The principle & design of an ultrasonic transducer system with auto-alignment mechanism is introduced. The system is used for detecting foreign bodies (FBs) in beverage containers. Variation in reflection amplitude is analysed as a function of ultrasound beam incident angle to beverage container surface. It is concluded there exists a quadratic relationship between the strength of the reflected signal & incident angle. Furthermore, a calculation for effective angular increment for searching the normal of a curved surface is introduced. Experiments conducted using the prototype demonstrate that FBs are detectable in various juices. Experiments also observed some false echo signals that occur due to curved container surface. Threshold in confined time region is therefore set to ensure no fail of detection in low signal to noise ratio.
