Kuo-Chih Chuang

Pointwise fiber Bragg grating displacement sensor system for dynamic measurements

A method for setting up a fiber Bragg grating (FBG) sensor which can measure the pointwise, out-of-plane or in-plane dynamic displacement is proposed. The proposed FBG sensor is reusable. A multiplexing demodulation system based on a single long-period fiber grating is used in this study. The experimental results of the steady-state motion for a multilayer piezoelectric actuator and the dynamic response of a cantilever beam subjected to impact loadings are presented. These results indicate that the proposed displacement sensor has the ability to measure the out-of-plane dynamic displacement with high sensitivity. Measurements for a piezoceramic plate excited by high frequency show that the proposed displacement sensor also has the ability to provide the in-plane dynamic displacement up to 20 kHz.

Investigation of the transient behavior of a cantilever using a point-wise fiber Bragg grating displacement sensor system

This paper presents a fiber Bragg grating (FBG) sensor system setup method to measure the transient response of dynamic displacement for a cantilever subjected to impact loadings. An LPFG filter-based wavelength?optical intensity modulation technique is used in this study. The transient responses of particle motions measured by an FBG displacement sensor are compared with those obtained simultaneously by a laser Doppler vibrometer (LDV). The resonant frequencies of the cantilever are determined by employing a fast Fourier transform on the transient displacement responses obtained from the FBG and the LDV. An optical full-field measurement technique called amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) is also used to provide the full-field vibration mode shapes and resonant frequencies of the cantilever. The resonant frequencies obtained from four experimental measurement techniques, i.e., FBG, LDV, AF-ESPI, and shaker, are compared with those predicted from theoretical and FEM numerical calculations. Furthermore, the amplitude of the frequency spectra obtained from the FBG and the LDV are emphasized from the mode shapes and impact locations of the steel ball. The proposed FBG displacement sensor is proved to be able to measure transient point-wise displacement responses which can also be used to determine the resonant frequencies of structures.

Multidimensional Dynamic Displacement and Strain Measurement Using an Intensity Demodulation-Based Fiber Bragg Grating Sensing System

We set up a multidimensional dynamic fiber Bragg grating (FBG) displacement and strain sensing system. The proposed sensing system allows the FBGs to have the ability to measure transient point-wise displacement (in-plane and out-of-plane) and strain responses simultaneously with high sensitivity. The sensing system employs a long-period fiber grating filter and two FBG filters to dynamically demodulate the responses of the FBG sensors. To demonstrate the dynamic sensing ability and the application of the proposed system, the transient elastic wave propagation in a solid subjected to vertical and lateral impact loadings are investigated. A laser Doppler vibrometer is employed in our experiments simultaneously to verify the transient responses of out-of-plane particle transient motions measured by the out-of-plane FBG displacement sensor. The in-plane displacement measurement ability is demonstrated by the responses obtained by two geometrically orthogonal in-plane FBG displacement sensors. Dynamic strain sensing ability of our all-fiber sensing system is also demonstrated. The experimental results both in time domain and frequency domain show that the proposed FBG sensing system is capable of performing real-time displacement (out-of-plane and in-plane) and strain measurements.

Experimental Investigation of the Cross-Sensitivity and Size Effects of Polyvinylidene Fluoride Film Sensors on Modal Testing

Due to advantages such as light weight, flexibility, and low cost, polyvinylidene fluoride (PVDF) films have been widely used in engineering applications as sensors for detecting strain, pressure, or micro-force. However, it is known that PVDF strain sensors have strain cross-sensitivity in mutually orthogonal directions. Furthermore, the size of the PVDF film sensor would also affect the dynamic strain sensing performance. In this paper, to investigate the cross-sensitivity and size effects experimentally, we employ PVDF film sensors to perform dynamic measurements on a cantilever beam. Since the vibrations of the cantilever beam are excited by impacts of a steel ball, the induced highly repeatable transient responses contain a wide range of resonant frequencies and thus can be used to investigate both the size and cross-sensitivity effects of the PVDF film sensors in a dynamic sensing environment. Based on the experimental results of the identified resonant frequencies compared with results obtained from a strain gauge, finite element calculations, and theoretical predictions, suggestions for the use of the PVDF strain sensor in modal testing are given in this paper.

Tracking control of a multilayer piezoelectric actuator using a fiber bragg grating displacement sensor system

This paper provides a fiber Bragg grating (FBG) sensor system which can measure the point-wise, out-of-plane displacement to examine the position-tracking control problem of a multilayer piezoelectric actuator (MPA). An FBG filter-based wavelength-optical intensity modulation technique is used in this study. A nominal system model is identified experimentally from the responses excited by random signals measured by an FBG displacement sensor that are simultaneously compared with those obtained from a laser Doppler vibrometer. To further investigate the sensing ability of the proposed system in a feedback control problem, control strategies including robust Halpha control, proportional-integralderivative control, and pseudoderivative feedback control are implemented. The characteristics of the step responses for each controller are examined. The experimental results show that the proposed sensor system is capable of performing the system identification and can serve as a feedback control sensor which has a displacement sensitivity of 5 mV/nm.

Polyvinylidene fluoride film sensors in collocated feedback structural control: application for suppressing impact-induced disturbances

Polyvinylidene fluoride (PVDF) films are light, flexible, and have high piezoelectricity. Because of these ad- vantages, they have been widely used as sensors in applications such as underwater investigation, nondestructive damage detection, robotics, and active vibration suppression. PVDF sensors are especially preferred over conventional strain gauges in active vibration control because the PVDF sensors are easy to cut into different sizes or shapes as piezoelectric actuators and they can then be placed as collocated pairs. In this work, to focus on demonstrating the dynamic sensing performance of the PVDF film sensor, we revisit the active vibration control problem of a cantilever beam using a collocated lead zirconate titanate (PZT) actuator/PVDF film sensor pair. Before applying active vibration control, the measurement characteristics of the PVDF film sensor are studied by simultaneous comparison with a strain gauge. The loading effect of the piezoelectric actuator on the cantilever beam is also investigated in this paper. Finally, four simple, robust active vibration controllers are employed with the collocated PZT/PVDF pair to suppress vibration of the cantilever beam subjected to impact loadings. The four controllers are the velocity feedback controller, the integral resonant controller (IRC), the resonant controller, and the positive position feedback (PPF) controller. Suppression of impact disturbances is especially suitable for the purpose of demonstrating the dynamic sensing performance of the PVDF sensor. The experimental results also provide suggestions for choosing between the previously mentioned controllers, which have been proven to be effective in suppressing impact-induced vibrations.

Application of a Fiber Bragg Grating-Based Sensing System on Investigating Dynamic Behaviors of a Cantilever Beam Under Impact or Moving Mass Loadings

By setting up a fiber Bragg grating (FBG) displacement and strain sensing system, this paper experimentally investigates dynamic behaviors of a cantilever beam under impact or moving mass loadings. Dynamic sensing ability of the FBG displacement sensor is demonstrated by simultaneously measuring with a noncontact Fotonic sensor. Responses obtained from the FBG strain sensor are compared with those obtained from polyvinylidene fluoride film sensors and a strain gauge. First, an impact loading is generated by an impact hammer, and transient out-of-plane displacement responses obtained from the proposed FBG displacement sensor are compared with finite element simulations. Then, vibrations of the cantilever beam subjected to impact loadings by a steel ball are investigated. Finally, with a high-speed camera to detect the moving speed, experimental study of the cantilever beam under a moving mass is performed. By using the FBG displacement and strain sensing system, three kinds of modes of the cantilever beam (i.e., bending modes, lateral bending modes, and torsional modes) are detected under impact or moving mass loadings. With the high sensitivity of the proposed FBG sensing system, relationships between the transient responses induced by impact or moving mass loading and the vibration modes are discussed.

Performance analysis of a fiber Bragg grating filter-based strain/temperature sensing system based on a modified Gaussian function approximation method

This paper analyzes the performance of a fiber Bragg grating (FBG) filter-based strain and/or temperature sensing system based on a modified Gaussian function (MGF) approximation method. Instead of using a conventional Gaussian function, we propose the MGF, which can capture the characteristics of the sidelobes of the reflected spectrum, to model the FBG sensor and filter. We experimentally demonstrate that, by considering the contributions of the sidelobes with the MGF approximation method, behaviors of the FBG filter-based FBG displacement and/or temperature sensing system can be predicted more accurately. The predicted behaviors include the saturation, the sensitivity, the sensing range, and the optimal initial Bragg wavelengths of the FBG sensing system.

PVDF energy harvester on flexible rings

In this paper, the elastic ring is laminated with a convolving PVDF layer on the rings inner surface for energy harvesting. With the segmentation technique, the piezoelectric layer is uniformly segmented into several energy harvesting patches. The generated energy is the function of electric signal and the capacitance of energy harvesting patch. For each harvester, the circumferential vibration induced modal energy, the transverse vibration induced modal energy and the total energy is evaluated. By discussing different case studies (e.g., harvester thickness and segment size), the maximum magnitudes of modal energies are plotted, compared and evaluated. When the segment size increases, the maximum energies exhibit the deficiency because of signal average and cancellation. This study is to serve as a design guideline to achieve a higher energy harvesting efficiency for practical applications.

Energy harvesting using a circular cylindrical shell laminated with a segmented piezoelectric layer

Energy harvesting based on the direct piezoelectric effect using the curvature structures is a new endeavor in engineering applications. This study focuses on energy harvesting from mechanical vibrations through a simply supported circular cylindrical shell laminated with segmented piezoelectric energy harvester patches. The voltage (or modal signal) induced by the modal strains of the piezoelectric patch due to the direct piezoelectric effect can be further converted to modal energy. The spatially distribution of the modal energy are evaluated and compared in two piezoelectric energy harvester patch sizes.