The pressure and horizontal particle velocity combined descriptions in the very low frequency acoustic field of shallow wa- ter integrated with the concept of effective depth of Pekeris wave- guide is proposed, especi...The pressure and horizontal particle velocity combined descriptions in the very low frequency acoustic field of shallow wa- ter integrated with the concept of effective depth of Pekeris wave- guide is proposed, especially the active component of the pressure and horizontal particle velocity cross-spectrum, also called ho- rizontal complex cross acoustic intensity, when only two normal modes are trapped in the waveguide. Both the approximate theo- retic analysis and the numerical results show that the sign of the horizontal complex cross acoustic intensity active component is independent of the range when vertically deployed receiving dual sensors are placed in appropriate depths, the sum of which is equal to the waveguide effective depth, so it can be used to tell whether the sound source is near the surface or underwater; while the range rate is expected to be measured by utilizing the sign distribution characteristic of the reactive component. The further robustness analysis of the depth classification algorithm shows that the existence of shear waves in semi infinite basement and the change of acoustic velocity profiles have few effects on the application of this method, and the seabed attenuation will limit the detection range, but the algorithm still has a good robustness in the valid detection range.展开更多
A bilayer membrane acoustic metamaterial was proposed to overcome the influence of the mass law on traditional acoustic materials and obtain a lightweight thin-layer structure that can effectively isolate low frequenc...A bilayer membrane acoustic metamaterial was proposed to overcome the influence of the mass law on traditional acoustic materials and obtain a lightweight thin-layer structure that can effectively isolate low frequency noise. The finite element analysis(FEA) results agree well with the experimental results.It is proved that the sound transmission losses(STLs) of the proposed structures are higher than those of same surface density acoustic materials. The introduction of the magnetic mass block is different from the traditional design method, in which only a passive mass block is fixed on the membrane. The magnetic force will cause tension in the membrane, increase membrane prestress, and improve overall structural stiffness. The effects of the geometry size on the STLs are discussed in detail. The kind of method presented in this paper can provide a new means for engineering noise control.展开更多
<strong>Background:</strong><b><span style="font-family:;" "=""> </span></b><span style="font-family:;" "="">In horses, thera...<strong>Background:</strong><b><span style="font-family:;" "=""> </span></b><span style="font-family:;" "="">In horses, therapeutic ultrasound has been shown to be beneficial for suspensory ligament injuries, and more generally to stimulate tissue repair and reduce localized pain. However, it has yet to be examined in relation to soft tissue injuries sustained during competition or in connection with rider/saddle interactions. <b>Aim: </b>The aim of the present study was to examine the efficacy of topical low-frequency therapeutic ultrasound on the shoulder muscles of injured horses. <b>Methods:</b></span><b><span style="font-family:;" "=""> </span></b><span style="font-family:;" "="">Muscle mass and cellular health was assessed for <i>M. trapezius</i> using non-invasive multi-frequency bioimpedance, and dynamic improvements in <i>M. trapezius</i> and <i>M. latissimus dorsi</i> were examined using acoustic myography (AMG). A total of 8 injured horses (painful to palpation and atrophied) were treated using an</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">EQ Pro Therapy unit, following a set protocol that comprised treatment every other day for 10 treatments. Pre-treatment values were then compared with post-treatment measurements (1 & 6 months later). </span><b><span style="font-family:;" "="">Results:</span></b><b><span style="font-family:;" "=""> </span></b><span style="font-family:;" "="">The mfBIA results for <i>M. trapezius</i> showed a significant improvement (P</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">0.05) of EQ Pro Therapy treatment for the membrane capacitance (Mc) and phase angle (PA) parameters when comparing the Pre <span>vs</span> Post</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">1 and Post</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">1 <span>vs</span> Post</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">2 measurements. Similar improvements were seen for the AMG measurements for <i>M. trapezius</i> and <i>M. latissimus dorsi</i> where statistically significant improvements in the muscle efficiency (E-score) and temporal summation (T-score) as well as the spatial summation (S-score) and mean of the ST-scores were noted</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">(P</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">0.05 to P</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">0.01).</span><span style="font-family:;" "=""> </span><b><span style="font-family:;" "="">Conclusion:</span></b><span style="font-family:;" "=""> The present findings suggest that </span><span style="font-family:;" "="">EQ Pro Therapy treatment is efficacious in terms of equine cases involving soft tissue shoulder muscle injuries (</span><span style="font-family:;" "="">painful to palpation and atrophied).</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">The main improvements noted were not only increased muscle mass and cellular health</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">but also </span><span style="font-family:;" "="">improved force production, better coordination</span><span style="font-family:;" "="">,</span><span style="font-family:;" "=""> and lateral balance, which persisted for at least six months after treatment.</span>展开更多
Ocean vector acoustic measurement is feasible affected by the hydrodynamic interference caused by the flow fluctuations and structural vibrations, especially in the very-low-frequency monitoring. Hence, a novel horizo...Ocean vector acoustic measurement is feasible affected by the hydrodynamic interference caused by the flow fluctuations and structural vibrations, especially in the very-low-frequency monitoring. Hence, a novel horizontal floating platform including a horizontal floating cable, vertical mooring cable and floating main body is proposed and described in this paper. It has the advantages of good maneuverability along with the current and multi-stage vibration isolation. The main application of this platform is to measure the ocean ambient noise coming from the wave fluctuation and the deterministic acoustic signals such as aquatic organisms, underwater targets and sailing vehicles. The influence of the current fluctuation on the attitude angle and flow induced vibration of cables and main body are analyzed with some previous sea test data. Moreover, the comparison between the vertical type platform used before and the horizontal type platform is also discussed. It is concluded that there is obvious relevance between the attitude angle and ocean current variation. Meanwhile, the abnormal influence on the main body is caused by the vibration transmission from the fluctuation of cables. There will be the influence on the accuracy of the acoustic measurement above 100 Hz, and the inherent vibration characteristic of the main body is the primary reason.展开更多
In order to solve the problem of carrier frequency blind estimation of PSK signals in electronic reconnaissance, a new estimation method was proposed. The phase shift keying(PSK) signal was divided into several over...In order to solve the problem of carrier frequency blind estimation of PSK signals in electronic reconnaissance, a new estimation method was proposed. The phase shift keying(PSK) signal was divided into several overlapping intervals which had equal length, and the spectrum concentration measures of every interval were extracted by the FFT. And then, using the grid-density clustering, the spectrum concentration measures were classified into two categories, the narrowband spectrum interval and the wideband spectrum interval. The narrowband spectrum interval was regarded as the characteristic class. The spectrums of the characteristic class were accumulated to estimate the carrier frequency of PSK signal. The proposed method had avoided the non linear operation in the traditional PSK signal carrier frequency estimation algorithm. Thus, the signal to noise ratio (SNR) threshold was remarkably decreased. Moreover, the proposed method did not need the prior knowledge of the signal, which was suitable to the electronic reconnaissance occasion. Experimental results had verified the validity of the proposed estimation method in low SNR.展开更多
Conventional parameter estimation methods for pseudo-random binary code-linear frequency modulation(PRBC-LFM)signals require prior knowledge,are computationally complex,and exhibit poor performance at low signal-to-no...Conventional parameter estimation methods for pseudo-random binary code-linear frequency modulation(PRBC-LFM)signals require prior knowledge,are computationally complex,and exhibit poor performance at low signal-to-noise ratios(SNRs).To overcome these problems,a blind parameter estimation method based on a Duffing oscillator array is proposed.A new relationship formula among the state of the Duffing oscillator,the pseudo-random sequence of the PRBC-LFM signal,and the frequency difference between the PRBC-LFM signal and the periodic driving force signal of the Duffing oscillator is derived,providing the theoretical basis for blind parameter estimation.Methods based on amplitude method,short-time Fourier transform method,and power spectrum entropy method are used to binarize the output of the Duffing oscillator array,and their performance is compared.The pseudo-random sequence is estimated using Duffing oscillator array synchronization,and the carrier frequency parameters are obtained by the relational expressions and characteristics of the difference frequency.Simulation results show that this blind estimation method overcomes limitations in prior knowledge and maintains good parameter estimation performance up to an SNR of-35 dB.展开更多
Based on chaotic oscillator system, this paper proposes a novel method on high frequency low signal-to-noise ratio BPSK(Binary Phase Shift Keying) signal detection. Chaotic oscillator system is a typical non-linear sy...Based on chaotic oscillator system, this paper proposes a novel method on high frequency low signal-to-noise ratio BPSK(Binary Phase Shift Keying) signal detection. Chaotic oscillator system is a typical non-linear system which is sensitive to periodic signals and immune to noise at the same time. Those properties make it possible to detect low signal-to-noise ratio signals. The BPSK signal is a common signal type which is widely used in modern communication. Starting from the analysis of advantages of chaotic oscillator system and signal features of the BPSK signal, we put forward a unique method that can detect low signal-to-noise ratio BPSK signals with high frequency. The simulation results show that the novel method can detect low signal-to-noise ratio BPSK signals with frequency in an order of magnitude of 108 Hz, and the input Signal-to-Noise Ratio threshold can be -20 dB.展开更多
In order to search for the seismic wave characteristics of low frequency signals in the Alxa Left Banner region,Inner Mongolia,the low frequency signals of seismic wave data are extracted from the earthquakes of MS5. ...In order to search for the seismic wave characteristics of low frequency signals in the Alxa Left Banner region,Inner Mongolia,the low frequency signals of seismic wave data are extracted from the earthquakes of MS5. 8 in 2015 and MS5. 0 in 2016 in this area. The results show that:① Before the MS5. 8 earthquake,the seismic stations located near the epicenter in Wuhai,Dongshengmiao,and Shizuishan recorded seismic waves that showed the phenomenon of spectrum shift from high to low frequency.② The low frequency signals recorded by different stations have obvious difference.③ According to the data recorded by the station closest to the epicenter,low-frequency signals were recorded about120 hours before the earthquake and had obvious anomalies. This may reflect slow slip before the earthquake.展开更多
The essay mainly studies a system of low frequency signal′s measurement and the extraction of its characteristic quantity,introduces how matlab analyzes and extracts low frequency signal.MATLAB,a visual programming s...The essay mainly studies a system of low frequency signal′s measurement and the extraction of its characteristic quantity,introduces how matlab analyzes and extracts low frequency signal.MATLAB,a visual programming software,designs testing program for mechanic vibration signal,analyzes and identifies vibration signal.The collected data shows the effectiveness of the system.Based on XM121 modules,the testing system collects and analyzes single channel signal.展开更多
We present a design method for calculating and optimizing sound absorption coefficient of multi-layered porous fibrous metals (PFM) in the low frequency range. PFM is simplified as an equivalent idealized sheet with...We present a design method for calculating and optimizing sound absorption coefficient of multi-layered porous fibrous metals (PFM) in the low frequency range. PFM is simplified as an equivalent idealized sheet with all metallic fibers aligned in one direction and distributed in periodic hexagonal patterns. We use a phenomenological model in the literature to investigate the effects of pore geometrical parameters (fiber diameter and gap) on sound absorption performance. The sound absorption coefficient of multi- layered PFMs is calculated using impedance translation theorem, To demonstrate the validity of the present model, we compare the predicted results with the experimental data. With the average sound absorption (low frequency range) as the objective function and the fiber gaps as the design variables, an optimization method for multi-layered fibrous metals is proposed. A new fibrous layout with given porosity of multi-layered fibrous metals is suggested to achieve optimal low frequency sound absorption. The sound absorption coefficient of the optimal multi-layered fibrous metal is higher than the single- layered fibrous metal, and a significant effect of the fibrous material on sound absorption is found due to the surface Dorosity of the multi-layered fibrous.展开更多
A new method of estimating the frequency-known signals from the strong background noise was presented first. Then the new method was used in the demodulation of the digital frequency modulation (FSK) signals. The new ...A new method of estimating the frequency-known signals from the strong background noise was presented first. Then the new method was used in the demodulation of the digital frequency modulation (FSK) signals. The new demodulation method can complete the demodulation of the FSK signals only with the carrier frequency and without any carrier phase information. The simulation results show that the performance of anti-noise of the new method is better than that of the incoherent demodulation method and the fluctuation of the carrier phase has little effect on the new method. So the new demodulation method has a fine prospect in the practical applications.展开更多
For radar targets flying at low altitude, multiple pathways produce fade or enhancement relative to the level that would be expected in a free-space environment. In this paper, a new detec- tion method based on a wide...For radar targets flying at low altitude, multiple pathways produce fade or enhancement relative to the level that would be expected in a free-space environment. In this paper, a new detec- tion method based on a wide-ranging multi-frequency radar for low angle targets is proposed. Sequential transmitting multiple pulses with different frequencies are first applied to decorrelate the cohe- rence of the direct and reflected echoes. After receiving all echoes, the multi-frequency samples are arranged in a sort descending ac- cording to the amplitude. Some high amplitude echoes in the same range cell are accumulated to improve the signal-to-noise ratio and the optimal number of high amplitude echoes is analyzed and given by experiments. Finally, simulation results are presented to verify the effectiveness of the method.展开更多
The electrical characteristics of tissue yield valuable information for the early diagnosis of pathological changes. Magneto-acoustic tomography( MAT) is a novel functional imaging approach for imaging electrical cond...The electrical characteristics of tissue yield valuable information for the early diagnosis of pathological changes. Magneto-acoustic tomography( MAT) is a novel functional imaging approach for imaging electrical conductivity. It combines the advantages of high spatial resolution of ultrasonic imaging and high contrast ratio of electrical impedance tomography. It has potential application value in the early tumor diagnosis and bioelectricity monitoring. The analysis and detection of the magneto acoustic signal have a key role in improving the contrast resolution,imaging resolution and reconstruction accuracy of the electrical conductivity image. In this paper,the amplitude,the waveform characteristics and the frequency characteristics of the magnetic sound signal are review ed by the theoretical research,simulation and testing experiments of the weak magneto-acoustic signal.展开更多
To improve the data rate of underwater acoustic frequency-hopped communications, frequency hopping is applied to different orders of fractional Fourier domain (FrFD), to enable non-intrusive, bandwidth-limited acousti...To improve the data rate of underwater acoustic frequency-hopped communications, frequency hopping is applied to different orders of fractional Fourier domain (FrFD), to enable non-intrusive, bandwidth-limited acoustic communications. An FrFD frequency-hopped communication method based on chirp modulation, namely multiple chirp shift keying-FrFD hopping (MCSK-FrFDH), is proposed for underwater acoustic channels. Validated by both simulations and experimental results, this method can reach a bandwidth efficiency twice more than conventional frequency-hopped methods with the same data rate and anti-multipath capability, suggesting that the proposed method achieves a better performance than the traditional frequency hopped communication in underwater acoustic communication channels. Results also show that in practical scenarios, the MCSK-FrFDH system with longer symbol length performs better at the low signal-to-noise ratio (SNR), while the system with larger frequency sweeping range performs better at a high SNR.展开更多
The Radon-ambiguity transform (RAT), although efficient for detecting the linear frequency modulated signals (LFMs), is troubled by the energy accumulation of noise in low signal-to-noise ratio (SNR). A secondor...The Radon-ambiguity transform (RAT), although efficient for detecting the linear frequency modulated signals (LFMs), is troubled by the energy accumulation of noise in low signal-to-noise ratio (SNR). A secondorder difference (SOD) method is proposed to treat with this problem. In the SOD method, the optimal search step and difference step are derived from the LFM rate resolution formula. The sharpness of the peaks of RAT is measured by curvature, and the sharpness, but not the magnitude of the peaks, is used to detect the LFMs. The SOD method removes the noise energy accumulation and reserves the drastically changing components integrally; thus, it improves the detection probability of LFMs in low SNR. The expected performance of the new method is verified by 100 Monte Carlo simulations.展开更多
Based on the efficient sound absorption characteristics of Helmholtz resonance structures in the range of medium and low frequency acoustic waves,this paper investigates an effective solution for light timber construc...Based on the efficient sound absorption characteristics of Helmholtz resonance structures in the range of medium and low frequency acoustic waves,this paper investigates an effective solution for light timber construction walls with acoustic problems.This study takes the light timber construction wall structure as the research object.Based on the Helmholtz resonance principle,the structure design of the wall unit,impedance tube experiment and COMSOL MULTIPHYSICS simulation calculation were carried out to obtain the change rule of acoustic performance of the Helmholtz resonance wall unit structure.The research results show that the overall stability of sound insulation of the structure is improved,and the frequency range with sound transmission loss more than 50 dB in the experimental group is 640–1600 Hz,while in the control group is 500–906 Hz and 1238–1600 Hz;the sound absorption performance of the structure is obviously better than that of the ordinary structure,especially in the low frequency acoustic wave range of 100–320 Hz,the sound absorption coefficient of the experimental group is more than 0.49,while the sound absorption coefficient of the control group is less than 0.1.It is expected that these results will contribute to the optimization of the acoustic performance of light timber construction walls and have high application and popularization value.展开更多
The accurate estimation of the rolling element bearing instantaneous rotational frequency(IRF) is the key capability of the order tracking method based on time-frequency analysis. The rolling element bearing IRF can b...The accurate estimation of the rolling element bearing instantaneous rotational frequency(IRF) is the key capability of the order tracking method based on time-frequency analysis. The rolling element bearing IRF can be accurately estimated according to the instantaneous fault characteristic frequency(IFCF). However, in an environment with a low signal-to-noise ratio(SNR), e.g., an incipient fault or function at a low speed, the signal contains strong background noise that seriously affects the effectiveness of the aforementioned method. An algorithm of signal preprocessing based on empirical mode decomposition(EMD) and wavelet shrinkage was proposed in this work. Compared with EMD denoising by the cross-correlation coefficient and kurtosis(CCK) criterion, the method of EMD soft-thresholding(ST) denoising can ensure the integrity of the signal, improve the SNR, and highlight fault features. The effectiveness of the algorithm for rolling element bearing IRF estimation by EMD ST denoising and the IFCF was validated by both simulated and experimental bearing vibration signals at a low SNR.展开更多
Based on the Burgers equation and Manley-Rowe equation, the derivation about nonlinear interaction of the acoustic waves has been done in this paper. After nonlinear interaction among the low-frequency weak waves and ...Based on the Burgers equation and Manley-Rowe equation, the derivation about nonlinear interaction of the acoustic waves has been done in this paper. After nonlinear interaction among the low-frequency weak waves and the pump wave, the analytical solutions of acoustic waves' amplitude in the field are deduced. The relationship between normalized energy of high-frequency and the change of acoustic energy before and after the nonlinear interaction of the acoustic waves is analyzed. The experimental results about the changes of the acoustic energy are presented. The study shows that new frequencies are generated and the energies of the low-frequency are modulated in a long term by the pump waves, which leads the energies of the low-frequency acoustic waves to change in the pulse trend in the process of the nonlinear interaction of the acoustic waves. The increase and decrease of the energies of the low-frequency are observed under certain typical conditions, which lays a foundation for practical engineering applications.展开更多
基金supported by the National Natural Science Foundation of China(1140440611374072)
文摘The pressure and horizontal particle velocity combined descriptions in the very low frequency acoustic field of shallow wa- ter integrated with the concept of effective depth of Pekeris wave- guide is proposed, especially the active component of the pressure and horizontal particle velocity cross-spectrum, also called ho- rizontal complex cross acoustic intensity, when only two normal modes are trapped in the waveguide. Both the approximate theo- retic analysis and the numerical results show that the sign of the horizontal complex cross acoustic intensity active component is independent of the range when vertically deployed receiving dual sensors are placed in appropriate depths, the sum of which is equal to the waveguide effective depth, so it can be used to tell whether the sound source is near the surface or underwater; while the range rate is expected to be measured by utilizing the sign distribution characteristic of the reactive component. The further robustness analysis of the depth classification algorithm shows that the existence of shear waves in semi infinite basement and the change of acoustic velocity profiles have few effects on the application of this method, and the seabed attenuation will limit the detection range, but the algorithm still has a good robustness in the valid detection range.
基金supported by the National Natural Science Foundation of China (11474230)the Fundamental Research Funds for the Central Universities (3102016QD056) for financial support
文摘A bilayer membrane acoustic metamaterial was proposed to overcome the influence of the mass law on traditional acoustic materials and obtain a lightweight thin-layer structure that can effectively isolate low frequency noise. The finite element analysis(FEA) results agree well with the experimental results.It is proved that the sound transmission losses(STLs) of the proposed structures are higher than those of same surface density acoustic materials. The introduction of the magnetic mass block is different from the traditional design method, in which only a passive mass block is fixed on the membrane. The magnetic force will cause tension in the membrane, increase membrane prestress, and improve overall structural stiffness. The effects of the geometry size on the STLs are discussed in detail. The kind of method presented in this paper can provide a new means for engineering noise control.
文摘<strong>Background:</strong><b><span style="font-family:;" "=""> </span></b><span style="font-family:;" "="">In horses, therapeutic ultrasound has been shown to be beneficial for suspensory ligament injuries, and more generally to stimulate tissue repair and reduce localized pain. However, it has yet to be examined in relation to soft tissue injuries sustained during competition or in connection with rider/saddle interactions. <b>Aim: </b>The aim of the present study was to examine the efficacy of topical low-frequency therapeutic ultrasound on the shoulder muscles of injured horses. <b>Methods:</b></span><b><span style="font-family:;" "=""> </span></b><span style="font-family:;" "="">Muscle mass and cellular health was assessed for <i>M. trapezius</i> using non-invasive multi-frequency bioimpedance, and dynamic improvements in <i>M. trapezius</i> and <i>M. latissimus dorsi</i> were examined using acoustic myography (AMG). A total of 8 injured horses (painful to palpation and atrophied) were treated using an</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">EQ Pro Therapy unit, following a set protocol that comprised treatment every other day for 10 treatments. Pre-treatment values were then compared with post-treatment measurements (1 & 6 months later). </span><b><span style="font-family:;" "="">Results:</span></b><b><span style="font-family:;" "=""> </span></b><span style="font-family:;" "="">The mfBIA results for <i>M. trapezius</i> showed a significant improvement (P</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">0.05) of EQ Pro Therapy treatment for the membrane capacitance (Mc) and phase angle (PA) parameters when comparing the Pre <span>vs</span> Post</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">1 and Post</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">1 <span>vs</span> Post</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">2 measurements. Similar improvements were seen for the AMG measurements for <i>M. trapezius</i> and <i>M. latissimus dorsi</i> where statistically significant improvements in the muscle efficiency (E-score) and temporal summation (T-score) as well as the spatial summation (S-score) and mean of the ST-scores were noted</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">(P</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">0.05 to P</span><span style="font-family:;" "=""> </span><span style="font-family:;" "=""><</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">0.01).</span><span style="font-family:;" "=""> </span><b><span style="font-family:;" "="">Conclusion:</span></b><span style="font-family:;" "=""> The present findings suggest that </span><span style="font-family:;" "="">EQ Pro Therapy treatment is efficacious in terms of equine cases involving soft tissue shoulder muscle injuries (</span><span style="font-family:;" "="">painful to palpation and atrophied).</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">The main improvements noted were not only increased muscle mass and cellular health</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">but also </span><span style="font-family:;" "="">improved force production, better coordination</span><span style="font-family:;" "="">,</span><span style="font-family:;" "=""> and lateral balance, which persisted for at least six months after treatment.</span>
基金financially supported by the National Natural Science Foundation of China(Grant No.61801275)Major Science and Technology Innovation This work is financially supported by the Stable Supporting Fund of Acoustic Science and Technology Laboratory(Grant No.SSJSWDZC2018014)+3 种基金the Major Science and Technology Innovation Project of Shandong Province(Grant No.2018YFJH0707)the Key Research and Development Plan(International Cooperation)Project of Shandong Province(Grant No.2018JHZ002)the International Science and Technology Cooperation Project of Shandong Academy of Sciences(Grant No.2019GHZD01)the provincial Key Research and Development Program of Shandong(Military and Civilian Integration)(Grant No.2016JMRH0541)
文摘Ocean vector acoustic measurement is feasible affected by the hydrodynamic interference caused by the flow fluctuations and structural vibrations, especially in the very-low-frequency monitoring. Hence, a novel horizontal floating platform including a horizontal floating cable, vertical mooring cable and floating main body is proposed and described in this paper. It has the advantages of good maneuverability along with the current and multi-stage vibration isolation. The main application of this platform is to measure the ocean ambient noise coming from the wave fluctuation and the deterministic acoustic signals such as aquatic organisms, underwater targets and sailing vehicles. The influence of the current fluctuation on the attitude angle and flow induced vibration of cables and main body are analyzed with some previous sea test data. Moreover, the comparison between the vertical type platform used before and the horizontal type platform is also discussed. It is concluded that there is obvious relevance between the attitude angle and ocean current variation. Meanwhile, the abnormal influence on the main body is caused by the vibration transmission from the fluctuation of cables. There will be the influence on the accuracy of the acoustic measurement above 100 Hz, and the inherent vibration characteristic of the main body is the primary reason.
文摘In order to solve the problem of carrier frequency blind estimation of PSK signals in electronic reconnaissance, a new estimation method was proposed. The phase shift keying(PSK) signal was divided into several overlapping intervals which had equal length, and the spectrum concentration measures of every interval were extracted by the FFT. And then, using the grid-density clustering, the spectrum concentration measures were classified into two categories, the narrowband spectrum interval and the wideband spectrum interval. The narrowband spectrum interval was regarded as the characteristic class. The spectrums of the characteristic class were accumulated to estimate the carrier frequency of PSK signal. The proposed method had avoided the non linear operation in the traditional PSK signal carrier frequency estimation algorithm. Thus, the signal to noise ratio (SNR) threshold was remarkably decreased. Moreover, the proposed method did not need the prior knowledge of the signal, which was suitable to the electronic reconnaissance occasion. Experimental results had verified the validity of the proposed estimation method in low SNR.
基金the National Natural Science Foundation of China(Grant Nos.61973037 and 61673066).
文摘Conventional parameter estimation methods for pseudo-random binary code-linear frequency modulation(PRBC-LFM)signals require prior knowledge,are computationally complex,and exhibit poor performance at low signal-to-noise ratios(SNRs).To overcome these problems,a blind parameter estimation method based on a Duffing oscillator array is proposed.A new relationship formula among the state of the Duffing oscillator,the pseudo-random sequence of the PRBC-LFM signal,and the frequency difference between the PRBC-LFM signal and the periodic driving force signal of the Duffing oscillator is derived,providing the theoretical basis for blind parameter estimation.Methods based on amplitude method,short-time Fourier transform method,and power spectrum entropy method are used to binarize the output of the Duffing oscillator array,and their performance is compared.The pseudo-random sequence is estimated using Duffing oscillator array synchronization,and the carrier frequency parameters are obtained by the relational expressions and characteristics of the difference frequency.Simulation results show that this blind estimation method overcomes limitations in prior knowledge and maintains good parameter estimation performance up to an SNR of-35 dB.
文摘Based on chaotic oscillator system, this paper proposes a novel method on high frequency low signal-to-noise ratio BPSK(Binary Phase Shift Keying) signal detection. Chaotic oscillator system is a typical non-linear system which is sensitive to periodic signals and immune to noise at the same time. Those properties make it possible to detect low signal-to-noise ratio signals. The BPSK signal is a common signal type which is widely used in modern communication. Starting from the analysis of advantages of chaotic oscillator system and signal features of the BPSK signal, we put forward a unique method that can detect low signal-to-noise ratio BPSK signals with high frequency. The simulation results show that the novel method can detect low signal-to-noise ratio BPSK signals with frequency in an order of magnitude of 108 Hz, and the input Signal-to-Noise Ratio threshold can be -20 dB.
基金the Major Scientific andTechnical Project of Department of Science and Technology,Inner Mongolia in 2016(Strong Earthquake Track in the Short Stage and Integration Innovation of Stereoscopic Observation Technology in Space and Ground)
文摘In order to search for the seismic wave characteristics of low frequency signals in the Alxa Left Banner region,Inner Mongolia,the low frequency signals of seismic wave data are extracted from the earthquakes of MS5. 8 in 2015 and MS5. 0 in 2016 in this area. The results show that:① Before the MS5. 8 earthquake,the seismic stations located near the epicenter in Wuhai,Dongshengmiao,and Shizuishan recorded seismic waves that showed the phenomenon of spectrum shift from high to low frequency.② The low frequency signals recorded by different stations have obvious difference.③ According to the data recorded by the station closest to the epicenter,low-frequency signals were recorded about120 hours before the earthquake and had obvious anomalies. This may reflect slow slip before the earthquake.
文摘The essay mainly studies a system of low frequency signal′s measurement and the extraction of its characteristic quantity,introduces how matlab analyzes and extracts low frequency signal.MATLAB,a visual programming software,designs testing program for mechanic vibration signal,analyzes and identifies vibration signal.The collected data shows the effectiveness of the system.Based on XM121 modules,the testing system collects and analyzes single channel signal.
基金the support of the National Basic Research Program(973 Program)of China(Grant No.2011CB610304)the National Natural Science Foundation of China(Grant Nos.11332004 and 11402046)+2 种基金China Postdoctoral Science Foundation(No.2015M571296)the 111 Project(B14013)the CATIC Industrial Production Projects(Grant No.CXY2013DLLG32)
文摘We present a design method for calculating and optimizing sound absorption coefficient of multi-layered porous fibrous metals (PFM) in the low frequency range. PFM is simplified as an equivalent idealized sheet with all metallic fibers aligned in one direction and distributed in periodic hexagonal patterns. We use a phenomenological model in the literature to investigate the effects of pore geometrical parameters (fiber diameter and gap) on sound absorption performance. The sound absorption coefficient of multi- layered PFMs is calculated using impedance translation theorem, To demonstrate the validity of the present model, we compare the predicted results with the experimental data. With the average sound absorption (low frequency range) as the objective function and the fiber gaps as the design variables, an optimization method for multi-layered fibrous metals is proposed. A new fibrous layout with given porosity of multi-layered fibrous metals is suggested to achieve optimal low frequency sound absorption. The sound absorption coefficient of the optimal multi-layered fibrous metal is higher than the single- layered fibrous metal, and a significant effect of the fibrous material on sound absorption is found due to the surface Dorosity of the multi-layered fibrous.
基金the National Natural Science Foundation of China (60272077) the Science Foundation of Aeronautics (02F53030).
文摘A new method of estimating the frequency-known signals from the strong background noise was presented first. Then the new method was used in the demodulation of the digital frequency modulation (FSK) signals. The new demodulation method can complete the demodulation of the FSK signals only with the carrier frequency and without any carrier phase information. The simulation results show that the performance of anti-noise of the new method is better than that of the incoherent demodulation method and the fluctuation of the carrier phase has little effect on the new method. So the new demodulation method has a fine prospect in the practical applications.
基金supported by the National Natural Science Foundation of China(6137213661372134+2 种基金61172137)the Fundamental Research Funds for the Central Universities(K5051202005)the China Scholarship Council(CSC)
文摘For radar targets flying at low altitude, multiple pathways produce fade or enhancement relative to the level that would be expected in a free-space environment. In this paper, a new detec- tion method based on a wide-ranging multi-frequency radar for low angle targets is proposed. Sequential transmitting multiple pulses with different frequencies are first applied to decorrelate the cohe- rence of the direct and reflected echoes. After receiving all echoes, the multi-frequency samples are arranged in a sort descending ac- cording to the amplitude. Some high amplitude echoes in the same range cell are accumulated to improve the signal-to-noise ratio and the optimal number of high amplitude echoes is analyzed and given by experiments. Finally, simulation results are presented to verify the effectiveness of the method.
基金supported by the Project of the National Natural Foundation of China (Grant Nos.61501523,81171424)
文摘The electrical characteristics of tissue yield valuable information for the early diagnosis of pathological changes. Magneto-acoustic tomography( MAT) is a novel functional imaging approach for imaging electrical conductivity. It combines the advantages of high spatial resolution of ultrasonic imaging and high contrast ratio of electrical impedance tomography. It has potential application value in the early tumor diagnosis and bioelectricity monitoring. The analysis and detection of the magneto acoustic signal have a key role in improving the contrast resolution,imaging resolution and reconstruction accuracy of the electrical conductivity image. In this paper,the amplitude,the waveform characteristics and the frequency characteristics of the magnetic sound signal are review ed by the theoretical research,simulation and testing experiments of the weak magneto-acoustic signal.
基金supported by the National Natural Science Foundation of China(4137604041676024)
文摘To improve the data rate of underwater acoustic frequency-hopped communications, frequency hopping is applied to different orders of fractional Fourier domain (FrFD), to enable non-intrusive, bandwidth-limited acoustic communications. An FrFD frequency-hopped communication method based on chirp modulation, namely multiple chirp shift keying-FrFD hopping (MCSK-FrFDH), is proposed for underwater acoustic channels. Validated by both simulations and experimental results, this method can reach a bandwidth efficiency twice more than conventional frequency-hopped methods with the same data rate and anti-multipath capability, suggesting that the proposed method achieves a better performance than the traditional frequency hopped communication in underwater acoustic communication channels. Results also show that in practical scenarios, the MCSK-FrFDH system with longer symbol length performs better at the low signal-to-noise ratio (SNR), while the system with larger frequency sweeping range performs better at a high SNR.
基金supported by the Program for New Century Excellent Talents in University, Ministry of Education (NCET-05-0803)
文摘The Radon-ambiguity transform (RAT), although efficient for detecting the linear frequency modulated signals (LFMs), is troubled by the energy accumulation of noise in low signal-to-noise ratio (SNR). A secondorder difference (SOD) method is proposed to treat with this problem. In the SOD method, the optimal search step and difference step are derived from the LFM rate resolution formula. The sharpness of the peaks of RAT is measured by curvature, and the sharpness, but not the magnitude of the peaks, is used to detect the LFMs. The SOD method removes the noise energy accumulation and reserves the drastically changing components integrally; thus, it improves the detection probability of LFMs in low SNR. The expected performance of the new method is verified by 100 Monte Carlo simulations.
文摘Based on the efficient sound absorption characteristics of Helmholtz resonance structures in the range of medium and low frequency acoustic waves,this paper investigates an effective solution for light timber construction walls with acoustic problems.This study takes the light timber construction wall structure as the research object.Based on the Helmholtz resonance principle,the structure design of the wall unit,impedance tube experiment and COMSOL MULTIPHYSICS simulation calculation were carried out to obtain the change rule of acoustic performance of the Helmholtz resonance wall unit structure.The research results show that the overall stability of sound insulation of the structure is improved,and the frequency range with sound transmission loss more than 50 dB in the experimental group is 640–1600 Hz,while in the control group is 500–906 Hz and 1238–1600 Hz;the sound absorption performance of the structure is obviously better than that of the ordinary structure,especially in the low frequency acoustic wave range of 100–320 Hz,the sound absorption coefficient of the experimental group is more than 0.49,while the sound absorption coefficient of the control group is less than 0.1.It is expected that these results will contribute to the optimization of the acoustic performance of light timber construction walls and have high application and popularization value.
基金Project(51275030)supported by the National Natural Science Foundation of ChinaProject(2016JBM051)supported by the Fundamental Research Funds for the Central Universities,China
文摘The accurate estimation of the rolling element bearing instantaneous rotational frequency(IRF) is the key capability of the order tracking method based on time-frequency analysis. The rolling element bearing IRF can be accurately estimated according to the instantaneous fault characteristic frequency(IFCF). However, in an environment with a low signal-to-noise ratio(SNR), e.g., an incipient fault or function at a low speed, the signal contains strong background noise that seriously affects the effectiveness of the aforementioned method. An algorithm of signal preprocessing based on empirical mode decomposition(EMD) and wavelet shrinkage was proposed in this work. Compared with EMD denoising by the cross-correlation coefficient and kurtosis(CCK) criterion, the method of EMD soft-thresholding(ST) denoising can ensure the integrity of the signal, improve the SNR, and highlight fault features. The effectiveness of the algorithm for rolling element bearing IRF estimation by EMD ST denoising and the IFCF was validated by both simulated and experimental bearing vibration signals at a low SNR.
基金financially supported by the Scientific Research Fund of Heilongjiang Provincial Education Department(Grant No.12541132)the Natural Science Youth Foundation of Heilongjiang Province of China(Grant No.QC2015082)
文摘Based on the Burgers equation and Manley-Rowe equation, the derivation about nonlinear interaction of the acoustic waves has been done in this paper. After nonlinear interaction among the low-frequency weak waves and the pump wave, the analytical solutions of acoustic waves' amplitude in the field are deduced. The relationship between normalized energy of high-frequency and the change of acoustic energy before and after the nonlinear interaction of the acoustic waves is analyzed. The experimental results about the changes of the acoustic energy are presented. The study shows that new frequencies are generated and the energies of the low-frequency are modulated in a long term by the pump waves, which leads the energies of the low-frequency acoustic waves to change in the pulse trend in the process of the nonlinear interaction of the acoustic waves. The increase and decrease of the energies of the low-frequency are observed under certain typical conditions, which lays a foundation for practical engineering applications.