Mardi C. Hastings

Detection of ultrasonic tones and simulated dolphin echolocation clicks by a teleost fish, the American shad (Alosa sapidissima)

The authors previously reported that American shad (Alosa sapidissima) can detect sounds from 100 Hz to 180 kHz, with two regions of best sensitivity, one from 200 to 800 Hz and the other from 25 to 150 kHz [Mann et al., Nature 389, 341 (1997)]. These results demonstrated ultrasonic hearing by shad, but thresholds at lower frequencies were potentially masked by background noise in the experimental room. In this study, the thresholds of the American shad in a quieter and smaller tank, as well as thresholds for detecting stimulated echolocation sounds of bottlenosed dolphins was determined. Shad had lower thresholds for detection (from 0.2 to 0.8 kHz) in the quieter and smaller tank compared with the previous experiment, with low-frequency background noise but similar thresholds at ultrasonic frequencies. Shad were also able to detect echolocation clicks with a threshold of 171 dB re: 1 microPa peak to peak. If spherical spreading and an absorption coefficient of 0.02 dB/m of dolphin echolocation clicks are assumed, shad should be able to detect echolocating Tursiops truncatus at ranges up to 187 m. The authors propose that ultrasonic hearing evolved in shad in response to selection pressures from echolocating odontocete cetaceans.

Application of small panel damping measurements to larger walls

Damping properties of a viscoelastic material were determined using a standard resonant beam technique. The damping material was then applied to 1 by 2 foot gypsum panels in a constrained layer construction. Damping loss factors in panels with and without the constrained layer were determined based on reverberation times after excitation at third-octave band center frequencies. The constrained damping layer had been designed to increase damping by an order of magnitude above that of a single gypsum panel at 2000 Hz; however, relative to a gypsum panel of the same overall thickness as the panel with the constrained layer, loss factors increased only by a factor of three to five. Next modal damping loss factors in 9 by 14 foot gypsum single and double walls were calculated from the experimentally determined quality factor for each modal resonance. Results showed that below 2500 Hz, modes in 1 by 2 foot gypsum panels had nearly the same damping loss factors as modes in a 9 by 14 foot gypsum wall of the same thickness; however, loss factors for the wall were an order of magnitude lower than those of the 1 by 2 foot panels at frequencies above 2500 Hz, the coincidence frequency for 5/8-inch thick gypsum plates. Thus it was inconclusive whether or not damping loss factors measured using small panels could be used to estimate the effect of a constrained damping layer on transmission loss through a 9 by 14 foot wall unless boundary conditions and modal frequencies were the same for each size.

Effects of gamma radiation on high-power infrared and visible laser diodes

The effects of gamma radiation on high-power semiconductor laser diodes were measured. While operating, five commercial near-infrared (785 nm, 60 mW) and six visible laser diodes (670 nm, 30 mW) were exposed to approximately 10 kGy at a relatively high dose rate (/spl ap/5 kGy/h). The far-field, output beam patterns were monitored during radiation and recovery, as well as the overall intensity (constant current mode) and the internal monitor photodiode current. The linear dimensions of the far-field beam patterns shrank in size by the end of radiation by 3%-20% for the IR lasers and 15%-20% for the visible. The ellipticity of the beams changed by -16% for the IR and +8% for the visible case. The intensity, as measured with an external camera, decreased during irradiation by a maximum of 2.7 dB for the visible laser and 2.5 dB for the infrared; however, the photodiode photocurrents changed by less than 1 dB. Both types of lasers recovered completely over several days. The near- and far-field patterns were examined both below and above threshold before and after radiation/recovery, with no evidence of defects or other gross changes.

Digital demodulation for passive homodyne optical fiber interferometry based on a 3 x 3 coupler

Two different types of 3 X 3 couplers, symmetric and quadrature, can be used for passive homodyne Mach-Zehnder optical fiber interferometry. The former provides intensity outputs proportional to cos(phi) that are shifted 120 degree(s) apart, and the latter linear combination of sin(phi) and cos(phi) , where (phi) is the optical phase difference between the sensing and reference arms. Many demodulation algorithms, both analog and digital, have been developed. Demodulation with both 3 X 3 couplers is simulated to determine the performance of algorithms when noise exists in the coupler outputs because of uncontrolled environmental inputs. Results of simulations and experimental evaluations of several demodulation schemes found in the literature are evaluated for comparison purposes. The simulation developed for this study can be used to evaluate different 3 X 3 coupler digital demodulation methods using experimental data as well as contrived numerical inputs.

Integration of the finite element and beam propagation methods to determine performance of microbend sensors

Many parameters contribute to the performance of microbend sensors. These include fiber core radius,ncladding radius, jacket radius, core and cladding refractive indices, core refractie index profile, fiber flexuralnrigidity, light source wavelength, light source power, spatial bend wavelength, number of bends and bendnamplitude. Electromagnetic wave theory predicts that power lost from the core in a microbend is optimum whennthe fibers spatial bend frequency equals the difference in propagation constants between the propagating andnradiated modes.

Engineering the development of optical fiber sensors for adverse environments

Optical fiber sensors and measurement systems must be engineered to meet tough environmental requirements necessary for applications outside the laboratory. No generalized computer-aided tools exist to help advance the development, design and use of these systems in the field. Computer-aided design tools currently being developed are described. Structural finite element analyses are coupled with opto-elastic analyses of all-fiber interferometers and serial microbend sensors for the distributed measurement of various physical quantities. The combined analyses are parameterized and implemented on personal computers or workstations for use as design and development tools to determine the performance of different sensor configurations in various environments. Potentially, these computer-aided tools could be used for failure diagnosis and redesigning of existing optical fiber sensors. Performances predicted by the computer simulations are verified with experimental data and numerical analyses from the literature. The long-term goal is to develop user-friendly software packages for sensor manufacturers and end-users.

Analysis of Tuning Cables for Reduction of Fluidborne Noise in Automotive Power Steering Hydraulic Lines

Noise and Noise Reducing Materials p. 27 Damping Measurement of Sound Insulating Layers on Thin Metal Sheets p. 33 Measurement of Airborne Noise Reduction of Production Door Components on a Buck p. 43 Acoustical Performance Testing of Automotive Weatherseals p. 47 Noise Measurements and Characterization of Automotive Dampers p. 53 Measurement of the Statistical Variation of Structural-Acoustic Characteristics of Automotive Vehicles p. 65

Simultaneous measurement of strain or acoustic pressure and temperature with an optical fiber interferometer

An all polarization-maintaining fiber Mach-Zehnder interferometer has been developed for simultaneous measurement of strain or acoustic pressure and temperature. The two forcefully maintained polarization states act as two separate interferometric sensors. In this study, longitudinal strain and heat were applied to the same portion of the fiber to experimentally evaluate cross-sensitivity effects created by simultaneous application. Experimental measurements using a passive homodyne demodulation scheme based on a 3 X 3 coupler agree well with those predicted by a finite element model of the fiber. In addition, response of the interferometer to simultaneous disturbances of acoustic pressure and temperature were calculated. Results of this study show that the cross-sensitivity is negligible and may be ignored for the fiber examined in this study. Furthermore, simultaneous measurement of temperature with another desired measurand has potential to eliminate measurement errors and limitations on resolution that currently limit the use of fiber interferometers in industrial and structural applications.

BIOMECHANICS OF HEARING IN FISH: FROM THE SONIC TO THE ULTRASONIC

De Vries, H.L. (1950) The mechanics of the labyrinth otoliths. Acta Otolaryngol. (Stockh.). 38, 262-273. Gauldie R.W. (1988) Function, form and time-keeping properties of fish otoliths. Comp. Biochem. Physiol. 91A, 359-401. Lychakov, D.V. & Rebane, Yu. T. (1993) Effect of otolith shape on directional sound perception in fishes. J. Evol. Biochem. Physiol. 28, 531-536. Lychakov, D.V. & Rebane, Yu. T. (2000) Otolith regularities. Hear. Res. 143, 83-102. Popper, A.N. & Fay, R.R. (1993) Sound detection and processing by fish: critical review and major research questions. Brain Behav. Evol. 41, 14-38. Protasov, V.R. (1965) Bioacoustic of Fish. Nauka; Moscow. (in Russian). Rim an, I.S. & Kreps, R.L. (194 7) Associated masses of solids of different shape. Trudy TsAGI. 637, 1-46 (in Russian).

Comparison of a new modal transfer matrix method with coupled-mode theory for simulation of long-period grating fiber sensors

The modal transfer matrix method (MTMM) is a new general- purpose technique developed by the authors as an alternative to coupled mode theory (CMT) to study complex optical waveguide systems. It is applied here to overcome the numerical accuracy limitation of the beam propagation method (BPM) when simulating long-period gratings (LPG). Simulation of a LPG optical fiber sensor with a broad-wavelength source using the MTMM is compared with analytical results based on CMT. A simple grating parameter study shows that both methods are in agreement, indicating that the MTMM is a promising method of analysis. In addition, the results reveal the potential effect of combined variation in grating amplitude, spatial wavelength, and length on sensor performance. By discretizing the waveguide into small elements, the MTMM reduces the problem domain size and makes use of proven electromagnetic numerical simulation methods. An appropriate numerical method, in this case the BPM, is selected to compute each elements modal transfer matrix. The elements are then combined to predict the output from the overall waveguide system.