In this paper, we describe a concealed weapons detection concept, based on nonlinear ultrasonic beam mixing in air, which offers advantages over traditional techniques. Two ultrasonic frequency signals at high sound pressures undergo nonlinear beam mixing to generate audio range difference frequency signals which can probe through thick clothing. While the low frequency beams penetrate, the beam collimation and resolution is determined by the ultrasound. We present our research from proof of concept to laboratory prototype tests to address two major challenges faced by the law enforcement community. The first is detection of hidden objects at a short range for use in the corrections field. Here, images contrasting weapons against a tissue simulating background, both of which are concealed under fabric, are shown with image resolution not possible using conventional acoustics. For the detection of weapons at distances up to 4.5 m (177 in.), custom parametric array transducers and dish receivers were employed to excite and analyze the acoustic signatures of concealed guns, knives, scissors and cell phones for use by the street level law enforcement community. Resonance excitation of objects, chirp signal excitation, database generation, spectrogram analysis and signal processing using advanced correlation algorithms at various stages in the development process are described. Some issues involved in realistic implementation are also discussed.
Nonlinear acoustic concealed weapons detection
Nichtlinearer akustischer Nachweis verborgener Waffen
Materials Evaluation ; 63 , 12 ; 1195-1202
2005
8 Seiten, 10 Bilder, 2 Tabellen, 28 Quellen
Aufsatz (Zeitschrift)
Englisch
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