ISSN 1061-8309, Russian Journal of Nondestructive Testing, 2012, Vol. 48, No. 10, pp. 609–613. © Pleiades Publishing, Ltd., 2012. 609 1 1. INTRODUCTION Ultrasonic straight beam pulse-echo tests are widely used for many applications such as the inspection of cast work pieces, forged work pieces and plates, as well as thickness measurements of pipelines, tubes and storage tanks. The ultrasound pulse is sent to the target material and the time-of-flight (TOF) between the sent pulse and the reflected echo is measured, from which the results can be drawn based on the ultra- sonic velocity in the material, to give information about the presence of defects or about the material’s thickness. Time resolution issue needs to be resolved when the material is thin or the distance between the defects is small. Furthermore, ultrasonic inspection of a material with parallel surfaces produces multiple reflec- tion of the backwall at regular intervals due to the travel of the ultrasonic wave back and forth within the specimen. The multiple reflections of the closely-spaced interfaces affect the quality of result presenta- tion. Many deconvolution techniques that have been investigated for resolution enhancement in ultrasonic applications are effective [1] and [2]. Tong feng et al. used the conventional least-mean-squares (LMS) adaptive filter due to its effectiveness, low computational complexity, and simplicity in resolving the tem- poral degradation caused by the narrow bandwidth of the transducer in ultrasonic nondestructive inspec- tion [3]. Real-time deconvolution of ultrasonic signals in scattering media, called multi-pattern adaptive deconvolution, which based on taking several reference signals from different depths, was proposed [4]. The computational cost of digital signal processing algorithms for ultrasonic NDT instruments is often complex. The sign LMS algorithms were initially developed to simplify the computational requirements of the adaptive LMS. In this paper, we suggest the use of sign LMS algorithms, namely, sign LMS, sign- data and sign-sign for signal processing in ultrasonic straight beam pulse-echo applications due to their simplicity and computational efficiency. They will carry out a specific deconvolution technique to improve resolution and to obtain quality-enriched presentations by extracting only two echoes of the interface multiple reflections. This process is called “selective deconvolution”. 1 The article is published in the original. Sign Least Mean Squares-Based Deconvolution Technique for Ultrasonic Testing 1 M. S. Mohammed and Kim Ki-Seong* Department of Mechanical Design Engineering, Chonnam National University, Yeosu 550-749, Korea e-mail: msiddeq@gmail.com, *e-mail: sngkim@chonnam.ac.kr Received August 8, 2011 Abstract—Sign LMS algorithms, members of the simplified adaptive least-mean-squares class, have been developed to reduce computational complexity and simplify hardware implementation. These advantages make them suitable to utilize in ultrasonic testing units, a class of applications requiring simple and efficient signal processing algorithms. This paper proposes a specific sign LMS adaptive fil- ters-based deconvolution technique for ultrasonic straight beam pulse-echo inspections. It extracts only two of the interface echoes multiple reflections for enhanced resolution and quality-enriched presentation; this technique is named “selective deconvolution”. Resolution enhancement and pre- sentation’s quality enrichment performance among the different sign LMS algorithms were investi- gated by experiments, and based on performance, the methods themselves were compared. Computa- tional requirements are also presented. The proposed technique with the various adaptive sign LMS filters gave satisfactory results. Keywords: adaptive LMS, sign LMS, resolution, selective deconvolution DOI: 10.1134/S1061830912100075 ACOUSTIC METHODS