1,721,019 research outputs found
Ultrasonic Guided waves Communications in smart materials: the case of tapered waveguides
No full textBesides being used for inspections, piezoelectric transducers can be adopted to communicate
the results of the inspection itself, for example a damage indicator, to a central processing
unit, thus avoiding the need of communication cables or radio modules. However, classical
coding and decoding procedures based on matched filters lose their effectiveness in case of
guided wave communications because of the detrimental effect of dispersion. A new decoding
procedure capable to compensate for dispersive guided waves signals propagating in regular
and irregular waveguides is proposed in this work. The presented procedure is suitable for
guided waves communications in irregular waveguides and can be applied in many
Structural Health Monitoring (SHM) applications. A proof-of-concept related to a tapered
steel rod will be demonstrated
Transducer-to-Transducer Communication in Guided Wave Based Structural Health Monitoring
No full textSystems for guided wave (GW) based structural health monitoring are limited in the frequency bandwidth of the excitation signal due to the underlying wave’s dispersion that causes a broadening of the waveform along the waveguide. Hence, bandlimited waveforms such as toneburst or chirp signals are widely employed. Recently, the authors have investigated the potential of phase-modulated signals, known from CDMA-communication systems, as a possible way to overcome such limitation. It was found that this class of excitation enables a parallel transmission and reception of all piezoelectric transducers which may lead to a significant reduction in the overall system complexity, because of channel switching is not required anymore. In particular, by means of matched filtering a pulse compression and signal demodulation can be achieved. In addition, the signal-to-noise ratio can be improved by considering phase modulation signals of longer code length. In this paper, we investigate additional properties of phase-modulated signals in terms of their capability to transmit digital information on the health status of the structure through the structure itself [1]. This may lead to autonomous GW-based SHM system where the sensor nodes do not communicate with each other through a wireless module, but where the information are being delivered through the waveguide. A proof-of-concept will be demonstrated here on an isotropic plate using both simulated signals and experimental measurements. The implementation of the concept requires to compensate the guided wave signals from dispersion. Here a suitable Warped Frequency transform [2] designed on the group velocity of the guided modes, is applied. Such transformation has two beneficial effects: 1) it compensates for the detrimental effect of dispersion, 2) it preserves the pseudo-orthogonality of the encoded pulses, because it is computed with a unitary operator
Directional Multi-Frequency Guided Waves Communications Using Discrete Frequency-Steerable Acoustic Transducers
Full text link: A novel directional transducer based on Guided Waves (GW) is introduced in this paper, designed for use in structural health monitoring (SHM) and acoustic data communication applications, i.e., systems in which the elastic medium serves as a transmission channel and information is conveyed through the medium via elastic waves. Such systems can overcome difficulties associated with traditional communication methods like wire-based or radio frequency (RF), which can be complex and have limitations in harsh environments or hard-to-reach places. However, the development of these techniques is hampered by GW dispersive and multi-modal propagation and by multi-path interference. The shortcomings can be effectively addressed by employing Frequency Steerable Acoustic Transducers (FSATs), which leverage their inherent directional capabilities. This can be achieved through the exploitation of a frequency-dependent spatial filtering effect, yielding to a direct correlation between the frequency content of the transmitted or received signals and the direction of propagation. The proposed transducer is designed to actuate or sense the A0 Lamb wave propagating in three orientations using varying frequencies, and has three channels with distinct frequencies for each direction, ranging from 50 kHz to 450 kHz. The transducer performance was verified through Finite Element (FE) simulations, accompanied by experimental testing using a Scanning Laser Doppler Vibrometer (SLDV). The unique frequency-steering capability of FSATs is combined with the On-Off Keying (OOK) modulation scheme to achieve frequency directivity in hardware, similar to ongoing research in 5G communications. The MIMO capabilities of the transducer were finally tested over a thin aluminum plate, showing excellent agreement with the FE simulation results
High resolution defect imaging in guided waves inspections by dispersion compensation and nonlinear data fusion
No full textPerformance of defect imaging procedures based on scattered guided waves (GW) acquired by a network of piezoelectric sensors relies mainly on the density of transducers adopted as well as on the accuracy in the time of flight (ToF) estimation. The dispersive and multimodal nature of GW makes this latter task complicated. In this work, a strategy to achieve high resolution defect imaging is proposed and tested to image cracks on an aluminum plate. In particular, first dispersion compensation and basis pursuit schemes are exploited to accurately extract the GW ToF information from the acquired dispersive signals and to translate it into distance of propagation (DoP). Next, the DoP is used to feed four beamforming techniques namely (i) delay and sum, (ii), weighted coherence-factor, (iii) channel rank and (iv) Capon beamformer, which outputs are finally integrated by a proposed nonlinear data-fusion technique. A quantitative comparison on experimental Lamb waves waveforms acquired with a Scanning Laser Doppler Vibrometer (SLDV) on a damaged aluminum plate shows the high resolution imaging performance of the proposed method
VERSATILE SENSOR NODE WITH ACOUSTIC DATA COMMUNICATION CAPABILITIES FOR FSAT NETWORKS IN GUIDED WAVE-BASED STRUCTURAL HEALTH MONITORING APPLICATIONS
No full textSpread spectrum pulse coding in lamb wave inspections
Full text linkIn order to enhance the inspection abilities of an ultrasound system, it can be convenient to increase the number of probes used for the monitoring. In case of multiple simultaneously-operated transmitting transducers, the possibility of interference among the multiple excitations injected in the system should be considered. To avoid such interference, one may use code division. This solution requires some special processing when applied to systems that rely on guided waves (GWs) inspections. In this work, a phase-modulation and pulse compression strategy for guided wave inspections which is based on the Warped Frequency transform is proposed
Unidirectional Frequency-Steerable Acoustic Transducer for guided ultrasonic wave damage imaging
No full textUltrasonic guided waves (GWs) are extensively utilized in nondestructive evaluation and structural health monitoring (SHM) fields. Typically, phased-array GW-based inspections consist of numerous piezoelectric transducers permanently attached to the monitored structure. However, these systems face challenges such as bulky hardware, a large number of transducers and cables for individual element control, complex circuitry and signal processing, high power consumption, and consequently high integration costs. To overcome these limitations, shaped transducers featuring inherent beam steering properties, such as Frequency Steerable Acoustic Transducers (FSATs) can be adopted. FSATs exploit a frequency-dependent spatial filtering effect, which is achieved by properly patterning the electrodes of the piezoelectric transducers. This allows the direction of the generated or sensed wave to be controlled simply by the spectral content of the actuated or received signal, a process so-called “In-sensor” signal processing. Initial generations of FSATs face a 180° ambiguity, where waves are simultaneously generated or sensed in both forward and backward directions. This could lead to uncertainty in defect localization or generate undesirable reflections. In this work, a novel unidirectional FSAT is proposed to eliminate this ambiguity through a new design strategy for unidirectional wave generation and sensing, addressed in the wavenumber domain. Finite element simulations and experimental testing on an aluminum plate validated the proposed frequency-dependent unidirectional beam steering concept. Additionally, the transducer was successfully used in pulse-echo mode for damage imaging, demonstrating 98% localization accuracy. The proposed embedded system can substantially reduce the software and hardware requirements of conventional solutions, paving the way for the development of permanent inspection systems
Low-Power MIMO Guided-Wave Communication
Full text linkThis article demonstrates the use of guided elastic waves (GEW) for multiple-in and multiple-out (MIMO) data communication in the framework of a structural health monitoring (SHM) system. Therefore, miniaturized low-voltage communication nodes have been developed. They are arranged in a spatially distributed and permanently installed network. Wireless exchange of encoded information across a metallic plate and a stiffened carbon-fiber reinforced plastics (CFRP) structure is investigated. A combination of square-wave excitation sequences and frequency-division multiplexing (FDM) is explored for parallel communication with multiple nodes. Moreover, the impact of the excitation-sequence length on the reliability of information transmission is studied in view of future energy-aware application scenarios. The presented system achieves in both studied structures error-free transmission at a data rate of 0.17 kbps (per carrier frequency) with a power consumption of 224 mW
Double-Stage DMAS With Fresnel Zone Filtering in Guided Waves Damage Imaging
No full text: Digital beamforming methods in plate-like structures are widely exploited for Lamb waves-based damage imaging. Among them, the delay and sum (DAS) imaging technique is the most popular thanks to its low-computational cost and ease of implementation. However, the imaging outputs are low quality due to the high levels of side lobes and limited off-axis signal rejection, which leads to limited image resolution and contrast. Recently, the delay multiply and sum (DMAS) beamforming has been applied to nondestructive testing (NDT) field as a promising DAS alternative able to enhance the imaging reconstruction in terms of contrast and damage detectability. However, DMAS is still affected by high levels of artifacts. To tackle this aspect, literature offers a beamforming algorithm called double-stage DMAS (DS-DMAS), first introduced in photoacoustic imaging and medical ultrasound imaging. In this article, the DS-DMAS performance is analyzed for Lamb waves inspection, to provide an exhaustive comparison between DAS, DMAS, and DS-DMAS. As a further step, a filtering process addressed as Fresnel zone filtering (FZF) is used to restrict the beamforming partial sums in a physical way to the area around the scattering point. The proposed approach is an adaptation of a well-established technique in seismic data processing called Fresnel migration, able to suppress artifacts and enhance the quality of the imaging. The algorithms have been compared and characterized by exploiting an online free dataset for guided waves inspection (ht.tp://openguidedwaves.de/) which collects piezo pitch-catch signals traveling through a quasi-isotropic carbon fiber-reinforced plate (CFRP) at different actuated frequencies and damage positions
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