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Microphone Based Acoustic Vector Sensor for Direction Finding with Bias Removal

Wajid Mohd, Kumar Arun, Bahl Rajendar

Archives of Acoustics

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2022

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Vol. 47, No. 2

151--167

EN

The acoustic vector sensor (AVS) is used to measure the acoustic intensity, which gives the direction-of-arrival (DOA) of an acoustic source. However, while estimating the DOA from the measured acoustic intensity the finite microphone separation (d) in a practical AVS causes angular bias. Also, in the presence of noise there exists a trade off between the bias (strictly increasing function of d) and variance (strictly decreasing function of d) of the DOA estimate. In this paper, we propose a novel method for mitigating the angular bias caused due to finite microphone separation in an AVS. We have reduced the variance by increasing the microphone separation and then removed the bias with the proposed bias model. Our approach employs the finite element method (FEM) and curves fitting to model the angular bias in terms of microphone separations and frequency of a narrowband signal. Further, the bias correction algorithm based on the intensity spectrum has been proposed to improve the DOA estimation accuracy of a broadband signal. Simulation results demonstrate that the proposed bias correction scheme significantly reduces the angular bias and improves the root mean square angular error (RMSAE) in the presence of noise. Experiments have been performed in an acoustic full anechoic room to corroborate the effect of microphone separation on DOA estimation and the efficacy of the bias correction method.

2

Direction Estimation and Tracking of Coherent Sources Using a Single Acoustic Vector Sensor

Wajid Mohd, Kumar Arun, Bahl Rajendar

Archives of Acoustics

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2020

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Vol. 45, No. 2

209--219

EN

A single acoustic vector sensor (AVS) cannot be used to find the direction-of-arrival (DOA) of two or more coherent (fully correlated) sources. We have proposed a technique for estimating DOAs (in 2D geometry) of two simultaneous coherent sources using single AVS under the assumption that acoustic sources enter in the field sequentially. The DOA estimation has been investigated with two different configurations of AVS, each consisting of three microphones in a plane. The technique has been also applied in tracking (a) an acoustic source in the presence of stationary interfering coherent source and (b) two coherent sources when the sources are changing their locations alternatively. The experimental environment has been generated using the Finite-Element Method tool viz. COMSOL to corroborate the proposed scheme.

3

Plasticity and swell-shrink behaviour of electrokinetically stabilized virgin expansive soil using calcium hydroxide and calcium chloride solutions as cationic fluids

James Jijo, James Archana, Kumar Arun, Gomathi Elumalai, Prasath Karunakaran Kamal

Civil and Environmental Engineering Reports

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2019

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Vol. 29, no. 1

128--146

EN

This investigation focussed on the plasticity and swell-shrink behaviour of an expansive soil that was stabilized using electro kinetic stabilization (EKS) techniques with cationic fluids for enhancement of stabilization. 0.25 M solutions of calcium hydroxide and calcium chloride were used as cationic fluids. An electro kinetic (EK) cell of dimensions 500 mm x 150 mm x 160 mm with inert graphite electrodes of size 140 mm x 160 mm x 5 mm was adopted for the stabilization process, carried out at an applied voltage of 40 V over a period of 6 hours. After the duration of the test, stabilized soil sample was subjected to Atterberg limits and free swell tests to determine its plasticity and swell-shrink characteristics. The results of the investigation found that both fluids were capable of reducing the plasticity and swell-shrink behaviour of the soil with different levels of effectiveness.

PL

W badaniach skupiono się na plastyczności i kurczeniu się gleby, która została ustabilizowana za pomocą technik stabilizacji elektrokinetycznej (EKS) z płynami kationowymi. Jako płyny kationowe stosowano 0,25 M roztwory wodorotlenku wapnia i chlorku wapnia. Do procesu stabilizacji przyjęto ogniwo elektrokinetyczne (EK) o wymiarach 500 mm x 150 mm x 160 mm z obojętnymi elektrodami grafitowymi o wymiarach 140 mm x 160 mm x 5 mm, przy zastosowaniu napięcia 40 V przez okres 6 godzin. Po zakończeniu testu stabilizowaną próbkę gleby poddano testom Atterberga i badaniom swobodnego spęcznienia w celu określenia jego plastyczności i charakterystyki kurczenia się. Wyniki badania wykazały, że oba płyny były w stanie zmniejszyć plastyczność i kurczenie się gleby przy różnych poziomach skuteczności.