Calibration sphere for low-frequency parametric sonars

Author Posting. © Acoustical Society of America, 2007. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 121 (2007): 1482-1490, doi:10.1121/1.2434244.The problem of calibrating parametric sonar systems at low difference frequencies used in backscattering applications is addressed. A particular parametric sonar is considered: the Simrad TOPAS PS18 Parametric Sub-bottom Profiler. This generates difference-frequency signals in the band 0.5–6 kHz. A standard target is specified according to optimization conditions based on maximizing the target strength consistent with the target strength being independent of orientation and the target being physically manageable. The second condition is expressed as the target having an immersion weight less than 200 N. The result is a 280-mm-diam sphere of aluminum. Its target strength varies from −43.4 dB at 0.5 kHz to −20.2 dB at 6 kHz. Maximum excursions in target strength over the frequency band due to uncertainty in material properties of the sphere are of order ±0.1 dB. Maximum excursions in target strength due to variations in mass density and sound speed of the immersion medium are larger, but can be eliminated by attention to the hydrographic conditions. The results are also applicable to the standard-target calibration of conventional sonars operating at low-kilohertz frequencies

Mitteilungen des URZ 2/1997

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Mitteilungen des URZ 2/1997

Intranet - Erwartungen und Entwicklungen JavaOS - ein Betriebssystem fuer Intranets Network Computer - Eine Verkaufsstrategie? Was gibt es schon? Netscape IFC's - Gestalten von graphische Nutzerinterfaces WWW-Sicherheitsaspekte - ein heisses Thema: Sicherheit im Netz Aufbau einer Certification Authority - z.B. IN e.V. Chemnitz Authentisierung und Verteilung von Konfigurationsfiles - am Bsp. UR

Tax-induced recruitment of TORC family coactivators is required for transcriptional activation of HTLV-I LTR (Young Scientists Award-winning presentation)

Ultrasonic transducers are electromechanical devices that covert electrical inputs (voltage, current) into mechanical outputs (force, velocity) and vice-versa. To completely characterize the relationship between these four parameters in general requires knowledge of all the elements of a 2×2 complex-valued “transduction” matrix as a function of frequency. In the literature it has typically been assumed that to obtain all the elements of this transduction matrix it is necessary to perform a combination of both electrical and mechanical measurements (see Sachse and Hsu [1], for example), which makes such a complete characterization rather difficult and expensive. Here, we will show that, by using an electroacoustic measurement model that completely characterizes an entire ultrasonic measurement system, it is possible in principle to set up a practical measurement method where the complete transduction matrix can be obtained by purely electrical measurements at the electrical port of the transducer. Having a practical procedure to completely characterize an ultrasonic transducer is important since it will allow one to make quantitative estimates of the influence of the transducer properties on an ultrasonic measurement process