Volume 108, Issue 2, August 2000
Index of content:
- BIOACOUSTICS 
Broadband time-domain reflectometry measurement of attenuation and phase velocity in highly attenuating suspensions with application to the ultrasound contrast medium Albunex®108(2000); http://dx.doi.org/10.1121/1.429614View Description Hide Description
We describe a technique for broadband measurements of the attenuation coefficient and phase velocity of highly attenuating liquid suspensions. To validate the technique we apply it to the ultrasound contrast agent Albunex® at concentrations ranging from particles/mL to particles/mL. These longitudinal wave measurements were performed on Albunex suspensions maintained at in a special time-domain reflectometer designed and constructed in our laboratory. The frequency-dependent attenuation coefficients and phase velocities obtained in the reflectometer are compared to broadband through-transmission measurements of these same quantities, which were also performed in our laboratory. Although comparison data between the two techniques are only available at lower concentrations, the agreement is quite good and serves to validate the methods described in this paper.
108(2000); http://dx.doi.org/10.1121/1.429615View Description Hide Description
Evidence is presented that the basic vocalized sound produced by some cockatoos, specifically the Australian sulfur-crested cockatoo (Cacatua galerita) and the gang-gang cockatoo (Callocephalon fimbriatum), has a chaotic acoustic structure rather than the harmonic structure characteristic of most birdsongs. These findings support those of Fee et al. [Nature (London) 395(3), 67–71 (1999)] on nonlinear period-doubling transitions in the song of the zebra finch (Taeniopygia guttata). It is suggested that syllables with chaotic structure may be a feature of the songs of many birds.
108(2000); http://dx.doi.org/10.1121/1.429616View Description Hide Description
The beam shape of a circular array transducer that is commonly used in intravascular ultrasound catheters was investigated in linear mode of operation. For this use, a simulation program which can simulate the radio frequency (rf)-response of a number of scatterers has been developed. The program is based on the impulse response method, which is implemented in the frequency domain. Due to the unusual geometry of the transducer, the far field gets peculiarly shaped for large apertures. Instead of having a far field with its maximum intensity in a single lobe on the acoustical axis, the far field splits up into a dual-lobe far field with maximum intensity in two lobes off the acoustical axis. A formula is derived that predicts the occurrence of these beam shapes.
108(2000); http://dx.doi.org/10.1121/1.429617View Description Hide Description
The research reported here aims at understanding the biosonar system of bats based on the properties of its natural inputs (ecological acoustics).Echoes from foliages are studied as examples of ubiquitous, natural targets. The echoproperties and their qualitative relationship to plant architecture are described. The echoes were found to be profoundly stochastic and in general neither Gaussian nor stationary. Consequently, features useful for discrimination of such target classes will be confined to estimated random process parameters. Several such statistical signal features which are sufficiently invariant to allow a classification of the used example plants were identified: the characteristic exponent and the dispersion of an α-stable model for the amplitude distribution, a crest factor defined as the ratio of maximum squared amplitude and signal energy, the dispersion of the first threshold passage distribution, the structure of the correlation matrix, and a nonstationarity in sound channel gain. Discrimination error probability could be reduced by combining features pairwise. The best combination was the crest factor and the correlation coefficient of a log-linear model of the time-variant sound channel gain; it yielded an estimated Bayes risk of 6.9% for data pooled from different views.