1997 Vol. 22 No. 4
1997, 22(4): 289-296.
DOI: 10.15949/j.cnki.0371-0025.1997.04.001
Abstract：
The longitudinal-torsional composite mode ultrasonic transducer is studied. The transducer consists of the front and back exponential metal horns, and the axially and tangentially polarized piezoelectric ceramic piles. The resonance frequency equations for the longitudinal and torsional vibrations in the transducer are derived. By changing the cross sectional radius decay coefficient of the exponential metal horns, the longitudinal and torsional vibrations in the transducer could resonate at the same resonance frequency. Experimental results show that the measured resonance frequency is in good agreement with the theoretical results, and the resonance frequency for the longitudinal vibration is basically the same as that for the torsional vibration in the transducer. This kind of transducer could be used in ultrasonic processing and other high power ultrasonic technologies.
The longitudinal-torsional composite mode ultrasonic transducer is studied. The transducer consists of the front and back exponential metal horns, and the axially and tangentially polarized piezoelectric ceramic piles. The resonance frequency equations for the longitudinal and torsional vibrations in the transducer are derived. By changing the cross sectional radius decay coefficient of the exponential metal horns, the longitudinal and torsional vibrations in the transducer could resonate at the same resonance frequency. Experimental results show that the measured resonance frequency is in good agreement with the theoretical results, and the resonance frequency for the longitudinal vibration is basically the same as that for the torsional vibration in the transducer. This kind of transducer could be used in ultrasonic processing and other high power ultrasonic technologies.
1997, 22(4): 297-302.
DOI: 10.15949/j.cnki.0371-0025.1997.04.002
Abstract：
Ultrasonic flaw detection in large-grained materials is difficult because of multiple scattering from material microstructure (grain noise). The Time Delay Neural Network (TDNN) has been used quite successfUlly to process time series data. Therefore, it is possible to achieve SNR enhancement in ultrasonic testing by using this technique. In this paper, a new TDNN architecture with two input variable,viz. wave form and its phase difference, is developed to reduce the grain noise. Experimental results demonstrate the ability of the TDNN architecture to reveal flaw echoes from high level of background noise.
Ultrasonic flaw detection in large-grained materials is difficult because of multiple scattering from material microstructure (grain noise). The Time Delay Neural Network (TDNN) has been used quite successfUlly to process time series data. Therefore, it is possible to achieve SNR enhancement in ultrasonic testing by using this technique. In this paper, a new TDNN architecture with two input variable,viz. wave form and its phase difference, is developed to reduce the grain noise. Experimental results demonstrate the ability of the TDNN architecture to reveal flaw echoes from high level of background noise.
Abstract：
In order to improve the resolution of acoustical holography, a new method, i. e. pulse wave holography, has been presented in the article. Theortical analysis and computer simulation show that using the limited frequency spectrum of pulse wave and the response to the limited frequency spectrum of the system, the pusle wave holography has a better resolution than the continuous wave one. Besides. adopting the phase information of reconstructed wave and deconvolution technology, the resolution can be improved further.
In order to improve the resolution of acoustical holography, a new method, i. e. pulse wave holography, has been presented in the article. Theortical analysis and computer simulation show that using the limited frequency spectrum of pulse wave and the response to the limited frequency spectrum of the system, the pusle wave holography has a better resolution than the continuous wave one. Besides. adopting the phase information of reconstructed wave and deconvolution technology, the resolution can be improved further.
Abstract：
Two-tone suppression (2TS) was studied in AC receptor potentials recorded from scale media in the third turn of guinea pig cochlea. Electrode of round window was used to monitor the CAP threshold. Amplitude-intensity functions for AC component were obtained before and after white-noise exposure. Results indicated that the phenomenon of 2TS wasrelated with nonlinearity of cochlea, and suppressed amplitude decreased with diminish of these high-level nonlinearities. The probability that 2TS caused by media ear and homophonic was diminished. A computer controlled sound stimulator and signal recording system was used in the study, in which FFT was also used to calculate the amplitude of receptor potentials.
Two-tone suppression (2TS) was studied in AC receptor potentials recorded from scale media in the third turn of guinea pig cochlea. Electrode of round window was used to monitor the CAP threshold. Amplitude-intensity functions for AC component were obtained before and after white-noise exposure. Results indicated that the phenomenon of 2TS wasrelated with nonlinearity of cochlea, and suppressed amplitude decreased with diminish of these high-level nonlinearities. The probability that 2TS caused by media ear and homophonic was diminished. A computer controlled sound stimulator and signal recording system was used in the study, in which FFT was also used to calculate the amplitude of receptor potentials.
1997, 22(4): 314-322.
DOI: 10.15949/j.cnki.0371-0025.1997.04.005
Abstract：
It is shown from both the numerical calculation and experiments research in the flow duct with outlet absorbing wedge that there does exist considerable noise reduction using single bypass added to the main duct, but the value and the spectrum of noise reduction sometimes are not satisfactory in the engineering practice. Furthermore, the outlet of practical duct is always connected with atmosphere directly, so there is not any absorbing wedge in the outlet. In order to resolve these two problems, a method for predicting the noise reduction in the practical duct using multiple bypasses and numerical samples are presented in the paper. It is proved correct by a site test, and there is noise reduction of 5 dB(A), even though the site test is not under the optimum situation.
It is shown from both the numerical calculation and experiments research in the flow duct with outlet absorbing wedge that there does exist considerable noise reduction using single bypass added to the main duct, but the value and the spectrum of noise reduction sometimes are not satisfactory in the engineering practice. Furthermore, the outlet of practical duct is always connected with atmosphere directly, so there is not any absorbing wedge in the outlet. In order to resolve these two problems, a method for predicting the noise reduction in the practical duct using multiple bypasses and numerical samples are presented in the paper. It is proved correct by a site test, and there is noise reduction of 5 dB(A), even though the site test is not under the optimum situation.
Abstract：
In this paper, the formulae of the vibration response and power flow in beam-stiffened plates in the far field with force excitation applied on the plate, have been obtained by using the Steepest Descent integral method, and the power flow characteristics have also been studied through computer simulation, it is shown that the stiffener acts as an extra lineal excitation applied on the plate and will change the power flow characteristics of the infinite plate; the greater the stiffness and the less the distance between exciting point and stiffener, the greater the influence. At last, experiments have been carried out by using the dual-accelerometer cross spectrum measurment technique, the test data agree well with the theoretical results.
In this paper, the formulae of the vibration response and power flow in beam-stiffened plates in the far field with force excitation applied on the plate, have been obtained by using the Steepest Descent integral method, and the power flow characteristics have also been studied through computer simulation, it is shown that the stiffener acts as an extra lineal excitation applied on the plate and will change the power flow characteristics of the infinite plate; the greater the stiffness and the less the distance between exciting point and stiffener, the greater the influence. At last, experiments have been carried out by using the dual-accelerometer cross spectrum measurment technique, the test data agree well with the theoretical results.
1997, 22(4): 329-337.
DOI: 10.15949/j.cnki.0371-0025.1997.04.007
Abstract：
In this paper, F ratio formula, which is used to measure the effectiveness of the parameters for representing speaker individual features, is employed to compare the effectiveness of LSP frequencies with that of CEP parameters. Some specific properties have been drawn from the so two kinds of parameters. Based on this work, LSP frequencies are determined as individual features. Then a hierarchical model for describing individual features of each speaker is proposed. According to the capability of interpolation with functional——link networks and the fuzzy statistical method of establishing membership functions, the membership functions of the fuzzy states are implemellted with such networks which are the basic units of the hierarchical model. During the identification procedure, the maximum degree of membership fUnction to speaker's model is used as the decision criterion. In small fixed vocabulary, ten Chinese digital voices (0-9), text-independent speaker identification test are carried out among 42 speakers. When the length of testing utterances is randomly concatenated with 5 digital voices, the correct identification rate is 99.76 percent.
In this paper, F ratio formula, which is used to measure the effectiveness of the parameters for representing speaker individual features, is employed to compare the effectiveness of LSP frequencies with that of CEP parameters. Some specific properties have been drawn from the so two kinds of parameters. Based on this work, LSP frequencies are determined as individual features. Then a hierarchical model for describing individual features of each speaker is proposed. According to the capability of interpolation with functional——link networks and the fuzzy statistical method of establishing membership functions, the membership functions of the fuzzy states are implemellted with such networks which are the basic units of the hierarchical model. During the identification procedure, the maximum degree of membership fUnction to speaker's model is used as the decision criterion. In small fixed vocabulary, ten Chinese digital voices (0-9), text-independent speaker identification test are carried out among 42 speakers. When the length of testing utterances is randomly concatenated with 5 digital voices, the correct identification rate is 99.76 percent.
Abstract：
With the finite element method, the influence of material property and geometryfactor of a cylindrical PVDF piezoelectric polymer hydrophone on the acceleration responce have been analyzed in the paper.
Compared with the theoretical analysis, the experiments of the hydrophone acceleration response have been performed. The experimental results is almost consistant with the theoretical calculation
With the finite element method, the influence of material property and geometryfactor of a cylindrical PVDF piezoelectric polymer hydrophone on the acceleration responce have been analyzed in the paper.
Compared with the theoretical analysis, the experiments of the hydrophone acceleration response have been performed. The experimental results is almost consistant with the theoretical calculation
Abstract：
For a long time, the classification of underwater acoustic objects has been a very difficult problem to be solved, because it is affected by many factors. Now, with the development of technique of artificial neural network (ANN), a lot of researchers have devoted to the classification subject using several of kinds of ANNs. In the paper, we first introduce the Pi-Sigma network (PSN), a higher order ANN, research it's two learning algorithms based respectively on the gradient descent method and the conjugate gradient method, and then use it for objects radiated-noise classification. Comparing with multiple layer perceptron (MLP) network, Pi-Sigma network has some advantages such as simple structure, rapid convergence speed and small storage needed and so on. The inputs of the Pi-Sigma net classifier are the feature vectors which are extracted by a constant Q bandpass filter bank. The classification results on the realistic data, which are noises radiated by different class objects, demonstrate the feasibility of the classification system consisted of a constant Q bandpass filter bank as a feature extractor and a Pi-Sigma net as a classifier, achieving a statisfactory classification accuracy:>=95%.
For a long time, the classification of underwater acoustic objects has been a very difficult problem to be solved, because it is affected by many factors. Now, with the development of technique of artificial neural network (ANN), a lot of researchers have devoted to the classification subject using several of kinds of ANNs. In the paper, we first introduce the Pi-Sigma network (PSN), a higher order ANN, research it's two learning algorithms based respectively on the gradient descent method and the conjugate gradient method, and then use it for objects radiated-noise classification. Comparing with multiple layer perceptron (MLP) network, Pi-Sigma network has some advantages such as simple structure, rapid convergence speed and small storage needed and so on. The inputs of the Pi-Sigma net classifier are the feature vectors which are extracted by a constant Q bandpass filter bank. The classification results on the realistic data, which are noises radiated by different class objects, demonstrate the feasibility of the classification system consisted of a constant Q bandpass filter bank as a feature extractor and a Pi-Sigma net as a classifier, achieving a statisfactory classification accuracy:>=95%.
Abstract：
In this paper, the acoustic inverse method was applied to deal with the scattering data measured in the layer under the sea surface, in which the volume fraction and the size distribution of the bubbles were obtained.
In this paper, the acoustic inverse method was applied to deal with the scattering data measured in the layer under the sea surface, in which the volume fraction and the size distribution of the bubbles were obtained.
Abstract：
Waveguide characterization estimation in shallow water using the complex mode approxi metion of acoustic field is presented. The advantages of the method are that (l) the dependence on the environment parameters will obviously decrease. (2) the waveguide characterization parameters(km, βm)can be obtained the same time, when the fine structure in the bottom medium, such as the number and thickness of layers, the velocity of compressive and shear wave, and attenuation is less known or unknown. (3) it can extract the bottom reflection coefficient V(k). Numerical examples illustrate that (1) the accuracy of km is at least 10-5, the related error of βm is mostly less than 20%, and the smaller the mode number, the smaller the related error is; (2) the reflection coefficient in the the bottom at low grazing angle can be obtained using by a vertical array which the total number of samples is N=18 and length L=90 m. The experimental data of 500 Hz is emphatically discussed here. The results for f=500 Hz wide impulse acoustic signal source which locates at zs=11 m, rs=21 km show that the extracted accuracy of km is between 10-4 and 10-5, the related error of βm is between 9% and 26%.
Waveguide characterization estimation in shallow water using the complex mode approxi metion of acoustic field is presented. The advantages of the method are that (l) the dependence on the environment parameters will obviously decrease. (2) the waveguide characterization parameters(km, βm)can be obtained the same time, when the fine structure in the bottom medium, such as the number and thickness of layers, the velocity of compressive and shear wave, and attenuation is less known or unknown. (3) it can extract the bottom reflection coefficient V(k). Numerical examples illustrate that (1) the accuracy of km is at least 10-5, the related error of βm is mostly less than 20%, and the smaller the mode number, the smaller the related error is; (2) the reflection coefficient in the the bottom at low grazing angle can be obtained using by a vertical array which the total number of samples is N=18 and length L=90 m. The experimental data of 500 Hz is emphatically discussed here. The results for f=500 Hz wide impulse acoustic signal source which locates at zs=11 m, rs=21 km show that the extracted accuracy of km is between 10-4 and 10-5, the related error of βm is between 9% and 26%.
1997, 22(4): 365-371.
DOI: 10.15949/j.cnki.0371-0025.1997.04.012
Abstract：
A standing wave ultrasonic motor driven by using piezoelectric ceramic elements is studied experimentally and theoretically in this paper. In this motor, a longitudinal-torsion (L-T) coupler with improving construction was proposed, and vibration modes of L-T coupler were analyzed by using finite element method (FEM); The frequency equation of driving stator was derived from electromechanical equivalent network. With the improvement of coupler of this motor, the rotational speed of the motor with diameter of Φ32 mm is increased to 430 r.p.m with no load, that is as 3~4 times as the original one, and the maximum torque out and efficiency of the motor are 6 kgf.cm and 17% respectively.
A standing wave ultrasonic motor driven by using piezoelectric ceramic elements is studied experimentally and theoretically in this paper. In this motor, a longitudinal-torsion (L-T) coupler with improving construction was proposed, and vibration modes of L-T coupler were analyzed by using finite element method (FEM); The frequency equation of driving stator was derived from electromechanical equivalent network. With the improvement of coupler of this motor, the rotational speed of the motor with diameter of Φ32 mm is increased to 430 r.p.m with no load, that is as 3~4 times as the original one, and the maximum torque out and efficiency of the motor are 6 kgf.cm and 17% respectively.
1997, 22(4): 372-379.
DOI: 10.15949/j.cnki.0371-0025.1997.04.013
Abstract：
An introduction of the acoustic information resources on the internet is given. More than 70 major acoustics sites on the internet are listed in the alphabetic order and a classification index is attached. The information concerning some important locations, which have links to numerous acoustics sites, is described and their web addresses are provided as the starting points for further search.
An introduction of the acoustic information resources on the internet is given. More than 70 major acoustics sites on the internet are listed in the alphabetic order and a classification index is attached. The information concerning some important locations, which have links to numerous acoustics sites, is described and their web addresses are provided as the starting points for further search.
