Geintra

Many ultrasonic systems based on time-of-flight measurements use signals encoded with binary sequences with similar properties to Gaussian noise. Afterwards, the corresponding echoes are detected correlating the received signal with the original sequence. Thus, an improvement of temporal precision, spatial resolution and robustness to noise is obtained, in comparison with methods based on threshold detection. Furthermore, it could be interesting to have several transducers emitting ultrasound waves over the same spatial zone, and at the same time, allowing measurements from different locations simultaneously. These ultrasonic systems need an asynchronous detection as the echoes could arrive at any moment depending on the transducer and reflector positions. In such case sequences (one in every emitter) with a high Auto-Correlation function and low sidelobes should be used, as well as with low aperiodic Cross-Correlation values among them. As a result, it is possible to detect, and separate according with the original source of the emitted signal, all the echoes even in the case of high noise or attenuation. In this work, three different systems are presented based on Kasami sequences, Complementary Sets of sequences and Loosely Synchronized (LS) sequences. All of them were originally intended for the use in ultrasonic Local Positioning Systems.