EMI Method Research Articles

An innovative data-driven probabilistic approach for damage detection in Electromechanical Impedance Technique

The electromechanical impedance method (EMI) has shown its damage detection capacity under hazardous environments. Moreover, it is cost-effective, because it involves a bonded piezoelectric transducer (PZT). But the daunting task in the EMI method is the selection of robust and effective damage index, frequency ranges, and combining the information for damage quantification. In this paper, an innovative standard deviation approach is used for the selection of effective frequency ranges. The novice nature of frequency range selection is based on the difference between healthy and damaged state data. Further, a data fusion technique is introduced for damage detection and classification using analytical and experimental data in this effective frequency range. This paper presents four samples of metal and composite with different damage scenarios to demonstrate the applicability of the method. The paper investigates damage in thin aluminium (Al) plate with holes using the EMI method. Further, simulated mass damage and impact damage study to the glass fiber reinforced polymer (GFRP) composite plate. A combined C-index statistical data-driven damage matrices are calculated and further compared with the RMSD index approach. The method looks suitable for identifying the damage location and damage severity simultaneously and is more effective for the less severe damage cases.

Pelatihan Bahasa Inggris untuk Guru Sekolah Dasar Gugus Pangeran Diponegoro, Kuningan

Abstract This community service aims at organizing English Language Training for SD Gugus Pangeran Diponegoro teachers located at SDN 2 Windusengkahan, Kuningan District, Kuningan Regency which has local curriculum content in English. Method of EMI is applied in this community service with singing and games media. The teachers really welcome this training with the hope that they can provide the best for their students when carrying out the learning process in the classroom. This training activity was carried out in three meetings which were carried out smoothly and became a reference for the implementation of further service. Keywords: English training, EMI method.

Non‐destructive damage detection on welded threaded bolts based on electromechanical impedance spectra

AbstractWithin a research project carried out at the Department of Civil Engineering and the Department of Mechanical Engineering of the University of Siegen, a new monitoring method for non‐destructive damage detection on bolts was developed and tested according to its applicability on real life structures. The so‐called EMI‐method is based on the measurement of electromechanical impedance spectra, which change with varying structural states and thus allow for a condition assessment.Structures vibrate in a combination of their natural modes, which can provide information about their structural condition. Their modal characteristics are system‐inherent quantities and are governed by geometry, system stiffnesses and mass allocation. If a system parameter changes, e.g. the bending stiffness of a bridge, this is reflected in the vibration analysis and the modal characteristics. To identify the modal characteristics of civil engineering structures, these are excited and the system response is measured. This principle is also used for damage detection by means of electro‐mechanical impedance spectra (EMI). The observed system‐inherent quantity is the frequency‐dependent mechanical impedance Zs(ω) of the structure. The method is based on the idea that the mechanical impedance of a structure or component to be measured changes as a result of damage (or loss of prestress in the case of bolts) and thus these changes can be detected.In the project, investigations were carried out on steel plates with orthogonally welded threaded bolts, which are used, for example, as fasteners for rail supporting points on bridges. Research objectives were on one hand the detection of the prestress stage and on the other hand the detection of fatigue damage in the weld seam. Within the scope of the project, it has been investigated to what extent a change of the prestressing load can be reliably detected by means of the EMI method. Furthermore, the influence of damage to the bolt on the impedance spectra was investigated.

Frequency domain electromagnetic induction: an efficient method for investigating Fort Ancient village dynamics

AbstractElectromagnetic induction (EMI) has been used in archaeology for decades, but still lags in use and development when compared to magnetometry and ground‐penetrating radar. While it has become more popular than electrical resistivity area survey, it is now less commonly used than electrical resistivity tomography. The EMI method is likely underutilized due to drift problems and a lack of multi‐sensor, vehicle‐towed systems capable of rapid, high‐density data collection. In this article we demonstrate not only the effectiveness of EMI survey, but a case where entire villages would have remained undetected without it. At the Singer‐Hieronymus Site in central Kentucky, USA, a vehicle‐towed frequency domain EMI survey detected the location of plazas, residential areas, and trash disposal areas across multiple Fort Ancient villages that contained both intact and heavily disturbed deposits. Additionally, three new villages were revealed. Through this process, we discovered how Fort Ancient village dynamics may be studied through a geophysical investigation of village shape, size, and spatial organization.

Investigation of the R260 Rail Steel Behavior at Varying Temperatures by EMI Method

Yapısal sağlık izleme (SHM)’de son yıllarda Elektromekanik Empedans (EMI) yöntemi yaygın olarak kullanılmaktadır. Bu yöntemde yapısal sağlığı denetlenecek yapıya kurşun-zirkonat-titanat (PZT) seramik sensör yaması eklenir. Empedans analizör kullanılarak empedans ve admittans karakteristikleri ölçülür. Bu ölçümler yapısal sağlığın değerlendirilmesinde referans karakteristiğini oluşturur. Bu karakteristiklerin yapıda hata, kusur vb. olmadığı sürece değişmemesi beklenir. Ancak değişen çevresel koşullar ve sıcaklık dalgalanmaları gibi bazı durumlarda bu karakteristiklerin değiştiği bilinmektedir. Eğer sıcaklık etkisi dikkate alınmazsa, yapıda hata, kusur vb. olmadığı halde varmış gibi yanlış yorumlamalara yol açar. Raylar sürekli olarak değişen çevresel koşullara maruz kalmaktadır. Bu çalışmada, R260 ray çeliğinin değişen sıcaklıklardaki davranışı EMI yöntemi kullanılarak incelenmiştir. Yapılan deneysel çalışmaların sonucunda, sıcaklık azaldıkça frekans ve genliğin değiştiği gözlenmiştir. Bu değişim hasar metrikleri kullanılarak yorumlanmıştır.

An EEMD-Based Electromagnetic Induction Method for Nondestructive Testing of Buried Metal Conductors

Nondestructive testing of substation grounding grids is an issue that has increasing importance. The traditional EMI method transforms the condition of the undergrounding conductors to the surficial induced electric signal in the sensing coil. However, The EMI signals excited by multiple coexisted faults combining with other unknown noises surrounding the substation often cause the failure of detection. Therefore, the observed EMI signals rather complex and cannot be used directly. To address this problem, the separation of individual signatures from the mixture is posed as an SCBSS problem. To extract the induced signal, an EEMD-based EMI method is proposed. The desired signal is then reconstructed to visualize the structure of the grounding grids by a virtual instrument that consists of DAQ and digital signal processing modules. The numerical simulation and practical experiments are employed. The results show the proposed method can be used to effectively detect the topological structure of grounding grid in real substations' electromagnetic environment.

Electromechanical Admittance Signature Analysis of Piezo-ceramic Transducers for NDE

Of the multiple applications of the piezoelectric ceramics transducers such as Lead-Zirconate-Titanate (PZT), one prominent one is in the field of non-destructive evaluation (NDE) using the Electromechanical Impedance method (EMI). In this method a piezo-ceramic transducer (PZT) is bonded on to the structure and actuated using a harmonic voltage at ultrasonic frequency ranges. The dynamics of the PZT-structure interaction is captured in the frequency response of the electrical admittance of the PZT, popularly called as the admittance signature. A mechanical damage in the structure alters the mass, stiffness and damping properties locally, which in turn alters the admittance signature. Many analytical and semi-analytical models of the EMI method that have been used are limited in application to simple systems. The coupled-field finite element modeling has been demonstrated to quite accurately predict the admittance signatures as obtained by the experimental EMI technique. This paper presents the results of identification and quantification studies of damage using the analysis of admittance signatures obtained by coupled-field FE model of a simple cantilever type plate in ANSYSTM.

Optimising geological mapping of glacial deposits using high-resolution electromagnetic induction data

There is a growing demand in modern society for detailed, localised geological maps and 3D models in connection with e.g. planning of major construction works, study of subsurface drainage systems, infiltration of storm water or risk assessment of contaminated waste dumps and pollution plumes. This demand is difficult to meet in Denmark as the surficial glacial deposits that cover most of the country are notoriously very heterogeneous. Standard geological maps are based on regional data collection, and their resolution is far from sufficient to identify structural elements on the 10–20 m scale needed in the above-mentioned applications. Geophysical mapping for geological characterisation of the upper c. 5 m of the subsurface can be carried out using for instance direct-current geoelectrical methods (e.g. Loke et al. 2013), induced polarisation (e.g. Revil et al. 2012) set up with 1–2 m electrode spacing, electromagnetic induction (EMI; e.g. Christiansen et al. 2016; Doolittle & Brevik 2014), ground penetrating radar (GPR; e.g. Neal 2004) or seismic refraction tomography using a multicomponent landstreamer (e.g. Brodic et al. 2015). The resulting geophysical maps show the distribution of the measured parameter, for instance electric resistivity or seismic velocity. To construct geological maps using geophysical methods, the data must be verified and calibrated with geological field observations. GPR imaging of geological structures require laborious interpretation before a geological map can be constructed, and the method is limited to low-loss materials such as sandy sediments (Neal 2004). A new approach, using a combination of shallow, highresolution EMI surveying and traditional spear-auger soil sampling along the same transects, was tested in an area of c. 2 km2 around the contaminated, former landfill site at Pillemark on Samsø (Fig. 1). The resistivity recorded using the EMI method is strongly related to the clay content, and this parameter is therefore well suited for geological mapping. The EMI method is also robust, data acquisition is 5–50 times faster than with other geophysical methods and the processing and inversion scheme is well defined (Christiansen et al. 2016).

Delamination detection in CFRP panels using EMI method with temperature compensation

In this paper result of detection and localization of artificially initiated delaminations in carbon fiber reinforced polymer (CFRP) samples were presented. Damage detection was based on electromechanical impedance method (EMI). This method utilizes electromechanical coupling of piezoelectric transducer with host structure. Due to this coupling mechanical resonances of structure can be seen in electrical impedance characteristic of a piezoelectric transducer. In the research real part of electrical impedance (resistance) was measured. Delamination in CFRP sample caused frequency shift of certain resonance frequencies visible in resistance characteristic. In this paper also changing temperature effects on EMI method were investigated. In order to remove this temperature induced effects compensation algorithm based on signal cross-correlation was utilized.

The compensation technique of tensile force effect on the electro-mechanical impedance method for structural health monitoring

In this article, the external axial tension applied on structure was considered in electro-mechanical impedance method. An experiment was performed to study the effect of external axial force on the electro-mechanical impedance–based structural health monitoring. The axial tensions were applied on both healthy and damaged steel beam pasted by surface-bonded piezoelectric transducers. The study results showed that the electrical admittance (the inverse of impedance) curves had an obvious tendency of decline with the increase in tension; thus, this effect would mislead the judgment of health status. Then, the artificial neural network based on radial basis function was introduced to compensate the effect of tension on EMI method. Numerical examples showed that artificial neural network method can prevent the root mean square deviation index from changing with increase in tension. An additional experiment was performed to verify the artificial neural network method. The same conclusion as the first experiment was obtained. The reasonable experiment result demonstrated that artificial neural network method has its generality for application.

Combined geophysical investigation for the detection of ancient metallurgical installations near Keratea City, Greece

Abstract Archaeological excavation in an area of Lavrio (mining area from ancient times) has revealed ancient metallurgical installations which offer valuable information on this activity at those times. Within this context, a combined geophysical investigation was carried out in a place near Keratea City to find out whether there are additional installations apart from those that have already been revealed in the immediate area. More importantly, the objective was to locate the ancient tanks which provided water to the installations. Archaeological and geological information have helped in the design of the survey. EMI method measuring apparent conductivity was used to cover the whole area of investigation. Conductivity maps in various investigation depths have positioned the tanks and stacked first derivative maps in two directions (the two directions of the revealed walls) show covered walls. The EMI survey has indicated the position of three (3) ERT profiles made with the dipole–dipole array, which presented the ancient tanks with great detail in depth. GPR profiles for the detection of walls were noisy with the coarse material surface layer but the interrelation with ERT and EMI results confirmed the detected features.

Electro-Mechanical Impedance Technique for Structural Health Monitoring of Composite Panels

Numerical modelling of EMI for damage detection has been presented in this paper. The PZT model is validated against the published experimental result for free disk and tied to the structure. The numerical modelling of the PZT patch will result in the admittance measure of the structure. The imaginary part of the admittance measure is used for developing a self-diagnostic sensor system. The real part of the admittance measure was used to develop a damage detection algorithm. Damage detection using EMI method was successfully applied to a simple composite disk and a stiffened panel. The EMI method is suitable for short range damage detection in structural parts with limited or no access.

Resonant frequency range utilized electro-mechanical impedance method for damage detection performance enhancement on composite structures

One of the problems when using EMI method on composite structures with large surface areas can lead to unsuccessful damage detection due to a vague change in the impedance signature. In addition, a threshold value is usually defined to differentiate a damaged case from an intact case. Therefore, the change in the impedance signature subjected to damage must be significant enough to overcome the effects from other factors which can also cause a change in the impedance signature. In this study, a concept of enhancing the damage detection ability of EMI method using a piezoceramic (PZT) material is reported. The proposed technique eliminates the trial-and-error approach when determining a suitable frequency range by using a resonant frequency range acquired in the lower frequency range below 80kHz, covering a large sensing area. The main idea is to create peaks in the impedance signature in a peak free zone by sacrificing the sensing area in order to significantly increase the sensitivity of the damage detection ability. The major advantages of the proposed technique is the utilization of the lower frequency range for damage identification using EMI method, while eliminating the time consuming problem of the trial-and-error method.

Structural Health Monitoring Using High-Frequency Electromechanical Impedance Signatures

An overview of recent advances in electromechanical impedance- (EMI-) based structural health monitoring is presented in this paper. The basic principle of the EMI method is to use high-frequency excitation to sense the local area of a structure. Changes in impedance indicate changes in the structure, which in turn indicate that damages appear. An accurate EMI model based on the method of reverberation-ray matrix is introduced to correlate changes in the signatures to physical parameters of structures for damage detection. Comparison with other numerical results and experimental data validates the present model. A brief remark of the feasibility of implementing the EMI method is considered and the effects of some physical parameters on EMI technique are also discussed.

EMI data from an archaeological resistive target revisited

In a previous work, we presented the analysis and interpretation of geophysical data acquired at the Floridablanca archaeological site in Patagonia, Argentina. The electromagnetic induction method (EMI) was used to detect and localize the anomalous zone of interest quickly. Afterwards, a quantitative characterization of the structure responsible for this anomaly was achieved by inverting geoelectrical data.In this work, we re‐analyse the EMI data to discover whether it could also provide us with quantitative information about our target, which exhibits a resistive signature with respect to the host medium. First, an alternative visualization of the data is carried out; this allows us to detect some features of the anomaly that could not be distinguished before. It also makes clear which of the configurations used in the data acquisition exhibits the best sensitivity and resolution. The EMI data corresponding to the anomalous zone are then adjusted with a trial‐and‐error procedure, using a 2D forward modelling method based on a Raleigh–Fourier approach. The response of two adobe walls with a tile deposit in between them is calculated and the resulting model shows good agreement with the model obtained from the inversion of the geoelectrical data. Also, the synthetic response of two adobe walls without the tile deposit is calculated; we find that this response is different and the data cannot be adjusted with this model. We conclude that the EMI method is appropriate for discriminating different types of resistive structure and that it can be used to obtain quantitative information when 2D modelling is performed.