Novel preprocessing technique to improve harmonic distortion in airborne parametric array

A novel modified preprocessing technique is proposed to reduce harmonic distortion in an airborne parametric array, which is designed to reproduce highly directed audible sound. This technique is based on the idea that the harmonic distortion is not fully canceled around 10 kHz because of the mismatch of phase and amplitude, even though previous simple preprocessing is activated. A digital filter is designed to compensate for this phase and amplitude mismatch. This linearization technique is verified by an experiment with an airborne parametric array for which the carrier frequency was 40 kHz. The results show that the second harmonic is reduced 11 dB and total harmonic distortion (THD) is improved 20% around 10 kHz compared to previous preprocessing. The proposed modified preprocessing is effective and good results render this technique suitable for the reproduction of high quality audible sound with high directivity.