ultrasonic sensors used for sonar systems in the water

Ultrasonic sensors for range-finding are the basis of many robotic and automatic
applications, such as obstacle avoidance and collision warning systems of cars, self-guided autonomous vehicles, fieldwork robots and so on. However, there is specified restriction when an airborne ultrasonic transducer is used in field operation since its merit of figure Q is higher(the frequency bandwidth is relative lower), and it is difficult to improve both of the directivity and large sensing range of the airborne ultrasonic transducer. Accordingly, it is still, even now, one of the challenging problems in ultrasonic field to develop the high performance ultrasonic transducer and the ultrasonic range-finding system in air.

An ultrasonic range-distance system consists of an ultrasonic transducer and a transmitting& receiver electronics and a signal processor. The originality of this paper is to lucubrate the fundamentals of the ultrasonic transducer which converts electrical energy to mechanical energy (sound pressure) and reciprocally, mechanical energy to electrical energy, the detecting arithmetic for the weak sound wave signal, and the implementation procedure of the ultrasonic ranging system with large measuring stroke. The main topics of this paper include:

(2)  According to the physical characteristics of the ultrasound wave and the piezoc

eramic material, as well as the performance of the inductive ultrasonic proximity sensors, the resonating mode and frequency of a piezoceramic disc oscillator were selected. By application of the acoustic impedance matching technique to the structure of the transducer, and the optimal matching technique of both mechanical and electrical impedances have the transmitted electronics, we had successfully enlarged the sensing-range and improved the sensing directivity of the transducer,which is capable of checking mufti-way noises.

(3)  It was proposed originally a new composite ultrasonic transducer combined with the piezo disc transducer and the cymbal-type receiver to cope with the doppler effect.

(4)  A novel optimal-design method for the push-pull convertor and its related formula for calculating the efficiency of energy-transforming were proposed originally, and the transmitting circuit implemented by the proposed method has better efficiency of energy converting.Furthermore, the receiving electronics with a novel time-gain control circuit and high signal-to-noise ratio (SNR) was designed and implemented to experiment with the ultrasonic distance measurement transducer.

(5)  By utilizing the fact that the correlation detection is equivalent to the matching detection a necessary modify formula for determining the time-of-flight (ToF) when using matching detection method was presented. A novel method was hereby proposed to improve the processing gain and real-time response of the range-finding system, that is, to use matching detection method based on binary phase-shift keying (2PSK) signal while the ultrasonic transmitted signal is in form of binary amplitude-shift keying (2ASK), and a fast matching detection algorithm was implemented by computing the cross-correlation function with two-step procedure for underwater depth sounder sensor system.

Experimental results show that the effective sensing range of the transducer is greater than 32 meters, and the width of beam is less than士50, which has better performance than that of the existing ones, for instance, the similar products in airducer catalog(AIRMAR Tech. CorpU.S.A.). The underwater acoustic transducer system developed in this paper has been applied to some other projects, for instance, which have provided one of the solution of field-object-detection for the key project of "Study on the navigational control theory and methods for mobile robotics in unknown environment" and the project of "Unmanned Campaign Platform"(An Advanced Research Project of the 10`" Five-year Plan, supported by Equipment Headquarters).

    It is no doubt that all the techniques adopted in this paper can directly be applied to develop sonar systems in the water with high cost performance.