APPLICATION OF PHASED ARRAYS IN COMBINATION WITH VIRTUAL DYNAMIC FOCUSING FOR ULTRASONIC TOMOGRAPHIC IMAGING OF METALS

摘要

The traditional phased antenna arrays operation principle is in forming the signals based on so-called focal laws, which is the set of parameters, defining the elements of array to be fired,time delays and others for both transmitting and receiving, herewith the ultrasonic beam is focused in different directions. The beam can be focused not only by the set angle, but also on the set depth. The availability of several focusing modes provides flexibility in work, but makes the setup of the system more difficult and demanding the qualified operator. But as the practice showed the focusing of the beam should not be necessarily made right before the sending of ultrasonic signal. The so-called Virtual Dynamic Focusing is available as an alternative, where each pair of elements of phased array sends and receives signals independently from others. Received and digitized signals of all possible pairs of elements are saved and then summarized for imaging the internal structure of testing object. At that the independent focusing in every point of received image is achieved, meaning focusing in every point of testing object. This increases the number of calculations during the testing process, but significantly improves the imaging of defects in a wider range of angles and depths. The paper detailed describes the operation of ultrasonic high-frequency tomographer for metals A1550 IntroVisor, developed by Acoustic Control Systems Ltd., Russia, which implements the algorithm of Virtual Dynamic Focusing. The up-to-date hardware microchip FPGA and optimized calculations allows quality on-line imaging of internal structure of testing object while scanning with image update rate not less then 25 times per second, which is the maximal frequency perceived by human eyes. The virtual focusing allows testing objects with less information about presumable depth and position of detects. It also significantly simplifies the use of the device, as no setup of different focal laws and other complex parameters is necessary, this way the device is user-friendly for every operator without any special training on operation. The paper contains also the results received with the tomographer A1550 IntroVisor on different objects, images of defects both artificial and natural by origin, specification and features of the tomographer A1550 IntroVisor, possible variants of antenna arrays, applicable for operation with the tomographer, their structure, distinctive features and application areas.