Christer Ullberg

Our interviewee this month is Christer Ullberg of Direct Conversion, a Swedish company specialising in X-ray detection…

Describe your current role
I am the Chief Technical Officer for Direct Conversion, which develops and manufactures photon-counting X-ray imaging detectors for use in NDE. I am responsible for the development of the new technologies that we will add to our product portfolio. A vital part of my job is listening to our customers in industry and then working on how to incorporate their particular needs and wishes into the creation of new types of detector. I also explore the potential of different converter materials for the detectors and I lead new sensor and application-specific integrated circuit (ASIC) designs. An ASIC is a microchip that has been designed for a specific rather than general purpose. At the moment, I am working on a four-side buttable ASIC, which means the chip can be attached to another chip using any of its four sides, rather than only three sides, as was previously the case. This breakthrough will allow the construction of detectors of much greater area and varied shapes.

What education or training route did you follow?
I had always been interested in electronics and was working in the field for several years before deciding to study the subject at the KTH Royal Institute of Technology in Stockholm.

What other roles and jobs have you had in the past?
I was a competitive cross-country skier at high school in Sweden and during that time I set up and ran a small company that developed hand-held computer timing devices for skiers. However, my career in testing began at Sweden’s national test house for product safety and there I tested according to national and international standards for electrical safety. I then moved into designing electronics and subsystems for satellites and high-altitude balloons at Aviation Capacity Resources AB (ACR AB). Obviously, the extreme conditions of space meant I was working to exceptionally rigorous quality requirements. One of the main challenges was to design in redundancy and identify suitable components for this unique environment. My next move was to XCounter, which has since evolved into Direct Conversion, as its second employee, working out of a single room at the university, and that is where I became intrigued by photon counting and the possibilities it offered for X-ray imaging. The idea of detecting every single X-ray photon was really fascinating in itself but also because, by doing so, we can see detailed information that has never been visible before.

What would you consider to be your biggest NDE achievements and challenges to date?
I think one of my most significant successes has been the development of the ASIC that is used in our detectors. This small piece of silicon carries an intense concentration of electrical functions and was developed to detect very small signals for X-ray. The ASIC makes it possible to carry out X-ray material discrimination at high spatial resolution with a single-shot exposure. Probably one of the biggest challenges I have faced is in identifying and sourcing good converter materials for our photon-counting products. While this is now a mature process, the path to this point has been a pretty long one with lots of iterations.

What do you think are the pressing challenges for the NDE industry?
With the introduction of new materials, such as carbon-fibre parts in complex shapes or high-power electronics modules, comes the need for new methods of non-destructive evaluation. In many areas of industry, faster throughput is always desirable and we need to stay focused on this.

What changes, if any, do you foresee for NDE in the future?
Looking ahead, I think we will see inspection techniques becoming increasingly sensitive to even smaller defects. As we continue to achieve faster throughput, we will see far greater volumes of items inspected and the results documented.

How would you describe NDE to someone who has not heard of it before?
Non-destructive evaluation is used to describe measurements that are quantitative in nature. For example, a non-destructive evaluation method would not only locate a defect, but it would also be used to measure something about that defect, such as its size, shape and orientation. This is in contrast to the broader non-destructive testing, which may not be quantitative.

Please get in touch if you have any recommendations for future interviewees or would like to be interviewed yourself. Contact the editor at ndtnews@bindt.org or email Maria Felice direct at  mvfelice@gmail.com

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