Narrowband Feature Research Articles

Comprehensive advancement in endoscopy: optical design, algorithm enhancement, and clinical validation for merged WLI and CBI imaging.

As endoscopic imaging technology advances, there is a growing clinical demand for enhanced imaging capabilities. Although conventional white light imaging (WLI) endoscopy offers realistic images, it often cannot reveal detailed characteristics of the mucosa. On the other hand, optical staining endoscopy, such as Compound Band Imaging (CBI), can discern subtle structures, serving to some extent as an optical biopsy. However, its image brightness is low, and the colors can be abrupt. These two techniques, commonly used in clinical settings, have complementary advantages. Nonetheless, they require different lighting conditions, which makes it challenging to combine their imaging strengths on living tissues. In this study, we introduce a novel endoscopic imaging technique that effectively combines the advantages of both WLI and CBI. Doctors don't need to manually switch between these two observation modes, as they can obtain the image information of both modes in one image. We calibrated an appropriate proportion for simultaneous illumination with the light required for WLI and CBI. We designed a new illumination spectrum tailored for gastrointestinal examination, achieving their fusion at the optical level. Using a new algorithm that focuses on enhancing specific hemoglobin tissue features, we restored narrow-band image characteristics lost due to the introduction of white light. Our hardware and software innovations not only boost the illumination brightness of the endoscope but also ensure the narrow-band feature details of the image. To evaluate the reliability and safety of the new endoscopic system, we conducted a series of tests in line with relevant international standards and validated the design parameters. For clinical trials, we collected a total of 256 sets of images, each set comprising images of the same lesion location captured using WLI, CBI, and our proposed method. We recruited four experienced clinicians to conduct subjective evaluations of the collected images. The results affirmed the significant advantages of our method. We believe that the novel endoscopic system we introduced has vast potential for clinical application in the future.

Average and statistical properties of coherent radiation from steady-state microbunching.

A promising accelerator light source mechanism called steady-state microbunching (SSMB) is being actively studied. With the combination of strong coherent radiation from microbunching and high repetition rate of a storage ring, high-average-power narrow-band radiation can be anticipated from an SSMB storage ring, with wavelengths ranging from THz to soft X-ray. Such a novel light source could provide new opportunities for accelerator photon science like high-resolution angle-resolved photoemission spectroscopy and industrial applications like extreme ultraviolet (EUV) lithography. In this paper, a theoretical and numerical study of the average and statistical properties of coherent radiation from SSMB are presented. The results show that 1 kW average-power quasi-continuous-wave EUV radiation can be obtained from an SSMB ring provided that an average current of 1 A and a microbunch train with bunch length of 3 nm can be formed at the radiator which is assumed to be an undulator. Together with the narrow-band feature, the EUV photon flux can reach 6 × 1015 photons s-1 within a 0.1 meV energy bandwidth, which is three orders of magnitude higher than that in a conventional synchrotron source and is appealing for fundamental condensed matter physics and other research. In this theoretical investigation, we have generalized the definition and derivation of the transverse form factor of an electron beam which can quantify the impact of its transverse size on coherent radiation. In particular, it has been shown that the narrow-band feature of SSMB radiation is strongly correlated with the finite transverse electron beam size. Considering the pointlike nature of electrons and quantum nature of radiation, the coherent radiation fluctuates from microbunch to microbunch, or for a single microbunch from turn to turn. Some important results concerning the statistical properties of SSMB radiation are presented, with a brief discussion on its potential applications, for example the beam diagnostics. The presented work is of value for the development of SSMB to better serve potential synchrotron radiation users. In addition, this also sheds light on understanding the radiation characteristics of free-electron lasers, coherent harmonic generation, etc.

Rectifying Nonreciprocal Perfect Absorber Based on Generalized Effective-Medium Theory for Composite Magnetic Metamaterials

In this work, we demonstrate the implementation of a nonreciprocal perfect absorber (NPA) made of composite magnetic metamaterials (MMs) consisting of an array of dielectric core loaded (DCL) ferrite rods with either hollow or dielectric cores. The NPA can be functionalized as a PA for the incident beam at a specified direction, while at the symmetric direction the absorption is very weak so that a strong reflection is observed due to the excitation of nonreciprocal magnetic surface plasmon. Interestingly, it is shown that the material loss might be beneficial to the absorption, but it will result in the degradation of nonreciprocal performance. For the delicately designed MMs, only a very small material loss is necessary and simultaneously ensures the high nonreciprocal performance of NPA. To interpret the high quality of NPA, we developed a generalized effective-medium theory for the composite MMs, which shows the direct consequence of the DCL ferrite rods with optimized core size and core permittivity. The partial wave analysis indicates that the nonreciprocal dipole resonance in DCL ferrite rod plays a crucial role in improving the nonreciprocity. The narrow band feature and the angular sensitivity make the NPA promising for the diode-like functionalities. In addition, by controlling the magnitude and orientation of bias magnetic field both the operating frequency and the nonreciprocity can be flexibly controlled, adding an additional degree of freedom. The concept proposed in this research is promising for microwave photonics and integrated photonics.

Synergetic Insulation and Induction Effects Selectively Optimize Multiresonance Thermally Activated Delayed Fluorescence.

Multiresonance (MR) emitters featuring narrowband emissions and theoretically 100% exciton harvesting are great potential for organic light-emitting diode (OLED) applications. However, how to functionalize MR molecules without scarifying emission color purity is still a key challenge. Herein, we report a feasible strategy for selective optimization of MR molecules, which is demonstrated by a blue MR emitter tCBNDASPO substituted with a diphenylphosphine oxide (DPPO) group. Compared to its DPPO-free parent molecule, tCBNDASPO preserves narrowband feature with full widths at half maximum (FWHM) values of 28 nm in film and 32 nm in OLEDs and achieves 40% increased photoluminescence (92%) and electroluminescence quantum efficiencies (28%). It is showed that insulation effect of P=O effectively confines the singlet excited state on MR core to keep emission color purity, and its induction effect enhances singlet radiation and triplet-to-singlet conversion. This synergism for selective optimization is based on rational linkage between MR core and functional groups.

Non-resonant waveguiding-spiralizer for generating acoustic orbital angular momentum with arbitrary number of channels

Acoustic orbital angular momentum (a-OAM) has important application values in several fields such as high-capacity acoustic communication or manipulation of objects. In this paper, a non-resonant waveguiding-spiralizer based on the spiral structure was proposed for generating a-OAM and achieved the wavefront rotation with any channels. Compared with active a-OAM generating devices, these waveguiding-spiral structures were compact enough that could be easily fabricated through three-dimensional (3D) printing technology. While compared with other passive a-OAM generating devices, the principle of wavefront rotation realized by the proposed device was geometrical aisles guiding, which belongs to the non-resonant structure. Therefore, it could effectively reduce the energy loss of sound wave, and avoid the narrow-band feature caused by the resonant structure. Most importantly, the working frequency could be adjusted to any working frequency bands by geometric scaling, and it could work in a variety of media or harsh conditions. In addition, the waveguiding-spiralizer could be designed for any number of channels to realize the multiplexing communication.

Mapping Plastic Greenhouses with Two-Temporal Sentinel-2 Images and 1D-CNN Deep Learning

Plastic greenhouses (PGs) are widely built near cities in China to produce vegetables and fruits. In order to promote sustainable agriculture, rural landscape construction, and better manage water resources, numerous remote sensing methods have been developed to identify and monitor the distribution of PGs, of which many map PGs based on spectral responses and geometric shapes. In this study, we proposed a new fine- and coarse-scale mapping approach using two-temporal Sentinel-2 images with various seasonal characteristics and a one-dimensional convolutional neural network (1D-CNN). Having applied this approach in a pilot area study, the results were summarized as follows: (1) A time-series analysis of Sentinel-2 images showed that the reflectance of greenhouses changes during crop growth and development. In particular, the red-edge and near-infrared bands undergo a significant increase and then decrease during the whole crop growth period. Thus, two critical period images, containing a substantial difference in greenhouse reflectance, were sufficient to carry out an accurate and efficient mapping result. (2) The 1D-CNN classifier was used to map greenhouses by capturing subtle details and the overall trend of the spectrum curve. Overall, our approach showed higher classification accuracy than other approaches using support vector machines (SVM) or random forests (RF). In addition, the greenhouse area identified was highly consistent with the existing surfaces observed in very high-resolution images, with a kappa co-efficient of 0.81. (3) The narrow band feature differences (red-edge and near infrared narrow bands) in two-temporal Sentinel-2 images played a significant role in high-precision greenhouse mapping. The classification accuracy with narrow band features was much better than the maps produced without narrow band features. This scheme provided a method to digitize greenhouse precisely and publish its statistics for free, which enable advanced decision support for agriculture management.

Real-time monitoring method for unauthorized working activities above the subway tunnel based on ultra-weak fiber Bragg grating vibration sensing array

Real-time monitoring of unauthorized working activities above the subway tunnel is an intractable issue. Illegal drill rig working is one of the most threatening way of intrusion. Nowadays, the distributed optic fiber sensing technology promises to provide a viable means for the long distance monitoring in the complex working conditions. To tackle the difficult problem of drill rig intrusion, we use the ultra-weak fiber Bragg grating vibration sensing array to acquire the vibration signals, and propose a real-time monitoring method based on the detection of the vibration due to the running engine. The alarm strategy identifies the engine vibration according to the narrow frequency band feature of the signal. Due to the continuity of engine working and randomness of noise interferences, the statistical analysis is adopted on the identification results. The intrusion location is achieved by the proposed method. We validate the proposed monitoring method in the field trials.

Broadband absorption of infrared dielectric resonators for passive radiative cooling

Infrared resonator metamaterials, exhibiting spectral selective absorption of light, have recently been of great interest for passive radiative cooling. In this approach, coolers radiate power passively, with emissivity equals to its absorptivity. However, high-efficient energy dissipation requires radiation windows of broad bandwidth, i.e. 8–14 μm, that challenges the narrow-band feature of resonators. Here, we numerically realize the broadband absorption (above 80% in 8–11 μm) for dielectric resonators over a wide incident angle range (0°–60°), predicting 12 °C cooling below the ambient temperature at nighttime. The electromagnetically resonating eigenmodes of the dielectric resonators are perturbated by losses to reshape the dispersion relation in radiation windows, which are implemented by two methods: inserting metal components and coating lossy dielectrics. Retrieval constitutive parameters, as well as S parameters, map the reshaping process for broadband considerations. Additionally, ideal transparency (nearly 100%) above the wavelength of 0.5 mm is achieved. These crucial features offer an effective solution to the microwave signals shielding problem generally encountered in previous radiative coolers, regarding applied scenes such as buildings and cars.

A Tunable Polymer-Metal Based Anti-Reflective Metasurface.

Anti-reflective surfaces are of great interest for optical devices, sensing, photovoltaics, and photocatalysis. However, most of the anti-reflective surfaces lack in situ tunability of the extinction with respect to wavelength. This communication demonstrates a tunable anti-reflective surface based on colloidal particles comprising a metal core with an electrochromic polymer shell. Random deposition of these particles on a reflective surface results in a decrease in the reflectance of up to 99.8% at the localized surface plasmon resonance frequency. This narrow band feature can be tuned by varying the pH or by application of an electric potential, resulting in wavelength shifts of up to 30 nm. Electrophoretic particle deposition is shown to be an efficient method for controlling the interparticle distance and thereby further optimizing the overall efficiency of the anti-reflective metasurface.

Nautical radar clutter suppression and small target detection based on image spectrum filtering and Hough transform

Here, a new clutter suppression and small target detection method was presented for nautical radars based on image spectrum filtering and Hough transform (HT). It is well known that sea clutter can be decomposed into texture component (TC) and spiky component (SC). First, the raw echo image was transferred to spectrum field, taking use of the narrow band feature of TC clutter in the image spectrum field, a 2D filter named as invert clutter response filter was designed to filter the energy of TC clutter in image spectrum field and then recovering the echo image. After that, a 2D CFAR detector was used to get a coarse detection report. Since the influence of the remaining SC clutter, quite a lot of false-alarmed detections may appear for the coarse detections. To solve this problem, the HT technique was proposed to extract real target track lines from many but distributed SC clutter caused false alarms. Measured and simulated results show that the proposed method is quite effective.

Transmit-Array, Metasurface-Based Tunable Polarizer and High-Performance Biosensor in the Visible Regime.

There are two types of metasurfaces, reflect-array and transmit-array,—which are classified on the basis of structural features. In this paper, we design a transmit-array metasurface for y-polarized incidence which is characterized by having a transmission spectrum with a narrow dip (i.e., less than 3 nm). Furthermore, a tunable polarizer is achieved using linear geometric configurations, realizing a transmittivity ratio between x- and y-polarized incidence ranging from 0.031% to 1%. Based on the narrow-band polarization sensitivity of our polarizer, a biosensor was designed to detect an environmental refractive index ranging from 1.30 to 1.39, with a factor of sensitivity S = 192 nm/RIU and figure of merit (FOM) = 64/RIU. In the case of a narrow-band feature and dips in transmission spectrums close to zero, FOM* can have a value as large as 92,333/RIU. This unique feature makes the novel transmit-array metasurface a potential market candidate in the field of biosensors. Moreover, transmit-array metasurfaces with lossless materials offer great convenience by means of detecting either the reflectance spectrum or the transmission spectrum.

An effective means for damage detection of bridges using the contact-point response of a moving test vehicle

To further the technique of indirect measurement, the contact-point response of a moving test vehicle is adopted for the damage detection of bridges. First, the contact-point response of the vehicle moving over the bridge is derived both analytically and in central difference form (for field use). Then, the instantaneous amplitude squared (IAS) of the driving component of the contact-point response is calculated by the Hilbert transform, making use of its narrow-band feature. The IAS peaks serve as the key parameter for damage detection. In the numerical simulation, a damage (crack) is modeled by a hinge-spring unit. The feasibility of the proposed method to detect the location and severity of a damage or multi damages of the bridge is verified. Also, the effects of surface roughness, vehicle speed, measurement noise and random traffic are studied. In the presence of ongoing traffic, the damages of the bridge are identified from the repeated or invariant IAS peaks generated for different traffic flows by the same test vehicle over the bridge.

Planar plasmonic chiral nanostructures.

A strong chiral optical response induced at a plasmonic Fano resonance in a planar Au heptamer nanostructure was experimentally and theoretically demonstrated. The scattering spectra show the characteristic narrow-band feature of Fano resonances for both left and right circular polarized lights, with a chiral response reaching 30% at the Fano resonance. Specifically, we systematically investigate the chiral response of planar heptamers with gradually changing the inter-particle rotation angles and separation distance. The chiral spectral characteristics clearly depend on the strength of Fano resonances and the associated near-field optical distributions. Finite element method simulations together with a multipole expansion method demonstrate that the enhanced chirality is caused by the excitation of magnetic quadrupolar and electric toroidal dipolar modes. Our work provides an effective method for the design of 2D nanostructures with a strong chiral response.

A Post-Matching Doherty Power Amplifier Employing Low-Order Impedance Inverters for Broadband Applications

This paper presents a modified Doherty configuration with extended bandwidth. The narrow band feature of the conventional Doherty amplifier is discussed in the view of the broadband matching. To extend the bandwidth, the post-matching architecture is employed in the proposed design. Meanwhile, broadband low-order impedance inverters are adopted to replace the quarter-wavelength transmission lines. Low-pass filter topologies are used to realize both the post matching network and the impedance inverters. A modified Doherty Power amplifier was designed and fabricated based on commercial GaN HEMT devices to validate the broadband characteristics of this configuration. The 6-dB backoff efficiencies of 47%-57% are obtained from 1.7 to 2.6 GHz (41.9% fractional bandwidth) and the measured maximum output power ranges from 44.9 to 46.3 dBm in the designed band. In particular, more than 40% efficiencies are measured at 10-dB backoff throughout the operation band.

Narrow-Band Type II Superlattice Photodetector With Detection Wavelength Shorter Than <inline-formula> <tex-math notation="LaTeX">$2~\mu \text{m}$ </tex-math></inline-formula>

We demonstrate that type II InAs/GaSb superlattice photodetector can reach the detection wavelength shorter than $2~\mu \text{m}$ by inserting AlSb barriers. The detector exhibits a narrow-band photoresponse feature ( $\delta \lambda /\lambda =10.3\%$ ). At 77 K, the photoresponse maximum is at 1.84 $\mu \text{m}$ and the Johnson noise limited detectivity is $1.1\times 10^{13}$ Jones. We show that unlike a typical broad-band response feature using the interband transitions, for a p-i-n detector in the short wavelength range, a narrow-band response feature is the case, which is ascribed to the stronger absorption for the higher energy photons from the n region.

Extreme Value Distribution and Peak Factor of Crosswind Response of Flexible Structures with Nonlinear Aeroelastic Effect

The crosswind response at the vicinity of vortex lock-in wind speed becomes an increasing concern in structural design of super tall buildings and other dynamically sensitive structures. Because of nonlinear aeroelastic effect of vortex shedding, the extreme value distribution and peak factor of crosswind response are distinctly different from traditional wind-induced stochastic buffeting response. This study establishes an effective approach for predicting extreme value distribution and peak factor of crosswind response of flexible structures on the basis of an improved understanding of the underlying mechanism. It is pointed out that the improved extreme theory of Gaussian processes with consideration of narrow-band feature cannot interpret the extreme crosswind response. This study, at the first time, reveals that the unique characteristics of extreme value distribution of crosswind response is primarily attributed to its hardening non-Gaussian distribution. An extensive analysis of simulated crosswind response illustrates that the extreme value distribution and peak factor can be estimated from those of an underlying Gaussian process based on the translation process theory. The translation function between non-Gaussian crosswind response and Gaussian process can be expressed in terms of Hermite polynomial model based on the first four statistical moments or quantified by mapping of cumulative distribution functions and curve fitting. Closed-form formulations are developed for calculating Hermite translation model coefficients, which permits the estimation of extreme value distribution and peak factor directly using the response kurtosis and bandwidth parameter. The characteristics of crosswind response and the proposed approach are also validated using full-scale vibration measurements of a wind-excited traffic-signal-support structure. This study not only clarified the mechanism responsible for the unique extreme value distribution of crosswind response with nonlinear aeroelastic effect but also established an effective simple approach for its estimation using the characteristics of response process.

Z‐mode maser instability

Although the cyclotron maser instability customarily involves the extraordinary (X) and ordinary (O) fast transverse electromagnetic wave modes, which directly escape and propagate long distances from the source region, the instability also excites the Z mode for a wide range of parameters. Even though Z mode is a nonescaping mode, it may convert to O mode in an inhomogeneous medium and be detected by remote means. This process is believed to explain radio emissions near cyclotron harmonics emitted both upward and downward from Earth's auroral ionosphere, as well as analogous emissions detected near Saturn. A more general analysis of the electron loss cone driven Z‐mode maser instability than previously reported reveals that for certain plasma‐to‐cyclotron‐frequency ratios, the unstable waves split into broadband and narrowband ranges of unstable modes and that these two bands are characterized by distinct polarizations. In previous studies of the Z‐mode maser, the maximum growth rate was considered without distinguishing the two bands. Although the maximum temporal growth rate sometimes corresponds to the narrowband feature, the broadband feature with a significant O‐mode‐like polarization may be of importance, since it can more easily convert to an escaping radiation. This paper presents analysis of maximum growth rates, wave propagation angles, and wave frequencies for the two band features of the loss cone driven Z‐mode maser instability as a function of the ratio of plasma‐to‐electron cyclotron frequency. The results are relevant to auroral radio emission phenomena, especially those observed near cyclotron harmonics at both Earth and Saturn.

Estimation of stochastic crosswind response of wind-excited tall buildings with nonlinear aerodynamic damping

This study addresses the analysis of crosswind response of tall buildings and flexible structures at wind speed region higher than the vortex lock-in speed, where nonlinear negative aerodynamic damping effect is significant. The modeling of nonlinear aerodynamic damping as a function of time-varying velocity and/or displacement of vibration is established based on motion-induced aerodynamic force information obtained from forced-vibration model testing in wind tunnel, referred to as harmonic balance. Response time history simulations are performed by solving the nonlinear equation of motion to explore the unique hardening non-Gaussian characteristics of crosswind response and its extreme value distribution with reduced peak factor. The response time history simulations also provide a bases for assessing the performance of analytical predictions of root-mean-square (RMS) response using crosswind loading spectrum and equivalent aerodynamic damping models. The limitations of the equivalent aerodynamic damping models as functions of RMS response derived from harmonic balance and statistical linearization with an assumption of Gaussian response are revealed. This study, at the first time, by using the method of equivalent nonlinear equation, presents complete analytical solutions of crosswind response statistics, including not only the RMS response, but also response kurtosis, response probability distribution, peak factor and extreme value distribution. The comparison of the analytical predictions with response simulation results illustrates that the method of equivalent nonlinear equation is very accurate in predicting crosswind response statistics that are influenced by the nonlinear aerodynamic damping. The narrow band feature of response is further considered in this study in the calculation of crossing rate using amplitude process, which leads to even better predictions of extreme statistics. This general framework can also be readily adopted in design codes and standards for calculating vortex-induced vibration of towers and chimneys.

OS0713 動弾性有限積分法を用いたレーザ励起ラム波の解析

Laser generation of Lamb wave in a thin plate is studied numerically. To this purpose, the EFIT (Elastodynamic Finite Integration Technique) is extended to incorporate coupled dynamic thermoelasticity. The energy input by the laser is modeled as a line heat source in the heat conduction equation. Based on this technique, the influence of the coupling term in the heat conduction equation on the temperature variation and the generated ultrasound waveform is evaluated. Moreover, Lamb wave generation behavior due to multiple laser beams is analyzed. It is shown that as the number of line sources increases, the generated AO-mode Lamb wave tends to acquire a narrow-band feature around a frequency determined by the interval of line sources and the dispersion curve of Lamb waves.

Planewave remittances of an axially excited chiral sculptured thin film with gain

Reflectances and transmittances of chiral sculptured thin films (STFs) with gain qualitatively differ from those of lossless and lossy chiral STFs, chiefly at the edges of the Bragg regime, for normally incident plane waves. The difference is explained in terms of the photonic density of states. A chiral STF with a central twist defect exhibits a reflection hole if there is no gain and emits narrowband radiation if there is gain, provided the thickness is not large. This narrowband feature diminishes as the thickness increases, and is replaced by an ultranarrowband transmission hole only if the chiral STF has neither gain nor loss.