James L. Aroyan

Computer modeling of acoustic beam formation in Delphinus delphis

It has been established that some dolphins possess well‐developed acoustic orientation (echolocation) and information gathering abilities, though substantially less is known about the system of sound generation and beam formation. Dolphins use a narrowly focused sound beam that emanates from the forehead and rostrum during echolocation. The primary objectives of this study were to simulate the effects of anatomical structure on beam formation, and to test the viability of various hypothetical sound source locations. Outlines from parasagittal x‐ray CT scans were used to construct a 2‐D model of the head of the common dolphin, Delphinus delphis. Finite difference techniques were used to simulate sound propagation through tissues modeled as inhomogeneous fluids. Preliminary simulations confirm that beam formation results primarily from reflection off of the skull and the skull‐supported air sac surfaces. For the frequencies tested, beam angles best approximate those measured by experimental methods for a so...

Supercomputer modeling of delphinid sonar beam formation

It has been established that some dolphins possess well‐developed acoustic orientation (echolocation) and information gathering abilities, though substantially less is known about the system of sound generation and beam formation. Dolphins use a narrowly focused sound beam that emanates from the forehead and rostrum during echolocation. The primary objectives of this study were to simulate the effects of modeled tissues on beam formation, and to test the viability of various hypothetical sound source locations. 2‐D simulations of sound propagation using parasagittal outlines from reconstructions of CT scans through the forehead tissues of two delphinids were conducted. Finite difference wave propagation programs were run on a Cray supercomputer. Preliminary simulations suggest that beam formation results primarily from reflection off of the skull and air sacs. These results do not depend strongly upon the precise values of velocity and density assumed for the bone. Beam angles closely approximate those me...

Acoustic pathways of hearing in the bottlenose dolphin, Tursiops truncatus

The acoustic pathways for the reception of sound in the Atlantic bottlenose dolphin were studied by measuring auditory brain‐stem‐evoked potential responses as a specially designed suction cup hydrophone was placed at different areas of the animal’s head. The dolphin was trained to come out of the water and beach on a rubber mat. Evoked responses were recorded differentially with suction cup surface electrodes placed between the parietal (noninverting) just posterior to the blowhole and mastoid (inverting). A transient signal was used as the stimulus and the amplitude of the stimulus was lowered in fixed dB steps until the evoked response reached a specific level close to the threshold level. The results indicate that the most sensitive portion of the lower jaw is slightly forward of the pan‐bone and about 3/4 of the way toward the front of the lower jaw and along certain spots on the bottom midline of the lower jaw. The relative sensitivity of different areas of the lower jaw was also determined. The mea...

P2I-2 Characteristics of SAW Grating Reflectors with Arbitrary Angles of Incidence in Ultrasonic Touch Sensors

Rayleigh-wave (SAW) touch panels are widely used in a number of applications such as information kiosks, interactive museum exhibits, and amusement arcade games. Such products involve 90deg scattering of Rayleigh waves by grating reflector arrays for which each reflector grating element is at an angle of 45deg with respect to the incident wave. Development of innovative ultrasonic touch sensors motivates generalization to arbitrary angles of incidence. Results are expressed in terms of monopole, dipole, and quadrupole scattering amplitudes from point-like perturbations. Via superposition, such results generalize to arbitrary geometry including that of grating arrays. The angular dependence of the reflection amplitude depends strongly on the mechanical properties of the reflector materials. This conclusion is supported by experiment, 3D ultrasonic simulation and analytic expressions derived from theory. Efficient as well as problematic combinations of reflector angles and materials may be determined from presented quantitative results

Obliquely incident rayleigh waves at a vertical edge - measured and simulated reflection coefficients

We present measured and calculated reflection and transmission coefficients for Rayleigh waves impinging at non- normal incidence on a sharp right-angle edge of an aluminum plate. Although the theory of longitudinal and shear acoustic waves at non-normal incidence on a boundary is well known (1), there are few results for the reflection coefficient of Rayleigh waves other than the case of normal incidence at a discontinuity (2). The needs of SAW touchscreen technology motivated us to fill this gap. A full-field, non-scanning acoustic imaging method based on laser interferometry (3) was used to capture images of Rayleigh waves reflecting off of and transmitting over a plate edge. Fits to such images provided reflection and transmission amplitudes. For the case of a 45° angle of incidence, serendipitous acoustic path geometry enabled an independent measurement via a purely acoustic method. Simulations were used to generate images in the same format as the experimental images, which were then analyzed with the same fitting procedure. Experiment and simulation both show that the transmission amplitude is significant and generally larger than the reflection amplitude at all angles.

Three‐dimensional computer modeling of biosonar emission in the common dolphin

Several delphinid species are known to possess a highly sophisticated and adaptable biosonar system, yet the exact acoustic mechanisms involved in signal generation, emission, and reception remain poorly understood. Recently, a novel computational approach was utilized in an investigation of the acoustical mechanisms of dolphin biosonar. Three‐dimensional acoustic simulation techniques and a new method for mapping acoustic tissue properties from x‐ray computed tomographic data were applied to models of the forehead and lower jaw tissues of the common dolphin, Delphinus delphis. This approach proved highly effective in studying the detailed processes of biosonar emission and reception in this animal. The results of the investigation which concern the emission system of this dolphin will be presented. These results include: (1) the common dolphin’s skull plays the predominant role in beam formation; (2) the melon contributes significantly to narrowing of the emitted beams; (3) the melon behaves as a wavegui...