35 research outputs found
A nearly perfect omnidirectional shear-horizontal (SH) wave transducer based on a thickness poled, thickness-shear (d15) piezoelectric ring
The fundamental shear horizontal (SH0) wave in plates is of great importance
in the field of nondestructive testing (NDT) and structural health monitoring
(SHM) since it is the unique non-dispersive guided wave mode. For practical
applications, a phased array system based on omnidirectional SH0 wave
transducers is most useful as it can cover a wide range of a plate. However, so
far very few omnidirectional SH wave transducers have been developed. In this
work, we proposed an omnidirectional SH piezoelectric transducer (OSH-PT) based
on a thickness poled piezoelectric ring. The ring is equally divided into
twelve sectors and the electric field is circumferentially applied, resulting
in a new thickness-shear (d15) mode. Finite element analysis shows that the
proposed OSH-PT can excite single-mode SH0 wave and receive the SH0 wave only.
Experiments were then conducted to examine the performance of the proposed
OSH-PT. Results indicated that it can generate and receive single-mode SH0 wave
in a wide frequency range with nearly uniform sensitivities along all
directions. Considering its quite simple configuration, compact size and low
cost, the proposed OSH-PT is expected to greatly promote the applications of SH
waves in the field of NDT and SHM
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High temperature electromagnetic acoustic transducer for guided wave testing
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThis research focuses on the theoretical analysis, development and experimental evaluation of a water cooled Electromagnetic Acoustic Transducer (EMAT) specifically designed for high-temperature Guided Wave Testing (GWT). Its novel design and detailed calculation of its optimum operating conditions resulted in its effectiveness at high temperatures for both short (500oC) and long-term inspection (250oC). All the steps followed for the theoretical and experimental investigation of the limitations of the existing technology and the development of a probe that can overcome these boundaries are presented. Finite Element Analysis (FEA) was performed for the optimization of the EMAT design and estimation of its ultrasonic and thermal properties at room and high temperatures over time. The wave mode purity profile of the Periodic Permanent Magnet (PPM) EMAT was theoretically studied as well as the effect of temperature rise on its ultrasonic performance. Thermal and Computational Fluid Dynamics (CFD) analysis was accomplished for the EMAT design optimization and calculation of its optimum operating conditions. The experimental validation of the theoretical study was also accomplished. The novel water cooled EMAT was developed and experimentally evaluated regarding its ultrasonic and thermal response at room and high temperatures. An empirical method for the enhancement of EMAT performance and its SNR was established. The wave mode purity characteristics of PPM EMAT were experimentally investigated via Laser vibrometry tests, which agreed with FEA results. The impedance analysis and ultrasonic evaluation of the EMAT at both room and high temperatures against various operating conditions were linked and compared to the results obtained from the ultrasonic, thermal and fluid FEA. In all cases, the experimental study is in good agreement with the theoretical results
Guided Lamb Wave Based 2-D Spiral Phased Array for Structural Health Monitoring of Thin Panel Structures
In almost all industries of mechanical, aerospace, and civil engineering fields, structural health monitoring (SHM) technology is essentially required for providing the reliable information of structural integrity of safety-critical structures, which can help reduce the risk of unexpected and sometimes catastrophic failures, and also offer cost-effective inspection and maintenance of the structures. State of the art SHM research on structural damage diagnosis is focused on developing global and real-time technologies to identify the existence, location, extent, and type of damage.
In order to detect and monitor the structural damage in plate-like structures, SHM technology based on guided Lamb wave (GLW) interrogation is becoming more attractive due to its potential benefits such as large inspection area coverage in short time, simple inspection mechanism, and sensitivity to small damage. However, the GLW method has a few critical issues such as dispersion nature, mode conversion and separation, and multiple-mode existence.
Phased array technique widely used in all aspects of civil, military, science, and medical industry fields may be employed to resolve the drawbacks of the GLW method. The GLW-based phased array approach is able to effectively examine and analyze complicated structural vibration responses in thin plate structures. Because the phased sensor array operates as a spatial filter for the GLW signals, the array signal processing method can enhance a desired signal component at a specific direction while eliminating other signal components from other directions.
This dissertation presents the development, the experimental validation, and the damage detection applications of an innovative signal processing algorithm based on two-dimensional (2-D) spiral phased array in conjunction with the GLW interrogation technique. It starts with general backgrounds of SHM and the associated technology including the GLW interrogation method. Then, it is focused on the fundamentals of the GLW-based phased array approach and the development of an innovative signal processing algorithm associated with the 2-D spiral phased sensor array. The SHM approach based on array responses determined by the proposed phased array algorithm implementation is addressed. The experimental validation of the GLW-based 2-D spiral phased array technology and the associated damage detection applications to thin isotropic plate and anisotropic composite plate structures are presented