Acoustic Directivity of an Ultrasonic Sensor Depending on Horn Guide Dimension

This study investigates the ultrasonic transmission and reception characteristics of an ultrasonic sensor combined with a horn guide to improve its acoustic directivity. Because an ultrasonic sensor with better directivity can measure longer distances, the purpose of this study is to determine the length and angle in the design of a horn guide to be combined with an ultrasonic sensor, which provides the best transmission and reception directivity. Finite element analysis and experiments were conducted to evaluate the ultrasonic transmission and reception characteristics of the horn guide. For the sensor with a driving frequency of 30 kHz, angles of 10˚, 20˚, and 30˚ and lengths of 10 mm, 20 mm, 30 mm, 40 mm, and 50 mm of the horn guide were considered. The commercial program ANSYS was used for sound pressure analysis and the results provided the axial sound pressure level and the beam pattern of the ultrasound at a specified distance from the sensor according to the horn guide geometry. In the experiment, the ultrasonic sensor with horn guide transmitted ultrasounds and measured the sound pressure of the ultrasounds reflected from a cylindrical wall. The results of the finite element analysis and the experiments showed that horn guides with an angle of 20˚ and a length of 50 mm exhibited the best transmission and reception performance. Experimental results of the ultrasonic sensor with a horn guide of this dimension were compared with the case without the horn guide, and it was confirmed that the angle of the nodal plane in the beam pattern was reduced by as much as 30 %, and thus the acoustic directivity was improved.