the design of the system helps it to react dramatically to minute changes in the geometrical features, which suggests that it could act as a good sensor. The Noncontact Nature of this device could help solve the infamous wear problem in nanoscale mechanical devices.

  • A frustrated nanomechanical device powered by the lateral Casimir force
    Applied Physics Letters, 2008
    Co-Authors: Mirfaez Miri, Ramin Golestanian
    Abstract:

    The coupling between corrugated surfaces due to the lateral Casimir force is employed to propose a nanoscale mechanical device composed of two racks and a pinion. The Noncontact Nature of the interaction allows for the system to be made frustrated by choosing the two racks to move in the same direction and forcing the pinion to choose between two opposite directions. This leads to a rich and sensitive phase behavior, which makes the device potentially useful as a mechanical sensor or amplifier. The device could also be used to make a mechanical clock signal of tunable frequency.

V.v. Varadan - One of the best experts on this subject based on the ideXlab platform.

  • In situ microwave characterization of nonplanar dielectric objects
    IEEE Transactions on Microwave Theory and Techniques, 2000
    Co-Authors: K.a. Jose, V.v. Varadan
    Abstract:

    In this paper, a novel experimental solution is presented for the nondestructive, Noncontact, and in situ characterization of dielectric objects of curved shape using a spot-focused freespace measurement system. Measurements were made on Plexiglas and glass samples of cylindrical shape with different radii of curvature, and the complex permittivities were computed from the measured S/sub 21/ and S/sub 12/. Comparing the results with planar samples shows that the curvature does not significantly affect the accuracy of the measured permittivity of cylindrical surfaces if the radii of curvature are large compared to the size of the focusing spot. Results for a number of curved samples agree with the published data and this demonstrates the usefulness of a spot-focused free-space system for in situ characterization and evaluation of materials and complex structures during processing and fabrication. The other benefit of this approach is the Noncontact Nature of the method, which permits measurement of solids and liquids in high/low-temperature environments. The spot-focused beam permits characterization of small or large samples.

  • In situ Microwave Characterization of Nonplanar
    2000
    Co-Authors: K.a. Jose, V.v. Varadan
    Abstract:

    In this paper, a novel experimental solution is pre- sented for the nondestructive, Noncontact, and in situ characteriza- tion of dielectric objects of curved shape using a spot-focused free- space measurement system. Measurements were made on Plexiglas and glass samples of cylindrical shape with different radii of curva- ture, and the complex permittivities were computed from the mea- sured and . Comparing the results with planar samples show that the curvature does not significantly affect the accuracy of the measured permittivity of cylindrical surfaces if the radii of curvature are large compared to the size of the focusing spot. Re- sults for a number of curved samples agree with the published data and this demonstrates the usefulness of a spot-focused free-space system for in situ characterization and evaluation of materials and complex structures during processing and fabrication. The other benefit of this approach is the Noncontact Nature of the method, which permits measurement of solids and liquids in high-/low-tem- perature environments. The spot-focused beam permits character- ization of small or large samples.