Becker Photonik (Germany)

Terahertz tomography allows for reliable non-destructive 3D inspection of plastic components at high resolution. The tomographic inspection from different projection angles avoids failure to detect details, which, in the case of one-sided inspection, would be obstructed by other features. The price to pay for this detailed imaging is long acquisition times for the tomographic data. To speed up the process of tomography imaging in the terahertz range, we demonstrate multi-channel setups for acquiring tomographic data utilizing arrays operating at around 70 and 300 GHz. The presented systems allow for an increase in measurement speed by at least a factor of eight up to several orders of magnitude.

Terahertz tomography is a non-contact inspection technique to image objects from multiple angles and reconstruct their 3D volume from intensity and time-of-flight transmission data, without the need for radiation protection measures. Unlike X-rays, terahertz radiation is subject to strong diffraction and refraction when propagating through dielectric materials, which often deteriorate the image reconstruction quality. Our solution to this problem applies ray tracing, considering the beam shape and an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$a$ </tex-math></inline-formula> priori model of the sample under investigation to predict the beam paths of the terahertz radiation. We present two reconstruction methods based on the resulting beam path predictions yielding higher image quality. Method 1 filters out beams deviating strongly, thus removing induced artifacts and errors from the reconstruction image. Method 2 employs off-axis measurements that acquire data along the full detection plane and in this way detect even strongly deflected beams. Considering these beams and the information they carry in the reconstruction enhances the image quality. Applying these methods to terahertz tomography, even complicated structures can be imaged. We display the significant enhancements achieved with the two methods by comparing the reconstruction results of different polymeric samples.

&lt;p&gt;Terahertz tomography is a non-contact inspection technique to image objects from multiple angles and reconstruct their 3D volume from intensity and time-of-flight transmission data, without the need for radiation protection measures. Unlike X-rays, terahertz radiation is subject to strong diffraction and refraction as it propagates through dielectric materials, which can deteriorate the image reconstruction quality. Our solution to this problem applies ray tracing, considering the beam shape and an &lt;em&gt;a priori&lt;/em&gt; model of the SUT to obtain high-quality image data. We present two reconstruction methods based on the resulting beam path predictions. Method 1 filters out strongly deviated beams, and thus removes the induced artifacts and errors from the reconstruction image. Method 2 employs off-axis measurements, acquiring data along the whole detection plane and this way detecting even strongly deviated beams. Considering these beams and the information they carry in the reconstruction enhances the image quality. Applying these methods to terahertz tomography, even complicated structures can be imaged, provided their feature size is above the diffraction limit. We display the significant enhancements achieved with the two methods by comparing the reconstruction results of different polymeric samples. &lt;/p&gt;

An active handheld millimeter wave imaging device for non-destructive testing has been developed. The system operates from 70 to 80 GHz and provides real-time imaging capabilities with depth information. The imaging concept is based on the effective aperture approach in combination with a sparse two-dimensional array of transmit and receive antennas. The system is designed to contain the antenna array, a signal-multiplexing-unit, FPGA-data-acquisition and signal synthesizers as well as a display for visualization in a single handheld enclosure. A USB 3.0 connection is used for data transfer to a mobile computer unit with consumer graphics card for parallel processing of the image reconstruction.