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This study investigates the dielectric properties of conductive biocomposites (CBs), which are integral to the development of advanced materials for flexible electronics and medical devices. A novel method employing Microwave Reflectometry (MR) is introduced, utilizing a miniaturized Vector Network Analyzer (m-VNA) and a dedicated sensing element (SE), to extract the dielectric properties of CBs. The method is grounded in a minimization principle, aligning the measured S 11 reflection scattering parameter with its electromagnetic (EM) simulation, facilitating a refined process for determining the dielectric properties. The experimental setup was meticulously engineered, optimized, and validated using reference dielectric samples (RDSs) with known dielectric properties. The method was then applied to three innovative CBs, resulting in an accurate extrapolation of their dielectric properties. The findings highlight the method's versatility, cost-efficiency, and applicability to ultra-thin and flexible biopolymer films, offering significant potential for advancements in flexible electronics and bio-sensing applications. [ABSTRACT FROM AUTHOR]

We present two methods for improved calibration of multi-point electron density measurements from incoherent scatter radars (ISR). They are based on the well-established Flatfield correction method used in imaging and photography, where we exploit the analogy between independent measurements in separate pixels in one image sensor and multi-beam radar measurements. Applying these correction methods adds to the current efforts of estimating the magic constant or system constant made for the calibration of multi-point radars, increasing data quality and usability by correcting for variable, unaccounted, and unpredictable variations in system gain. This second-level calibration is especially valuable for studies of plasma patches, irregularities, turbulence, and other research where inter-beam changes and fluctuations of electron density are of interest. The methods are strictly based on electron density data measured by the individual radar and require no external input. This is of particular interest when independent measurements of electron densities for calibration are available only in one pointing direction or not at all. A correction factor is estimated in both methods, which is subsequently used to scale the electron density measurements of a multi-beam ISR experiment run on a phased array radar such as RISR-N, RISR-C, PFISR, or the future EISCAT3D radar. This procedure could improve overall data quality if used as part of the data-processing chain for multi-beam ISRs, both for existing data and for future experiments on new multi-beam radars. [ABSTRACT FROM AUTHOR]

Despite recent improvements in microscopy, it is still difficult to apply superresolution microscopy for deep imaging due to the deterioration of light convergence properties in thick specimens. As a strategy to avoid such optical limitations for deep super-resolution imaging, we focused on super-resolution radial fluctuation (SRRF), a super-resolution technique based on image analysis. In this study, we applied SRRF to two-photon microscopy (2P-SRRF) and characterized its spatial resolution, suitability for deep observation, and morphological reproducibility in real brain tissue. By the comparison with structured illumination microscopy (SIM), it was confirmed that 2P-SRRF exhibited two-point resolution and morphological reproducibility comparable to that of SIM. The improvement in spatial resolution was also demonstrated at depths of more than several hundred micrometers in a brain-mimetic environment. After optimizing SRRF processing parameters, we successfully demonstrated in vivo high-resolution imaging of the fifth layer of the cerebral cortex using 2P-SRRF. This is the first report on the application of SRRF to in vivo two-photon imaging. This method can be easily applied to existing two-photon microscopes and can expand the visualization range of super-resolution imaging studies. [ABSTRACT FROM AUTHOR]

The low-frequency fluctuations of the atomic density within the cell can induce the longterm drift of the K-Rb-21Ne spin-exchange relaxation-free (SERF) co-magnetometer output, such that the accurate measurement of in situ atomic density is of great significance for improving the performance of co-magnetometer. In this paper, the complex refractive index model of the spin ensembles under the hybrid optical pumping condition is established first, according to which the relation between atomic density and its complex refractive index is revealed and an optical heterodyne-based scheme for atomic density detection is proposed. The dependence of the atomic density on the demodulated phase signal from the optical heterodyne-based scheme is provided by numerical simulations. After that, a dual acousto-optics frequency shifter (AOFS)-based optical heterodyne interferometry is constructed with a noise level below 1 mrad/ Hz for frequencies > 1 Hz, and a compact SERF co-magnetometer is implemented as the testing medium, by which the atomic density detection with resolution of 0.40 K @ 473 K is reached and the experimental results agree well with theoretical simulations. Moreover, the detection scheme proposed in this paper has the properties of high detection sensitivity and immunity to laser power fluctuation, which are also proved experimentally. [ABSTRACT FROM AUTHOR]

Antipodal Vivaldi antennas hold significant importance in medical applications, particularly in the field of microwave imaging, due to their wideband characteristics and efficient radiation properties. These antennas have shown promising results, enabling precise tumor localization and characterization in breast cancer detection, thus facilitating early diagnosis and improving patient outcomes (vers la conclusion). This paper presents the development of a prototype antipodal antenna through a meticulous process that involved using an electromagnetic solver that utilizes the Finite Element Method (FEM) for conceptualization and subsequent realization of the proposed antenna. Rigorous testing in our laboratory has demonstrated auspicious and concrete results, showcasing the antenna's exceptional performance in terms of radiation patterns and efficacy in the Ultra-Wide Band (UWB) frequency region. Furthermore, we found a strong correlation between the simulated and measured values of the reflection coefficients (S11), validating the accuracy and reliability of our design approach. These findings mark substantial progress in our pursuit of developing a low-cost imaging system for early breast cancer detection. [ABSTRACT FROM AUTHOR]

The microwave imaging system for breast tumor/cancer detection requires high sensitivity to detect abnormal tissue that has little contrast in high-density breasts. This paper proposes a qualitative microwave imaging system simulation based on inverse scattering using the sensitivity-maps method. This method utilizes two measurement types for system calibration: a reference object as a scatterer-free background and a calibration object to obtain the system’s impulse response. The object under test (OUT) consists of an object with low dielectric contrast and a phantom with multiple low dielectric contrasts (multi-contrast). Reconstruction is carried out on three types of S-parameter measurement data, namely S11, S21, and a combination of both. S-parameters are measured at several frequencies, which are 3, 10, 14, 15, 16, 20 GHz, and the combination of all those frequencies (multifrequency). Reconstructed images show that the system is capable of reconstructing dielectric objects accurately. Quantitatively, the results show that the multifrequency S21 measurement yields the best image quality with relative root mean squared error (RRMSE) values of 0.1272 and structural similarity index (SSIM) of 0.9076. The designed imaging system also successfully reconstructs multi-contrast phantom accurately with RRMSE of 0.1434 and SSIM of 0.4609. [ABSTRACT FROM AUTHOR]

Skin cancer is one of the most commonly diffused cancers in the world and its incidence rates have constantly increased in recent years. At the current state of the art, there is a lack of objective, quick and non-invasive methods for diagnosing this condition; this, combined with hospital crowding, may lead to late diagnosis. Starting from these considerations, this paper addresses the implementation of a microwave reflectometry based-system that can be used as a non-invasive method for the in-vivo diagnosis and early detection of biological abnormalities, such as skin cancer. This system relies on the dielectric contrasts existing between normal and anomalous skin tissues at microwave frequencies (in a frequency range up to 3 GHz). In particular, a truncated open-ended coaxial probe was designed, manufactured and tested to sense (in combination with a miniaturized Vector Network Analyzer) the variations of skin dielectric properties in a group of volunteer patients. The specific data processing demonstrated the suitability of the system for discriminating malignant and benign lesions from healthy skin, ensuring simultaneously effectiveness, low cost, compactness, comfortability, and high sensitivity.

Glass fiber-reinforced polymer (GFRP) is widely used in engineering fields involving aerospace, energy, transportation, etc. If internal buried defects occur due to hostile environments during fabrication and practical service, the structural integrity and safety of GFRP structures would be severely undermined. Therefore, it is indispensable to carry out effective quantitative nondestructive testing (NDT) of internal defects buried within GFRP structures. Along with the development of composite materials, microwave NDT is promising in non-intrusive inspection of defects in GFRPs. In this paper, quantitative screening of the subsurface impact damage and air void in a unidirectional GFRP via microwave reflectometry was intensively investigated. The influence of the microwave polarization direction with respect to the GFRP fiber direction on the reflection coefficient was investigated by using the equivalent relative permittivity calculated with theoretical analysis. Following this, a microwave NDT system was built up for further investigation regarding the imaging and quantitative evaluation of buried defects in GFRPs. A direct-wave suppression method based on singular-value decomposition was proposed to obtain high-quality defect images. The defect in-plane area was subsequently assessed via a proposed defect-edge identification method. The simulation and experimental results revealed that (1) the testing sensitivity to buried defects was the highest when the electric-field polarization direction is parallel to the GFRP fiber direction; and (2) the averaged evaluation accuracy regarding the in-plane area of the buried defect reached approximately 90% by applying the microwave reflectometry together with the proposed processing methods. [ABSTRACT FROM AUTHOR]

The European Shock Tube for High-Enthalpy Research is a new state-of-the-art facility, tailored for the reproduction of spacecraft planetary entries in support of future European exploration missions, developed by an international consortium led by Instituto de Plasmas e Fusão Nuclear and funded by the European Space Agency. Deployed state-of-the-art diagnostics include vacuum-ultraviolet to ultraviolet, visible, and mid-infrared optical spectroscopy setups, and a microwave interferometry setup. This work examines the specifications and requirements for high-speed flow measurements, and discusses the design choices for the main diagnostics. The spectroscopy setup covers a spectral window between 120 and 5000 nm, and the microwave interferometer can measure electron densities up to 1.5 × 1020 electrons/m3. The main design drivers and technological choices derived from the requirements are discussed in detail herein. [ABSTRACT FROM AUTHOR]

Providing energy from fusion and finding ways to scale up the fusion process to commercial proportions in an efficient, economical, and environmentally benign way is one of the grand challenges for engineering. Controlling the burning plasma in real-time is one of the critical issues that need to be addressed. Plasma Position Reflectometry (PPR) is expected to have an important role in next-generation fusion machines, such as DEMO, as a diagnostic to monitor the position and shape of the plasma continuously, complementing magnetic diagnostics. The reflectometry diagnostic uses radar science methods in the microwave and millimetre wave frequency ranges and is envisaged to measure the radial edge density profile at several poloidal angles providing data for the feedback control of the plasma position and shape. While significant steps have already been given to accomplish that goal, with proof of concept tested first in ASDEX-Upgrade and afterward in COMPASS, important, ground-breaking work is still ongoing. The Divertor Test Tokamak (DTT) facility presents itself as the appropriate future fusion device to implement, develop, and test a PPR system, thus contributing to building a knowledge database in plasma position reflectometry required for its application in DEMO. At DEMO, the PPR diagnostic's in-vessel antennas and waveguides, as well as the magnetic diagnostics, may be exposed to neutron irradiation fluences 5 to 50 times greater than those experienced by ITER. In the event of failure of either the magnetic or microwave diagnostics, the equilibrium control of the DEMO plasma may be jeopardized. It is, therefore, imperative to ensure that these systems are designed in such a way that they can be replaced if necessary. To perform reflectometry measurements at the 16 envisaged poloidal locations in DEMO, plasma-facing antennas and waveguides are needed to route the microwaves between the plasma through the DEMO upper ports (UPs) to the diagnostic hall. The main integration approach for this diagnostic is to incorporate these groups of antennas and waveguides into a diagnostics slim cassette (DSC), which is a dedicated complete poloidal segment specifically designed to be integrated with the water-cooled lithium lead (WCLL) breeding blanket system. This contribution presents the multiple engineering and physics challenges addressed while designing reflectometry diagnostics using radio science techniques. Namely, short-range dedicated radars for plasma position and shape control in future fusion experiments, the advances enabled by the designs for ITER and DEMO, and the future perspectives. One key development is in electronics, aiming at an advanced compact coherent fast frequency sweeping RF back-end [23–100 GHz in few μs] that is being developed at IPFN-IST using commercial Monolithic Microwave Integrated Circuits (MMIC). The compactness of this back-end design is crucial for the successful integration of many measurement channels in the reduced space available in future fusion machines. Prototype tests of these devices are foreseen to be performed in current nuclear fusion machines. [ABSTRACT FROM AUTHOR]

Automated brain tumor segmentation from reconstructed microwave (RMW) brain images and image classification is essential for the investigation and monitoring of the progression of brain disease. The manual detection, classification, and segmentation of tumors are extremely time-consuming but crucial tasks due to the tumor's pattern. In this paper, we propose a new lightweight segmentation model called MicrowaveSegNet (MSegNet), which segments the brain tumor, and a new classifier called the BrainImageNet (BINet) model to classify the RMW images. Initially, three hundred (300) RMW brain image samples were obtained from our sensors-based microwave brain imaging (SMBI) system to create an original dataset. Then, image preprocessing and augmentation techniques were applied to make 6000 training images per fold for a 5-fold cross-validation. Later, the MSegNet and BINet were compared to state-of-the-art segmentation and classification models to verify their performance. The MSegNet has achieved an Intersection-over-Union (IoU) and Dice score of 86.92% and 93.10%, respectively, for tumor segmentation. The BINet has achieved an accuracy, precision, recall, F1-score, and specificity of 89.33%, 88.74%, 88.67%, 88.61%, and 94.33%, respectively, for three-class classification using raw RMW images, whereas it achieved 98.33%, 98.35%, 98.33%, 98.33%, and 99.17%, respectively, for segmented RMW images. Therefore, the proposed cascaded model can be used in the SMBI system. [ABSTRACT FROM AUTHOR]

The production of broadband, terawatt terahertz (THz) pulses has been demonstrated by irradiating relativistic lasers on solid targets. However, the generation of extremely powerful, narrow-band and frequency-tunable THz pulses remains a challenge. Here, we present a novel approach for such THz pulses, in which a plasma wiggler is elaborated by a table-top laser and a near-critical density plasma. In such a wiggler, the laser-accelerated electrons emit THz radiations with a period closely related to the plasma thickness. The theoretical model and numerical simulations predict that a THz pulse with a laser--THz energy conversion of over 2.0%, an ultra-strong field exceeding 80 GV/m, a divergence angle of approximately 20° and a center frequency tunable from 4.4 to 1.5 THz can be generated from a laser of 430 mJ. Furthermore, we demonstrate that this method can work across a wide range of laser and plasma parameters, offering potential for future applications with extremely powerful THz pulses. [ABSTRACT FROM AUTHOR]

In a typical laboratory nanodusty plasma, nanometer-sized solid dust particles can be generated from the polymerization of reactive plasma species. The interplay between the plasma and the dust gives rise to behavior that is vastly different from that of pristine plasmas. Two of the key parameters in nanodusty plasma physics are, among other things, the dust particle size and the dust density. In this work, we introduce a novel method for the determination of these two quantities from the measurement of the free electron density using microwave cavity resonance spectroscopy and laser light extinction measurements. When comparing these two measurements to theory, one can determine the best-fitting dust particle size and dust density. Generally, cyclic behavior of the dust particle size and dust density was observed, of which the trends were relatively insensitive to varying the most stringent input assumptions. Finally, this method has been used to explore the behavior of the dust particle size and dust density for varying plasma powers. [ABSTRACT FROM AUTHOR]

This paper presents the design, simulation and experimental validation of a gradient-index (GRIN) metasurface lens operating at 8 GHz for microwave imaging applications. The unit cell of the metasurface consists of an electric-LC (ELC) resonator. The effective refractive index of the metasurface is controlled by varying the capacitive gap at the center of the unit cell. This allows the design of a gradient index surface. A one-dimensional gradient index lens is designed and tested at first to describe the operational principle of such lenses. The design methodology is extended to a 2D gradient index lens for its potential application as a microwave imaging device. The metasurface lenses are designed and analyzed using full-wave finite element (FEM) solver. The proposed 2D lens has an aperture of size 119 mm (3.17λ) × 119 mm (3.17λ) and thickness of only 0.6 mm (0.016λ). Horn antenna is used as source of plane waves incident on the lens to evaluate the focusing performance. Field distributions of the theoretical designs and fabricated lenses are analyzed and are shown to be in good agreement. A microwave nondestructive evaluation (NDE) experiment is performed with the 2D prototype lens to image a machined groove in a Teflon sample placed at the focal plane of the lens. [ABSTRACT FROM AUTHOR]

A preliminary system for microwave thorax imaging is designed and experiments are conducted. A compact low-profile symmetrical dipole antenna operating at 915 MHz is designed for the system. An acrylic rectangular box is fabricated as the experiment phantom to mimic an ordinary human thorax. Graduated cylinders with different diameters are used as imaging targets. During measurement, each antenna acts in turn as a transmitter and other antennas act as the receivers. One-step supervised descent method (SDM) is adopted as the imaging algorithm. Results under different scenarios indicate that structural information can be reconstructed with the one-step SDM. This study verifies the feasibility of microwave thorax imaging. [ABSTRACT FROM AUTHOR]

Soil monitoring is a key topic from several perspectives, such as moisture level control for irrigation management and anti-contamination purposes. Monitoring the latter is becoming even more important due to increasing environmental pollution. As a direct consequence, there is a strong demand for innovative monitoring systems that are low cost, provide for quasi-real time and in situ monitoring, high sensitivity, and adequate accuracy. Starting from these considerations, this paper addresses the implementation of a microwave reflectometry based-system utilizing a customized bifilar probe and a miniaturized Vector Network Analyzer (m-VNA). The main objective is to relate frequency-domain (FD) measurements to the features of interest, such as the water content and/or the percentage of some polluting substances, through an innovative automatable procedure to retrieve the Debye dielectric parameters of the soil under different conditions. The results from this study confirm the potential of microwave reflectometry for moisture monitoring and contamination detection. [ABSTRACT FROM AUTHOR]

• Electron-density diagnosis of the POINT system on the EAST was evaluated. • Experiment and simulation system VVUQ was applied to an entire plasma diagnostic system. • Uncertainties were identified, quantified, and minimized. • POINT system become a high-precision electron-density diagnostic system for the EAST. The verification, validation, and uncertainty quantification (VVUQ) analysis is a systematic method for identifying and quantifying uncertainties in complex engineering projects. This method has been used by the International Atomic Energy Agency as a critical assessment method in the field of high-precision plasma diagnostics in tokamaks. Starting from the basic theory to the final results, it assesses every process to obtain the uncertainties, system confidence level, and similarity between the model and experimental assessments. In this study, we evaluated the electron-density diagnosis of the polarimeter/interferometer system on an experimental advanced superconducting tokamak using a cylindrical simulation model. This study applied the VVUQ to an entire plasma diagnostic system for the first time, coupled with the statistical concepts of confidence and similarity. Through the VVUQ process, the uncertainty from the simulation code, diagnostic code, and engineering errors were identified, quantified, and minimized. [ABSTRACT FROM AUTHOR]

To investigate the behavior of plasma generated in the shock tube, microwave reflectometry is proposed to extract the permittivity $\epsilon _{r}$ of plasma. To remove the influence of parasitic reflections caused by the surroundings, a calibration process is introduced and the unknown calibration coefficients are determined by utilizing microwave interferometry as the reference technique. The shock tube is modeled as a three-layered medium to calculate the reflection coefficient. A time-dependent reconstruction algorithm is applied and theoretically validated to eliminate the multiple solutions in the inverse problem. By comparing the permittivities extracted with microwave reflectometry and interferometry, the effects of plasma diffusion are demonstrated with a modified analytical model in the beginning time region of experiments. In addition, the nonuniform flow in the generated plasma located near the end time region is also observed. The determination of the effective time region for electron density $N_{e}$ and collision frequency $v_{e}$ extraction is discussed as well. Finally, the differences between microwave reflectometry and interferometry in terms of averaged $N_{e}$ < $1{\times }10^{17} m^{-3}$ and averaged $v_{e}$ < $1.5{\times }10^{9} s^{-1}$ are investigated in the effective time region

A novel approach in addressing cyclone global navigation satellite system (CyGNSS) intersatellite and GPS-related calibration issues is proposed, based on a track-wise $\sigma ^{o}$ bias correction method. This method makes use of both ancillary data from numerical weather prediction models and a semiempirical geophysical model function. Care is taken, so the track-wise $\sigma ^{o}$ bias correction maintains CyGNSS signal sensitivity. Both intersatellite and GPS-related calibration issues are removed after correction. Long-term $\sigma ^{o}$ downward trend, observed throughout the CyGNSS mission, is greatly reduced. Using the corrected $\sigma ^{o}$ measurements, a wind retrieval method is also presented and its product thoroughly assessed for a three-year period against European Centre for Medium-Range Weather Forecasts (ECMWFs), Advanced Scatterometer (ASCAT) A/B, Advanced Microwave Scanning Radiometer (AMSR)-2, GMI, WindSat, hurricane weather research and forecasting (HWRF) model, and the stepped frequency microwave radiometer (SFMR) winds. The overall wind speed bias and standard deviation of the error (stde) against ECMWF are 0.16 and 1.19 m/s, while these are −0.11 and 1.12 m/s against ASCAT A/B, respectively. The same metrics against AMSR-2/GMI/WindSat (combined) are −0.19 and 1.11 m/s, respectively. The bias and stde against soil moisture active passive (SMAP) are −0.38 and 1.90 m/s, respectively. In the tropical cyclone environment, the bias and stde against HWRF are −0.54 and 2.90 m/s, and −4.71 and 5.88 m/s with SFMR. Finally, CyGNSS wind performance is gauged in the presence of rain. Below 10 m/s, the bias between CyGNSS and ECMWF increases as the rain rate increases. Between 10 and 15 m/s, biases are mostly absent. Above 15 m/s, results are inconclusive due to the low number of collocated rain samples. Overall, the presented CyGNSS wind speed product both exhibits consistency and reliability, showing promise of using GNSS-R derived winds for operational purposes. [ABSTRACT FROM AUTHOR]

• A 13-channel far-infrared (FIR) laser Polarimeter/Interferometer has been designed for the HL-3 tokamak, including eight horizontally-viewing channels and five oblique channels. • The novel structure of support tower allows us to arrange multi-channel light-path on both sides. • Multichannel line-integral electron densities have been successfully measured by the interferometric measurement in 2023, with a time resolution of <1.0 microsecond. The interferometer system will be upgraded to the three-wave based Polarimeter/Interferometer. Aiming to achieve important parameters of the electron density and plasma current density profile, a multi-channel far-infrared (FIR) laser Polarimeter/Interferometer is being developed for HL-3 tokamak by using the formic-acid laser source (HCOOH, λ=432.5 μm). All the 13 probing channels were distributed in two columns, including eight horizontally-viewing channels and five oblique channels. The stainless steel support tower (7.0 m high) was specially designed, and itself novel structure allowed us to arrange the light-paths of horizontal channels and oblique channels on two sides, respectively. Copper corner-cube-reflector (CCR) was mounted in the vacuum vessel to retrace the incident wave. In 2023, multi-channel line-integral electron densities were successfully derived by the interferometric measurement, with a time resolution of 1.0μs, line-integral density resolution of ∼5.0 × 1016/cm2. Right now, the interferometer system is being upgraded to three-wave based Polarimeter/Interferometer, which is able to simultaneously measure the electron density and Faraday rotation angle. [ABSTRACT FROM AUTHOR]

• The dispersion interferometer based on CO 2 laser was developed for Globus-M2 tokamak. • Time resolution = 20 μs, spatial resolution = 0.02 m, measurement accuracy ≤ 1017 m −2. • During the year long operation, DI has proven to be reliable diagnostic at Globus-M2. • It is planned to use DI measurements for plasma density stabilizing in Globus-M2. The dispersion interferometry diagnostic (DI) based on the CO 2 -laser was commissioned at the Globus-M2 tokamak for absolute measurements of the line-integrated electron density (IED) along the chord in the equatorial plane. IED measurement error corresponding to the intrinsic noise of the acquisition device was below 1017 m −2 with time and spatial resolution 20µs and 2 cm, respectively. Inference of the IED using the second harmonic interference was done by means of spectral algorithm. Execution of the algorithm is performed at the FPGA in real-time mode. During the year long operation, DI was proven to be reliable and robust IED diagnostic at Globus-M2. [ABSTRACT FROM AUTHOR]

Microwave reflectometry, having its origins in ionosphere probing techniques to evaluate electronic density, has become one of the most important diagnostics for the same quantity in fusion plasmas. Reflectometry will play a major role in next-generation machines, in particular in DEMO, where it is expected to provide plasma positioning, shaping, and tracking data. The ability to have an ever-increasing comprehensive description of reflectometry is particularly important since it allows us to assess the measuring capabilities of existing experimental systems and to predict the performance of new diagnostic concepts based on probing waves. Furthermore, wave propagation in a thermonuclear plasma with fluctuating electronic densities is far from straightforward and the need for a numerical full-wave treatment becomes fundamental. We will present the reader with the fundamentals of this technique and introduce the usage and evolution of FDTD in reflectometry, using as an example, the synthetic diagnostics setup that uses the family of REFMUL* codes, which is employed in the assessment of the performance of several reflectometry systems in different fusion machines. [ABSTRACT FROM AUTHOR]

Global navigation satellite system reflectometry (GNSS-R) has found many applications in the field of Earth observation including ocean wind-speed detection, ice altimetry, soil moisture monitoring, and more. The main focus of GNSS-R research to date has been on forward-scattered reflections, but theoretical work has proposed a backscattering regime and associated new application opportunities, including marine target detection. This article discusses the methods and results of processing the U.K. TechDemoSat-1 raw data collections in a backscattering regime for the first time, with initial results from sea ice datasets presented. The research has also identified a key problem with the backscatter method-for certain geometries the power from the specular point (forward scattered) may contaminate the data. The theory behind this and a method for predicting such occurrences is also discussed.

A portable fast chirp frequency-modulated continuous-wave (FMCW) reflectometer is presented to locate and monitor fast varying discontinuities or faults on transmission lines. This frequency-domain reflectometry (FDR) approach exploits and adapts the advantages of the closely related and frequently employed FMCW radar principle to transmission line reflectometry and overcomes the limitations of commonly used time-domain reflectometry (TDR) methods. The signal generation is based on direct digital synthesis (DDS) and frequency multiplication in order to exploit the advantages of DDS technology, e.g., fast and agile sweep time, and to overcome the drawbacks of analog signal sources related to nonlinearities, temperature sensitivity, or phase noise. By this means, the presented reflectometer provides highly linear, broadband, and fast swept chirp pulses with a duration on the order of microseconds with an initial frequency in the lower UHF-band and a bandwidth of 5.2 GHz. The system concept, its hardware realization, and performance specifications are introduced. The first laboratory test results for static transmission lines and a dynamic measurement setup are presented. The results demonstrate the effectiveness, versatility, and fine ranging capabilities on the order of 2 cm of this approach. [ABSTRACT FROM AUTHOR]

In this work, an innovative system for structural health monitoring of metallic pipes is presented. The proposed system relies on using the pipeline as a waveguide for the propagation of an electromagnetic (EM) signal; possible anomalies in the pipe provoke the partial reflection of the propagating EM signal. Different from previous works that address similar applications, in this work, the EM test signal is injected in the pipeline/waveguide through a coaxial/waveguide transition that is made on the pipe surface (rather than on a cross section as generally done). In practical applications, this strategy would allow connecting more easily the test equipment to the operating, buried pipes. In addition, because reflections caused by anomalies may be difficult to identify with adequate accuracy, the authors have developed a dedicated processing strategy for the analysis of the reflections caused by anomalies. More specifically, by analyzing the measured reflected signal and correlating it to the ideal reflected signal, it is possible to improve the localization of anomalies along the pipe. The proposed system, along with the processing and operating strategies, was validated through full-wave simulations and experimental tests carried out on a steel pipe in the presence of intentionally provoked anomalies. [ABSTRACT FROM AUTHOR]

Intra-abdominal hypertension, defined as an intra-abdominal pressure (IAP) equal to or above 12 mmHg is one of the major risk-factors for increased morbidity (organ failure) and mortality in critically ill patients. Therefore, IAP monitoring is highly recommended in intensive care unit (ICU) patients to predict development of abdominal compartment syndrome and to provide a better care for patients hospitalized in the ICU. The IAP measurement through the bladder is the actual reference standard advocated by the abdominal compartment society; however, this measurement technique is cumbersome, non-continuous, and carries a potential risk for urinary tract infections and urethral injury. Using microwave reflectometry has been proposed as one of the most promising IAP measurement alternatives. In this study, a novel radar-based method known as transient radar method (TRM) has been used to monitor the IAP in an in vitro model with an advanced abdominal wall phantom. In the second part of the study, further regression analyses have been done to calibrate the TRM system and measure the absolute value of IAP. A correlation of –0.97 with a p-value of 0.0001 was found between the IAP and the reflection response of the abdominal wall phantom. Additionally, a quadratic relation with a bias of −0.06 mmHg was found between IAP obtained from the TRM technique and the IAP values recorded by a pressure gauge. This study showed a promising future for further developing the TRM technique to use it in clinical monitoring.

This work presents a microwave reflectometry-based system for monitoring large concrete structures (during the curing process and also while the structure is in use), through the combined use of punctual and diffused sensing elements. In particular, the adoption of punctual probes on a reference concrete specimen allows the development of an innovative and accurate calibration procedure, useful to obtain the value of the water content on a larger structure made of the same material. Additionally, a wire-like diffused sensing element can be permanently embedded in buildings and used to monitor the structure along the entire length of the sensing element. The adopted diffused sensing element can be used not only to detect dielectric variation during the curing process, but also throughout the service life of the structure. The combined use of punctual and diffused sensing elements represents an important innovation from a procedural point of view, able to provide detailed and quantitative information on the health status of the structure both during and after construction.

An O-mode microwave reflectometry system has been developed to measure the density fluctuation on Zheda Plasma Experiment Device (ZPED). The microwave frequency range of this diagnostic system is from 10 GHz to 18 GHz, corresponding to the cutoff densities from 0.13×1019m-3 to 0.4×1019m-3. The density fluctuations are measured with a fixed microwave frequency for plasma in different magnetic field. It has been observed that the density fluctuation power changes with the magnetic field nonlinearly: the density fluctuations increase linearly with the magnetic field when the magnetic field is less than the critical magnetic field, while almost no change when the magnetic field is larger than the critical magnetic field. [ABSTRACT FROM AUTHOR]

The characteristic frequencies of a system provide important information on the phenomena that govern its physical properties. In this framework, there has recently been renewed interest in cryogenic microwave characterization for condensed matter systems since it allows to probe energy scales of the order of a few μeV. However, broadband measurements of the absolute value of a sample response in this frequency range are extremely sensitive to its environment and require a careful calibration. In this paper, we present an in situ calibration method for cryogenic broadband microwave reflectometry experiments that is both simple to implement and through which the effect of the sample electromagnetic environment can be minimized. The calibration references are provided here by the sample itself, at three reference temperatures where its impedance is assumed or measured, and not by external standards as is usual. We compare the frequency-dependent complex impedance (0.1–2 GHz) of an a-Nb15Si85 superconducting thin film obtained through this Sample-Based Calibration (SBC) and through an Open-Short-Load Standard Calibration (SC) when working at a very low temperature (0.02–4 K) and show that the SBC allows us to obtain the absolute response of the sample. This method brings the calibration planes as close as possible to the sample, so that the environment electrodynamic response does not affect the measurement, provided it is temperature independent. This results in a heightened sensitivity, for a given experimental set–up. [ABSTRACT FROM AUTHOR]

Microwave and millimeter-wave reflectometry, a form of continuous-wave surface penetrating radar, is an emerging nondestructive inspection technique that is suitable for nonmetallic pipelines. This paper shows a $K$ -band microwave reflectometry instrument implemented onto an in-line pipe-crawling robot, which raster-scanned cracks and external wall loss on a high-density polyethylene (HDPE) pipe of diameter 150 mm and wall thickness 9.8 mm. The pipe was scanned with three environments surrounding the pipe that approximated the use cases of overground HDPE pipelines, plastic-lined metal pipes, and undersea HDPE pipelines. The instrument was most sensitive when cracks were oriented parallel to its magnetic (H) plane. Any small variation in the standoff distance between the instrument’s probe antenna and the pipe wall, which was not easy to avoid, was found to obscure the image. To mitigate this problem, a sensitivity analysis showed that an optimal frequency can be chosen at which standoff distance can vary by up to ±0.75 mm within a certain range without distorting the indications of defects on the image. [ABSTRACT FROM AUTHOR]

Acknowledgments I wish to thank all of the authors and peer reviewers for their valuable contributions to this Special Issue, "Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry". Microwave/millimeter wave devices and systems have been developed as core technologies in the fields of communication and measurement. The purpose of this Special Issue is to introduce recent advancements in microwave/millimeter wave diagnostic technologies and the current status of their applications. [Extracted from the article]

Highlights • There is a physical link between SRP albedo-area and observed albedo-area. • The same BRDFs must be used to model both SRP force and light curves. • Data fusion is key in estimating mass and albedo-area of an RSO. Abstract There are many Resident Space Objects (RSOs) in the Geostationary Earth Orbit (GEO) regime, both operational and debris. The primary non-gravitational force acting on these RSOs is Solar Radiation Pressure (SRP), which is sensitive to the RSO's area-to-mass ratio. Sparse observation data and mismodeling of non-gravitational forces has constrained the state of practice in tracking and characterizing RSOs. Accurate identification, characterization, tracking, and motion prediction of RSOs is a high priority research issue as it shall aid in assessing collision probabilities in the GEO regime, and orbital safety writ large. Previous work in characterizing RSOs has taken a preliminary step in exploiting fused astrometric and photometric data to estimate the RSO mass, shape, attitude, and size. This works, in theory, since angles data are sensitive to SRP albedo-area-to-mass ratio, and photometric data are sensitive to shape, attitude, and observed albedo-area. By fusing these two data types, mass and albedo-area both become observable parameters and can be estimated as independent quantities. However, previous work in mass and albedo-area estimation has not quantified and assessed the fundamental physical link between SRP albedo-area and observed albedo-area. The observed albedo-area is always a function of the SRP albedo-area along the line of sight of the observer. This is the physical relationship that this current research exploits. It is shown through simulation that due to this physical link, and through the fusion of astrometric and photometric data, it is possible to observe the mass of a space object when the area is not known. Results for data from 100 trajectories generated from randomly sampled initial conditions are shown. It is seen that even when the area of the object is not known, the uncertainty in mass can be lowered from an initial value of 800 kg to the range 500–700 kg for 72% of the samples, 200–500 kg for 13% of the samples, and 0–200 kg for 15% of the samples. It is further shown that although the uncertainties are large, the actual errors in mass are much lower, with the error RMS being less than 100 kg for 30% of the samples, between 100 and 200 kg for another 30%, and between 200 and 300 kg for 24% of the samples. [ABSTRACT FROM AUTHOR]

A cyclone global navigation satellite system (CYGNSS) $\sigma _o$ calibration analysis is presented using version 2.0 of the Level 1 dataset available on PO.DAAC. Three separate analyzes are conducted, namely, an examination of the specular bin location (in delay) and $\sigma _o$ relationship, an investigation of the impact of recently improved characterizations of the GPS effective isotropically radiated power on CYGNSS $\sigma _o$ , and an intersatellite $\sigma _o$ calibration analysis. We first noted a correlation between the specular delay bin location and $\sigma _o$ , where an increase in the specular delay bin resulted in an increase in $\sigma _o$ regardless of the wind speed level; a specular delay bin location ranging from 4.75 to 5.00 and from 7.00 to 7.25 resulted in a 14.74 and 17.72 dB median $\sigma _o$ , respectively. Noticeable improvements in the median $\sigma _o$ were present in the version 2.0 dataset, when separating the data by GPS block type: for blocks IIR, IIF, and IIR-M, median $\sigma _o$ were 15.39, 15.42, and 15.10 dB, respectively (compared to 19.38, 20.53, and 21.38 dB in version 1.1). Finally, an unexpected correlation between the instrument noise floor and $\sigma _o$ was observed for all eight observatories while conducting the intersatellite $\sigma _o$ calibration analysis. Approximately 0–1 dB absolute $\sigma _o$ difference biases (with up to $\sim$ 1 dB standard deviation) between spacecrafts were observed. A report of this analysis was presented to CYGNSS scientists and engineers, who eventually found an issue with the D/A DDM scaling algorithm. We expect better statistical performances in future releases of the data. [ABSTRACT FROM AUTHOR]

Stellar variability from pulsations and granulation presents a source of correlated noise that can impact the accuracy and precision of multiband photometric transit observations of exoplanets. This can potentially cause biased measurements in the transmission or emission spectrum or underestimation of the final error bars on the spectrum. ARIEL is a future space telescope and instrument designed to perform a transit spectroscopic survey of a large sample of exoplanets. In this paper, we perform simulations to assess the impact of stellar variability arising from pulsations and granulation on ARIEL observations of GJ 1214b and HD 209458b. We take into account the correlated nature of stellar noise, quantify it, and compare it to photon noise. In the range 1.95–7.8 |$\mu$| m, stellar pulsation and granulation noise has insignificant impact compared to photon noise for both targets. In the visual range, the contribution increases significantly but remains small in absolute terms and will have minimal impact on the transmission spectra of the targets studied. The impact of pulsation and granulation will be greatest for planets with low scale height atmospheres and long transit times around bright stars. [ABSTRACT FROM AUTHOR]

E-science of photometric data requires automatic procedures and a precise recognition of periodic patterns to perform science as well as possible on large data. Analytical equations that enable us to set the best constraints to properly reduce processing time and hence optimize signal searches play a crucial role in this matter. These are increasingly important because the production of unbiased samples from variability indices and statistical parameters has not been achievable so far. We discuss the constraints used in periodic signals detection methods as well as the uncertainties in the estimation of periods and amplitudes. The frequency resolution necessary to investigate a time series is assessed with a new approach that estimates the necessary sampling resolution from shifts on the phase diagrams for successive frequency grid points. We demonstrate the underlying meaning of the oversampling factor. We reassess the frequency resolutions required to find the variability periods of EA stars and use the new resolutions to analyse a small sample of EA upCatalina stars, i.e. EA stars previously classified as having insufficient number of observations at the eclipses. As a result, the variability periods of four EA upstars were determined. Moreover, we have a new approach to estimate the amplitude and period variations. From these estimations, information about the intrinsic variations of the sources is obtained. For a complete characterization of the light-curve signal, the period uncertainty and period variation must be determined. Constraints on periodic signal searches were analysed and delimited. [ABSTRACT FROM AUTHOR]

A very long-term near-infrared variable star survey towards the Large and Small Magellanic Clouds (LMC and SMC) was carried out using the 1.4 m InfraRed Survey Facility at the South African Astronomical Observatory. This project was initiated in 2000 December in the LMC, and in 2001 July in the SMC. Since then an area of 3 deg2along the bar in the LMC and an area of 1 deg2in the central part of the SMC have been repeatedly observed. This survey is ongoing, but results obtained with data taken until 2017 December are reported in this paper. Over more than 15 yr we have observed the two survey areas more than one hundred times. This is the first survey that provides near-infrared time-series data with such a long time baseline and on such a large scale. This paper describes the observations in the SMC and publishes a point source photometric catalogue, a variable source catalogue, and time-series data. [ABSTRACT FROM AUTHOR]

We present a study of the high-resolution optical spectrum for the hot post-asymptotic giant branch (post-AGB) star, Hen 3−1013, identified as the optical counterpart of the infrared source IRAS 14331−6435. For the first time, the detailed identifications of the observed absorption and emission features in the wavelength range 3700–9000 Å is carried out. Absorption lines of H i, He i, C i, N i, O i, Ne i C ii, N ii, O ii, Si ii, S ii, Ar ii, Fe ii, Mn ii, Cr ii, Ti ii, Co ii, Ni ii, S iii, Fe iii, and S iv were detected. From the absorption lines, we derived heliocentric radial velocities of V r= −29.6 ± 0.4  km s−1. We have identified emission permitted lines of O i, N i, Fe ii, Mg ii, Si ii, and Al ii. The forbidden lines of [N i ], [Fe ii ], [Cr ii ], and [Ni ii ] have been identified also. Analysis of [Ni ii ] lines in the gaseous shell gives an estimate for the electron density N e∼ 107cm−3and the expansion velocity of the nebula V exp= 12  km s−1. The mean radial velocity as measured from emission features of the envelope is V r= −36.0 ± 0.4 km s−1. The Balmer lines H α, H β, and H γ show P Cyg behaviour which indicate ongoing post-AGB mass loss. Based on ASAS and ASAS-SN data, we have detected rapid photometric variability in Hen 3−1013 with an amplitude up to 0.2 mag in the V band. The star's low-resolution spectrum underwent no significant changes from 1994 to 2012. Based on archival data, we have traced the photometric history of the star over more than 100 yr. No significant changes in the star brightness have been found. [ABSTRACT FROM AUTHOR]

We present a catalogue of distances, masses, and ages for ∼3 million stars in the second Gaia data release with spectroscopic parameters available from the large spectroscopic surveys: APOGEE, Gaia -ESO, GALAH, LAMOST, RAVE, and SEGUE. We use a Bayesian framework to characterize the probability density functions of distance, mass, and age using photometric, spectroscopic, and astrometric information, supplemented with spectroscopic masses where available for giant stars. Furthermore, we provide posterior extinction estimates (AV) to every star using published extinction maps as a prior input. We provide an appendix with extinction coefficients for Gaia photometry derived from stellar models, which account for variation with intrinsic colour and total extinction. Our pipeline provides output estimates of the spectroscopic parameters, which can be used to inform improved spectroscopic analysis. We complement our catalogues with Galactocentric coordinates and actions with associated uncertainties. As a demonstration of the power of our catalogue, we produce velocity dispersion profiles of the disc separated by age and Galactocentric radius (between 3 and |$15\, \mathrm{kpc}$| from the Galactic centre). This suggests that the velocity dispersion profiles flatten with radius in the outer Galaxy (⁠|$\gt\!8\, \mathrm{kpc}$|⁠) and that at all radii the velocity dispersion follows the smooth power law with age observed in the solar neighbourhood. [ABSTRACT FROM AUTHOR]

We present a sub-arcsecond crossmatch of Gaia DR2 against the INT Photometric H α Survey of the Northern Galactic Plane Data Release 2 (IPHAS DR2) and the Kepler -INT Survey (KIS). The resulting value-added catalogues (VACs) provide additional precise photometry to the Gaia photometry (r, i, and H α for IPHAS, with additional U and g for KIS). In building the catalogue, proper motions given in Gaia DR2 are wound back to match the epochs of IPHAS DR2, thus ensuring high proper motion objects are appropriately crossmatched. The catalogues contain 7927 224 and 791 071 sources for IPHAS and KIS, respectively. The requirement of >5σ parallax detection for every included source means that distances out to 1–1.5 kpc are well covered. We define two additional parameters for each catalogued object: (i) f c, a magnitude-dependent tracer of the quality of the Gaia astrometric fit; (ii) f FP, the false-positive rate for parallax measurements determined from astrometric fits of a given quality at a given magnitude. Selection cuts based on these parameters can be used to clean colour–magnitude and colour–colour diagrams in a controlled and justified manner. We provide both full and light versions of the VAC, with VAC-light containing only objects that represent our recommended trade-off between purity and completeness. Uses of the catalogues include the identification of new variable stars in the matched data sets, and more complete identification of H α-excess emission objects due to separation of high-luminosity stars from the main sequence. [ABSTRACT FROM AUTHOR]

An experimental test on the ability to observe an extrasolar planetary transit using limited photometric equipment from an Earth based Amateur Observatory. [ABSTRACT FROM AUTHOR]

Abstract We present an analysis of high-resolution imaging of an exoplanet by a meter-class telescope positioned at a real image of the exoplanet created by the solar gravity lens. We assume an exoplanet viewed in full phase and a simple deconvolution method to correct for the intrinsic blur caused by aberrations in the solar gravity lens, and account for the foreground light of the solar corona. We derive equations for the measurement times required for the telescope to produce such a high-resolution image, and find that due to shot noise considerations these times are large compared to human lifespans. We also discuss how measurement times could potentially be significantly shorter for exoplanets with special orbital and rotational parameters. Highlights • The solar corona greatly increases imaging times needed at the solar gravity lens. • High measurement precision is needed to construct solar gravity lens images. • Hundreds of years are likely needed to image exoplanets at the solar gravity lens. [ABSTRACT FROM AUTHOR]

The Chinese Space Station Optical Survey (CSS-OS) is a major science project of the Space Application System of the China Manned Space Program. This survey is planned to perform both photometric imaging and slitless spectroscopic observations, and it will focus on different cosmological and astronomical goals. Most of these goals are tightly dependent on the accuracy of photometric redshift (photo- z) measurement, especially for the weak gravitational lensing survey as a main science driver. In this work, we assess if the current filter definition can provide accurate photo- z measurement to meet the science requirement. We use the COSMOS galaxy catalogue to create a mock catalogue for the CSS-OS. We compare different photo- z codes and fitting methods that use the spectral energy distribution template-fitting technique, and choose to use a modified lephare code in photo- z fitting process. Then we investigate the CSS-OS photo- z accuracy in certain ranges of filter parameters, such as band position, width, and slope. We find that the current CSS-OS filter definition can achieve reasonably good photo-z results with σ z  ∼ 0.02 and outlier fraction ∼3 per cent. [ABSTRACT FROM AUTHOR]

V909 Cas is a little-studied example of a β (Beta) Cep pulsating variable star, located in the OB association Cas OB8 in the Perseus spiral arm of the Milky Way. Photometric observations in 2016-'17 provided thirty new times of pulsation extrema and enabled its mean pulsation period to be determined as 0.2067798(I)d. From spectro scop ic observations we determined its interstellar extinction and absolute magnitude and luminosity, and located it with other β Cep stars in the OB instability region of the H-R diagram. [ABSTRACT FROM AUTHOR]

We present two added-value interfaces (AVIs) for analyzing photometric and spectroscopic data observed by the Gaia satellite. The Gaia Added-Value Interface for Temporal Analysis (GAVITEA) is used to calculate an estimate for the spin state and shape of an asteroid from its photometric data, and the Gaia Added-Value Interface for Spectral Classification (GAVISC) provides tools to define the taxonomic type and surface absorption coefficient based on spectroscopic asteroid data. Computations are mainly carried out using well-known methods of asteroid data analysis but the AVIs also offer the possibility to test novel methods that are specifically developed for analyzing temporally sparse photometric data, typical for Gaia. [ABSTRACT FROM AUTHOR]

Building on the first paper in this series (Duncan et al. 2018), we present a study investigating the performance of Gaussian process photometric redshift (photo-z) estimates for galaxies and active galactic nuclei (AGNs) detected in deep radio continuum surveys. A Gaussian process redshift code is used to produce photo-z estimates targeting specific subsets of both the AGN population -- infrared (IR), X-ray, and optically selected AGNs -- and the general galaxy population. The new estimates for the AGN population are found to perform significantly better at z > 1 than the template-based photo-z estimates presented in our previous study. Our new photo-z estimates are then combined with template estimates through hierarchical Bayesian combination to produce a hybrid consensus estimate that outperforms both of the individual methods across all source types. Photo-z estimates for radio sources that are X-ray sources or optical/IR AGNs are significantly improved in comparison to previous template- only estimates -- with outlier fractions and robust scatter reduced by up to a factor of -4. The ability of our method to combine the strengths of the two input photo-z techniques and the large improvements we observe illustrate its potential for enabling future exploitation of deep radio continuum surveys for both the study of galaxy and black hole coevolution and for cosmological studies. [ABSTRACT FROM AUTHOR]