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In literature, it is known that a Light Emitting Diode (LED) could be used as a light sensor. It is also known that its emitted light spectrum and sensitivity spectrum can be partially overlapped. This work presents how commercial LEDs can be used as light emitters and simultaneously as sensors of the reflected portion of the light emitted by themselves. The realized devices present a unique characteristic: the transmitter and the receiver coincide spatially as they are the same device. This ensures the perfect overlapping between transmission and reception radiation lobes that could provide many benefits in several applications like as distance measurements or image sensors. Some simple electronic configurations that use LEDs as detectors of their own emitted light are presented. It has been also demonstrated how these LEDsTx-Rx can work as image sensors by acquiring an image of a simple test object, and how they can realize distance sensors with respect to other known techniques. Further advantages can be obtained by realizing LEDTx-Rx array in single integrated devices. With the realization of such devices, it will be also possible to experiment new constructive solutions for commonly used applications, without the need of using separate emitter and receiver.

In this study, the temperature influence on the spectral responsivity of a Light Emitting Diode (LED) used as a photoreceptor, combined to light source spectrum is correlated to electrical characteristics in order to propose an alternative method to estimate LED junction temperature, regardless of the absolute illumination intensity and based on the direct correlation between the integral of the product of two optical spectra and the photo-generated currents. A laboratory test bench for experimental optical measurements has been set in order to enable any characterizing of photoelectric devices in terms of spectral behaviour, in a wavelength range placed between 400–1000 nm, and of current-voltage characteristics as function of temperature by using two different illumination sources. The temperature is analysed in a range from 5 °C up to 85 °C, so as to evaluate thermal variation effects on the sensor performance. The photo-generated current of two LEDs with different peak wavelengths has been studied. Research has observed and mathematically analysed what follows: since the photo-generated current strictly depends on the combination between the spectral response of the photoreceptor and the lighting source response, it becomes possible to estimate indirectly the junction temperature of the LEDs by considering the ratio between the photogenerated currents obtained by using two different illumination sources. Such results may for one thing increase knowledge in the fields where LEDs are used as photo-detectors for many applications and for another, they could be extended to generic photodetectors, thus providing useful information in photovoltaic field, for instance.

This paper describes the implementation of a structural health monitoring (SHM) method for mechanical components and structures in composite materials with a focus on carbon-fiber-overwrapped pressure vessels (COPVs) used in the aerospace industry. Two flex arrays of polyvinylidene fluoride (PVDF) interdigital transducers have been designed, realized, and mounted on the COPV to generate guided Lamb waves (mode $A_0$ ) for damage assessment. We developed a custom electronic instrument capable of performing two functions using the same transducers: passive-mode detection of impacts and active-mode damage assessment using Lamb waves. The impact detection is based on an accurate evaluation of the time of arrival and was successfully tested with low-velocity impacts (7 and 30 J). Damage detection and progression is based on the calculation of a damage index matrix which compares a set of signals acquired from the transducers with a baseline. This paper also investigates the advantage of tuning the active-mode frequency to obtain the maximum transducer response in the presence of structural variations of the specimen, and therefore, the highest sensitivity to damage.

This work presents an improved interdigital transducer for ultrasonic guided-wave generation and reception in structural health monitoring systems, where each finger constitutes an independent electrode that can be driven and sensed with a multichannel system. The new design aims at improving the versatility in wavelength selectivity of the classical interdigital transducer. Preliminary tests have shown that the fingers work correctly as a time-delayed periodic array.

Composite material structures are commonly used in many industrial sectors (aerospace, automotive, transportation), and can operate in harsh environments where impacts with other parts or debris may cause critical safety and functionality issues. This work presents a method for improving the accuracy of impact position determination using acoustic source triangulation schemes based on the data collected by piezoelectric sensors attached to the structure. A novel approach is used to estimate the Differential Time-of-Arrival (DToA) between the impact response signals collected by a triplet of sensors, overcoming the limitations of classical methods that rely on amplitude thresholds calibrated for a specific sensor type. An experimental evaluation of the proposed technique was performed with specially made circular piezopolymer (PVDF) sensors designed for Structural Health Monitoring (SHM) applications, and compared with commercial piezoelectric SHM sensors of similar dimensions. Test impacts at low energies from 35 mJ to 600 mJ were generated in a laboratory by free-falling metal spheres on a 500 mm × 500 mm × 1.25 mm quasi-isotropic Carbon Fiber Reinforced Polymer (CFRP) laminate plate. From the analysis of many impact signals, the resulting localization error was improved for all types of sensors and, in particular, for the circular PVDF sensor an average error of 20.3 mm and a standard deviation of 8.9 mm was obtained.

A new device is presented for the detection of compliant objects buried in shallow soil by their vibrational characteristics. The device is based on the concept of a sensorized prodder that can measure the acceleration of a point on the surface of the object with a rigid steel rod. This paper presents a simple model able to simulate the acceleration frequency response of the system composed of the prodder and a buried object. Direct laboratory measurements and/or parametric inspection of the mechanical characteristics of the prodder device and the test objects allow us to select a suitable frequency range to detect compliant objects. The developed equivalent lumped circuit model allows investigation of the natural resonant frequency of the designed prodder device and of the test objects at different depths. The object is vibrated applying a contact force generated by an electrodynamic actuator driven with a series of frequency-modulated burst signals. The fully assembled device is light and of compact size, and it has been tested both mounted on a robotic arm and handheld. In good agreement with the simulations, the results of the tests carried out in the laboratory and in an outdoor test bed showed that the responses of the compliant and rigid test objects were well distinguishable in the frequency range from 100 to 1000 Hz.

Many reusable components of aerospace structures are manufactured with composite materials, like carbon fiber overwrapped metal vessels (COPV). Ultrasonic Lamb waves are commonly used to monitor these components. Damage caused by impacts or due to the mechanical stress suffered by high pressure vessels required an innovative approach for structural health monitoring (SHM) using ultrasonic transducers. This work describes the design and development of a system that uses arrays of conformable piezoelectric interdigital transducers (IDTs) connected to a custom data acquisition system for real-time monitoring of a COPV.

Impact damage is one of the major concerns in maintenance of structures built from composite materials. For example damages induced by impact in composite overwrapped pressure vessel (COPV) operating in space conditions required an innovative approach for structural health monitoring (SHM) with piezoelectric transducers. Automated impact detection and characterization on structures has been an elusive goal due to the transitory nature of the detectable signals involved. The work describes the development of a real-time electronic system for automated impact detection on a scale model of COPV using piezoelectric transducers connected to a mixed analog-digital electronics.

Nuclear safeguards applications require highly specialized and secure systems for identification and authentication of copper canisters that has been recently introduced for long term geological repository of nuclear spent fuel. Following an ultrasonic characterization of velocity and attenuation of copper cylinders, a numerical model for the scattering of a set of Flat Bottom Holes (FBHs) randomly placed on a circular path is implemented. The random position, height and diameter of each FBH is used to generate a unique ultrasonic fingerprint that can be acquired with an ultrasonic probe scanning the surface of the copper canister along the circular path where the centers of FBHs are placed. According to the copper lid geometry a new method is required for the identification of the copper canisters; a solution is proposed with inclined FBHs with reduced distance from the probe in order to achieve high signal to noise ratio at 5 MHz. This solution can be easily implemented with an immersion probe thanks to the existing copper lid external cavity that can be filled with water. The characteristics of the ultrasonic fingerprint are analyzed in term of dynamic and robustness for identification with laboratory prototypes.

This paper describes the design and fabrication of a 16-element transducer array for airborne ultrasonic imaging operating at 150 kHz, that can operate both at close range (50 mm) in the near field of a synthetic aperture, and up to 250 mm. The proposed imaging technique is based on a modified version of the delay and sum algorithm implemented with a synthetic aperture where each pixel amplitude is determined by the integration of the signal obtained by the coherent summation of the acquired signals over a delayed window with fixed length. The image reconstruction methods using raw data provides the possibility to detect targets with smaller feature size on the order of one wavelength because the coherent signals summation over the selected window length while the image reconstruction methods using the summation of enveloped signals increases the amplitude response at the expenses of a lower spatial resolution. For the implementation of this system it is important to design compact airborne transducers with large field of view and this can be obtained with a new design of hemi-cylindrical polyvinylidene fluoride film transducers directly mounted on a printed circuit board. This new method is low cost and has repeatable transducer characteristics. The complete system is compact, with a modular architecture, in which eight boards with dual ultrasonic channels are mounted on a mother board. Each daughter board hosts a microcontroller unit and can operate with transducers in the bandwidth 40–200 kHz with on-board data acquisition, pre-processing and transfer on a dedicated bus.

An experimental setup for acoustoseismic detection of shallow buried objects is presented. The seismic (Rayleigh) waves were generated by exciting an acoustic airborne source by a series of sine-wave bursts, which were designed to cover a frequency range (100-1000 Hz) large enough to distinguish the vibrational characteristics of buried compliant objects. The signals were recorded by means of contact-acceleration microelectromechanical- system sensors moved above different buried objects (compliant and rigid). Signal acquisitions on only sandy soil revealed the natural variability of the outdoor test bed. This variability of soil parameters pointed out the difficulties of buried-object detection based on the amplitude thresholding of the signal spectrum. For this aim, the signals were processed in both time and frequency domains. An audio-channel output was devised to avail of the human hearing apparatus in distinguishing the buried objects according to spatial variations of the acceleration signals obtained by scanning the soil surface.

The high spatial resolution offered by the holographic radar operating in the frequency range 2GHz–8GHz can be fully exploited in field surveys if the radar head can scan large areas with spatial resolution and accuracy corresponding to a fraction of the wavelength. For the typical operating frequencies this requires a millimeter resolution of the acquisition system. For achieving these requirements a robot scanner is proposed and the realization of the main blocks is described. The advantage of this approach for fast and accurate subsurface imaging is demonstrated with laboratory experiments for the detection of defects on the bonding of thermal insulating material on a metal sheet. For more complex environments like natural soil a multisensory system is proposed and a low cost range meter with special design of the ultrasonic transducers is proposed. The profile of the surface is an important information for obtaining the best resolution of buried object underneath irregular surfaces.

A complete 3-D ultrasonic pulsed Doppler system has been developed to measure quantitatively the velocity vector field of a fluid flow independently of the probe position. The probe consists of four 2.5 MHz piezocomposite ultrasonic transducers (one central transmitter and three receivers separated by 120 degrees ) to measure the velocity projections along three different directions. The Doppler shift of the three channels is calculated by analog phase and quadrature demodulation, then digitally processed to extract the mean velocity from the complex spectrum. The accuracy of the 3-D Doppler technique has been tested on a moving string phantom providing an error of about 4% for both amplitude and direction with an acquisition window of 100 ms.

The paper describes the design, the technology, and the characterization of an array of 16 elements of airborne ultrasonic transducers. The array is connected to a dedicated electronic platform that provides the 16 channels programmable analog front-end electronics and the synchronization and data acquisition and transmission for real-time target detection and tracking or for high-resolution imaging. The transducers are designed to operate at 150 kHz to cover a distance of about 200 mm and with featured narrow vertical directivity and wide horizontal directivity to scan an almost plane section with a linear array configuration.

During the last 10 years, the structural health monitoring (SHM) technique based on Lamb waves, involving intelligent sensors spread on the structure like biological receptors on the human body, achieved good and promising results showing broad-based economic benefits. There are a few who demonstrated SHM systems based on the use of a network of piezoceramic sensors applied directly to the structure for monitoring and surveying, controlled by a dedicated control unit, the health of the structure itself (detection of cracks, delaminations, disbonds, and corrosion to monitoring the mechanical impacts on metal and composite structures, etc.). The work describes a new approach for the development of this SHM system based on flexible piezopolymer transducers (PPTs) which have some advantages over the piezoceramic thin disk transducers in space applications.

This paper presents the experimental results for an acousto-seismic buried landmine detection method. The excitation source used was a woofer loudspeaker and lightweight silicon MEMS accelerometers were adopted to measure the ground surface acceleration. The experiments were performed in an outdoor unconsohdated sand test-bed with several kinds of compliant and rigid test-objects, all buried at depth of 4cm and placed at distances ranging from 10cm to 50cm. The different responses of the compliant and rigid objects was processed in both time and frequency domains. A novel audio representation of the acquired signals was developed for exploiting the human-hearing capabilities for the identification of buried objects.

Acoustic methods have been recently investigated for the detection of shallow landmines. Some plastic landmines have a compliant case which can made to vibrate by an airborne excitation like a loudspeaker. Our study is based on the possibility to detect landmines by contact or non-contact sensors like accelerometers or phonometers. Phonometers can provide sufficient seismic sensitivity but their response is influenced by direct acoustic wave coupling from the driving source. On the contrary accelerometers are much less influenced by the direct acoustic wave coupling and they have high sensitivity to acquire soil surface vibrations. In our experiments we can measure typical accelerations in order of 2 m/s2 with sensitivity of 800 mV/g. The acceleration signal elaboration and visualization developed in this work demonstrates the suitability of these sensors for acoustic landmine detection study and allows a fast analysis to evaluate the presence of a buried landmine.

Acoustic methods have been recently investigated for the detection of shallow landmines. Some plastic landmines have a flexible case which can made to vibrate by an airborne excitation like a loudspeaker. The soil-mine system shows a resonant behavior which is used as a signature to discriminate from other rigid objects. The mechanical resonance can be detected at the soil surface by a remote sensing systems like a laser interferometer. An equivalent physical model of the mine-soil system has been investigated having the known physical characteristics of mine simulants. The authors designed and built a test-object with known mechanical characteristics (mass, elasticity, damping factor). The model has been characterized in laboratory and the results compared with the classic mass-spring loss oscillator described by Voigt. The vibrations at the soil surface have been measured in various positions with a micro machined accelerometer. The results of the simulations for the acceleration of the soil-mine system agree well with the experiment. The calibrated mine model is useful to investigate the variation of the resonance frequency for various buried depths and to compare the results for different soils in different environmental conditions.

In this work we presented a hardware-software platform, which was designed to be expandable, modular, and adaptable to any other system which needs to produce significant and easily readable real time images. Such platform, being completely programmable, can also be reconfigured in dependence of the object being investigated.

Presents FEBO, a new spectrogoniometer installed in the Photometric Laboratory of the University of Florence for bidirectional reflectance measurements. The system uses an industrial robot arm for positioning a detector around the target on a 2/spl times/1 m/sup 2/ area, at angles up to /spl plusmn/90/spl deg/ around the zenith. The spectral detector is an intensified CCD OMA, coupled with an optical fiber, allowing a narrow detection angle in the spectral range of 250-900 nm, on a target area of 95/spl times/95 mm/sup 2/. Other detectors can be mounted directly on the FEBO arm, for infrared measurements. Target integration is achieved by scanning the detector over the target area, under computer control by the FEBO software, which provides also data visualisation, storage and detector response calibration. Results of a first experiment on a spruce canopy is also described, showing the variation of NDVI with detection and illumination angles.

The aim of this work is to present a novel apparatus for experimental activity in research where a high frequency signal must be acquired and processed in real-time, and represented through a multi-image visualization tool. The proposed apparatus is a hardware and software platform dedicated to signal and/or image processing and fast data visualization. Currently the system is employed for studying new algorithms for biological tissue ultrasound investigation 1,2. Real-time operation mode designates clinical environment as its elective application because fast data processing is a necessary prerequisite in order to evaluate the on-line diagnostic performance of different investigation methods. Furthermore, for research purposes, the possibility to have simultaneous views of different ultrasonic parameters is essential for an efficient analysis, verification and modelling of the specific ultrasound-media interaction phenomenon .

Novel radio frequency processing techniques for biological tissue characterization with ultrasound are presented in order to improve the diagnostic power of ultrasonic echographic systems. Spectral images of biological “in-vitro” and “in-vivo” tissue, obtained through the Discrete Wavelet Packet Transform (DWPT) are presented, as well as velocity vector maps of blood flow obtained with 2-D Doppler investigation. The implementation of the Discrete Wavelet Packet Transform through a digital filter produces, for each acquired frame, real time spectral maps, in different frequency bands. Multi-parametric images are composed by merging these maps using a dedicated “balance image fusion” algorithm. New blood images, obtained without using the Doppler effect, for “in-vivo” and “in-vitro” experiments are presented based on the exploitation of non-linear ultrasound-medium interaction effects [1,2,3,4]. The proposed spectral processing procedure seems to be suitable to perform tissue characterization. Pathological portions inside tissue could be detected thanks to their different echo frequency content which in turns is determined by linear and non-linear ultrasonicmedium interaction. The target of future clinical applications is to investigate the potential of the procedure as a “virtual biopsy”. Vector Doppler multi parametric images are obtained with compound measurements of Doppler shifts along different directions, and superimposing the resulting 2-D velocity vector maps to the conventional morphological B-mode representation [5,6,7] The results, here presented, were produced by employing a hardware and software platform dedicated to ultrasonic signal and image processing [8,9,10]. The radiofrequency signal for multi parametric calculation and presentation with a multiprocessing digital architecture was used. This platform provides a multi analysis and

An experimental system was developed to acquire and visualise in real-time two-dimensional (2-D) velocity maps. Data acquisition is performed by using a modified commercial echograph based on a 5-MHz, 128-element linear-array transducer with electronic focussing and beam steering. Additional electronics were integrated into the echograph to implement a 2-D Doppler system capable of measuring the velocity component on the scanning plane. Suitable axial and lateral scanning methods were studied to obtain Doppler measurements over a scanning area. A colour image of the estimated velocity field is presented in real time on a personal computer using different visualisation techniques. The system performance was tested experimentally both in vitro and in vivo on a human carotid artery.

The aim of the work is to present a novel apparatus for experimental activity in research of new methods for studying material and biological tissue with ultrasound. FEMMINA (Fast Echographic Multiparametric Multi Imaging Novel Apparatus) is a hardware and software platform dedicated to ultrasonic signal and image processing. It uses the radiofrequency signal for multiparametric calculation and presentation with a multiprocessing digital architecture. The architecture is designed to be modular, expandable and aimed at embracing different ultrasonic investigation techniques. It provides a multianalysis and interactive image system not only for clinical usage but also for all applications where a high image rate production is required. In order to obtain an efficient interactive system, it was also necessary to realize a fast signal processing, as well as to implement a fast visualization tool for managing multiple images. The platform is completely programmable, and for a specific application it can be on-line reconfigured in dependence of the parameters that, from time to time, must be evaluated. Spectral images of biological in-vitro and in-vivo tissue, obtained through the Discrete Wavelet Transform (DWT) by using new processing algorithms are presented as preliminary applications of the platform, as well as vector images for blood flow 2-D Doppler investigation. Innovative blood images, obtained without using the Doppler effect, and novel vector distribution images for blood velocity are reported.

The aim of this work is the development of a three-dimensional (3D) PW Doppler system capable of measuring the velocity vector field (module and direction) without correction for the probe-to-flow angle. The applications of this instrument are in the field medical imaging of blood flow, and for industrial applications. The 3D PW Doppler method was studied theoretically by the authors1 and it can be used for volumetric scans of flow and quantitative estimation of the velocity vector field in the region of interest. In medical applications where the determination of the probe-to-flow angle is often inaccurate, this technique allows to eliminate the uncertainty due to the angle correction.

A strong interest is growing in improving the diagnostic capabilities of current ultrasonic Doppler systems. In particular a consistent research effort is directed toward the development of new Doppler techniques capable to estimate the three-dimensional (3-D) velocity of blood flow.

This paper reports the result of a study for the application of ultrasonic investigation techniques to detect optically transparent impurities in opaque fluid. Two different detection methods are proposed for the control of vials containing pharmaceutical products and for the application in an industrial environment.

Few studies have examined the influence of ethnic-cultural variables on pain perception and behavioural distress in children. Not considering possible cultural variations of pain manifestation may lead to inadequate assessment and treatment of pain. Goal To evaluate wether differences exist between Italian and non-Italian children with regards to pain perception and behavioural distress during the same invasive procedure. Methods Cross-sectional analytical trial. A group of Italian children (group A) and a group of Chinese children (group B) aged 3 to 11 were observed during a standardized venipuncture for blood sample drawing. Pain was self-rated with a 1–10 Wong faces scale or a 1–10 numeric scale. Behavioural distress was measured with the Observational Behaviour Distress Scale (OBDS, 1–33). Results 246 children were examined, 191 in group A and 55 in group B. In preschool age (3 to 5, n=76), neither mean pain rates nor mean OBDS rates were statistically different in the two groups. On the opposite, in the 6–11 age (n=170), mean pain rate was 2.9 in group A and 4.8 in group B (Anova p=0.00001) while mean OBDS rate was 6.6 in group A and 2.3 in group Bi (Anova p=0.0005). Discussion Our data show that duiring venipuncture Chinese children have less marked behavioural distress manifestations than their Italian peers, even though the perceived pain is higher in Chinese children.

In this work the performance of a prototype three-dimensional (3D) PW Doppler system producing 3D velocity field maps is analyzed by means of measurements on phantoms with known velocity profiles and of simulations. The developed 3-D Doppler system gives a measurement of the velocity vector in a sample volume by means of a probe consisting of four confocal annular array transducers oriented along different directions and three programmable analogue Doppler channels.