Near field acoustic holography (NAH) theory for cyclostationary sound field and its application

The cyclostationary near field acoustic holography (CYNAH) technique is proposed with a view to overcome the limitations of the traditional near field acoustic holography (NAH) technique in analyzing cyclostationary sound field. Because of the modulation of such kind of sound signal, the sidebands appear in the spectrum of sound pressure. Therefore, the power of modulating wave components cannot be correctly shown by the power spectral density (PSD) of sound pressure in NAH hologram with the disturbance of sidebands. The cyclic spectrum density (CSD) of sound pressure is shown by the CYNAH hologram instead of the spectrum. The influence of sidebands can be subdued by CYNAH because of the demodulation function of the CSD. The CYNAH hologram of an alternating motor, as an instance of cyclostationary source, is obtained in an anechoic-chamber. The results of experiment show that this approach can obtain more information about cyclostationary sound field than NAH can.