1,721,047 research outputs found
A design strategy for highly directional piezoelectric transducers for Lamb waves inspections
No full textDrastic hardware simplification and cost reduction of Guided Waves (GWs) based systems can be achieved by using shaped transducers that present inherent directional capabilities when generating and sensing elastic waves. Directional transducers for GW generation and sensing are achieved by patterning the piezoelectric material lay-out and the electrodes. The peculiar electrodes’ shape produces a spatial filtering effect which is frequency-dependent,
so that a direct relationship can be established between the direction of propagation (wavenumber) and the spectral content of the transmitted/received signal. This kind of transducer has been named Frequency Steerable Acoustic Transducers (FSATs). In this work, a transducer’s shape design strategy is presented which is able to enhance the
accuracy of the desired Directivity function approximation. The proposed design strategy is based on Dithering techniques. The effectiveness of the novel transducer design methodology is shown through a numerical validation with application to defect detection in an aluminum plate
A design strategy to improve the directivity of wavenumber-spiral frequency-steerable acoustic transducers
Full text linkDrastic hardware simplification and cost reduction of Guided Wave (GW) based systems can be achieved by using piezoelectric transducers that, shaped according to a frequency based beam steering concept, present inherent directional capabilities exhibiting preferential radiation/sensing directions. In particular, directional GWs generation and sensing can be achieved by patterning the piezoelectric material lay-out and the electrodes. Frequency steerable acoustic transducers (FSATs) peculiar electrodes' shape produces a spatial filtering effect which is frequency-dependent, so that a direct relationship can be established between the direction of propagation (wavenumber) and the spectral content of the transmitted/received signal. In this paper we present a novel design strategy of FSAT that enables enhanced sensor directivity by using a local variation of the density of the piezoelectric material
A stamp size, 40mA, 5 grams sensor node for impact detection and location
No full textIn this work, a stamp-size footprint, low power, and light weight sensor node for impact detection and location on laminate composite and metallic structures is presented. This device passively exploits the guided waves originated by the impacts and is meant as a basic building block for smart structure sensor networks development. It draws power from a two-wire differential data-over-power (DoP) network communication interface, which is also used for half-duplex communication at 200 kbps with a gateway device and the other nodes in the network. Each node measures roughly 30mm×23mm, consumes less than 35mA, and weighs less than 5 g, making it attractive for aerospace systems where size, power and weight reduction are crucial. Elastic waves generated from impacts and propagating on the structure
to be monitored are converted to electrical signals by an innovative, patent-pending, spiral shaped piezoelectric transducer. Signals are simultaneously acquired at 1 Msps on each channel and processed by an embedded STM32F3 low-voltage 32-bit mixed-signal MCU with DSP and FPU instructions. A 128 KiB SPI serial SRAM is used for data storage while program instructions are stored in the MCU embedded 256 KiB flash. A low-voltage, high-speed, half-duplex RS485 transceiver is used to interface the MCU to the bus through a filtering mesh of passive components. This mesh also connects to a low-dropout voltage regulator, allowing it to draw power from the DoP bus without interfering with data transmission. A separate gateway device is also presented: it is capable to simultaneously interface and
feed the DoP bus by drawing power either from a common PC USB2.0 port or from an external power supply. A network counting up to 64 nodes on a single wire can be implemented and interfaced to a PC for real-time impact detection applications. This network can be extended to an arbitrary number of nodes by means of signal repeaters
A New Generation of Frequency Steerable Transducers for Lamb Waves Inspections
No full textGuided Waves (GW) inspection is a popular methodology employed by many Structural Health Monitoring (SHM) systems. GW inspection is typically achieved through phased arrays featuring a large number of piezoelectric transducers. The weight penalty, the complex circuitry, and maintenance concerns associated with wiring a large number of transducers have to be addressed for widespread field deployment of these type of SHM systems. Drastic hardware simplification and cost reduction of Guided wave (GWs) based systems can be achieved by using shaped transducers that present inherent directional capabilities when generating and sensing elastic waves. In particular, Frequency steerable acoustic transducers (FSATs) are based on a spatial filtering effect which is frequency-dependent, so that a direct relationship can be established between the direction of propagation and the spectral content of the transmitted/received differential signals [1]. However, in the first practical realizations of FSATs, two main limitations appeared: i) waves are excited or sensed contemporarily in one direction and in the opposite direction (180° ambiguity), ii) just a relatively rude approximation of the desired directivity has been achieved, resulting in a wave generation/detection even in directions other than the desired one. In this work, a new generation of FSATs is proposed, which allows overcoming the above mentioned limitations. In particular, the 180° ambiguity is eliminated by combining the information of 2 differential signals rather than one [1], as happened for the 1st generation FSATs. The result of this combination is a signal whose spectrum peaks at a frequency “f_d”. The piezoelectric load distribution of the 2nd generation FSAT is designed so that the value of “f_d” varies as a function of the wave direction of propagation in the whole angular range [0-360°]. The proposed embedded system allows to operate on composite panels tackling anisotropic and dispersive propagation, and to implement a SHM system with lower weight and size w.r.t. the actual structural monitoring systems. References [1] E. Baravelli et al., IEEE TIM, 62(8), 2013. [2] L. De Marchi et al., “Piezoelectric sensor, method and apparatus for guided waves inspections in real time,” 2015, temporary patent no. MI2015A000556
Dispositivo, sistema e metodo per la diagnostica strutturale in tempo reale con onde elastiche guidate
No full textThe present invention relates to a method for making a device for monitoring the structural integrity of structures such as beams, plates and shells, made of isotropic, anisotropic and/or laminated material, and to such a device. The method provides to define a asymmetric directivity function D(k1,k2) that has, in the domain of wave numbers, a plurality of maxima arranged on different concentric circumferences having center in the origin of the axes. Then a load distribution in spatial coordinates f(x1,x2) is computed by inverse Fourier transform of the directivity function D(k1,k2). Then therefore the device is made with the electrodes, whose shape is obtained by gathering the values of the load distribution f(x1,x2) in the plane having for coordinates the set of real numbers and imaginary numbers, defining at least two sectors of said plane that comprise at least one real value and one imaginary value, and making a number of electrodes equal to the number of the defined sectors, wherein each electrode has a shape corresponding to the points of the load distribution f(x1,x2) that lie in the same sector. Electronic components comprising the device made by such method and a method for monitoring the structural integrity of the above structures employing the device are further described
A novel shaped piezoelectric sensor for impact localization in plate structures
No full textImpact localization in plate-like structures by means of Lamb waves is an important task in structural health monitoring applications. Passive-only networks of piezoelectric wafer active sensors (PWAS) can be exploited to this aim. In this work, a novel piezoelectric sensor for guided wave detection on laminate composite and metallic structures is presented. Such device is capable of revealing the direction of the incoming waves thanks to its peculiar shape. A small footprint, low power, and light weight sensor node was also implemented. This device is meant as a basic building block for smart structure passive sensor networks development. Elastic waves generated from impacts and propagating on the structure are recorded by the shaped transducer and then processed by a microcontroller embedded on the sensor node. The effectiveness of the proposed technology was assessed with an experimental validation
A small footprint, low power, and light weight sensor node and dedicated processing for modal analysis
No full textStructural Health Monitoring functionalities are aimed at constantly assessing the health of a building in order to prevent dramatic consequence of a damage. This work describes a well-defined wireless sensor network system installed over a steel beam capable to perform modal parameters estimation, such as natural vibration frequencies and modal shapes. Signal Processing Techniques were aimed at computing Power Spectral Density of the acceleration signals acquired, dealing with parametric and non parametric approaches. Algorithms in frequency domain, together with the Second Order Blind Identification method were implemented for modal shapes reconstruction. Beside a satisfactory agreement between the theoretical model and the output response of the algorithms implemented, versatility, easiness of reconfiguration, scalability and compatibility with long term installation are among the most powerful advantages of the architecture proposed. Light weight, low power consumption also enhance the capabilities of the system to provide real-time information in a relatively cheap way
Piezo-transducer's shape design as a pre-processing tool in guided wave inspections
No full textStructural health monitoring is an important task in several industrial applications. For example, passive-only networks of piezoelectric sensors can be exploited to detect and localize impacts or anomalous acoustic emissions for the early identification of crack initiation and growth from the analysis of the emitted ultrasonic guided waves. In this work, a shaped piezoelectric sensor and the dedicated electronics for guided wave detection on laminate composite and metallic structures is presented. This device is meant as a basic building block for the development of passive sensor networks in smart structure applications. Elastic waves propagating on the structure are recorded by the transducer composed by multiple, irregularly shaped electrodes and then processed by a microcontroller embedded on the sensor node. The irregular shaping of the transducer electrodes is exploited to simplify the signal processing procedures that are necessary to detect the wave direction of arrival
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