Reduction of blind zone in ultrasonic transmitter/receiver transducers

Abstract

Most ultrasonic sensorial systems are based on transducers that work as emitters and receivers in the same scanning process. This fact implies that, during the emission process, the reception stage stays disabled, in order to avoid the emission coupled. This disabling interval provides that the nearest area to the transducers, the blind zone, cannot be scanned, since echoes coming from reflectors placed inside it are overlapped with the coupled emission. On the other hand, the encoding of the ultrasonic emission by binary sequences allows the process gain to be increased, so better precision is achieved and higher levels of noise are supported by the system. The length of the used binary sequence determines not only the process gain, but also the duration of the emission interval. The usage of long sequences to improve the performance also implies the existence of a larger blind zone, where reflectors are not detected. This work presents a novel encoding technique, based on Golay complementary pairs, where the dimension of the blind zone is reduced to negligible distances thanks to some features from the binary sequences.