Surface Condition Sensing With Broadband and Highly Directional PMUT Array

Ultrasound propagation attenuation coefficient detection is a widely used technique for distinguishing different media types. Multifrequency ultrasound detection provides comprehensive information but requires ultrasonic transducers with a broad bandwidth. This study presents a piezoelectric micromachined ultrasonic transducer (PMUT) array that integrates multiple frequency elements with optimized spacing to achieve the fusion of multiple vibration modes, resulting in a -6 dB emission fractional bandwidth of 230% and pulse-echo fractional bandwidth up to 146%. This ultrawide bandwidth facilitates accurate pulse-echo signal reception across a broad frequency range while minimizing signal overlap caused by ringdown effects. Moreover, optimizing the PMUT array size relative to wavelength achieved a highly directional 5° acoustic beam, ensuring effective penetration through high attenuation or multilayered structures. Experimental results indicate that attenuation coefficients in ice and liquid correlate with their material composition and structural properties. These findings highlight the significant potential of the PMUT array for identifying and analyzing surface media, with promising applications in power supply systems, transportation, industrial production, and so on.