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•Overcoming the diffraction limit in a direct terahertz imaging system in transmission mode.•An entirely new use of the Terajet effect for resolution enhancement of terahertz ...imaging.•Experimental demonstration of the feasibility of overcoming the diffraction limit.•A special pinhole structure was designated and characterised to validate results.
We report on resolution enhancement of sub-terahertz (THz) images by using the terajet effect. A mesoscale cuboid dielectric particle, used to establish the terajet, was placed in front of an object located at the focus of the THz beam. The object under study was based on a printed circuit board (PCB) perforated with different holes with diameters ranging from 1.8 to 3.0 mm and separated from each other by a distance that varies from 0.25 to 4 mm. The sample was illuminated by a continuous wave source at a frequency of 0.3 THz and the image was obtained using a sensor based on a strained-Si Field-Effect Transistor. The image was formed pixel-by-pixel in a transmission mode configuration. A clearer image with enhanced resolution was obtained when the mesoscale cube was introduced in the optical path. The terajet effect made possible to resolve a separation between holes of around 0.5 mm (lower than the wavelength, 1 mm), that is, below the diffraction limit. The method described is easy to implement, cost effective and could be used to improve the resolution of any real imaging system.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper, we propose a computational approach for description of radiation transfer in a quasi-ordered medium and study the impact of scattering on electromagnetic wave propagation and image ...formation. It combines finite-difference time-domain method, Monte Carlo simulations, and radiative transfer theory. Using, as an example, terahertz (THz) imaging, we analyze the modulation transfer function (MTF) of the imaging system operated at 0.25 THz for scattering material layers placed between the object and the imaging plane. We experimentally study imaging of bar-pattern test objects through a quasi-ordered scattering medium. Both numerical and experimental results are in good agreement and demonstrate an impact of quasi-ordered scatterers on quality of THz images, i.e., particular combination of the electromagnetic wavelength and parameters of scattering materials could enhance MTF compared with ones with random particle structures.
Terahertz (THz) imaging and spectroscopy set-ups require fine optical alignment or precise control of spatial mode profile. We demonstrate universal, convenient and easy-to-use imaging—resonant and ...broadband antenna coupled ultrasensitive titanium-based—dedicated to accurately adjust and control spatial mode profiles without additional focusing optical components of weak power THz sources. Versatile operation of the devices is shown using different kinds of THz—electronic multiplier sources, optical THz mixer-based frequency domain and femtosecond optoelectronic THz time-domain spectrometers as well as optically pumped molecular THz laser. Features of the microbolometers within 0.15–0.6 THz range are exposed and discussed, their ability to detect spatial mode profiles beyond the antennas resonances, up to 2.52 THz, are explored. Polarization-sensitive mode control possibilities are examined in details. The suitability of the resonant antenna-coupled microbolometers to resolve low-absorbing objects at 0.3 THz is revealed via direct, dark field and phase contrast imaging techniques as well.
Terahertz Image Restoration Benchmarking Dataset Zhang, Yixiong; Su, Zhipeng; Qi, Feng ...
ICASSP 2022 - 2022 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP),
2022-May-23
Conference Proceeding
The paper introduces a new terahertz (THz) image benchmarking dataset for THz imaging. The degradation of THz image quality is one of the main problems caused by system noise, intrinsic ...long-wavelength, and diffraction phenomena. In this paper, the point spread function of the THz imaging process is reconstructed firstly. The THz datasets with ground-truth and degraded images are then synthesized using the point spread function (PSF). We propose a Dense Instantiation Normalization Block (DIN Block) to reconstruct clean THz images. Based on the DIN block, a powerful multi-stage network is designed, named as DINet. DINet achieves the state-of-the-art (SOTA) restoration performance on image rain removal datasets and the proposed THz datasets. To the best of our knowledge, the THz image benchmarking dataset is the first public dataset, which is available at https://github.com/hellogry/THzDatasets
A subsurface imaging system based on a terahertz time-domain spectrometer (THz-TDS) is described in this paper. The system performance has been simulated in terms of spatial resolution, penetration ...capabilities and SNR. Moreover, a commercial THz-TDS has been used to perform the proof-of-concept of the described system.
Peer Reviewed
Terahertz (THz) imaging has the potential to detect breast tumors during breast-conserving surgery accurately. Over the past decade, many research groups have extensively studied THz imaging and ...spectroscopy techniques for identifying breast tumors. This manuscript presents the recent development of THz imaging techniques for breast cancer detection. The dielectric properties of breast tissues in the THz range, THz imaging and spectroscopy systems, THz radiation sources, and THz breast imaging studies are discussed. In addition, numerous chemometrics methods applied to improve THz image resolution and data collection processing are summarized. Finally, challenges and future research directions of THz breast imaging are presented.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A single dielectric resonator antenna (DRA) capable of enhancing the antenna gain of each element of a <inline-formula> <tex-math notation="LaTeX">2\times 2 </tex-math></inline-formula> terahertz ...(THz) antenna array realized in a 0.18-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> CMOS technology is proposed in this paper. The DRA implemented in a low-cost integrated-passive-device technology is flip-chip packaged onto the CMOS antenna array chip through low-loss gold bumps. By designing the DRA to work at the higher order mode of TE<inline-formula> <tex-math notation="LaTeX">_{3,\delta,9} </tex-math></inline-formula>, only a single DRA, instead of conventionally needing four DRAs, is required to simultaneously improve the antenna gain of each element of the <inline-formula> <tex-math notation="LaTeX">2\times 2 </tex-math></inline-formula> antenna array. This not only simplifies the assembly process, but it can also reduce the assembly cost. Moreover, the DRA can provide great antenna gain enhancement because of being made of high-resistivity silicon material and higher order mode operation. The simulated antenna gain of each on-chip patch antenna of the <inline-formula> <tex-math notation="LaTeX">2\times 2 </tex-math></inline-formula> CMOS antenna array can be increased from 0.1 to 8.6 dBi at 339 GHz as the DRA is added. To characterize the proposed DRA, four identical power detectors (PDs) are designed and integrated with each element of the <inline-formula> <tex-math notation="LaTeX">2\times 2 </tex-math></inline-formula> THz antenna array. By measuring the voltage responsivity of each PD output, the characteristics of each antenna of the antenna array with the proposed DRA, including the gain enhancement level and radiation pattern, can be acquired. The measurement results match well with the simulated ones, verifying the proposed DRA operation principle. The four PDs with the proposed DRA are also successfully employed to demonstrate a THz imaging system at 340 GHz. To the best of our knowledge, the proposed DRA is the one with the highest order operation mode at THz frequencies reported thus far.
This paper presents a hybrid device for real-time measurement and imaging of solid and liquid contaminants that may occur in steam generators. The device uses a dedicated Near Infra-Red device to ...determine the type of contaminants and a THz imaging system which measures the amount of contaminants as well as its flow rate. The NIR device can also determine the concentration of contaminants at sub-mg accuracy when its value is relatively low using spectrometry technique combined with principal component analysis (PCA). In case of relatively high concentration, the THz imaging system which uses block-based motion estimation algorithm can determine the velocity of individual contaminant particles to compute the global motion vector, the intensity and direction of which represents the overall flow rate and flow regime of the contaminants. The usage of image processing techniques together with NIR spectrometry constitutes a new promising step in flow metering. This is demonstrated by the extensive experiments which have been conducted for different scenario where the NIR subsystem system could determine the concentration of water droplets and solid contaminants with a maximum uncertainty of +/- 1.45% and +/- 1.16% respectively.
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