Low-frequency acoustic source localization based on the cross-spectral time reversal method corrected in wavenumber domain

Abstract

Near-filed acoustic holography can break the half wavelength limit by reversing the propagation matrix and achieve high-resolution for low-frequency source localization, but it will encounter the ill-posed problem. The subwavelength focusing also can be obtained by correcting the wavenumber spectrum of monopole time-reversed field into that of dipole time-reversed field through near field measurement, which can avoid the ill-posed problem. To further improve the identification accuracy of low-frequency sources in the strong noise environment, a cross-spectrum time reversal method corrected in wavenumber domain is proposed (CS-TR). First, a cross-spectrum time reversal function based on pressure measurement on a plane in the near field is constructed to obtain the initial time-reversed result. Then, the cross-spectrum time-reversed field is transformed into wavenumber domain, and the filter term that contains evanescent waves is corrected to make the result contains more evanescent waves which can improve the localization resolution of low-frequency sources. The essence of the cross-spectrum of the focusing result is to calculate the cross-correlation of signals from all directions, which can not only increase the content of evanescent waves during the correction process in wavenumber domain, but also can highlight the energy difference between signal and noise, making the localization capability significantly improved for low-frequency sources. Numerical simulation and experimental results show that the CS-TR method can significantly improve the spatial resolution at low frequencies. Multiple acoustic sources at 100 Hz were effectively identified when the signal-to-noise ratio (SNR) was 0 dB, and the spatial resolution reached 1/34 wavelength.