Lamb wave-based mapping of plate structures via frontier exploration

High-performance ultrasonic transducer based on PZT piezoelectric ceramic for high-temperature NDE

Piezoelectric ultrasonic transducers (PUT) are applied in a wide range of fields such as non-destructive evaluation (NDE), medical imaging and petroleum exploration, etc. Nevertheless, most PUTs cannot achieve high performance and high operating temperatures simultaneously because of the inverse correlation between piezoelectric property and operating temperature. In this paper, a high-performance ultrasonic transducer based on PZT-5A type piezoelectric ceramic (S35) for high-temperature NDE over 300 °C was proposed. Firstly, it is found that the d₃₃, k_p, and k_t of the S35 ceramic plate show great temperature stability from 50 °C to 300 °C, which is attributed to the stabilisation of the phase structure and no occurrence of obvious depolarization behavior before the Curie temperature. And then, a single-element PUT based on S35 was fabricated, and pulse-echo tests from 50 °C to 300 °C in confined heating environments were executed. The peak-to-peak value (V_pp) varies from 2.58 V to 0.753 V, which results from the increase of the permittivity of the piezoelectric element and the degradation of the acoustic contact, and the -6dB BW demonstrates excellent temperature stability with a variation less than 10%. These results indicate the great potential of this high-performance ultrasonic transducer for high-temperature NDE.

Ultrasonic Lamb wave detection of a channel in a double-casing well

In cement-bonding evaluation, channel detection by ultrasonic Lamb waves has been widely studied and applied in single-casing wells. However, its feasibility in double-casing wells remains unknown. The relationship between ultrasonic Lamb waves and channels based on finite-difference time-domain simulations was investigated. According to the Lamb wave propagation, channels near interfaces were determined by the Lamb wave amplitude changes. A channel detection approach in double-casing wells was proposed. The ability of the proposed strategy to accurately detect the spatial position and geometric shape of the channels in double-casing wells was seen. This study provided guidance in double-casing cement-bonding evaluation.

Inverse modeling and experimental validation for reconstructing wave sources on a 2D solid from surficial measurement

This paper discusses a source inversion method for the reconstruction of moving or stationary wave sources on the top surface of a two-dimensional (2D) linear elastic solid. This adjoint-gradient-based source inversion method uses vibrational measurements from sensors at the top surface of the solid, which can be heterogeneous and damped, to reconstruct temporal and spatial distributions of the wave sources. The finite element method (FEM) is used to obtain wave solutions with the high-resolution discretization of source functions in space and time leading the number of inversion parameters to range in the millions. Numerical experiments, in which the iterative inversion procedure begins with an initial guess of zero loading at all points in space and time, show that the presented approach is effective at reconstructing horizontal and vertical components of force (i.e., normal and shear tractions) for multiple simultaneous moving dynamic distributed loads without any prior knowledge about the loads except that all loading is applied along the top surface of the solid. Provided that moving loads on roadways are applied to the top surface, it is shown that updating the guessed loading at just surface nodes, rather than at all nodes in space, greatly improves the inversion results. The inversion is shown to be as effective at reconstructing loads on the top surface of a solid when the solid is horizontally layered with multiple materials as when the solid it is homogeneous. Reducing the distance between sensors improves the accuracy of the inversion while reducing the width of distributed loads leads to less accurate results. The authors also validate the presented inversion method by using experimental data obtained from lab-scale tests at a high frequency (100 kHz) for a stationary load on a homogeneous solid.

Experimental investigation on characteristics of graphene acoustic transducers driven by electrostatic and electromagnetic forces

Acoustic transducers with graphene film have high sensitivity and wide bandwidth of frequency response as receivers. However, they exist in transmitting mode with low radiation performance. We propose an effective approach to enhance radiation performance of the graphene acoustic transducer by embedding a coil in insulating layer, and investigate the characteristics of graphene acoustic transducers by experiments. A graphene acoustic transducer is designed and fabricated. The highest receiving sensitivity of the transducer is -30 dB. The output sound pressure level of the transducer is more than 3 dB on average in the range of 2 ∼ 16 kHz compared without a coil. And the sound pressure level increases by 6 dB on average in the range of 40 ∼ 45 kHz. These results demonstrate that the graphene transducer maintains high receiving performance, and also improves acoustic radiation performance, which greatly expands its application field.

Recurrence analysis of friction based dry-couplant ultrasonic Lamb waves in plate-like structures

In this study, the effect of friction on the generation of dry-coupled Lamb waves is experimentally investigated. Recurrence analysis is performed to analyze the complex behavior of friction based dry-coupled Lamb waves. In particular, the effect of the normal force, which is necessary for a stronger dry-coupled Lamb wave generation and the friction, on the transmission of mechanical energy and determinism characteristics of Lamb waves are investigated. The results verify that larger friction coefficient and friction force are crucial for generation and propagation of strong Lamb waves supporting the fact that the main mechanism to transfer mechanical energy using dry-couplant is friction. The sensitivity of Lamb waves to the friction coefficient, highlights the importance of designing specific pads with respect to condition of the surface. Besides, the results show that the normal force and friction coefficient can change the determinism characteristics behavior of multimode Lamb waves. Furthermore, it is shown that the determinism value is sensitive to the friction coefficient and normal force. A similar trend is observed in the determinism values and friction coefficient. In general, a smaller friction coefficient indicates smaller determinism value. Additionally, it is shown that a normal load can change the behavior of a system, as observed from recurrence plots, owing to changes in the Lamb waves trajectories in the phase-space domain. In addition, it is shown that recurrence plots enable the detection of mode transitions in multimode Lamb waves. Recurrence analysis is a complementary tool to frequency domain methods for accurate analysis of multimode Lamb waves behavior.

Multi-objective optimization for joint actuator and sensor placement for guided waves based structural health monitoring using fibre Bragg grating sensors

Structural Health Monitoring (SHM) systems have a potential to reduce lifecycle costs of structures. As a result, there is a lot of active research in the area for SHM of civil and mechanical structures. Guided waves (GW) based SHM techniques allow monitoring of large plate-like structures with a few sensors and have been identified as the most promising of techniques for SHM. Fibre Bragg grating (FBG) sensors due to their low weight, and ability to be multiplexed have been long thought to be ideal sensors for SHM. The recent development of the edge filtering approach has increased their sensitivity to GW sensing and made them ideal sensors. Unfortunately the FBG sensors are passive sensors and show directional sensitivity. These operational constraints make extension of the earlier developed GW based SHM techniques for FBG sensors difficult. Recently the authors developed a technique for damage detection specifically designed for a network with FBG sensors. This paper builds on the past work by the authors and develops a methodology for a design of an actuator-sensor (AS) network for improving the damage assessment capability of the previously proposed method. The paper develops a multi objective optimization technique for the joint optimization of actuator and sensor placement for a network with FBG sensors. The joint optimization of the actuators and sensors is necessary due to the passive nature of the FBG sensors and also incorporates the directional nature of the FBG sensors. The paper develops an integer encoded NSGA-II for the optimization of the AS network. The objectives for the optimization are derived from the specific damage detection technique tailored for the use of FBG sensors. The objective are: coverage with at least 2 AS pairs, coverage with at least 1 edge reflected path and the cost of the deployed network. The results indicate that the encoding of the objectives of the optimization is valid and indeed the damage detection capabilities of the AS network are as predicted analytically. The paper for the first time develops a joint optimization of network for FBG sensors. It is also the first attempt at a truly multi-objective optimization of the AS network and promises to have applications on real structures.