1,720,965 research outputs found
A piezoelectric coded-excitation scanning acoustic transducer for Lamb wave inspections
Full text linkSeveral techniques for Guided Wave (GW) inspections have already been developed. Most of them rely on extensive sensor deployment and damage localization algorithms characterized by significant computational costs. However, there is a growing demand for simpler, more autonomous, and more affordable systems across various fields. In particular, the implementation of wireless, battery-powered systems with a reduced number of sensor nodes and simpler processing would greatly facilitate the transition of this inspection technology on the field. Following this direction, this work presents the design of a novel piezoelectric transducer composed of four different patches, i.e. with only four input/output channels, to scan a given area. The peculiar piezo-load distributions allow the association of different spectral binary sequences for each 6∘ discrete angular step. By evaluating the distance-of-flights (DoFs) of detected peaks, the range coordinates for multiple defects are identified. Meanwhile, the angular information is extracted by demodulating binary sequences of peaks with comparable DoFs across several frequency bands. Since the transducer is designed as an encoder, it is referred to as coded-excitation scanning acoustic transducer (CESAT). More specifically, the Gray code is used to generate spectral patterns to reduce the uncertainty between two adjacent angular steps. A new quantization procedure for the optimal generation of the piezo distributions is also proposed. Ad hoc signal processing algorithms, suitable for embedded applications, were developed to extract multi-target range and angle information. The processing is based on the frequency decomposition of the recorded signal using an FIR filter bank and on dispersion compensation procedures for pulse 're-compression'. The transducer encoder behavior is validated through a finite element analysis. Finally, numerical simulations were performed to assess the effectiveness of the CESAT and associated signal processing in multi-defect detection and localization tasks
A Combination of Chirp Spread Spectrum and Frequency Hopping for Guided Waves-based Digital Data Communication with Frequency Steerable Acoustic Transducers
Full text linkTo facilitate Guided Waves (GWs) communication in terms of hardware simplification and cost reductions, shaped transducers with inherent directional properties can be used. A promising example of such devices is provided by Frequency Steerable Acoustic Transducers (FSATs), where the propagation direction of waves is controlled by the frequency content of the transmitted/acquired signals, thanks to the spatial filtering effect. These peculiar characteristics make the FSAT devices particularly suited for implementation of frequency-based modulation protocols, in which the signal content assigned to each user is uniquely encoded by a corresponding carrier tone. In this work, the special directivity of FSATs is paired with a novel encoding strategy, which is based on a combination of Chirp Spread Spectrum (CSS) and Frequency Hopping (FH) multiplexing, similar to the LoRaWan solution adopted in radio-frequency environments. The devised strategy is aimed at suppressing the inherent destructive interference due to GWs dispersion and multi-path fading
Enabling Spatial Multiplexing in Guided Waves-based Communication: the case of Quadrature Amplitude Modulation realized via Discrete Frequency Steerable Acoustic Transducers
Full text linkGuided Waves (GWs) communication using conventional transducers, e.g., PZT, encounters quite a few problems, such as complex hardware systems and waves multipath interference. To overcome such drawbacks, Frequency Steerable Acoustic Transducers (FSATs) which benefit from inherent directional capabilities can be fruitfully adopted to implement a spatial multiplexing strategy. The FSATs work on the frequency-dependent spatial filtering effect to generate/receive waves, resulting in a direct relationship between the direction of propagation and the frequency content of the transmitted/received signals. Thanks to this unique frequency-steering capability, FSATs are best suited to implement frequency-driven modulation protocols, such as the ones typically exploited for GWs-based data communication. Among these, the Quadrature Amplitude Modulation (QAM) scheme is advantageous in terms of noise immunity. Thus, the objective of this work is to combine QAM with the built-in spatial multiplexing capabilities of FSATs to realize, in hardware, frequency directivity, like the solutions that are currently being investigated in 5G communications
Enabling Directional Frequency-Selective Power Transmission in Ultrasonic Guided Wave Inspections
Full text linkIn this paper, an Ultrasonic Wireless Power Transfer
system is introduced, featuring a novel piezoelectric transducer
called the Frequency-Steerable Acoustic Transducer (FSAT). The
focus is on utilizing FSAT’s directional properties for efficient
power transmission via ultrasonic guided waves, particularly
suited for supplying power to inaccessible sensor nodes in
structural health monitoring applications. Through finite element
simulations and experimental tests, the power transfer process
is analyzed, investigating the relationship between transmission
frequency, transmitted and received voltage, and power effi-
ciency. Furthermore, comparative evaluations with traditional
piezoelectric transducers are conducted, both through FE simu-
lations and experimental tests. The results highlight the superior
performance of FSAT for ultrasonic wireless power transfer
applications by achieving over 16 times higher voltage using
FSAT than traditional piezoelectric transducers
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
Optimal Array Design and Directive Sensors for Guided Waves DoA Estimation
Full text linkThe estimation of Direction of Arrival (DoA) of guided ultrasonic waves is an important task in many Structural Health Monitoring (SHM) applications. The aim is to locate sources of elastic waves which can be generated by impacts or defects in the inspected structures. In this paper, the array geometry and the shape of the piezo-sensors are designed to optimize the DoA estimation on a pre-defined angular sector, from acquisitions affected by noise and interference. In the proposed approach, the DoA of a wave generated by a single source is considered as a random variable that is uniformly distributed in a given range. The wave velocity is assumed to be unknown and the DoA estimation is performed by measuring the Differences in Time of Arrival (DToAs) of wavefronts impinging on the sensors. The optimization procedure of sensors positioning is based on the computation of the DoA and wave velocity parameters Cramér-Rao Matrix Bound (CRMB) with a Bayesian approach. An efficient DoA estimator is found based on the DToAs Gauss-Markov estimator for a three sensors array. Moreover, a novel directive sensor for guided waves is introduced to cancel out undesired Acoustic Sources impinging from DoAs out of the given angles range. Numerical results show the capability to filter directional interference of the novel sensor and a considerably improved DoA estimation performance provided by the optimized sensor cluster in the pre-defined angular sector, as compared to conventional approaches
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
Design of a Novel Pulser for Frequency Selective-based Power and Data Transmission
Full text linkThis paper proposes an ultrasonic system based
on an innovative piezoelectric device, the Frequency Steerable
Acoustic Transducer (FSAT). The FSAT’s high directivity can
be exploited for structural inspection, and through-metal data
communication and wireless power transfer. These three func-
tions are fundamental in an autonomous sensor system developed
for condition monitoring, which is a central requirement in
many sectors, such as automotive. A novel pulser, made up of
a signal generator and a power amplifier, has been designed
and simulated, for effectively driving the FSAT transducer.
Experimental results showed that the designed power amplifier
is able to reach a gain of 17.80 dB driving the piezoelectric
transducer with a maximum peak-to-peak voltage of 24 V and
that its bandwidth is [3.1-964] kHz. Experiments have been
carried out showing a great improvement in trasmission using
the designed amplifier
Ultrasonic Wireless Power Transfer in Metal Structures using Frequency-Steerable Acoustic Transducers and Impedance Matching
Full text linkUltrasonic Wireless Power Transfer (UWPT) has been widely investigated in recent years as a promising solution for powering inaccessible sensor nodes in structural health monitoring (SHM) applications without affecting materials' in-tegrity and overcoming metal shielding effect. In this work, the Frequency-Steerable Acoustic Transducer (FSAT) has been considered as an innovative device for ultrasonic guided waves-based energy transmission thanks to its directional properties. Power transmission and conversion from ultrasonic waves have been investigated, along with techniques exploiting impedance matching to ensure maximum power transfer and sufficient voltage at the receiver side. More specifically, FSAT's output impedance is measured and two impedance-matching networks are proposed and characterized: a parallel-connected inductor and a magnetic transformer. Experimental results conducted on a 1 mm thick aluminum plate with two FSATs bonded at a 50 cm distance pointed out a maximum received power value of 164 μW at 83 kHz, with a 23 V peak-to-peak voltage in transmission. The received power and voltage are sufficient to energize a low-end MCU and micropower management circuits on a sensor node
VERSATILE SENSOR NODE WITH ACOUSTIC DATA COMMUNICATION CAPABILITIES FOR FSAT NETWORKS IN GUIDED WAVE-BASED STRUCTURAL HEALTH MONITORING APPLICATIONS
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