Prof. Perngjin F. Pai Profile

Prof. Perngjin F. Pai

Retired C. W. LaPierre Professor at Univ of Missouri

SPIE Involvement:

Author | Editor

Publications (25)

Proceedings Article | 14 December 2015 Paper

Two-dimensional acoustic metamaterial structure for potential image processing

Hongwei Sun, Yu Han, Ying Li, Frank Pai

Proceedings Volume 9815, 981520 (2015) https://doi.org/10.1117/12.2230066

KEYWORDS: Metamaterials, Acoustics, Wave propagation, Electromagnetic radiation, Magnetism, Absorption, Image processing, Refractive index, Image filtering, Ultrasonography

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SPIE Press Book | 18 November 2015

Theory and Design of Acoustic Metamaterials

KEYWORDS: Metamaterials, Acoustics, Crystals, Resonators, Photonic crystals, Absorption, Solids, Wave propagation, Wave plates, Optimization (mathematics)

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Theory and Design of Acoustic Metamaterials

Proceedings Article | 23 March 2015 Paper

Design of multi-stopband metamaterial plates for absorption of broadband elastic waves and vibration

Hao Peng, P. Pai

Proceedings Volume 9438, 94380X (2015) https://doi.org/10.1117/12.2084197

KEYWORDS: Metamaterials, Acoustics, Wave plates, Absorption, Wave propagation, Numerical integration, Scattering, Resonators, Doppler effect, Earthquakes

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Proceedings Article | 9 March 2014 Paper

Acoustic metamaterial structures based on multi-frequency vibration absorbers

P. Frank Pai, Hao Peng

Proceedings Volume 9064, 90641X (2014) https://doi.org/10.1117/12.2045061

KEYWORDS: Metamaterials, Acoustics, Wave propagation, Absorption, Finite element methods, Electromagnetic radiation, Beam propagation method, Dispersion, Composites, Chemical species

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This paper presents a new metamaterial beam based on multi-frequency vibration absorbers for broadband vibration absorption. The proposed metamaterial beam consists of a uniform isotropic beam and small two-mass spring-mass- damper subsystems at many locations along the beam to act as multi-frequency vibration absorbers. For an infinite metamaterial beam, governing equations of a unit cell are derived using the extended Hamilton principle. The existence of two stopbands is demonstrated using a model based on averaging material properties over a cell length and a model based on finite element modeling and the Bloch-Floquet theory for periodic structures. For a finite metamaterial beam, because these two idealized models cannot be used for finite beams and/or elastic waves having short wavelengths, a finite-element method is used for detailed modeling and analysis. The concepts of negative effective mass and effective stiffness and how the spring-mass-damper subsystem creates two stopbands are explained in detail. Numerical simulations reveal that the actual working mechanism of the proposed metamaterial beam is based on the concept of conventional mechanical vibration absorbers. For an incoming wave with a frequency in one of the two stopbands, the absorbers are excited to vibrate in their optical modes to create shear forces to straighten the beam and stop the wave propagation. For an incoming wave with a frequency outside of but between the two stopbands, it can be efficiently damped out by the damper with the second mass of each absorber. Hence, the two stopbands are connected into a wide stopband. Numerical examples validate the concept and show that the structure’s boundary conditions do not have significant influence on the absorption of high-frequency waves. However, for absorption of low-frequency waves, the structure’s boundary conditions and resonance frequencies and the location and spatial distribution of absorbers need to be considered in design, and it is better to use heavier masses for absorbers.

Proceedings Article | 17 April 2013 Paper

Actual working mechanisms of smart metamaterial structures

P. Frank Pai, Mannur Sundaresan

Proceedings Volume 8695, 86952M (2013) https://doi.org/10.1117/12.2009792

KEYWORDS: Metamaterials, Acoustics, Wave propagation, Finite element methods, Absorption, Beam propagation method, Manufacturing, Electromagnetism, Numerical simulations, Electromagnetic radiation

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Here we present methods for modeling, analysis, and design of metamaterial beams for broadband vibration absorption/isolation. The proposed metamaterial beam consists of a uniform isotropic beam with many small spring-mass- damper subsystems integrated at separated locations along the beam to act as vibration absorbers. For a unit cell of an infinite metamaterial beam, governing equations are derived using the extended Hamilton principle. The existence of stopband is demonstrated using a model based on averaging material properties over a cell length and a model based on finite element modeling and the Bloch-Floquet theory for periodic structures. However, these two idealized models cannot be used for finite beams and/or elastic waves having short wavelengths. For finite metamaterial beams, a linear finite element method is used for detailed modeling and analysis. Both translational and rotational absorbers are considered. Because results show that rotational absorbers are not efficient, only translational absorbers are recommended for practical designs. The concepts of negative effective mass and stiffness and how the spring-mass-damper subsystems create a stopband are explained in detail. Numerical simulations reveal that the actual working mechanism of the proposed metamaterial beam is based on the concept of conventional mechanical vibration absorbers. It uses the incoming elastic wave in the beam to resonate the integrated spring-mass-damper absorbers to vibrate in their optical mode at frequencies close to but above their local resonance frequencies to create shear forces and bending moments to straighten the beam and stop the wave propagation. This concept can be easily extended to design a broadband absorber that works for elastic waves of short and long wavelengths. Numerical examples validate the concept and show that, for high-frequency waves, the structure’s boundary conditions do not have significant influence on the absorbers’ function. However, for absorption of low-frequency waves, the boundary conditions and resonant modes of the structure need to be considered in the design. With appropriate design calculations, finite discrete spring-mass- damper absorbers can be used, and hence expensive micro- or nano-manufacturing techniques are not needed for design and manufacturing of such metamaterial beams for broadband vibration absorption/isolation.

Proceedings Article | 17 April 2013 Paper

Dynamic characteristics and vibration-based damage inspection of structures with actual fatigue cracks

P. Frank Pai, Jun Liu, Mannur Sundaresan

Proceedings Volume 8695, 869533 (2013) https://doi.org/10.1117/12.2009722

KEYWORDS: Inspection, Time-frequency analysis, Signal processing, Data modeling, System identification, Complex systems, Temporal resolution, Data processing, Imaging systems, Dynamical systems

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Proceedings Article | 20 April 2012 Paper

Identification of nonlinearities for damage inspection of thin-walled structures

P. Frank Pai, Mannur Sundaresan, Bao Anh Nguyen

Proceedings Volume 8348, 83482F (2012) https://doi.org/10.1117/12.914399

KEYWORDS: Time-frequency analysis, Complex systems, Signal processing, Modulation, System identification, Dynamical systems, Fourier transforms, Nonlinear optics, Inspection, Wavelet transforms

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This paper shows that time-frequency analysis is most appropriate for nonlinearity identification, and presents advanced signal processing techniques that combine time-frequency decomposition and perturbation methods for parametric and non-parametric identification of thin-walled structures and other dynamical systems. Hilbert-Huang transform (HHT) is a recent data-driven adaptive time-frequency analysis technique that combines the use of empirical mode decomposition (EMD) and Hilbert transform (HT). Because EMD does not use predetermined basis functions and function orthogonality for component extraction, HHT provides more concise component decomposition and more accurate timefrequency analysis than the short-time Fourier transform and wavelet transform for extraction of system characteristics and nonlinearities. However, HHT's accuracy seriously suffers from the end effect caused by the discontinuity-induced Gibbs' phenomenon. Moreover, because HHT requires a long set of data obtained by high-frequency sampling, it is not appropriate for online frequency tracking. This paper presents a conjugate-pair decomposition (CPD) method that requires only a few recent data points sampled at a low frequency for sliding-window point-by-point adaptive timefrequency analysis and can be used for online frequency tracking. To improve adaptive time-frequency analysis, a methodology is developed by combining HHT and CPD for noise filtering in the time domain, reducing the end effect, and dissolving other mathematical and numerical problems in time-frequency analysis. For parametric identification of a nonlinear system, the methodology processes one steady-state response and/or one free damped transient response and uses amplitude-dependent dynamic characteristics derived from perturbation analysis to determine the type and order of nonlinearity and system parameters. For non-parametric identification, the methodology uses the maximum displacement states to determine the displacement-stiffness curve and the maximum velocity states to determine the velocity-damping curve. Numerical simulations and experimental verifications of several nonlinear discrete and continuous systems show that the proposed methodology can provide accurate parametric and non-parametric identifications of different nonlinear dynamical systems.

Proceedings Article | 18 April 2011 Paper

Time-frequency and space-wavenumber analysis for damage inspection of thin-walled structures

P. Frank Pai, Mannur Sundaresan

Proceedings Volume 7984, 79842J (2011) https://doi.org/10.1117/12.880329

KEYWORDS: Time-frequency analysis, Inspection, Signal processing, Transform theory, Damage detection, Data modeling, Fourier transforms, Temporal resolution, Time metrology, Dynamical systems

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Proceedings Article | 9 April 2010 Paper

Dynamics characterization and health monitoring of membrane structures by time-frequency analysis

Xin Qian, Xingwen Du, P. Frank Pai

Proceedings Volume 7650, 765035 (2010) https://doi.org/10.1117/12.847617

KEYWORDS: Time-frequency analysis, Signal processing, Nonlinear optics, Data processing, Interference (communication), Modulation, Wave propagation, System identification, Damage detection, Space telescopes

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Proceedings Article | 9 April 2010 Paper

Damage inspection and health monitoring of dynamical systems by advanced time-frequency analysis

P. Frank Pai, Genyong Wu, Xin Qian

Proceedings Volume 7650, 76500H (2010) https://doi.org/10.1117/12.847307

KEYWORDS: Dynamical systems, Signal processing, Inspection, Time-frequency analysis, Nonlinear optics, Complex systems, Data processing, System identification, Fourier transforms, Data analysis

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Proceedings Article | 8 April 2009 Paper

Online three-point frequency tracking method for structural health monitoring

P. Frank Pai, Aaron Rosengren

Proceedings Volume 7295, 72951L (2009) https://doi.org/10.1117/12.814970

KEYWORDS: Signal processing, Structural health monitoring, Automatic tracking, Fourier transforms, Interference (communication), Data processing, Detection and tracking algorithms, Wave propagation, Complex systems, Data analysis

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Proceedings Article | 21 April 2008 Paper

Structural damage detection and estimation by amplitude and frequency modulation analysis

P. Frank Pai

Proceedings Volume 6935, 69351S (2008) https://doi.org/10.1117/12.773883

KEYWORDS: Signal processing, Frequency modulation, Damage detection, Wavelets, Fourier transforms, Modulation, Time-frequency analysis, Interference (communication), Complex systems, Nonlinear optics

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Presented here is an amplitude and frequency modulation method (AFMM) for extracting damage-induced nonlinear characteristics and intermittent transient responses by processing steady-state/transient responses using the empirical mode decomposition, Hilbert-Huang transform (HHT), and nonlinear dynamic characteristics derived from perturbation analysis. A sliding-window fitting (SWF) method is derived to show the physical implication of the proposed method and other methods for time-frequency signal decomposition. Similar to the short-time Fourier transform and wavelet transform the SWF uses windowed regular harmonics and function orthogonality to extract time-localized regular and/or distorted harmonics. On the other hand the HHT uses the apparent time scales revealed by the signal's local maxima and minima to sequentially sift components of different time scales, starting from high-frequency to low-frequency ones. Because HHT does not use predetermined basis functions and function orthogonality for component extraction, it provides more accurate instant amplitudes and frequencies of extracted components for accurate estimation of system characteristics and nonlinearities. Moreover, because the first component extracted from HHT contains all original discontinuities, its time-varying amplitude and frequency are excellent indicators for pinpointing times and locations of impulsive external loads and damages that cause intermittent responses. However, the discontinuity-induced Gibbs' effect makes HHT analysis inaccurate around the two data ends. On the other hand, the SWF analysis is not affected by Gibbs' effect, but it cannot extract accurate time-varying frequencies and amplitudes. Numerical results show that the proposed AFMM can provide accurate estimations of softening and hardening effects, different orders of nonlinearity, linear and nonlinear system parameters, and time instants of intermittent transient responses for damage detection and estimation.

Proceedings Article | 21 April 2008 Paper

Damage detection in concrete and cementitious composites

Hwai-Chung Wu, P. Frank Pai

Proceedings Volume 6935, 69351K (2008) https://doi.org/10.1117/12.779465

KEYWORDS: Modulation, Ultrasonics, Cements, Acoustics, Nondestructive evaluation, Signal attenuation, Damage detection, Composites, Interfaces, Testing and analysis

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Proceedings Article | 11 April 2007 Paper

Application of Hilbert-Huang transformation for detection of damage in concrete

Hwai-Chung Wu, P. Frank Pai, Kraig Warnemuende

Proceedings Volume 6532, 65320Q (2007) https://doi.org/10.1117/12.716653

KEYWORDS: Modulation, Nondestructive evaluation, Ultrasonics, Acoustics, Signal attenuation, Interfaces, Time metrology, Transducers, Testing and analysis, Nonlinear optics

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Proceedings Article | 15 March 2006 Paper

Hilbert-Huang decomposition of time signals for structural damage detection

P. Frank Pai, Lu Huang

Proceedings Volume 6177, 61770Q (2006) https://doi.org/10.1117/12.654820

KEYWORDS: Modulation, Damage detection, Wavelets, Signal detection, Oscillators, Fourier transforms, Wavelet transforms, Complex systems, Data processing, Error analysis

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This paper presents methods for characterizing nonlinearities and sudden disturbances in stationary/transient responses by decomposing signals using the Hilbert-Huang transform (HHT) and a sliding-window fitting (SWF) technique. Similar to the wavelet transform SWF uses windowed regular harmonics and their orthogonality to extract local harmonic components. However, SWF decomposes a signal into less components because it allows distorted harmonics, and it provides time-varying amplitudes and frequencies of extracted components that can reveal system's nonlinearities. To extract components from a signal HHT uses the apparent time scales shown by the local maxima and minima of the signal (instead of using orthogonality of chosen fitting functions) and cubic spline fitting of extrema to sequentially sift components of different time scales, starting from highfrequency ones to low-frequency ones. Because it does not use orthogonality of functions, HHT provides more accurate time-varying amplitudes and frequencies of extracted components for accurate estimation of system characteristics and nonlinearities. Because the first extracted component contains all original discontinuities, its time-varying amplitude and frequency are excellent indicators of sudden transient disturbances. However, the discontinuity-induced Gibbs' phenomenon makes HHT analysis inaccurate around the two data ends. On the other hand, the SWF analysis has no Gibbs' phenomenon at the two data ends, but it cannot extract accurate modulation frequencies due to the use of non-orthogonal basic functions in the sliding-window least-squares curve-fitting process. Numerical and experimental results show that HHT can provide accurate extraction of intrawave amplitude- and phase-modulation, distorted harmonic response under a single-frequency harmonic excitation, softening and hardening effects, different orders of nonlinearity, interwave amplitude- and phasemodulation, multiple-mode vibrations caused by internal/external resonances, and instants of impact loading on a structure from stationary/transient responses. These phenomena are keys for performing dynamics-based structural damage detection and health monitoring.

Proceedings Article | 16 May 2005 Paper

Camera-based digital real-time static and dynamic testing of deployable/inflatable structures

P. Pai, Jiazhu Hu

Proceedings Volume 5758, (2005) https://doi.org/10.1117/12.599205

KEYWORDS: Cameras, Motion analysis, Sensors, Complex systems, Imaging systems, Structural design, 3D metrology, Distortion, Digital cameras, Structural analysis

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Proceedings Article | 9 May 2005 Paper

Dynamics-based model-independent local inspection method for damage detection of large structures

P. Frank Pai, Lu Huang

Proceedings Volume 5768, (2005) https://doi.org/10.1117/12.599220

KEYWORDS: Inspection, Damage detection, Data modeling, Signal processing, Nondestructive evaluation, Velocity measurements, Aluminum, Sensors, Time metrology, Error analysis

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Proceedings Article | 21 July 2004 Paper

Structural boundary effects and their applications to health monitoring

Perngjin Pai, Lu Huang, Sharath Gopalakrishnamurthy, Jaycee Chung

Proceedings Volume 5394, (2004) https://doi.org/10.1117/12.538111

KEYWORDS: Beam shaping, Data modeling, Damage detection, Numerical simulations, Ferroelectric materials, Aluminum, Shape analysis, Chemical elements, Defect detection, Finite element methods

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Proceedings Article | 1 August 2003 Paper

Dynamics-based damage inspection of an aircraft wing panel

P. Pai, Byeong-Seok Kim, Jaycee Chung

Proceedings Volume 5046, (2003) https://doi.org/10.1117/12.484111

KEYWORDS: Damage detection, Defect detection, Inspection, Ferroelectric materials, Finite element methods, Actuators, Time metrology, Nondestructive evaluation, Process modeling, Data modeling

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Proceedings Article | 11 June 2002 Paper

Detection and estimation of defects in a circular plate using operational deflection shapes

Perngjin Pai, Yunje Oh, Byeong-Seok Kim

Proceedings Volume 4702, (2002) https://doi.org/10.1117/12.469898

KEYWORDS: Defect detection, Bessel functions, Computing systems, Head, Video, Aluminum, Chemical elements, Damage detection, Shape analysis, Finite element methods

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Proceedings Article | 24 July 2001 Paper

Structural damage detection and estimation using a scanning laser vibrometer

Perngjin Pai, Seung-Yoon Lee, Mark Schulz

Proceedings Volume 4335, (2001) https://doi.org/10.1117/12.434160

KEYWORDS: Beam shaping, Data modeling, Ferroelectric materials, Damage detection, Aluminum, Mechanics, Optical testing, Nondestructive evaluation, Electroluminescence, Laser marking

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Proceedings Article | 22 June 2000 Paper

Locating structural damage using operational deflection shapes

Perngjin Pai, Si Jin

Proceedings Volume 3985, (2000) https://doi.org/10.1117/12.388831

KEYWORDS: Data modeling, Damage detection, Ferroelectric materials, Aluminum, Laser development, Detector development, Actuators, Chlorine, Signal detection, Beam shaping

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Proceedings Article | 14 June 2000 Paper

Active fiber composites for structural health monitoring

Mark Schulz, Mannur Sundaresan, Anindya Ghoshal, Perngjin Pai

Proceedings Volume 3992, (2000) https://doi.org/10.1117/12.388196

KEYWORDS: Sensors, Composites, Wave propagation, Electrodes, Structural health monitoring, Acoustic emission, Ferroelectric materials, Nondestructive evaluation, Acoustics, Dielectrics

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Proceedings Article | 4 June 1999 Paper

Structural vibration suppression using PZT patches and higher-order saturation phenomena

Perngjin Pai, Bernd Rommel, Mark Schulz

Proceedings Volume 3667, (1999) https://doi.org/10.1117/12.350111

KEYWORDS: Ferroelectric materials, Sensors, Actuators, Control systems, Complex systems, Numerical integration, Feedback control, Simulink, Finite element methods, Bridges

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Proceedings Article | 24 July 1998 Paper

Vibration suppression of a skew cantilever plate using PZT patches

Perngjin Pai, Bernd Rommel, Ahmad Naser, Mark Schulz

Proceedings Volume 3323, (1998) https://doi.org/10.1117/12.316327

KEYWORDS: Ferroelectric materials, Sensors, Actuators, Control systems, Vibration control, Aluminum, Complex systems, Simulink, Nonlinear control, Aerospace engineering

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