313 research outputs found
Clusters of shaped ultrasonic transducers for lamb waves’ DoA estimation
No full textThe direction of arrival (DoA) estimation of Lamb waves is a fundamental task to locate acoustic events, such as those caused by impacts in plates or shells. To perform this task, a novel cluster of piezoelectric sensors is presented in this work. The designed cluster is composed by three irregularly shaped patch transducers (P1, P2 e P3). This is in contrast with the approaches that are typically presented in literature which are based on isotropic piezo-disks. In our approach, the transducers are shaped with a procedure based on the Radon Transform, so that the difference in time of arrival (DToA) of the Lamb waves at patches P1 and P2 is linearly related to the DoA, while P3 is designed so that it is possible to perform the estimation of DoA without knowing the actual wave velocity. The numerical validation shows that the performance in the DoA estimation achieved by means of the proposed cluster compares favorably with respect to clusters of conventional sensors, even in the case of noise-affected measurements
Frequency Steerable Transducers for Ultrasonic Structural Health Monitoring
No full textUltrasonic Structural Health monitoring systems are typically implemented through phased arrays featuring a large number of piezoelectric transducers. However, the permanent installation of such a large number of transducers could hamper the widespread field deployment of SHM systems. To this aim, a possible solution is in the shaping of the piezoelectric transducer electrodes to achieve the capability of steering the ultrasonic beam by simply controlling the central frequency of the actuated pulse. This solution enables the imaging of large 2D areas by actuating just two differential signals. In this work, some recent realizations of Frequency steerable transducers (FSATs) will be presented, detailing the design, simulation, and experimental characterization strategy and the signal processing techniques which can be applied on the acquired signals. It will be shown that FSATs offer several features, such as inherent hardware directivity, and reduced sidelobes, which are essential in the realization of the next generation of ultrasonic Structural Health Monitoring systems
Impact of noise model on the performance of algorithms for fault diagnosis in rolling bearings
No full textCondition monitoring of rolling bearings is attracting much interest since most of the production slowdowns depends on the damaging of these components. Several algorithms for fault detection have appeared in the technical literature in the last decade. In most cases, performance is assessed over both synthetic and experimental data. Unfortunately, the computer simulations adopt signal models that are trivial and are not able to predict the actual performance on the field. In this work we propose a framework suitable to fairly, quantitatively and objectively compare different algorithms for fault detection in rolling bearings. The vibration signal is obtained through computer simulations. The signal entailed by the damage is generated through the model at "impact-delay-line" already available in the technical literature. The machine noise is generated as a wideband component with the possible superposition of narrowband components. The wideband component has been modeled as additive white Gaussian noise, additive white noise drawn from an alpha-stable distribution and additive noise stemming from an autoregressive process. Narrowband components are modeled through trains of Gaussian pulses. The performance of three well known algorithms for fault detection are compared in terms of capability in identifying the theoretical cyclic frequencies related to a damage. In these scenarios the behavior of fault detectors are definitely far from that predicted by classical wideband noise models like, for instance, additive white Gaussian noise
Flavonoids and renin-angiotensin-aldosteron system modulation: cocoa, flavanol and blood pressure
No full textFlavonoids and renin-angiotensin-aldosteron system modulation: cocoa, flavanol and blood pressure
No full textShaped sensor for material agnostic Lamb waves direction of arrival (DoA) estimation
No full textIn this work, a sensor formed by clustering three ad-hoc shaped piezoelectric patches is proposed for guided waves direction of arrival (DoA) estimation in laminate composite and metallic structures. The irregular shaping of the transducer electrodes allows to simplify the signal processing procedures which are necessary to detect the wave DoA. The cluster is conceived so that there is a linear dependence between the difference in time of arrival (DToA) of the wavefront at two of the sensor patches and the DoA of the wavefront itself. The third piezoelectric patch is shaped so that the estimation of the DoA from the DToA can be performed without knowing the actual wave velocity. The transducer performance in terms of DoA estimation accuracy are evaluated through numerical simulations, in which the plate response to a point source is evaluated in the frequency domain using the Green's function approach. Results show that the standard deviation of the error in the estimation of the DoA is less than 2°. This device is meant as a basic building block for the development of passive sensor networks in smart structure applications
Modelling and simulation of a vibrating membrane for the acquisition of lung sounds
No full textThe lack of general doctors and physicians represents the main problem for most of the modern national health systems. The high operating and maintenance costs of hospitals and clinics complete the critical picture. The development of new diagnostic tools can play a fundamental role in tackling these challenges. Recent studies have shown that electronic stethoscopes can raise the diagnostic suspicion of several pulmonary diseases, for instance interstitial lung diseases. The vibrating membrane, or diaphragm, is a fundamental component of the stethoscope that significantly affects its performance. Despite several theoretical and experimental studies are available about membrane vibration, the exact role of the diaphragm in a stethoscope for the acoustic coupling is still mostly unclear. In this paper we investigate the effect of the diaphragm on the sensibility and bandwidth of electronic stethoscopes. We setup a 1D numerical simulation of the system composed by the lung, human body, vibrating membrane and microphone. The parameters are devised from breathing mechanics and from the datasheets of a commercial diaphragm and microphone. The performance predicted by numerical simulations have been compared to experimental measurements on our prototype of electronic stethoscope. In particular, the predicted pressure at the input of the microphone is very close to that experimentally measured during outpatient visits at the University Hospital of Modena (Italy)
POSSIBLE EVIDENCE OF QUANTUM-SIZE EFFECTS IN X-RAY PHOTOEMISSION SPECTRA OF ULTRATHIN SI LAYERS
No full textThis letter reports the experimental evidence of a 2.3 eV blue shift of the plasmon loss lines observed in the x-ray photoelectron spectra of an ultrathin Si layer equivalent to 1.5 X 10(15) at./cm(2) deposited onto a randomly oriented Al2O3 Single crystal. The plasmon line shifts, which is roughly proportional to the deposited Si(mass)(-2/3), are attributed to quantum confinement effects in agreement with electron energy loss measurements performed on nanosized Si particles
RELATIONSHIPS BETWEEN BILE-SALTS HYDROPHILICITY AND PHOSPHOLIPID-COMPOSITION IN BILE OF VARIOUS ANIMAL SPECIES
No full textThe prediction of total body water from bioelectrical impedance in patients with anorexia nervosa
No full textTotal body water (TBW) was measured by deuterium oxide (D2O) dilution and predicted from bioelectrical impedance (Z) in nineteen anorexic and twenty-seven control women. The equation of Kushner et al, (1992) based on the impedance index (ZI = height(2)/Z) gave biases of 0.9 (SD 2.5) and 0.8 (SD 2.5) litres in controls and patients respectively (NS, ANOVA). The ZI-based equation of Deurenberg et al, (1993) gave biases of 1.5 (SD 2.4) litres (NS) and 3.0 (SD 2.1) litres (P < 0.001) in controls and patients respectively. Despite the fact that weight was the most powerful predictor of TBW on the study sample (n 46, r(2) 0.90, P < 0.0001, SE of the estimate 1.6 litres, CV 5.7 %), the formulas of Segal et al. (1991) and Kushner et al, (1992) based on the association of weight and ZI gave an inaccurate prediction of TBW in both control and anorexic subjects, with a bias ranging from -3.2 (SD 2.4) to 2.9 (SD 2.1) litres (P less than or equal to 0001). Population-specific formulas based on ZI (n 46) gave a more accurate prediction of TBW by bioelectrical impedance analysis on the study subjects, with biases of -0.1 (SD 1.8) and 0.5 (SD 1.7) litres in controls and patients respectively (NS). However, the individual bias was sometimes high. It is concluded that bioelectrical impedance analysis can be used to predict TBW in anorexic women at a population level, but the predictions are less good than those based on body weight alone
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