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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. Source

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. Source

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. Source

Liu J.,CAS Beijing Institute of Acoustics | Wang L.,CAS Beijing Institute of Acoustics
Sensors and Actuators, B: Chemical

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. Source

Liu J.,CAS Beijing Institute of Acoustics | He S.,CAS Beijing Institute of Acoustics
International Journal of Solids and Structures

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. Source

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