摘要:

Measurements were made of the free dielectric constant and the dielectric loss tangent of piezoelectric polyvinylidene fluoride (PVDF) at frequencies between 1 kHz and 5 MHz and temperatures between − 28°C and + 51°C. Samples of nonvoided and voided PVDF were tested. The dielectric constant increases with increasing temperature and/or decreasing frequency, ranging from about 3 to 11 for the voided material and from about 4 to 14 for the nonvoided material. The dielectric loss tangent (dissipation factor) ranged from about 0.02 at low frequencies and high temperatures to about 0.3 at high frequencies and high temperatures. The voided material was not as 1ossy as the nonvoided material, with maximum values 0.2 for the voided material and 0.3 for the nonvoided material. A slight temperature aging effect was observed; an increase of a few percent in dielectric constant resulted from cycling the samples to 51°C.

ISSN:0001-4966    

DOI:10.1121/1.2022045

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The ultrasonic wave propagation characteristics were measured for IN‐100, a powder metallurgy alloy used for aircraft engine components. Attenuation, velocity, and backscattered microstructural noise were measured on several research samples. The data were obtained with a variety of different transducers placed either in a waterbath or in sample contact for a frequency range from about 2 to 18 MHz and statistically averaged over numerous volume elements of the samples. Micrographical examination provided size and number distributions for grain and pore structure. The results showed that the predominant source for the ultrasonic attenuation and backscatter was a dense (∼ 100/mm3) distribution of small micropores (∼ 10 μm radius). Two samples with different micropore densities were studied in detail to test the feasibility of calculating microstructural parameters from ultrasonic backscatter data in the regime for which the wavelength is much larger than the size of the individual scattering centers. The results suggest a way towards the nondestructive detection and characterization of anomalous distributions of micropores in a variety of materials when conventional ultrasonic imaging is difficult. The findings are potentially significant toward the application of the early detection of potential sites for stress‐induced void coalescence leading to crack initiation and subsequent failure.

ISSN:0001-4966    

DOI:10.1121/1.2022048

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

There are three principal causes of shallow or secondary sound channels in the North Pacific Ocean: Temperature inversions, water mass intrusions, and dynamic interleaving. Our analysis shows temperature inversions to be widespread throughout the Subarctic North Pacific, water mass intrusions and dynamic interleaving are more associated with specific locations. Examples are given of each type of shallow sound channel, showing their acoustic and oceanographic characteristics. Estimates of the distribution and duration of these channels is given.

ISSN:0001-4966    

DOI:10.1121/1.2022052

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The propagation of very‐low‐frequency [VLF, 20 Hz and less) acoustic signals in the deep ocean has been studied [A. N. Guthrieet al., J. Acoust. Soc. Am.56,58–59 (1974)] without taking bottom interaction into account. To investigate the effect of bottom interaction, implicit finite difference (IFD) techniques are used to solve the parabolic equation to study VLF (1

ISSN:0001-4966    

DOI:10.1121/1.2022058

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

For some time the Pennsylvania State University has had a program for using computer graphics to produce films for acoustics education. A sample of such a film will be presented in this talk. The original technique for producing these films, involving frame‐by‐frame exposures, was time consuming. However, we are now using in our research a relatively inexpensive (∼$7000) system which produces complex graphic output moving in real‐time. This system, which has a high resolution (2096 × 2096 points), will be described in detail, and, if circumstances permit, will be demonstrated during the talk.

ISSN:0001-4966    

DOI:10.1121/1.2022064

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The computer has applications in nearly every facet of engineering. At Michigan Tech, to complement our CAD/CAM system we have introduced experimental modal analysis to our undergraduate students. The course assumes a background in vibrations and numerical methods, from which we introduce concepts in digital signal processing, and the use of the discrete Fourier transform. The emphasis of this course is to apply numerical techniques to experimental vibrations. Commercially available modal analysis software is used to extract modal parameters from the structures under test. The core of the student experience is a project exploring state‐of‐the‐art concepts in modal analysis. A discussion of the projects and their results is presented. The results of student polling at the conclusion of the course indicated that problems existed in scheduling of computer time, and that project definitions were insufficient for the level of the student. Changes to be made in the course structure include the application of personal computers equipment to the course and the incorporation of a common data base with the on‐line CAD/CAM software.

ISSN:0001-4966    

DOI:10.1121/1.2022065

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The goal was to measure the contribution of semantic and syntactic constraints to the probability of word recognition in sentences. Normally hearing adult Ss listened to sets of four‐word sentences at four S/N ratios. There were three types of sentences: (1) zero predictability, i.e., nonsense word strings; (2) low predictability, i.e., syntactically correct but semantically anomolous sentences; (3) high predictability, i.e., syntactically and semantically correct sentences. Word recognition probabilities were measured for each condition. The contribution of syntax was computed as the ratio of the logarithms of error probability in the low and zero predictability sentences. The contribution of semantics was computed as the ratio of the logarithms of error probability in high and low predictability sentences. The resulting parameterkis the amount by which the number of independent channels of acoustical information would need to be increased in order to produce the measured increase of recognition probability. Average values ofkwere 1.4 and 2.0 for syntax and semantics, respectively. Statistical analysis revealed thatkwas independent of S/N ratio. [Work supported by PSC. CUNY award 6‐63137.]

ISSN:0001-4966    

DOI:10.1121/1.2022071

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

It is by now well‐established that the listener makes very precise adjustments for speaking rate when perceiving the phonetic structure of speech. The concern of the present investigation was the nature of the rate information to which the listener adjusts. When a speaker changes rate, he or she alters the timing of articulatory gestures. One consequence is a change in the acoustic form of the speech signal—for example, a change in its overall duration. Such changes provide auditory information about speaking rate. Additionally, however, some of these articulatory gestures are visible on the face of the talker and, therefore, provide visual information about the talker's rate of speech. We asked whether the effective rate information for phonetic perception is limited to the auditory domain or, alternatively, whether visual information about rate from the face also influences the perception of speech. To investigate this question, we paired acoustic versions of /bi/ and /pi/ produced by a talker, at a medium rate of speech, with a video display of the same talker producing these syllables at fast and slow rates of speech. The phenomenal experience that resulted from any given audio‐visual pairing was that of a unified percept of a single syllable, produced at a single rate of speech. We found that the variation in the speaking rate of the syllable on the video display (with the rate of the acoustic syllable kept constant) systematically influenced not only the judged rate of the syllable, but also the identification of the syllable as /bi/ or /pi/. These results suggest that at least under some circumstances, auditory and visual information about articulatory timing jointly influence phonetic perception. [Research supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2022075

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The detectability of three‐component complexes was measured as a function of the number of interaurally phase‐reversed components, which components were phase‐reversed, and the frequency spacing between the components. The center frequency of the complex was always 750 Hz, and the frequency spacing (Δf) was 20, 50, 100, or 250 Hz. The duration of the signal was 100 ms. All signals were presented against a continuous lowpass noise (2.5‐kHz cutoff frequency) whose noise‐power per unit bandwidth was 41.5 dB. In general, the detectability of a complex improved as the number of antiphasic components increased from one to three. Thresholds measured when all three components were presented but only one was antiphasic were greater than those obtained for single antiphasic tones, even when Δfs were large relative to critical bandwidths. The deleterious effect of homophasic components on detection is consistent with the notion that the binaural system integrates interaural information across ranges of frequency that are considerably wider than the critical bandwidth.

ISSN:0001-4966    

DOI:10.1121/1.2022089

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

We have again measured interaural time discrimination performance for 55‐dB‐SPL 500‐Hz tonal targets in the presence of tonal maskers of various frequencies and intensities, with interaural phase angles of 0 and 180 deg. For some masker frequencies we also added a 0–200‐Hz noise masker to prevent subjects from using the locations of low‐frequency combination tones as perceptual cues. In general, we found that higher‐intensity tonal masker at frequencies near that of the target degrade discrimination performance for the targets, and that performance is worse when the target and masker are presented with different interaural phase angles. This dependence of discrimination on the interaural masker phase is more consistent with data obtained in broadband maskers than we had previously reported, and is observed both when target and masker images are perceived separately, and when they are heard as a single fused image. The perceptual cues to perform the task depend on the frequency and intensity of the masker. We will also discuss ways in which these data maybe accounted for in terms of common models of binaural interaction. [Supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2022092

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP