Highly anisotropic beam patterns for a pot-like ultrasonic sensor with penetrating slots configuration

Abstract

Obstacle detection by using ultrasonic proximity sensors has been adopted in automotive industry so as to improve safeties. A pot-like aluminum structure with a piezoelectric ceramic stuck on the inner bottom vibrating plate is usually used to generate and to receive ultrasound in this type of proximity sensor. In practice, the proximity sensor needs an anisotropic beam, whose beam width is wide in the horizontal direction and narrow in the vertical direction, since ground is not perceived as a real obstacle in vehicle applications. In this application, the design degree of freedom was typically constrained by a car designer. For the visual effect of a car body, a flat radiating surface was required and the size of the ultrasonic sensor was limited down to 15 mm in diameter. To obtain the narrower beam width in the vertical direction, raising its operating frequency has been an effective method adopted even though it also narrows the beam width in the horizontal direction and it results in higher sound absorption in air. To circumvent the need to raise the frequency, a new configuration of a pot-like ultrasonic sensor with highly anisotropic beam pattern under previously defined constraints was developed in this research. This configuration was characterized by a pair of 3 penetrating slots on the opposite side of its cylindrical shell in the vertical direction. In this study, the frequency of the ultrasonic sensor was fixed at 48 kHz, which is identical to the frequency of today's parking ultrasonic sensor, and a finite element simulation was introduced in this configuration design. In addition, the far-field pressure beam patterns were measured using a standard microphone in an anechoic room. Finally, we identified that the isotropy of this type ultrasonic sensor, which is defined as an H/V ratio, exceeds 3. We concluded that these penetrating slots would affect the beam pattern of an ultrasonic sensor significantly. Both the design methodologies and the experimental verifications will be detailed in this paper.