Remote, 3D ultrasonic imaging in extreme environments using 2D laser induced phased arrays

The application of "phased array ultrasonics" has had a profound impact on science and medicine. It is the technology at the heart of all medical ultrasonic imaging systems and sonars. This proposal brings the equivalent of phased array technology to laser ultrasonics for remote, volumetric, 3D ultrasonic imaging.

In laser ultrasonics the sound is generated through the rapid thermal heating and expansion of the material under test, due to the incident laser radiation. However, there are serious signal-to-noise limitations associated with this technique, which could be addressed using an array configuration just as it happens with conventional, transducer based arrays. Up to now it has been very difficult to perform phased array ultrasonics with lasers because the technology to focus and steer the ultrasonic bulk waves for generation or detection puts severe demands on hardware (multiple lasers for ultrasonic generation or complicated experimental setups) and cost. The proposed work will be based on synthesising the Laser Induced Phased Arrays (LIPAs) in post processing, by first acquiring the Full Matrix and then applying a suitable imaging algorithm (e.g. the Total Focusing Method - TFM). The post processing of the optical based data in LIPAs, keeps the experimental setup simple and cost effective. These remote, couplant-free ultrasonic arrays, made of light, can be applied in extreme environments, for in-line process monitoring or in-service volumetric inspection. The aim of the proposed research is to develop a laser based ultrasonic measurement capability for remote, nondestructive, quantitative evaluation and 3D ultrasonic imaging in extreme environments for safety critical applications, where conventional arrays cannot be applied. 2D LIPAs will be able to image a given defect from a range of angles, obtaining characterisation detail far beyond what is achievable with a 1D array.

The core research objectives within this project are:
* Development of laser induced phased arrays for 3D ultrasonic imaging using FMC and TFM.
* Optimisation of the data collection method to laser ultrasonics to improve speed of process.
* Optimisation of the TFM imaging algorithm to laser ultrasonics for efficient ultrasonic imaging.
* Demonstration of system's industrial application potential for inspection and process monitoring in extreme environments.

The success of this work will benefit the non-destructive testing community, the laser ultrasonics community and will enable engineers and material scientists in need of a technique to address extreme environments and places of restricted access, to test the performance of their structures, either during the manufacturing process (e.g. additive manufacturing) or in-service (e.g. in situ inspection of radioactive waste containers). Examples of potential applications include: process understanding and control for manufacturing in extreme environments such as welding and additive manufacturing, increasing process reliability which is crucial for the future of additive manufacturing; in situ ultrasonic inspection in aero-engines or power generators. Other applications are expected in fields such as chemistry, biology and biomedical imaging where remote ultrasonic imaging is needed in sterilised or corrosive environments.

The aim of the proposed research is a laser based ultrasonic measurement capability for remote, non destructive, quantitative evaluation and 3D ultrasonic imaging. These remote, couplant-free ultrasonic arrays, made of light, will be applied in extreme environments, for in-line process monitoring or in-service volumetric inspection of safety critical applications, where conventional arrays cannot be applied.

Such capability is expected to enhance UK's competitiveness in manufacturing, sensing and non-destructive testing (NDT). Advanced materials push the performance limits to extreme environments and can only be used safely if appropriate sensing technologies have been developed. This is why it is expected that the impact from the proposed research will be transformative: it will enable engineers and materials scientists to test the performance of their structures, either during the manufacturing process (e.g. additive manufacturing) or in-service (e.g. in situ inspection of radioactive waste containers), something that is not possible with the existing technology. Just as importantly, reduced usage of resources and safer management of nuclear waste benefit society as a whole and are part of this project's social impact.

The primary beneficiaries of this research are the NDT community, the laser ultrasonics community, engineers and material scientists in need of a technique to address extreme environments and places of restricted access.

The proposed work is anticipated to benefit a broad range of end-users including the additive manufacturing, power generation, aerospace and oil & gas sectors. This is both from enabling general NDT of components as well as process monitoring. A wider impact is expected in fields such as chemistry, biology and biomedical imaging where remote ultrasonic imaging is needed in sterilised or corrosive environments which a remote technique that is able to offer 3D ultrasonic imaging, in extreme environments will be able to address, unlike the currently existing technology.

There will be a Research fellow and a University funded PhD student directly involved in this research. By the end of their respective projects they will have been exposed to a variety of NDT ultrasound techniques, they will be aware of the challenges in the field and will have a multi-disciplinary approach to remote ultrasonic imaging. They will be working in close collaboration with the industry and academic world and it is anticipated that, as they progress with their respective careers they will further influence the field.