Views:3 Author:Site Editor Publish Time: 2018-10-08 Origin:Site
The ultrasonic ranging system developed has a range of more than 32 meters, a beamwidth of less than 100, and a bandwidth of about 4 kHz (22-25. 5 kHz). If a combined ultrasonic transducer structure is used, the bandwidth can be extended to 8 kHz. A large-range ultrasonic ranging system composed of such a transducer can meet the application requirements of a vehicle safety driving assistance system or an unmanned combat platform. The main work and conclusions are as follows:
The mathematical expressions of the radial vibration and axial vibration mode of the ultrasonic transducers are established, which provides a theoretical basis for the design and fabrication of micro-small receivers. The combined transducer structure scheme of "disc type piezoelectric vibrator as the main transducer and transducer as the auxiliary receiver" is proposed, which provides a new dimension for expanding the piezoelectric ultrasonic transducer frequency band. Using the linear propagation characteristics of sound waves in the Fresnel zone of the sound source is an ultrasonic wave with a unique acoustic window structure is designed and fabricated.
The ultrasonic distance measurement sensor provides a new structural solution to improve the multi-path interference performance of the ultrasonic transducer. The optimal design method of the push-pull converter and the calculation formula of the energy conversion efficiency are proposed. The traditional design method of the push-pull converter is improved, and the electromechanical energy conversion efficiency of the ultrasonic generator is improved.In order to suppress the "reverberation" phenomenon in the large-range ultrasonic ranging system, the impedance characteristics of the piezoelectric transducer are analyzed and measured, the impedance matching circuit of the piezoelectric transducer is designed and fabricated, and the ultrasonic propagation process is utilized. In the energy absorption attenuation characteristics, a novel time-gain variable circuit was designed and fabricated.In order to improve the robustness and real-time performance of ultrasonic distance sensor, an envelope correlation detection method and a coarse and precise two-step digital correlation algorithm are introduced, and the application of convolution algorithm (matching detection method) to calculate the range time is given. Modified formula improved ASK modulation and demodulation algorithm (ASK modulation PSK demodulation) is proposed to enhance the anti-multipath interference performance of the ultrasonic measurement system.
The ultrasonic sensor to measure distance developed by the above theoretical methods and technical means exceeds the maximum working distance (30 meters) of the most advanced American Airducer series ultrasonic sensors. So far, the MSK-based ASK modulation and PSK demodulation proposed. The algorithm can increase the processing gain of the ultrasonic ranging system by more than 20dB (M sequence length ); while is using the coarse and precise two-step digital correlation algorithm, the calculation speed is higher than the direct algorithm (k is thick) .The ratio of fine step distance is k> 1. The above conclusions indicate that the software and hardware techniques and theoretical methods adopted or proposed in this paper can help to increase the working distance of the ultrasonic transducer and broaden the working frequency band of the ultrasonic transducer. It enhances the directivity and anti-multipath interference capability of the ultrasonic transducer, as well as improving the real-time and processing gain of the ultrasonic ranging system.
Although the technical indicators of the ultrasonic transducer for distance mesurements have met the design requirements, the existing ultrasonic transducers, ultrasonic transmitting and receiving circuit boards are only test prototypes in the mechanical structure, circuit design ,manufacturing process, and experimental methods. On the other hand, there are still some unsatisfactory things, and the fish needs to be improved .