Liu J.,CAS Beijing Institute of Acoustics |
Wang L.,CAS Beijing Institute of Acoustics
Sensors and Actuators, B: Chemical | Year: 2014
In this study, we investigate the dynamics and response of a humidity sensor based on a polymer-coated Love wave device. A review is presented for the theoretical model of Love waves in a layered structure with a viscoelastic layer on a piezoelectric substrate. Numerical illustrations are executed for the mass velocity sensitivity and mass loss sensitivity of a polymer-coated device. The BET equation and its improved equation are introduced to describe the adsorption mechanism of gas on the detector surface. A method is introduced for calculating the surface area of the polymer layer, which is proved a porous material. An experiment is performed for a humidity sensor based on a Love wave device consisting of two 28 μm-periodic interdigital transducers, a 0.47 μm-thick PVA layer, and an ST-90°X quartz substrate. The operation frequency and insertion loss of the Love wave device are measured by using a network analyzer; the relative surface area of the PVA layer is calculated through comparing the fitted and the theoretical frequency shift caused by the monolayer of water molecules. The frequency shifts and insertion loss increments are shown as functions respect to the relative humidity; the theoretical curves agree well the experimental results. © 2014 Elsevier B.V.
Cai Y.,CAS Beijing Institute of Acoustics |
Wu M.,CAS Beijing Institute of Acoustics |
Yang J.,CAS Beijing Institute of Acoustics
Journal of the Acoustical Society of America | Year: 2014
This paper describes a method for focusing the reproduced sound in the bright zone without disturbing other people in the dark zone in personal audio systems. The proposed method combines the least-squares and acoustic contrast criteria. A constrained parameter is introduced to tune the balance between two performance indices, namely, the acoustic contrast and the spatial average error. An efficient implementation of this method using convex optimization is presented. Offline simulations and real-time experiments using a linear loudspeaker array are conducted to evaluate the performance of the presented method. Results show that compared with the traditional acoustic contrast control method, the proposed method can improve the flatness of response in the bright zone by sacrificing the level of acoustic contrast. © 2014 Acoustical Society of America.
Zheng C.,CAS Beijing Institute of Acoustics |
Li X.,CAS Beijing Institute of Acoustics
Applied Acoustics | Year: 2012
Although cepstrum-based harmonics-to-noise-ratio techniques have been widely used in speech processing, they are as yet not applied to detect multiple sinusoids in unknown colored noise. By studying the impact of sinusoids on cepstral coefficients in theory, a truncated cepstrum thresholding technique is proposed to estimate the unknown colored noise power spectral density, which can be used to estimate the local signal-to-noise-ratio (LSNR) in the frequency domain. This paper suggests the use of the LSNR as a test statistic to detect the sinusoids in unknown colored noise. Numerical simulation results show that the proposed test statistic is much better than the existing test statistics in unknown colored noise environments. © 2012 Elsevier Ltd. All rights reserved.
Liu J.,CAS Beijing Institute of Acoustics
Smart Materials and Structures | Year: 2014
A theoretical method is used to analyze the performance of Love wave sensors with multiple viscoelastic guiding layers on a piezoelectric substrate. The method is based upon the theoretical model for multi-elastic-layer piezoelectric Love waves and the Maxwell-Weichert model for viscoelastic materials. The relationship between sensor performance and the characteristics of Love waves is discussed. Numerical calculation is completed for a Love wave delay line consisting of a viscoelastic SU-8 layer, an elastic SiO2 layer, an ST-90°X quartz substrate and two interdigital transducers (IDTs) with a period of 40 μm deposited on the substrate surface. The calculated results prove that a Love wave sensor with such a two-layer structure can achieve better performance than a Love wave sensor with only one (visco)elastic or elastic guiding layer. Some interesting abnormal phenomena, such as an oscillation in mass velocity sensitivity (S mv ), are predicted at the area where tail-raising occurs in the propagation velocity. The method and the numerical results presented in this work may help in the development of a high-performing Love wave sensor with multiple layers. © 2014 IOP Publishing Ltd.
Li Q.,CAS Beijing Institute of Acoustics
Shengxue Xuebao/Acta Acustica | Year: 2015
The study of wave guide invariant in underwater acoustics is one of attracted topics in recent 30 years. The interferences of direct wave and reflect wave from sea surface and sea bottom of underwater target radiated noise inherent the information of target distance. Extraction of these distance information will provide a possible new way in passive ranging for underwater target. The theoretical analysis and the results of at sea experiments show that the LOFAR (Low Frequency Analysis Record) figure inherently contains the range and moving information of passive acoustic sources, even in the situation that the receiver is only one single hydrophone. The theoretical analysis of extraction of target distance information by using wave guide invariant is presented in this paper. It is shown that, based on the interference striation pattern of target, the hydrophone array system is possible to extract the distance information with quite high array gain. Although the mathematical constrain conditions in forming interference striation pattern are different for individual array element, but it is proved that the differences of time delays between array elements can be used in compensation of beamforming. The theoretical analysis, system simulation and some results of at sea experiment show a new way in passive ranging and target recognition. ©, 2015, Science Press. All right reserved.
Liu J.,CAS Beijing Institute of Acoustics |
He S.,CAS Beijing Institute of Acoustics
International Journal of Solids and Structures | Year: 2010
Love waves propagating in a layered structure with an elastic layer deposited on a piezoelectric substrate are analytically investigated. We present a general dispersion equation that describes the properties of Love waves in the structure. A detailed discussion regarding the dispersion equation is presented, and the parameters for Love-mode sensors are also introduced. The properties of Love waves are illustrated by means of sample results for a layered structure with an SiO2 layer sputtered on an ST-cut 90°X-propagating quartz substrate. Interestingly, we found that a threshold-normalized layer thickness existed for the fundamental Love mode in such a structure. © 2009 Elsevier Ltd. All rights reserved.
Liu J.,CAS Beijing Institute of Acoustics
AIP Advances | Year: 2014
Dispersion equation is an important tool for analyzing propagation properties of acoustic waves in layered structures. For Love wave (LW) sensors, the dispersion equation with an isotropic-considered substrate is too rough to get accurate solutions; the full dispersion equation with a piezoelectric- considered substrate is too complicated to get simple and practical expressions for optimizing LW-based sensors. In this work, a dispersion equation is introduced for Love waves in a layered structure with an anisotropic-considered substrate and an isotropic guiding layer; an intuitive expression for mass sensitivity is also derived based on the dispersion equation. The new equations are in simple forms similar to the previously reported simplified model with an isotropic substrate. By introducing the Maxwell-Weichert model, these equations are also applicable to the LW device incorporating a viscoelastic guiding layer; the mass velocity sensitivity and the mass propagation loss sensitivity are obtained from the real part and the imaginary part of the complex mass sensitivity, respectively. With Love waves in an elastic SiO2 layer on an ST-90°X quartz structure, for example, comparisons are carried out between the velocities and normalized sensitivities calculated by using different dispersion equations and corresponding mass sensitivities. Numerical results of the method presented in this work are very close to those of the method with a piezoelectric-considered substrate. Another numerical calculation is carried out for the case of a LW sensor with a viscoelastic guiding layer. If the viscosity of the layer is not too big, the effect on the real part of the velocity and the mass velocity sensitivity is relatively small; the propagation loss and the mass loss sensitivity are proportional to the viscosity of the guiding layer. © 2014 Author(s).
Guo D.,Ecole Polytechnique Federale de Lausanne |
Guo D.,CAS Beijing Institute of Acoustics |
Setter N.,Ecole Polytechnique Federale de Lausanne
Macromolecules | Year: 2013
We demonstrate a distinct confinement induced cooperative lattice orientation change in ultrathin P(VDF-TrFE) films by using various characterization techniques, including X-ray diffraction (XRD), two-dimensional X-ray diffraction (2D-XRD), grazing incidence X-ray diffraction (GIXD), and infrared reflection absorption spectra (IRRAS). Both the polymer chains and the molecular dipoles that are perpendicular to the polymer backbone showed a lying-down orientation change with decreasing thickness. The dipole orientation change showed a good correlation with the thickness dependence of remnant polarization, which were measured from highly reproducible ferroelectric loops in a wide range of thickness (30-250 nm) on inert electrode with suppressed "dead layer" effect. A simple microscopic molecular dipole interaction model revealed that the free energy of different orientation states was related to the thickness and lateral dimension of the polymer crystallites. The findings reveal a unique molecular orientation driven size effect in ferroelectric polymer films, providing new insights into the nature of ferroelectricity and orientation mechanisms in polymers relevant to the design of emerging flexible electronic devices. © 2013 American Chemical Society.
Zheng C.,CAS Beijing Institute of Acoustics
Signal Processing | Year: 2012
This paper studies the impact of multiple sinusoids on the statistical properties of log-periodogram and cepstral coefficients. We derive explicit expressions for the means and the covariances of both the log-periodogram and cepstral coefficients for processes with mixed spectra. The numerical simulations are given to verify the analytical results. © 2012 Elsevier B.V. All rights reserved.
Ying D.,CAS Beijing Institute of Acoustics |
Yan Y.,CAS Beijing Institute of Acoustics
IEEE Signal Processing Letters | Year: 2013
Heavy computational load and acoustic interferences are two major problems to speech source localization in real applications. Conventional methods can mitigate one problem, but deteriorate the other. This letter proposes an algorithm of direction-of-arrival (DOA) estimation, which is both computationally efficient and robust in the presence of acoustic interferences. The robustness is considered in two aspects. One is the eigenanalysis-based enhancement to reduce acoustic interferences such as noise and reverberation. The other is the coefficients that weight the pairwise time delays to mitigate the effect of delay outliers on DOA. The high computational efficiency is achieved by making use of a concave cost function, from which, the optimal estimate of DOA is given by a closed-form solution. The grid-search method often adopted in conventional algorithms is no longer used in this algorithm. We conduct some experiments in both simulated and real environments with a 9-element circular array. The proposed algorithm runs about ten times faster than Steered Response Power PHAse Transform (SRP-PHAT), and outperforms SRP-PHAT in terms of robustness. © 1994-2012 IEEE.