Widely used medical imaging systems in clinics currently rely on X-rays, magnetic resonance imaging, ultrasound, computed tomography, and positron emission tomography. The aforementioned technologies ...provide clinical data with a variety of resolution, implementation cost, and use complexity, where some of them rely on ionizing radiation. Microwave sensing and imaging (MSI) is an alternative method based on nonionizing electromagnetic (EM) signals operating over the frequency range covering hundreds of megahertz to tens of gigahertz. The advantages of using EM signals are low health risk, low cost implementation, low operational cost, ease of use, and user friendliness. Advancements made in microelectronics, material science, and embedded systems make it possible for miniaturization and integration into portable, handheld, mobile devices with networking capability. MSI has been used for tumor detection, blood clot/stroke detection, heart imaging, bone imaging, cancer detection, and localization of in-body RF sources. The fundamental notion of MSI is that it exploits the tissue-dependent dielectric contrast to reconstruct signals and images using radar-based or tomographic imaging techniques. This paper presents a comprehensive overview of the active MSI for various medical applications, for which the motivation, challenges, possible solutions, and future directions are discussed.
Microwave Photonic Systems Yao, Jianping
Journal of lightwave technology,
10/2022, Letnik:
40, Številka:
20
Journal Article
Recenzirano
Recent advances in microwave photonic systems are reviewed, including system architectures for photonic generation of low-phase-noise microwave signals, linearly chirped microwave waveforms, and ...random microwave waveforms, photonic processing of microwave signals using microwave photonic filters based on incoherent and coherent detection, and radio over fiber links based on coherent detection with increased spectral efficiency and sensitivity. Microwave photonic systems for high-speed and high-resolution optical sensing are also discussed.
Electromagnetic (EM) radio-wave technologies for medical imaging represent an emerging alternative diagnostic modality with some unique features, which is attracting the attention of many researchers ...worldwide. Diagnostic devices based on EM technology have no side-effects, as they exploit non-ionizing radiation, and their intrinsic low cost makes them sustainable for healthcare systems. This Special Issue provides a comprehensive account of this very active research area by gathering contributions that cover a variety of topics ranging from fundamental research questions to experimental validation and clinical translation.
Total precipitable water (TPW) values derived from Constellation Observing System for Meteorology, Ionosphere and Climate-2 (COSMIC-2) are compared with those derived from Special Sensor Microwave ...Imager Sounder (SSMIS), Global Precipitation Measurement (GPM) Microwave Imager (GMI), and Advanced Microwave Scanning Radiometer-2 (AMSR-2) over the ocean from October 1, 2019 to February 16, 2020. The overall comparison results indicate that TPW values derived from SSMIS, AMSR-2, and GMI have a good correlation and agreement with COSMIC-2 TPW values with the correlation coefficients greater than 0.99 and root mean square (rms) no greater than 2.7 mm. We compare TPW derived from three different microwave radiometers with COSMIC-2 TPW over the subtropical and tropical oceans. The differences illustrate that TPW values derived from three different microwave radiometers are more consistent with COSMIC-2 TPW values over the subtropical ocean than those over the tropical ocean. In addition, we also analyze the relationship between the TPW retrieval accuracy derived from three different microwave radiometers and environmental factors, including cloud, rain rate, wind speed, and surface temperature. The results indicate that four environmental factors have an important influence on the TPW retrieval from three different microwave radiometers.
Retrievals of sea ice thickness from passive microwave measurements have been limited to thin ice because microwaves penetrate at most the upper 50 cm of sea ice. To overcome such a limitation, a ...method of retrieving Arctic basin-scale ice thickness is developed. The physical background of this method is that the scattering optical thickness at microwave frequencies within the freeboard layer is linearly proportional to the physical thickness of the ice freeboard. In this study, we relate the optical thickness estimated from the Advanced Microwave Scanning Radiometer 2 (AMSR2) with ice freeboard estimated from the CryoSat-2 (CS2) by employing a piecewise linear fit. The results show a strong linear relationship between the AMSR2-estimated and CS2-measured ice freeboards with a correlation coefficient of 0.85 and bias and RMSE of 0.0001 and 0.04 m, respectively; this evidence suggests that the method can provide Arctic basin-scale ice freeboard with a comparable accuracy level of CS2. The method is also applied to estimate ice freeboard for the periods of the Scanning Multichannel Microwave Radiometer (SMMR) (1978-1987) and AMSR-E (2002-2011). It is shown that the area-averaged ice freeboard has decreased significantly with the linear trends of 1.5 cm/decade. In addition, there seems to be a change of ice freeboard distributions over the Arctic. Furthermore, the algorithm is extended to the ice thickness retrieval by using the hydrostatic balance equation, showing that operational basin-scale ice thickness retrieval will be possible from satellite passive microwave measurements if a realistic snow depth on sea ice is employed.
The optoelectronic oscillator (OEO) has attracted a great deal of attention in recent years as a high-performance microwave source. Thanks to the high quality-factor (Q-factor) provided by the ...optical delay line, the OEO can generate spectrally pure microwave signals with ultralow phase noise. Various approaches for realization of OEO architectures for the generation of single-frequency microwave signals have been demonstrated in the past two decades. Seeded by the microwave signal generated by OEO, the generation of complex microwave waveforms has been demonstrated, which can be used in applications such as radar and communication systems. OEO has also been demonstrated to perform other specific functionalities in different applications, including optical pulses and frequency comb generation, optical sensing, low-power microwave signal detection, and optical signal processing. This paper reviews the developments of OEO over the past two decades. An integrated OEO with monolithically integrated photonic parts and radio frequency subsections is reported as a promising example toward the monolithic integration of OEO. Key features of OEO and prospects for future development of the integration of OEO are also described.
Radio frequency signals can interfere with the radiation emanated from the earth atmospheres and affect the quality of the data received from spaceborne microwave instruments. For microwave radiation ...imager (MWRI) carried on China's Fengyun-3 series satellites, the data contaminated by radio frequency interference (RFI) are usually identified and labeled as poor quality. In this study, using the high correlation between the observed brightness temperatures (TB) of MWRI channels, an RFI identification and correction method is developed through machine learning techniques. Compared with traditional methods, the new method can simultaneously identify and correct RFI affected data. Since it is trained with global MWRI data, the method works well for both land and oceans. Our analysis show that the MWRI data affected by RFI can be corrected to the quality level close to RFI-free regions.
An optically tunable optoelectronic oscillator (OEO) with a wide frequency tunable range incorporating a tunable microwave photonic filter implemented based on phase-modulation to ...intensity-modulation conversion using a phase-shifted fiber Bragg grating (PS-FBG) is proposed and experimentally demonstrated. The PS-FBG in conjunction with two optical phase modulators in the OEO loop form a high-Q, wideband and frequency-tunable microwave photonic bandpass filter, to achieve simultaneously single-frequency selection and frequency tuning. Since the tuning of the microwave filter is achieved by tuning the wavelength of the incident light wave, the tunability can be easily realized at a high speed. A theoretical analysis is performed, which is verified by an experiment. A microwave signal with a frequency tunable from 3 GHz to 28 GHz is generated. To the best of our knowledge, this is the widest frequency tunable range ever achieved by an OEO. The phase noise performance of the OEO is also investigated.
Fabricating microwave absorbers (MA) with strong attenuation capability and lightweight is still a challenge problem, which limit their further applications in our daily life. Herein, magnetic vortex ...core-shell Fe3O4@C nanorings (FNR-C) with excellent microwave absorption property have been successfully prepared by a facile strategy. Electron holography analysis is carried out to detect the magnetic vortex structure of FNR-C. Furthermore, the microwave absorption properties of these samples are investigated in terms of complex permittivity and permeability. The FNR-C exhibits a strong reflection loss value of −61.54 dB at 16.9 GHz with a thickness of 1.50 mm and a low filling ratio of 25%. It’s the first time to take magnetic vortex into discussion. The unexceptionable attenuation ability is mainly attributed to the eddy current loss enhanced by combination of confinement vortex and strain-driven vortex. Besides, thanks to the dielectric feature of carbon, the Fe3O4 core is beneficial for the impedance match. Our findings provide a guidance to the development of nanoferrite@carbon hybrid materials with excellent microwave absorption property from the perspective of magnetic vortex.
Nanoferrite@carbon hybrid materials exhibited an excellence electromagnetic absorption performance due to the synergistic effects of the magnetic and dielectric loss among Fe3O4 nanorings and carbon layer. Display omitted
In order to cover the warm end of Earth-scene brightness temperature (TB) range of passive microwave radiometers, intercalibration over warm scenes is necessary. This article presents a methodology ...to intercalibrate the microwave radiation imager (MWRI) on the Chinese second-generation meteorological satellite Fengyun 3C (FY-3C) with the Global Precipitation Measurement (GPM) Microwave Imager (GMI) over the warm scenes of dense forests using the double-difference (DD) method. Based on the microwave radiative transfer model (RTM), an intercalibration method is developed, in which a modified land surface emissivity (LSE) model for dense forests is proposed. The forests with optically thick canopy are identified in terms of polarization TB differences and normalized difference vegetation index (NDVI) extracted from the latest vegetation product of Moderate-Resolution Imaging Spectroradiometer (MODIS). The matching TBs between FY-3C MWRI and GMI over dense forest warm scenes are collected and analyzed together with the TBs over ocean surfaces obtained by Zeng and Jiang (2020). The results show that: 1) FY-3C MWRI's observations are generally underestimated, and the intercalibration biases are polynomial functions of observations; 2) the intercalibration biases at the warm end are relatively smaller than those at the cold end; and 3) the calibration in the ascending orbits (MWRIA) is relatively better than that in the descending orbits (MWRID). At the tropical rain forest scene TBs defined in this work, the intercalibration biases (mean ± standard deviation at the mean) in the FY-3C MWRI channels of 10 V, 10 H, 18 V, 18 H, 23 V, 36 V, 36 H, 89 V, and 89 H are, respectively, −1.3 ± 0.7, −1.9 ± 1.1, 1.6 ± 0.6, 2.5 ± 0.8, −0.2 ± 0.5, −2.0 ± 0.6, −2.4 ± 0.7, −0.2 ± 0.6, and −0.1 ± 0.6 K for the ascending orbits, while they are, respectively, −4.0 ± 0.8, −5.4 ± 1.2, −1.4 ± 0.7, −1.2 ± 0.8, −2.9 ± 0.5, −4.9 ± 0.7, −5.5 ± 0.7, −2.7 ± 0.8, and −2.3 ± 0.7 K for the descending orbits. The in-orbit calibration coefficients of GMI are successfully transferred to FY-3C MWRI.
