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.
The aim of the vector Doppler (VD) 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 flow conditions. Clinical applications require a real-time operating mode and the capability to perform Doppler measurements over a defined volume. The combination of these two characteristics produces a real-time vector velocity map. In previous works the authors investigated the theory of pulsed wave (PW) vector Doppler and developed an experimental system capable of producing off-line 3D vector velocity maps. Afterwards, for producing dynamic velocity vector maps, we realized a new 2D vector Doppler system based on a modified commercial echograph. The measurement and presentation of a vector velocity field requires a correct spatial sampling that must satisfy the Shannon criterion. In this work we tackled this problem, establishing a relationship between sampling steps and scanning system characteristics. Another problem posed by the vector Doppler technique is the data representation in real-time that should be easy to interpret for the physician. With this in mine we attempted a multimedia solution that uses both interpolated images and sound to represent the information of the measured vector velocity map. These presentation techniques were experimented for real-time scanning on flow phantoms and preliminary measurements in vivo on a human carotid artery.
This paper explores the applications of a high-resolution imaging technique to vascular ultrasound diagnosis, with emphasis on investigation of the carotid vessel. With the present diagnostic systems, it is difficult to measure quantitatively the extension of the lesions and to characterize the tissue; quantitative images require enough spatial resolution and dynamic to reveal fine high-risk pathologies. A broadband synthetic aperture technique with multi-offset probes is developed to improve the lesion characterization by the evaluation of local scattering parameters. This technique works with weak scatterers embedded in a constant velocity medium, large aperture, and isotropic sources and receivers. The features of this technique are: axial and lateral spatial resolution of the order of the wavelength, high dynamic range, quantitative measurements of the size and scattering intensity of the inhomogeneities, and capabilities of investigation of inclined layer. The evaluation of the performances in real condition is carried out by a software simulator in which different experimental situations can be reproduced. Images of simulated anatomic test-objects are presented. The images are obtained with an inversion process of the synthesized ultrasonic signals, collected on the linear aperture by a limited number of finite size transducers.