Real Implementation of Ultrasonic Phased Array Technology Using Advanced Signal Processing Algorithms

Over the past few years, the improvement in the field of ultrasonic non-destructive testing has led to significant advances in ultrasonic signal processing and image construction techniques. Many techniques have been proposed to improve the flaw and crack detection processes. In general, these techniques can be divided into two main parts. As first, many proposals have been focused on construction of ultrasonic transducers and systems. The second part is mainly focused on proposal of efficient signal processing algorithms that improve sensitivity (noise reduction) during ultrasonic signal acquisition. This paper combine both parts. We present our developed ultrasonic portable system with implemented phased array technology. All acquired ultrasonic signals using commercial phased array transducer are consequently processed using our proposed filtering algorithms. These algorithms are necessary to obtain unambiguous information about detected flaws and cracks. The detected flaws can be than easily visualize. For material bulk visualization we use phased array technology. Introduction – Ultrasonic Non-destructive testing Ultrasonic non-destructive testing (UT) is commonly used for flaw detection in materials. Ultrasound uses the transmission of high-frequency sound waves in a material to detect a discontinuity or to locate changes in material properties [1]. Ultrasonic wave propagation in tested materials is essentially influenced by the tested material structure. In general, due to material structure the acquired ultrasonic signal can be corrupted with relatively high noise level, commonly called backscattering noise. In present, the most desired task is to detect the fault echo in ultrasonic signal; it means to locate the cracks or defects in tested materials. The flaw detection efficiency is mainly influenced by the noise level and on this account the efficient signal processing techniques used for noise reduction are proposed. As all acquired signals are processed with our implemented signal processing methods than all signals are reconstructed to create flaw visualization using phased array technology. Ultrasonic portable system with implemented phased array technology During the last two years, we have been developing a completely new ultrasonic non-destructive testing portable instrument. The main goal was to develop the highly robustness ultrasonic portable instrument including conventional ultrasonic testing [1], EMAT testing [2, 3] and testing based on phased array ultrasonic technology [3]. All these non-destructive methods were successfully implemented into one device called “DEFECTOBOOK DIO1000’. Except implemented ultrasonic non-destructive testing methods we were focused on proposal of efficient signal processing algorithms that contribute for flaw detection and efficiently suppress noise. Conventional ultrasonic testing and EMAT testing have been already implemented in DIO2000 system three years ago. The main objective of our new instrument was to have implemented phased array technology as well. This makes our system universal in many industrial applications. Our phased array technology is based on transmitting of ultrasonic waves from all elements simultaneously and consequently receiving of all reflected signals back to phased array transducer. For our experiments we use commercial phased array transducer including sixteen elements. As we are still in developing stage, we plan to implement sampling phased array technology [5] based on gradual transition of each element with consequent receiving using all elements. Fig. 1. Ultrasonic portable instrument DEFECTOBOOK DIO1000 All mentioned non-destructive testing methods were implemented based on previous research. First of all, we have implemented conventional ultrasonic method and EMAT testing method. As all acquired ultrasonic signals are corrupted with relatively higher noise level, methods used for effective noise reduction were searched. During the research we have tested many algorithms used for noise reduction but the main goal was to find efficient noise reduction and simple methods that could be easily implemented as algorithm processing the signals in real time. This goal was successfully achieved and averaging, digital filters and correlation methods were implemented into DIO1000 signal processor. Signal processing algorithms – Averaging and Digital filters Averaging Averaging [6] the ultrasonic signal is a common method of enhancing the signal-to-noise (S/N) ratio. This method slows down data acquisition, because the pulse repetition rate of ultrasonic instruments is orders of magnitudes slower than the processing time needed to perform averaging. In general, many (e.g. 64) signals are acquired and these are averaged over all signals. The main advantage of averaging is that this method is relatively easier to implement. On the other hand, the main disadvantage is that number of acquired signals and consequent averaging of these signals essentially makes the processing time much higher. But, of course with used digital signal processor it can be used for real time application. On the following Fig. 2, there can be seen the example of using averaging by 64 acquired signals. The acquired signal (see Fig. 2a) is corrupted with relatively higher effective noise level amplitude. By using averaging (see Fig. 2b) of 64 signals, both flaw echo and back-wall echo are easily visible. 0 5 10 -1 -0.5 0 0.5 1