Journal of Infrared, Millimeter, and Terahertz Waves最新文献

We present two ideas to simplify the measurement and analysis of terahertz time-domain spectroscopic ellipsometry data of ultrathin films. The measurement is simplified by using a specially designed sample holder with mirrors, which can be mounted on a cryostat. It allows us to perform spectroscopic ellipsometry by simply inserting the holder into a conventional terahertz spectroscopy system for measurements in transmission geometry. The analysis of the obtained data is simplified by considering a single interface with a certain sheet conductivity ({sigma }_{s}) (since the film thickness is significantly smaller than the wavelength of the terahertz light). We demonstrate the application of these ideas by evaluating the sheet conductivities of two perovskite rare-earth nickelate thin films in the temperature range 78–478 K. The use of this particular analytical method and the sample holder design will help to establish terahertz time-domain spectroscopic ellipsometry as a characterization technique for ultrathin films.

Recent developments in communication networks are catering to dynamic requirements as well as providing facilities for future potential applications that are significantly expanded. This necessitates the emergence of mm-wave components that exhibit desirable electrical characteristics, such as compactness, cost efficiency, and minimal manufacturing complexity. Gap waveguide (GW) technology is being considered a potential solution since it provides a promising guiding structure for millimetre-wave applications. This paper presents a novel out-of-phase power divider using the standard waveguide WR-15 interface. The presented power divider is based on a trapped printed gap waveguide (TPGW), which is designed to employ aperture coupling to achieve a stable (180^{circ }) phase imbalance. The power divider and transition have been designed and optimised to minimise the reflection coefficient at the input WR-15 port within the desired frequency range of 50-65 GHz. A deep matching level of beyond (-)20 dB is sufficient to obtain a relative bandwidth of 29% at 60 GHz. A back-to-back model is developed to validate the performance of the proposed power divider configuration and a standard WR-15 waveguide. Furthermore, mathematical analyses are performed to investigate the relationship between the back-to-back model and the individual power divider. A prototype for the proposed power divider through a back-to-back structure is fabricated to validate its performance, and good agreement is achieved between the simulated and measured results.

We provide a comprehensive technical analysis of the data acquisition process with oscillating delay lines for Terahertz-time domain spectroscopy. The utilization of these rapid stages, particularly in high-repetition-rate systems, is known to enable an effective reduction of noise content through averaging. However, caution must be exercised to optimize the data averaging process, with the goal of significantly optimizing the dynamic range (DR) and signal-to-noise ratio (SNR). Here we discuss some pitfalls to avoid and the effect of improper data handling on the dynamic range obtainable. A free and open-source program, called parrot (Processing All Rapidly & Reliably Obtained THz-traces), is provided alongside this publication to overcome the discussed pitfalls and facilitate the acceleration of experimental setups and data analysis, thereby enhancing signal fidelity and reproducibility.

Deep geothermal drilling is a necessary technological stage to produce renewable energy by “enhanced geothermal systems” everywhere. However, the high cost and complexity of deep drilling through hard rock formations is a major barrier to its commercialization. One approach to reach affordability and reduce the cost of deep drilling is to use millimeter-wave (mmw) gyrotron radiation to melt or vaporize rocks. In this paper, the results of an experimental study of mmw radiation absorption by hard rocks are presented. Electromagnetic attenuation and reflection were measured in W-band at frequencies from 75 to 110 GHz in eight rock samples from six different geological formations originated in Israel. The results show that the mmw radiation absorption in hard rocks ranges from 90 to 99% per centimeter. The absorption varies slightly with rock type and is relatively independent of frequency but has reached higher values at the upper W band for all samples. The study suggests that high-power mmw radiation is a promising technology for deep geothermal drilling. The results of this experiment, attenuation, and reflection of W-band radiation in hard rocks provide valuable information for the design and optimization of mmw-based drilling systems, and will support the design and optimization of gyrotron based hard rock drilling equipment for geothermal applications.

This work reports an ultra-low noise, multi-stage stagger-tuned low-noise amplifier (MS-ST-LNA) over the D-band performance and achieves a best trade-off between noise, bandwidth, and gain parameters. The ultra-low-noise is achieved in three ways: First, the high-gain 3-stage stagger tuned amplifier (STA) realizes a 3X gain compared to the conventional single-stage amplifier, which sets a low floor noise. Second, the stagger-tuned amplifier achieves 1.6 times lower noise than the traditional single-stage amplifier. Finally, the stagger tune realizes a high-order transfer function, which mitigates the high-frequency noise. The full LNA is implemented and fabricated using a commercial nano-manufacturing 9-nm graphene film FET on a silicon wafer using a 0.065-μm commercial process, occupying an area of 0.21 mm². The proposed design achieves an optimum performance: a maximum measured gain of 20.5 dB and a minimum noise figure (NF) of 4.2 dB over 123.7 to 162.5 GHz. The proposed LNA consumes ultra-low power consumption of 21.3 mW under the power supply of 1.2 V.

Conventional baseband processing techniques for communication must be adapted to the specificities of terahertz channels. Currently, there is limited research on channel coding applicable to terahertz bands, particularly in terms of performing real-time tests that differentiate them from offline processing. This paper presents a test platform for a 300 GHz wireless communication system based on the PXIe platform. The experiment utilizes a high-performance, low-complexity serial scheduling approach with the Minimum Sum-Log Likelihood Ratio Belief Propagation (MS-LLR-BP) soft decision decoding algorithm to test point-to-point real-time line-of-sight communication for low-density parity-check (LDPC) code communication systems. The results indicate that the implementation of LDPC coding in QPSK terahertz wireless transmission systems results in a performance enhancement of approximately 25–55% in bit error rate (BER), demonstrating the excellent performance of LDPC codes against terahertz channel fading. This highlights their potential in future ultra-high-speed communication systems.

Indoor wireless systems at 60 GHz provide much higher throughput than today’s solutions but need more closely spaced access points. Radio-over-Fiber advancements are a promising solution for the signal distribution. We propose a broadband IF-over-Fiber architecture comprised of miniaturized electronic components for quadrature modulation and upconversion. The 60 GHz wireless generation is realized by transmitting at intermediate frequency (IF) at 10 GHz over single mode fiber (SMF) and upconversion at the base station (BS) front-end with low-cost electronic components on printed circuit board (PCB). The central station (CS) includes an electronic IQ modulator for the provision of multi-Gbps quadrature data modulation formats and successively increase the spectral efficiency of the wirelessly transmitted data. The BS front-end comprises of the 60 GHz upconverter and a 60 GHz planar 2(times )2 microstrip antenna array. The 10 GHz IF carrier allows an optical transmission with higher spectral efficiency in optical domain, as well as it is less susceptible to dispersion induced power fading inherent in optical fiber. The optical fronthaul link of the 10 GHz IF signal modulated with up to 2 Gbps payload data over SMF lengths of 2 km, 12.8 km and 25.6 km has been studied. The system analysis is made with respect to error vector magnitude (EVM), eye and constellation diagrams. The recovered QPSK data has signal-to-noise of 14 dB corresponding to EVM of 20% for transmission over 25.6 km SMF.

Measurements of terahertz absorption spectra of pharmaceutical hydrate samples are achieved under a normal humidity condition by combining terahertz frequency-domain spectroscopy with a newly proposed method for suppressing absorption peaks caused by water vapor. In this method, only simple mathematical operations such as subtraction, thresholding, interpolation, and smoothing are applied to extinction (or absorbance) data obtained by locating samples under a normal humidity condition. By considering the difference in spectral line width between narrow absorption peaks caused by water vapor and the relatively wide absorption peaks caused by active pharmaceutical ingredients (APIs) in solid forms, the absorption peaks caused by water vapor can be effectively suppressed without affecting the absorption peaks of the APIs in the samples. In the present study, levofloxacin hydrates were used as samples to investigate the performance of the proposed method. Spectra were obtained under both dry and normal humidity conditions. The temperature of the samples was raised from 300 to 363 K to dehydrate them and brought back to 313 K to observe hydration under the normal humidity condition. Spectra obtained under the normal humidity condition were processed with the proposed method. The spectra of the hydrates obtained under the dry condition were slightly different from those obtained under the normal humidity condition and processed by our method. Dehydration during the measurements under the dry condition was suggested. Stable and reliable results are expected by measuring spectra under normal humidity conditions and applying the proposed method to suppress absorption peaks by water vapor.

Passive millimeter-wave (MMW) and TeraHertz (THz) imaging systems have become increasingly popular in recent years due to their cost-effectiveness and non-invasive characteristics compared to active systems, prompting a surge in research interest. Evaluating the quality of reconstructed images used in these systems is essential for revealing the fine details. General image quality metrics such as the structural similarity index (SSIM) and the peak signal-to-noise ratio (PSNR) require a reference image in order to compare the reconstructed image. However, there is a notable gap in the literature regarding the evaluation of reconstruction or deconvolution algorithms with a reference image in the passive MMW/THz bands. This study proposes a reference image generation technique for passive MMW/THz imaging systems using an infrared imaging system that shares a similar physical background. Then, passive MMW/THz images were evaluated using the reference images at varying target distances and spatial resolutions. Besides these, the assessment of passive MMW/THz images with the SSIM and PSNR metrics after the reconstruction algorithms were performed. The metrics SSIM and PSNR, are inadequate in the evaluation of reconstruction algorithms alone in terms of concealed object (CO) detection. Because of this reason, the contrast level (CL) method was proposed to address the application-based shortcomings of PSNR and SSIM metrics. Hence, the image quality metric, CL, indicates that the Richardson–Lucy (RL) algorithm yielded superior results in variable optical configurations and target distances with the aid of CL metric. Finally, contrast enhancement techniques were developed in order to increase the contrast level of the CO. As a result, the introduction of these novel methods—the reference image generation technique using an infrared imaging system in passive MMW/THz bands, the evaluation of the reconstructed images with the application-based CL metric, and contrast enhancement techniques for single-band or multi-band imaging methods—holds the potential for the development of innovative techniques. These advancements may contribute to the creation of new applications within the passive MMW/THz bands, particularly focusing on the improvement of detection methods in the future.

A millimeter wave interferometer based on a Ka-band CW signal generator and a high-speed oscilloscope has been implemented, which makes it possible to carry out measurements without frequency conversion. The experimental measurements of the amplitude of transverse deformations of a metal rod caused by impact loading have been carried out. A good agreement between the calculated and measured data was revealed, demonstrating the possibility to measure microsecond-duration surface deviations with an accuracy of about 1 μm and a relative error of about 8%.