Selection Of Excitation Frequency Research Articles

Effect of Single and Multi-Direction Coil for Differential Probe on Depth Crack Defect Measurement with Different Excitation Frequency Selection in Eddy Current Inspection

In recent years, a number of studies in Non-Destructive Evaluation (NDE) have been conducted on the sensitivity of probes in assessing the depth of cracks based on input stimulation. Range frequency and crack depth have been suggested as relevant features for input excitation waveform forms. The construction of an encircling coil for a differential probe (ECDP) and an encircling coil for an absolute probe (ECAP) was discussed in this paper. For the defect, the Multi-Frequency (MF) measuring method was used to compare ECDP with single direction and multi-direction turn coil growth. The measurement method was based on the coupling of ECDP and ECAP. By comparing the resulting signal between the probes, it is clear that the ECDP (with longitudinal and transverse coils) is very effective in measuring the various types of defects in the frequency ranges. The ideal excitation frequencies for inspection testing are 30kHz and 60kHz.

Investigation into the transmission of guided waves across bolt jointed plates

Bolt joints are extensively used in aerospace and civil engineering. Online monitoring of bolt looseness is crucial to ensure the function and safety of these structures. Understanding the interaction between guided waves and the joint interfaces can aid in the design and optimization of such monitoring systems, and hence becomes important. However, the influence of contact area on guided wave energy passing through these jointed plates is still not clear. In this paper, a semi-analytic method, which combines finite element models with a wave superposition method, is proposed to predict the transmission of guided waves in joint interfaces. The wave mode conversions in the contact area are included. The model was validated by comparison with independent finite element models. In addition, the influence of the contact length on transmission coefficients of guided waves passing through the joint interface is investigated. The results were experimentally validated by wire electrical discharge machined specimens with various contact areas. Then, the transmitted guided wave and the contact area in a bolt jointed plate under different torques were measured experimentally and compared with the present method. The results of the two different experiments agree well with those predicted using the semi-analytic method, respectively. In particular, the experimental results of the bolt jointed plate show that the direct S0 wave packet energy decreases with the bolt preload, which can be explained by the proposed model. Thus, the proposed semi-analytic method demonstrates efficiency in the prediction of the power transmission coefficient and has potential applications in the selection of excitation frequencies in the online monitoring of jointed structures. On this basis, a normalized power transmission coefficient can be directly calculated by the energy of the first S0 wave packet in the received signal to monitor bolt torque.

Identification and parameter estimation of non-polynomial forms of damping nonlinearity in dynamic systems

Damping is often assumed to viscous and linear in modelling a dynamic system. However, damping is inherently nonlinear and often is in non-polynomial forms such as Coulomb damping, bilinear, or quadratic damping. Recently, non-polynomial forms of damping have found wide applications in vibration isolators and absorbers. However, not much study is available for the identification of these non-polynomial forms of damping. The present work attempts to develop an identification and parameter estimation procedure for two non-polynomial damping forms, i.e., bilinear damping and quadratic damping. First, response harmonic amplitudes are formulating using Volterra series and equivalent linearised damping; and then they are compared with representative polynomial forms, i.e., square damping and cubic damping. Bilinear damping was identified employing a method of harmonic probing and studying first and second harmonic amplitude characteristics. Similar way, quadratic damping is identifying using first and third harmonic characteristics. Finally, a parameter estimation procedure is developed as a step-by-step algorithm and demonstrated through numerical simulation and error analysis. It is shown that reasonable accuracy can be obtained in estimation of the nonlinear parameters with proper selection of excitation frequencies and excitation levels.

Analysis of Large-Signal Output Capacitance of Transistors Using Sawyer–Tower Circuit

A detailed analysis of the Sawyer–Tower method used in the measurement of large-signal output capacitance ( $\boldsymbol {C}_{{\textrm {o}}}$ ) of power transistors is presented, followed by important design recommendations to obtain accurate results. Key factors affecting the proper implementation of the technique, such as power amplifier characteristics, load slew rate, reference capacitor ( $\boldsymbol {C}_{\text {ref}}$ ), and reverse conduction of the device, are addressed, with accompanying simulation and experimental results for Si, SiC, and GaN devices. A thorough investigation of the selection of $\boldsymbol {C}_{\text {ref}}$ is presented, with a new equation to correctly determine its value for a given voltage swing and output capacitance range of the device under test (DUT). We report that the Sawyer–Tower circuit imposes the DUT to enter steady-state reverse conduction under certain conditions, thus leading to charge–voltage ( QV ) hysteresis patterns unrelated to $\boldsymbol {C}_{{\textrm {o}}}$ . Our analysis reveals that the origin of this phenomenon is related to DUT’s leakage current and it could be minimized by the proper selection of excitation frequency. This article intends to provide an effective guide on designing and using the Sawyer–Tower circuit, and to induce further scientific insight on characterizing $\boldsymbol {C}_{{\textrm {o}}}$ .

Breaking of waves on thin films over topographies

In the present study, we performed experiments on the evolution of gravity-driven nonlinear traveling free surface waves over strongly undulated inclines. We focused on the impact of the excitation frequency and amplitude and the substrates’ shape and periodicity on the traveling wave. Thereby, we revealed phenomena concerning the amplitude evolution of convectively unstable waves. We can classify the wave evolution in three categories: (1) A normal exponential growth of the wave until it reaches a saturation amplitude. (2) An exponential growth of the wave and an abrupt collapse of the wave leading to a wave with a saturated amplitude, which is sensibly smaller than the maximal amplitude. (3) An alternating exponential growth and breaking of the wave. By using Fourier analysis, we investigated the waves in more detail. Furthermore, we report (a) a selection of excitation frequencies for the wave breaking, (b) a major impact of the steady state free surface, especially its mean or global curvature, (c) a bubble formation occurring at the wave breaking, (d) an overlap of the wave front, and (e) a formation of a jet during wave breaking.

Modelling nonlinearity of guided ultrasonic waves in fatigued materials using a nonlinear local interaction simulation approach and a spring model

Modelling and numerical simulation – based on the framework of the Local Interaction Simulation Approach – was developed to have more insight into nonlinear attributes of guided ultrasonic waves propagating in fatigued metallic materials. Various sources of nonlinearity were considered in this modelling work, with particular emphases on higher-order harmonic generation and accumulation of nonlinearity along wave propagation. The material hyper-elasticity was considered in the model using an energy density approach based on the Landau–Lifshitz formulation; and the “breathing” motion pattern of a fatigue crack in the material was interrogated using a spring model. Upon the successful validation with the model prepared in the commercial software based on the Finite Element Methods, two scenarios were comparatively investigated, i.e. the lower and higher frequency regime. In the first case propagation of a basic symmetric mode pair was simulated using the model to observe a cumulative characteristic of the second harmonic mode with nonlinear hyper-elastic material definition upon appropriate selection of excitation frequency. In the second case, the higher-order symmetric mode pair was excited according to the “internal resonance” conditions, revealing a strong dependence of manifested nonlinearity on numerical parameters. Moreover, it was shown that with the use of the wave from the low frequency regime it was easier to differentiate later stages of the crack development, being in contrary to waves in the high frequency regime, which allowed to clearly observe early stages of the crack expansion. Such outcome lays the foundation to develop the damage detection and monitoring scheme in the field of Structural Health Monitoring based on utilising the nonlinear features of guided ultrasonic waves.

Efficient swept sine chirp excitation in the non-linear vibro-acoustic wave modulation technique used for damage detection

In this article, the non-linear vibro-acoustic modulation technique is used for structural damage detection. A new experimental configuration and data processing strategy are proposed to improve the damage detection capability of the technique. The swept sine chirp excitation is used for both low-frequency vibration/modal and high-frequency ultrasonic excitations. The adaptive resampling procedure is then applied to extract information about modulation intensity that relates to damage. The proposed method is illustrated using numerical simulations and experimental tests. The latter involves crack detection in an aluminium beam. The results of the proposed method are compared with the classical approach based on single harmonic excitation, demonstrating that similar damage detection information can be extracted. However, the major advantage of the proposed method is simplicity and robustness since no a priori selection of excitation frequencies is needed. As a result, crack detection is more reliable and unambiguous.

Model Updating of a Concrete Beam with Extensive Distributed Damage Using Experimental Frequency Response Function

An experimental verification of a parameter estimation algorithm for finite-element (FE) model updating for damage quantification of a concrete beam with extensive damage is presented using the measured frequency response function (FRF) data. The intact stage of the beam and four progressive damage stages are investigated to update the FE model to quantify the damage across the beam. The method uses a subset of measured FRF data for FE model updating via a quasi-linear sensitivity equation of structural response. A least-squares algorithm with an appropriate weighting technique is used for parameter estimation. Proper selection of excitation frequency ranges for model updating is addressed. Predicted equivalent stiffnesses demonstrate the success and robustness of the method in damage quantification, even when using only a subset of the measured FRF data.

A frequency selection scheme for increased imaging speed in ECT

Electrical capacitance tomography (ECT) is a method to determine the material distribution within the interior of a closed object by measuring the capacitance values across externally mounted electrodes. Traditionally, an ac excitation pulse is applied to a pair of electrodes that form a capacitor during each measurement step, in order to determine the capacitance from the output current measured. This paper investigates how the speed of inter-electrode capacitance measurement can be improved by applying and receiving multiple excitation signals simultaneously on multiple electrodes. An excitation frequency selection scheme is derived to discuss the effect of bandwidth on the interference between the simultaneously sampled measurement channels. The new scheme opens up new possibilities for ECT as an effective tool for online, real-time monitoring of a wide range of dynamical processes.

Design and Experiment of PZT Network-based Structural Health Monitoring Scanning System

The active Lamb wave and piezoelectric transducer (PZT)-based structural health monitoring (SHM) technology is a kind of efficient approach to estimate the health state of aircraft structure. In practical applications, PZT networks are needed to monitor large scale structures. Scanning many of the different PZT actuator-sensor channels within these PZT networks to achieve on-line SHM task is important. Based on a peripheral component interconnect extensions for instrumentation (PXI) platform, an active Lamb wave and PZT network-based integrated multi-channel scanning system (PXI-ISS) is developed for the purpose of practical applications of SHM, which is compact and portable, and can scan large numbers of actuator-sensor channels and perform damage assessing automatically. A PXI-based 4 channels gain-programmable charge amplifier, an external scanning module with 276 actuator-sensor channels and integrated SHM software are proposed and discussed in detail. The experimental research on a carbon fiber composite wing box of an unmanned aerial vehicle (UAV) for verifying the functions of the PXI-ISS is mainly discussed, including the design of PZTs layer, the method of excitation frequency selection, functional test of damage imaging, stability test of the PXI-ISS, and the loading effect on signals. The experimental results have verified the stability and damage functions of this system.