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Recent advancements in ultrasonic testing have seen significant strides, with a focus on improving inspection speed, sensitivity, and data management. Advanced nondestructive equipment manufacturers have been at the forefront of these developments, introducing plane wave imaging as part of their commitment to revolutionizing nondestructive testing techniques. In this article, we explore the principles, applications, and benefits of plane wave imaging, shedding light on its role in shaping the landscape of ultrasonic inspections.

Introduction to Plane Wave Imaging

Plane wave imaging represents a groundbreaking approach within the realm of phased array ultrasonic testing, specifically designed to enhance the capabilities of the total focusing method. The total focusing method technique, incorporated into the American Society of Mechanical Engineers, or ASME, codes in 2019, offers high-resolution imaging, but challenges arise in terms of productivity and data size. Advanced nondestructive testing equipment providers recognized these challenges and introduced plane wave imaging as a solution.

At its core, plane wave imaging combines the efficiency of a sectorial scan commonly used in phased array ultrasonic testing with the spatial resolution prowess of total focusing method. This amalgamation addresses the need for improved inspection speeds and enhanced sensitivity, particularly crucial for applications involving high attenuation like the one encountered in High Density Polyethylene (HDPE) piping, thick components, stainless steel welds, or large scattering for High Temperature Hydrogen Attack (HTHA).

The Challenge of Assessing the Integrity of Complex Materials

Inspecting equipment and materials that lead to high attenuation of the ultrasound presents a unique set of challenges. Attenuation can come from the material itself, such as viscoelasticity from HDPE, large thicknesses, larger grains, or defects that generate a lot of scattering like HTHA. No matter what the source of the attenuation is, it leads to poorer signal-to-noise ratio, which is even worse when the application requires looking for small defects.

Advanced Focusing Techniques as a Solution

OEMs have addressed these challenges by employing advanced focusing techniques in phased array ultrasonic testing inspections. Full matrix capture and total focusing method are integral components of these techniques.

Full matrix capture involves capturing A-scan signals from every transmitter-receiver pair in an array, allowing for the generation of ultrasonic images with advanced focusing techniques. On the other hand, plane wave imaging stands out as an alternative firing technique. Plane wave imaging uses a large aperture for pulsing and performs a sectorial scan to insonify volume of the component with individual reception from each element. This method provides benefits such as higher sensitivity, better signal-to-noise ratio, or SNR, and increased scanning speed.

HTHA indications imaged with full matrix capture and plane wave imaging.
HTHA indications imaged with full matrix capture and plane wave imaging. Image Source: Eddyfi Technologies

Advantages of Plane Wave Imaging

Plane wave imaging data acquisition offers several advantages compared to traditional full matrix capture methods. The emitted pulse from the full aperture in plane wave imaging has more energy leading to greater sensitivity and improved signal-to-noise ratio at higher scanning speeds. The technique’s firing sequence is significantly shorter than full matrix capture, resulting in a two-to-four times higher acquisition rate, enabling quicker inspection speeds. Operators can choose to use more or less angles during the excitation process to favor either the sensitivity or productivity giving added flexibility.

Effective Phased Array Inspection Techniques

When dealing with attenuative materials, the choice of the phased array probe is key. For attenuation caused by viscoelasticity or large thicknesses, phased array probes with a lower frequency and larger pitch are recommended. For dissimilar metal welds, especially those involving austenitic materials, dual linear or 2D matrix arrays is recommended. For high temperature hydrogen attack applications, probes with better focusing on the passive plane lead to improved sensitivity.

There are commercially available phased array ultrasonic testing instruments designed as a compact solution that incorporates advanced methods such as plane wave imaging and total focusing method. These instruments stand out for their exceptional signal quality, enabling high amplification without signal distortion. The real-time multi-total focusing method processing onboard, combined with full matrix capture and plane wave imaging data acquisition features, positions these systems as a leader for inspections of attenuative materials.

Topaz portable and Emerald desktop date acquisition instruments
Portable and desktop data acquisition instruments offer plane wave imaging. Image Source: Eddyfi Technologies

Benefits of Plane Wave Imaging and Total Focusing Method Integration

The integration of plane wave imaging with total focusing method provides a host of benefits, including improved flaw detection and characterization, increased inspection coverage, enhanced speed, and superior data quality for informed decision-making. Plane wave imaging surpasses traditional methods in terms of speed, delivering comparable resolution, coverage, and capabilities to traditional full matrix capture firing and standard phased array ultrasonic testing. This not only saves inspection time but also ensures that high-resolution images, a hallmark of total focusing methods, are maintained.

Plane Wave Imaging offers big improvement in productivity
Plane wave imaging offers the same spatial resolution as total focusing method with a big improvement in productivity. Image Source: Eddyfi Technologies

Maintaining the right parameters, especially in terms of frequency and wave mode, remains crucial for success in many inspections of attenuative materials. Dedicated probes are often required for these inspections, emphasizing the importance of selecting the right equipment and techniques.

Post-Processing Capabilities and Data Management

In the ever-evolving landscape of nondestructive testing, the ability to handle data efficiently is paramount. Advanced nondestructive evaluation solution providers have implemented innovative solutions to address this aspect, notably with the introduction of plane wave imaging and its integration with total focusing method techniques. The post-processing capabilities of plane wave imaging data further contribute to its appeal. The ability to change the position and size of the total focusing method image after acquisition, adjust the number of pixels, calculate different modes, change thickness or geometry, and alter material properties demonstrates the flexibility plane wave imaging provides to inspectors. While it is possible to record full matrix capture elementary data for post-processing, the amount of data becomes quickly prohibitive. As plane wave imaging uses less excitations it also generates less elementary data making it easier to manage. The capability to save elementary data, while managing data file sizes effectively, opens avenues for detailed analysis and modification of inspection parameters.


In conclusion, plane wave imaging has emerged as a pivotal technology in the field of ultrasonic testing, specifically within the realm of phased array ultrasonic testing and total focusing method. Advanced inspection technology equipment providers’ commitment to innovation and pushing the boundaries of inspection capabilities is evident in the development and integration of plane wave imaging with total focusing method techniques.

The advantages offered by plane wave imaging, such as enhanced sensitivity, improved signal-to-noise ratio, and higher inspection speeds, make it a valuable addition to the arsenal of inspection tools. The real-time imaging capabilities, coupled with efficient data management and post-processing features, position plane wave imaging as a game-changer in the inspection of attenuative materials such stainless steel and dissimilar metal welds, thick components, viscoelastic materials, and diffusing defects.

As industries continue to demand higher standards of inspection for safety and quality assurance, technologies like plane wave imaging pave the way for more efficient, reliable, and accurate nondestructive testing methods. The journey of plane wave imaging from concept to application underscores the dynamic nature of the nondestructive testing landscape and the importance of continuous innovation in ensuring the integrity of critical components across various industries.