Lamb wave transducers made of piezoelectric macro-fiber composite

During recent years, an intensive research activity concerning the application of Lamb waves (LWs) for SHM has been observed. LWs may be generated and sensed using different types of transducers, and their selection is essential for the SHM system’s performance. Results of the investigation of three types of transducers based on macro-fiber composite (MFC) are presented in this paper; two types of commercially available MFC actuators are compared with a novel type of custom-designed interdigital transducer also based on the MFC substrate. After a short presentation of the piezoelectric transducer designed for SHM applications, details concerning the proposed interdigital transducer design are provided. Beampatterns of the investigated transducers are first compared using numerical FEM simulations, and next, the numerically obtained beampatterns are verified experimentally using laser vibrometry. In the final part of this paper, advantages and disadvantages of the investigated transducers ar

RESTORING THE PASSIVITY OF SHUNT DAMPING CIRCUITS BASED ON THE SYNTHETIC INDUCTANCE BY THERMAL ENERGY HARVESTING

For decades people have used ambient energy, e.g., that of rushing streams or wind to obtain usable power. Starting with very low energy conversion, through constant development we have now reached the stage of extensive possibilities of harvesting the energy from the environment we live in. Today, there exist almost unconstrained opportunities to energize a broad spectrum of devices by energy available almost anywhere and of whichever form. One of the great advantages of energy harvesting is to make small electronic devices autonomous eliminating the need ofpower supply and mainte­nance. Shunt damping systems are unfavorably influenced by the size and mass of the coil inductors. While substituting bulky inductors with synthetic inductors one losses the passivity of the system gaining its practicability. Nevertheless, in order to outperform the actively driven systems, it is indispensable to return the passive properties of the system maintaining its performance. This paper presents the feasibility study ofpowering the passive shunt damping devices by the work that is lost irrevocably in a bearing node. The heat generated in a bearing is converted via the thermoelectric phenomenon and then used to power the synthetic inductance circuitry. In the paper it is shown that the required power levels can be satisfied by the thermoelectric generator paired to a moderately loaded bearing

Vision-based motion analysis of a kitesurfer

Kitesurfing is a relatively recent phenomenon with raising popularity worldwide – a recently developed extreme water sport considered a high-risk injury sport. It combines elements of several other sports, in particular sailing, surfing, windsurfing, wakeboarding, and snowboarding. The main purpose of authors’ research in the present paper is to use a vision system technique for measuring a kitesurfer’s body movements in order to analyze group of activated muscles during take-off and handle pass maneuver reproduced in the laboratory conditions

Celebrations for the 50-Year Anniversary of IFToMM

In this paper celebrations of the fifty-years anniversary of IFToMM, the International Federation for the Promotion of Mechanism and Machine Science, is reported with main aspects of the event that has been organized on 30 June 2019 during a special session at the IFToMM World Congress in Krakow, Poland. Memories of the celebration are illustrated with photos and historical data

COMPUTER-AIDED PROTOTYPING OF INTERDIGITAL TRANSDUCERS FOR THE STRUCTURAL HEALTH MONITORING OF PLANAR STRUCTURES

In recent years an intensive research activity into the application of guided waves (GWs) for structural health monitoring (SHM) can be observed. For instance, Lamb waves (LWs) have shown a great potential in monitoring of thin, planar structures. However, due to the dispersive and multimodal nature of the LWs, their snapshots can consist of many pulses even for an intact structure, which makes damage detection very complex. Moreover, small PZT transducers, most commonly used in SHM systems, act normally as omni-directional wave sources; therefore, dense or sparse transducers networks are required for damage localization. Some of the above-mentioned drawbacks of single PZT emitters and sensors can be overcome using interdigital transducers (IDT) designed to excite and sense a single, selected mode. The mode-tuning is performed by changing the span of finger electrodes to match the wavelength of the excited mode for the selected frequency. An IDT is a directional source, therefore, it generates a wave steered to the direction perpendicular to the electrodes. The width of the excited main lobe can be determined by the length of the electrodes. Since many parameters of the IDTs influence the LWs propagation, techniques for the simulation of the wave excitation and propagation are needed. In the paper, numerical tools for the computer aided design and virtual prototyping of the IDTs are presented. The simulation technique is based on the frequency-dependent transfer function of the structure, and due to its computational efficiency it can be used for fast testing of IDTs’ performance and for preliminary transducer design for further finite element simulations, and prototyping

Damage imaging in composites using nonlinear vibro‐acoustic wave modulations

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CONTROL OF MICRO-INVERTERS AS AN OVERVOLTAGE PREVENTION METHOD UNDER HIGH PV PENETRATION

Low voltage (LV) residential grids are generally not designed for high penetration of photovoltaic (PV) distributed generation. Maximization of PV output is not only opposed by solar energy intermittency, but also by grid impacts in form of reverse power flow and overvoltage. More intelligent control of PV inverters is required to balance the voltage requirements of the grid and maximum energy yield wanted by the end user. This paper discusses how micro-inverter topology could be utilized to handle overvoltage problem and avoid power output losses by applying an innovative control method. Control is realized as partial generation shedding at PV module level which is an optimized alternative comparing to conventional, entire PV array tripping in the event of overvoltage

VIBROTHERMOGRAPHY FOR IMPACT DAMAGE DETECTION IN COMPOSITES STRUCTURES

The paper investigates modelling aspects related to application of vibrothermography for detection of barely visible impact damage in composite structures. Low-velocity impact tests were performed to introduce multiple delaminations into carbon/epoxy composite plate. Damage severity was revealed using well-established non-destructive evaluation techniques. Vibrothermography was used subsequently to show good agreement with classical damage detection techniques. Following these experimental investigations, numerical simulations were performed to assess feasibility and sensitivity of vibrothermography for impact damage detection. Numerical results were validated using experimental data showing very good qualitative and encouraging quantitative agreement. The study demonstrates that virtual impact damage detection using vibrothermography can be performed as part of structural design to assess sensitivity of the method in real engineering applications. Copyright © 2012 John Wiley & Sons, Ltd