X-ray detectors

X-ray technology is very important for non-destructive material testing. Decisive for the performance of this inspection technology is the X-ray detector or the X-ray image. Based on the X-ray image, decisions are made about the object to be inspected either by humans themselves or based on image processing algorithms or AI. Whereas in the past X-ray film or image intensifiers were used in the first place as imaging elements, digital X-ray detectors are now mostly used in both the medical and industrial sectors.

Since the detectors are exposed to X-ray radiation during image acquisition, high radiation stability of the detectors is crucial for good and consistent image quality. In 24/7 industrial operation, image intensifiers, flat panel detectors and conventional line scan cameras are irreversibly damaged after a short period of use due to the high radiation energy and must be replaced. The X-ray radiation is not completely absorbed by the scintillator and damages the semiconductor directly behind it. Scattered radiation from the object and the detector housing itself also hits and damages the readout electronics at the side of the active, imaging semiconductor. This is noticeable, among other things, by pixel and column defects, the failure of individual pixels or entire columns and rows of the detector.

The XEye X-ray detectors developed at the Fraunhofer Development Center X-ray Technology EZRT ensure reliable results in industrial X-ray inspection for years to come. Tracking image processing parameters for automatic defect detection is no longer necessary due to the stable image quality.

Fraunhofer EZRT has been working for more than twenty years on the development of X-ray detectors that provide constant image quality comparable to that of flat panel detectors, even at high X-ray energies. The principle of XEye X-ray detectors is based on the digital recording of a scintillator (luminescent foil), which - excited by X-rays - emits visible light. Several optical cameras capture overlapping sections of the scintillator, and the individual images are then seamlessly merged to form an overall image. The patented radiation protection concept, which shields all electronic and optical components from X-ray radiation up to currently 450 kV tube voltage, ensures a long service life and consistently high image quality of the XEye X-ray detectors.

In addition to the advantages listed, the strength of XEye technology lies in its flexibility. Up to now, XEye detectors have mainly been used in classical X-ray systems for NDT in combination with industrial X-ray sources with max. 2 KW tube power and X-ray energies up to typically 225 to 450 keV. Due to the basic principle of XEye, the optical imaging of a scintillator, XEye X-ray detectors can also be used for systems where linear accelerators or a synchrotron serve as radiation source. Of course, the internal design, i.e. the optical light path and the shielding of XEye detectors for energies up to "only" 450 keV differ here.

Another variant of the XEye technology is the use of high-speed image sensors. This allows the development of both large and high-resolution X-ray detectors with an imaging frequency of up to 4 kHz, for example, which are capable of recording fast and dynamic processes in a time-resolved manner. Depending on the design, these XEye high-speed cameras can be operated with normal industrial X-ray sources as well as with linear accelerators or a synchrotron. Due to the extremely high data rate, the image data cannot be transferred step-by-step to a PC and evaluated. Therefore, these detectors are not suitable for 24/7 operation, but are designed for individual experiments and test series. However, the use of XEye technology ensures sufficient radiation protection.

XEye X-ray cameras are successfully used in a wide range of industrial applications, such as the inspection of longitudinal welds on steel pipes. For more than eight years, the detectors have been capturing X-ray images around the clock without any change in image quality. In the automotive industry, XEye detectors are used for reliable inspection of, for example, chassis castings and wheels in the production cycle. XEye detectors are also used in various CT systems such as CT of engine pistons in the manufacturing cycle or CT for phenotyping of plants. Other areas of use include inspection of electronic assemblies, detection of foreign objects in food, or counting SMT components on coils.