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When pipe defects are generated above the T-type support structure location, it is difficult to distinguish the reflection signals caused by the weld bead at the support structure from the reflection echoes of pipe defects. Therefore, in order to effectively detect pipe defects, a waveform subtraction method with a circumferential shear horizontal (CSH) guided wave is proposed, which is generated by an electromagnetic acoustic transducer (EMAT). First, a CSH0 guided wave mode with a center frequency of 500 kHz is selected to establish a three-dimensional model with and without pipe defects above the support structure. Following this, the influence of different widths of support structures on the echo signal is compared. Moreover, simulation and experimental results are used to compare the influence of different welding qualities on the detection results. Finally, the waveform subtraction method is used to process the simulation and experimental signals, and the influence of pipe defects with different lengths and depths is discussed. The results show that the non-through crack defect of 5 mm × 1 mm (length × depth) can be detected. The results show that this method can effectively detect the cracks by eliminating the influence of the weld echo, which provides a new concept for the detection of the defect above the support structure. [ABSTRACT FROM AUTHOR]

Guided wave Electro Magnetic Acoustic Transducers (EMATs) offer an elegant method for structural inspection and localisation relative to geometric features, such as welds. This paper presents a Lorentz force EMAT construction framework, where a numerical model has been developed for optimising Printed Circuit Board (PCB) coil parameters as well as a methodology for optimising magnet array parameters to a user's needs. This framework was validated experimentally to show its effectiveness through comparison to an industry built EMAT. The framework was then used to design and manufacture a Side-Shifted Unidirectional Periodic Permanent Magnet (PPM) EMAT for use on a mobile robotic system, which uses guided waves for ranging to build internal maps of a given subject, identifying welded sections, defects and other structural elements. The unidirectional transducer setup was shown to operate in simulation and was then manufactured to compare to the bidirectional transmitter and two-receiver configurations on a localisation system. The unidirectional setup was shown to have clear benefits over the bidirectional setup for mapping an unknown environment using guided waves as there were no dead spots of mapping where signal direction could not be interpreted. Additionally, overall package size was significantly reduced, which in turn allows more measurements to be taken within confined spaces and increases robotic crawler mobility. [ABSTRACT FROM AUTHOR]

In this work, wide band radio-frequency (RF) shear-horizontal surface acoustic wave (SH-SAW) resonators were designed and fabricated to attain a large effective electromechanical coupling (${k}^{2}$) over 35% near 1-GHz based on a thin-film lithium niobate (LiNbO3/LN) on insulator layered substrate. In this study, the single-crystalline LiNbO3 thin film was bonded to a (100)-silicon carrier wafer with an intermediate silicon dioxide (SiO2) layer to form a simple and low-cost hetero acoustic impedance waveguide. Fabricated resonators with Au-electrodes show scalable wavelengths from $3.2~\mu \text{m}$ to $4.4~\mu \text{m}$ (770 to 1008 MHz) featuring ${k}^{2} >35$ % and ${Q}$ of 250, which are sufficient for wide band RF filtering applications. Additionally, the potential of the SH-SAW resonator is demonstrated by a numerically synthesized ladder filter with a center frequency of 970 MHz, a 3-dB fractional bandwidth of 29.6%, and an insertion loss (IL) around 1.8 dB. It suggests the feasibility of developing wide bandwidth acoustic RF devices for potential 5G wireless communication through further design and fabrication optimizations. [ABSTRACT FROM AUTHOR]

In this paper, a novel 2D analytical model based on the Huygens’s principle of wave propagation is proposed in order to predict the directivity patterns of contact type ultrasonic transducers in the generation of guided waves (GWs). The developed model is able to estimate the directivity patterns at any distance, at any excitation frequency and for any configuration and shape of the transducers with prior information of phase dispersive characteristics of the guided wave modes and the behavior of transducer. This, in turn, facilitates to choose the appropriate transducer or arrays of transducers, suitable guided wave modes and excitation frequency for the nondestructive testing (NDT) and structural health monitoring (SHM) applications. The model is demonstrated for P1-type macro-fiber composite (MFC) transducer glued on a 2 mm thick aluminum (Al) alloy plate. The directivity patterns of MFC transducer in the generation of fundamental guided Lamb modes (the S0 and A0) and shear horizontal mode (the SH0) are successfully obtained at 80 kHz, 5-period excitation signal. The results are verified using 3D finite element (FE) modelling and experimental investigation. The results obtained using the proposed model shows the good agreement with those obtained using numerical simulations and experimental analysis. The calculation time using the analytical model was significantly shorter as compared to the time spent in experimental analysis and FE numerical modelling. [ABSTRACT FROM AUTHOR]

ABSTRACT A computational frequency analysis of secondary wave mode generation is considered in this paper. Secondary wave mode conversion at the tip of a through-thickness slit in a circular isotropic plate is analysed similar to a classical Sommerfeld's diffraction problem. The analysis is useful for quantitative non-destructive evaluation of fatigue cracked plate structures that involve propagation of a single wave mode (a vertically polarised symmetric Lamb mode) and measurement of the amplitude of a new mode (a horizontally polarised shear mode). A two-dimensional finite element model is first introduced as a baseline reference for the non-dispersive scenario. This model is used to study the effect that P-wave angle of incidence has on the mode converted S-wave from the tip of the slit. A dispersive three-dimensional finite element model of the circular plate is then introduced at a number of frequency-thickness products within the range 0.5-3 MHz.mm−1. Within this frequency-thickness range, significant changes to the through-thickness displacement profiles of the incident S0 Lamb mode occur. The secondary SH0 plate wave mode generated by mode conversion from the 45o incident S0 Lamb mode at the tip of a slit is analysed to establish the efficiency of the mode conversion. Visualisations of the wave fields demonstrate that at frequency-thickness products higher than the first symmetric Lamé mode (where there is no in-plane surface displacement), the in-plane through-thickness displacement profile of the incident S0 Lamb mode becomes incompatible with that of the SH0 plate mode, and the mode conversion phenomenon is thus severely compromised. [ABSTRACT FROM AUTHOR]