Audio Directional Ultrasonic Sensors

Audio Beam is a revolutionary way of projecting audio signal in a highly directional manner to the listener. This new technique creates a narrow sound beam by the self-demodulation effect of the amplitude-modulated sound wave in the air. With this nonlinear interaction, a high-directivity ultrasonic loudspeaker design is developed which can generate beam of audio. The beam forming theory and phased array patterns were studied in this paper. A new method was presented to determine the directivity of sound produced by the transducer array. The effect of element number and array pattern on the audio pressure was also studied. It demonstrates that the proper amount and special array pattern of the elements can lead to sharper directivity, suppress the side lobe amplitude, and eliminate the back lobes, which are the essential conditions to yield high-directional ultrasound beam in-air application. The Poly Vinylidene Fluoride (PVDF) membrane was chosen to produce ultrasonic in transducer due to its higher sensitivity and better flexibility than other piezoelectric material. At the mean time, harmonic analysis to the PVDF film vibration was performed using ANSYS. The results show that the PVDF membrane can produce an ultrasound with a fixed resonance frequency. Two different ultrasonic transducers, based on Poly Vinylidene Fluoride (PVDF) membranes have been designed and fabricated in air application. A special hemi-cylindrical geometry PVDF film has been successfully applied in the transducer structure design to obtain an audio beam since it can work in air at a lower frequency. Experimental test has been performed to get the resonance frequency of the transducer. The agreement of results in theory and testing showed the emitter had the capability for focusing the sound in a fixed direction.