Axial vibration of ultrasonic transducers

The structure of the multi-node disk ultrasonic transducers, the horn function is to amplify the ultrasonic amplitude, and the large disk can improve the transducer's pointing. The working principle of this type of transducer is to connect a longitudinal conical horn and the longitudinal piezoelectric vibrator to vibrate the air medium. When multi-mode vibration occurs, multiple pitch circles will be produced on the piezo disc. On both sides of the pitch circle, the vibrational points on the surface of the disk vibrate has opposite phases, so that the radiated sound field is weakened by the opposite phase cancellation. In order to overcome this shortcoming, the thickness of one side disk of the pitch circle can be changed by a wavelength to form a concave-convex groove to compensate the phase difference between the pitch circles, thereby improving the radiation efficiency of the transducer. 

There are many related research institutions and manufacturers at home and abroad to develop and produce such ultrasonic distance range transducer. Developing ultrasonic topography transducers with a working distance of about 15m (National Natural Science Foundation and National Program Funding Project, level transducers produced by Canada's Milltronics Company, all belong to multi-wavelength disk transducers.

Experiments show that when the transducer operates at a frequency of 24 kHz and the diameter of the disk is greater than 240 mm.The transducer of the multi-segment disc has the advantages of high sensitivity, large working distance (about 15m) and small beam half angle  multi-wave joint.The disadvantages of the ultrasonic distance sensor circuit are the large size and complicated by manufacturing process.

The sandwich transducer diagram is a typical ultrasonic transducer structure which is consisting of a front and rear cover plate, a piezoelectric vibrator and a stress screw. Where the rear cover is generally in the shape of a cylinder; the front cover is mostly in the shape of a conical horn to increase the radiation area in the underwater acoustic application, the flare is usually cut or partially cut to fit the array structure; The piezoelectric vibrators in the middle are mostly longitudinally polarized piezoelectric ceramic discs, or they can be radially polarized piezoelectric ceramic tubes. High-strength stress screws are used to fasten the front and rear covers and piezoelectric vibrators. The transducer structure was first proposed by French physicist Lang Zhiwan, so it is also known as the Langevin transducer.

The transducers produced by Bindicator of the United States, the WSS series of level transducers of Sense of Germany, and the XTC/XPS series of level transducers of Milltronics of Canada also adopt a sandwich structure. As a distance measuring sensor, the working frequency of the sandwich transducer is generally between 15khz and 60 kHz, and the peak-to-peak value of the pulse voltage for exciting the piezoelectric vibrator is usually 3200 V, and a good acoustic matching layer is attached to the radiation surface. Such transducers are capable of producing  high acoustic energy. The sandwich transducer is bulky and costly, and consumes a lot of power, but it is suitable to use in the situations where high power or large thrust is required.