Narrow-edged Acoustical Beamforming Utilizing Phase Inversion for Frequency Modulation-based Parametric Array Loudspeaker

Parametric array loudspeakers (PALs) can achieve narrow directivity with the straightness of ultrasonic waves. However, the acoustic beam formed by small-scale PALs has a tendency to spread easily. We have previously proposed a narrow-edged beamforming based on phase inversion for common amplitude modulation-based PALs; however, it decreased the sound pressure significantly when forming a narrow acoustic beam. In this study, we focus on frequency modulation-based PALs, in which a modulated wave has a constant envelope and can hold more energy in a limited amplitude. The phase inversion strategy is discussed to use phase cancellation in both ultrasound and audible sound for a narrow beam. The experimental results show that the proposed method can achieve narrow-edged acoustical beam while reducing the decrease in sound pressure.