Talking about Flat-Panel Detector's Resolution
August 23, 2021 | Christian Jeuschede
When we look for the optimal flat-panel detector, it’s not all about the highest possible resolution. Christian Jeuschede explains why we still stick to 139 µm respectively 150 µm pixel pitch instead of 100 µm and what to have in mind when chosing the best fit.
When we look for the optimal flat-panel detector, it’s not all about the highest possible resolution. With our high-energy and high-resolution computed tomography system YXLON FF85 CT, we offer two different detector arrays. And I want to show you why they are the best fit for your applications and why we still stick to 139 µm respectively 150 µm pixel pitch instead of 100 µm.
According to your requirements, you have the choice:
The detector 4343HE is our high-energy version which, due to its electronics at the side and the fact that it’s fully shielded, can be used with up to 600 kV. The pixel pitch is 139 µm, the pixel matrix is 3072 x 3072. It has a frame rate of four frames per second in full resolution and 15 frames per second in the binning mode. The active area is approx. 43 x 43 cm.
The detector 4343N has the same technique as the 4343CT detector used with the YXLON FF35 CT and the YXLON FF20 CT systems. The pixel pitch is 150 µm, the pixel matrix is 2880 x 2880. The great advantage of 4343N is that the electronics are much more sensitive and linear, and the frame rate is much higher; 15 frames per second in full resolution compared to the four frames of 4343HE what means that it is much faster. Due to the internal shielding, it is currently only available for up to 450 kV.
For our common understanding:
Pixel Pitch is the distance from the mid-point of one pixel to the mid-point of his neighbor pixel. The smaller the distance, the higher is the resolution of the pictures achieved.
The Pixel Matrix means the arrangement and the number of pixels the detector contains. The more pixels I have the higher is the resolution.
When you use the Binning Mode, pixels merge into pixel blocks of 2 by 2. This method leads to a better signal-to-noise ratio, a faster frame rate, and a decrease in the data volume. Consequently, this means a reduced resolution. The frames are the single images taken by the detector. Thus, the more frames you acquire per second, the faster the detector and the CT system works.
Let us do some calculations:
In former CT systems, detectors with a pixel pitch of 200 µm, were used and nobody can deny that the 200 µm pitch resolution is not sufficient anymore for today's requirements. Many people nowadays ask for a resolution of 100 µm in a 400 mm x 400 mm detector. However, we are convinced that 139 µm and 150 µm are currently the optimal resolutions for CT users’ inspection and post-processing tasks.
Please have a look:
The file of a single CT-scan of e. g. a piston with a 200 µm pixel pitch detector and a pixel matrix of 2048 x 2048 has a size of 16 GB. If we go down to a pixel pitch of 150 µm, we already have a 46 GB CT file size with a 2880 x 2880 pixel matrix. The 100 µm detector and 4096 x 4096 pixels have a CT file size of 134 GB.
Assume that we are working with a PC with 512 GB RAM, which is already quite powerful. If you now need a horizontal scan-field extension (because of a large inspection part), the file size with a 200 µm detector increases to 107 GB, with a 150 µm pixel pitch detector, we have 307 GB scan data, and with 100 µm, we already have a CT file size of 857 GB. That means, with a PC configuration of 512 GB, a simple horizontal scan-field extension is not possible anymore using a 100 µm detector with 4096 x 4096 pixels. Depending on the reconstruction algorithm, the data could perhaps get reconstructed but there is neither a chance to open it in full resolution nor doing any analysis like defect detections, etc. The data size with a simple scan-field extension is too big with a 100 µm detector. To avoid these problems when using a 100 µm detector and a scan-field extension, you could use the binning mode. But then you would have a 200 µm pixel pitch which was state of the art more than 10 years ago.
If we additionally needed a 2-times vertical scan-field extension, the file size would result in 214 GB with a 200 µm detector, 614 GB with a 150 µm detector, and 1.7 TB with a 100 µm one. Even with a PC with 1 TB of memory (1024 GB RAM), there was no way to open it or perform a defect detection with VGSTUDIO MAX, etc. And a three-times scan-field extension would result in approx. 2.5 TB with a 100 µm pixel pitch detector. It‘s a no-show for a scan-field extension or, in general, to inspect large parts with full resolution.
With a memory of 1024 GB RAM, it becomes apparent that the pixel pitch of 139 µm or 150 µm is the optimal resolution to work with because all scan-field extensions are still possible, and you use the full resolution of your CT system.
Automotive cast part with porosity
-> Visit YXLON UX20
Lithium-ion battery (LIB), ROI scan
-> Visit our blog post
' The New Challenges in Quality Control'
Cast rotor showing porosity, courtesy Fraunhofer IFAM
-> Visit our blog post 'A Look into the Hidden'
3D-printed hip cup, courtesy AMPower
-> Visit our landing page 'Additive Manufacturing'
Car headlight -> Visit YXLON FF85 CT
Airbag cover -> Visit YXLON FF35 CT
When you intend to purchase a CT system and evaluate which detector array fits your requirements best, it is not always the highest resolution you need. Put in mind that all features of your CT system should work together in the most variable way in order to achieve optimum results of all your inspection parts.
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