L. Capineri

Advanced image-processing technique for real-time interpretation of ground-penetrating radar images

This work presents the development of an advanced image analysis technique capable of locating buried objects by ground‐penetrating radar (GPR) images. The technique requires only a small amount of operator intervention and is fast enough to provide quasi‐engineering drawings in real time. The work is intended to simplify the interpretation of the complex pattern found in GPR images. A theoretical development of the method is presented. Results on synthetic and real images from different buried objects are presented, and errors < 7% on the object position are observed with laboratory test objects.

A Doppler system for dynamic vector velocity maps.

The aim of the vector Doppler technique is the quantitative reconstruction of a velocity field independently of the ultrasonic probe axis to flow angle. In particular, vector Doppler is interesting for studying vascular pathologies related to complex blood flows. A problem of vector Doppler is data representation in real-time that should be easy to interpret for the physician. In this work, we present a technique for dynamic display of vector velocity maps and some experimental results obtained in vitro with 2-D vector Doppler on flow phantoms reproducing complex flow conditions. An improvement in the map presentation was obtained by using velocity vector field interpolation. In this work, we considered the problem of spatial sampling for vector Doppler, establishing a relationship between sampling steps and scanning system characteristics. Finally, we developed a novel multimedia solution that uses both interpolated images and sound to discriminate between laminar and turbulent flows.

Holographic Subsurface Radar of RASCAN Type: Development and Applications

Holographic subsurface radars (HSR) are not in common usage now; possibly because of the historical view amongst radar practitioners that high attenuation of electromagnetic waves in most media of interest will not allow sufficient depth of penetration. It is true that the fundamental physics of HSR prevent the possibility to change receiver amplification with time (i.e., depth) to adapt to lossy media (as is possible with impulse subsurface radar or ISR). However, use of HSR for surveying of shallow subsurface objects, defects, or inhomogeneities is an increasingly proven area of application. In this case, HSR can record images with higher resolution than is possible for ISR images. The RASCAN family of holographic radars is presented along with technical specifications and typical case histories. Among the applications considered are civil and historic building surveys, nondestructive testing of dielectric materials, security applications, and humanitarian demining. Each application area is illustrated by relevant data acquired in laboratory experiments or field tests. This paper presents experiments with RASCAN imaging in media with different degrees of attenuation, and illustrates the principle of HSR through an optical analogy.

A real-time two-dimensional pulsed-wave Doppler system

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 Estimation of Buried Pipe Diameters by Generalized Hough Transform of Radar Data

The generalized Hough transform method is applied to the measurement of the diameters of buried cylindrical pipes by Ground Penetration Radar (GPR). 600 MHz radar scans across long pipes, buried in one metre or so of soil, show complex reflection patterns consisting of a series of inverted hyperbolic arcs. The time of flight t(y) as the radar probe is scanned along an axis, y, perpendicular to the pipe, shows an arc whose shape and position depends on 4 unknown variables: y0, the position of the center of the pipe along the scan, z0, the depth of the pipe center, R0, its radius and V0 the velocity in the medium. Analytic expressions for the solution of these variables have been obtained. They use sets of times ti at corresponding positions yi, along the arc, depending on the number of variables to be determined. In the generalized Hough method many such sets of times are chosen randomly from points on the arcs. The results are presented for example as peaks in an accumulator space for each variable. The method is demonstrated for a 0.18 m radius concrete pipe buried at a nominal 1 m depth in a road. Using data acquired at 600MHz frequency (around 0.16m wavelength in soil) the estimated radius was 0.174 ± 0.059 m.

Characterization of a Silicon Strip Detector and a YAG:Ce Calorimeter for a Proton Computed Radiography Apparatus

Today, there is a steadily growing interest in the use of proton beams for tumor therapy, as they permit to tightly shape the dose delivered to the target reducing the exposure of the surrounding healthy tissues. Nonetheless, accuracy in the determination of the dose distribution in proton-therapy is up to now limited by the uncertainty in stopping powers, which are presently calculated from the photon attenuation coefficients measured by X-ray tomography. Proton computed tomography apparatus (pCT) has been proposed to directly measure the stopping power and reduce this uncertainty. Main problem with proton imaging is the blurring effect introduced by multiple Coulomb scattering: single proton tracking is a promising technique to face this difficulty. As a first step towards a pCT system, we designed a proton radiography (pCR) prototype based on a silicon microstrip tracker (to characterize particle trajectories) and a segmented YAG:Ce calorimeter (to measure their residual energy). Aim of the system is to detect protons with a ~1 MHz particle rate of and with kinetic energy in the range 250-270 MeV, high enough to pass through human body. Design and development of the pCR prototype, as well as the characterization of its single components, are described in this paper.

ESTIMATION OF RELATIVE PERMITTIVITY OF SHALLOW SOILS BY USING THE GROUND PENETRATING RADAR RESPONSE FROM DIFFERENT BURIED TARGETS

Combined ground penetrating radar and metal detector equipment are now avail- able (e.g., MINEHOUND, ERA Technology-Vallon GmbH) for landmine detection. The perfor- mance of the radar detector is in∞uenced by the electromagnetic characteristics of the soil. In this paper we present an experimental procedure that uses the same equipment for the detec- tion and calibration by means of signal processing procedures for the estimation of the relative permittivity of the soil. The experimental uncertainties of this method are also reported.

A 3-D PW ultrasonic Doppler flowmeter: theory and experimental characterization

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/spl deg/) 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.

Comparisons between PZT and PVDF thick films technologies in the design of low-cost pyroelectric sensors

This paper compares the characteristics of two types of four quadrant pyroelectric sensors, made with screen-printed PZT and PVDF thick films, respectively, which we used for low-cost contactless position determination and laser beam positioning. For the comparison we used their responsivities, measured with a CO2 laser, and their respective noise figures. For sensors designing we simulated the PZT sensor responsivity using an equivalent thermo-electric model already demonstrated for multilayer PVDF sensors. The barely known model parameters of the PZT and electrodes layers were deduced from the best fit of the temporal voltage response to two square wave periodic signals. The peak current responsivity, the bandwidth and the NEP of the various samples indicate PZT most suited for low-noise and PVDF for high frequency and large bandwidth IR laser beam applications, respectively.

Time-of-flight diffraction tomography for NDT applications

Abstract An ultrasonic imaging system based on a direct time-space reconstruction algorithm has been developed. The radio-frequency signals are collected along a linear synthetic aperture with point sources and receivers in separate positions. This allows the investigation of defects with different incident angles and the final image is less sensitive to the defect characteristics of size, shape and orientation. Theoretical formulae for the lateral and the axial resolution are derived and the actual system performance is evaluated with a computer testing program. Theoretical models of ultrasonic scattering from simple artificial defects embedded in metals, based on the Born approximation and the geometrical theory of diffraction, are employed to simulate signals from some simplified objects covering a broad ka range, with ka up to about 5. Comparisons between theoretical, simulated and experimental lateral and axial resolution are reported, with lateral resolutions found by experiment of 1.34γ, by simulation λ compared with the theoretical limit of 0.36λ.