Multispectral Detectors Research Articles

Multifunctional-hierarchical flexible metasurface with simultaneous low infrared emissivity, broadband microwave absorption, and dynamic visible camouflage

Sophisticated multispectral detectors have made single-band camouflage materials ineffective, consequently leading to significant advancements in metasurfaces that possess both infrared (IR), radar, and visible stealth capabilities. However, the mutual constraints of stealth principles across different bands and the demand for environment-adaptive camouflage raise challenges to existing multispectral compatible stealth solutions. Here a multifunctional-hierarchical flexible metasurface (MHFM) including an infrared suppression layer (IRSL), three microwave absorbing layers (MAL), an environmental adaptation layer (EAL), and a total reflective sheet (TRS), was designed to simultaneously achieve IR, radar, and dynamic visible stealth. Unlike the direct stacking of functional layers in existing solutions, the EAL is directly integrated with the first MAL as a part of the absorbing structure. As a proof-of-concept, an MHFM sample with an area of 300 × 300 mm2 and a minimum linewidth of 20 µm is demonstrated. The excellent multispectral camouflage performance is verified in experiments, showing low infrared emissivity (0.229, covering the wavelength of 3∼14 µm), the high absorption efficiency of over 90% in 2.53∼34.56 GHz, and dynamic camouflage in both grassland and desert environments. Our work presents a new solution for adaptive visible camouflage and competitive IR-radar stealth that is prospectively applicable in complex environments.

Simultaneous assessment of NAD(P)H and flavins with multispectral fluorescence lifetime imaging microscopy at a single excitation wavelength of 750nm.

Autofluorescence characteristics of the reduced nicotinamide adenine dinucleotide and oxidized flavin cofactors are important for the evaluation of the metabolic status of the cells. The approaches that involve a detailed analysis of both spectral and time characteristics of the autofluorescence signals may provide additional insights into the biochemical processes in the cells and biological tissues and facilitate the transition of spectral fluorescence lifetime imaging into clinical applications. We present the experiments on multispectral fluorescence lifetime imaging with a detailed analysis of the fluorescence decays and spectral profiles of the reduced nicotinamide adenine dinucleotide and oxidized flavin under a single excitation wavelength aimed at understanding whether the use of multispectral detection is helpful for metabolic imaging of cancer cells. We use two-photon spectral fluorescence lifetime imaging microscopy. Starting from model solutions, we switched to cell cultures treated by metabolic inhibitors and then studied the metabolism of cells within tumor spheroids. The use of a multispectral detector in combination with an excitation at a single wavelength of 750nm allows the identification of fluorescence signals from three components: free and bound NAD(P)H, and flavins based on the global fitting procedure. Multispectral data make it possible to assess not only the lifetime but also the spectral shifts of emission of flavins caused by chemical perturbations. Altogether, the informative parameters of the developed approach are the ratio of free and bound NAD(P)H amplitudes, the decay time of bound NAD(P)H, the amplitude of flavin fluorescence signal, the fluorescence decay time of flavins, and the spectral shift of the emission signal of flavins. Hence, with multispectral fluorescence lifetime imaging, we get five independent parameters, of which three are related to flavins. The approach to probe the metabolic state of cells in culture and spheroids using excitation at a single wavelength of 750nm and a fluorescence time-resolved spectral detection with the consequent global analysis of the data not only simplifies image acquisition protocol but also allows to disentangle the impacts of free and bound NAD(P)H, and flavin components evaluate changes in their fluorescence parameters (emission spectra and fluorescence lifetime) upon treating cells with metabolic inhibitors and sense metabolic heterogeneity within 3D tumor spheroids.

Multispectral Hierarchical Metamaterials with Broadband Microwave Absorption, Gradient Infrared Emissivity, and High Visible Transparency

AbstractThe rapid progression of multispectral detectors poses a serious threat to weapon systems and personnel. The efficiency of stealth camouflage materials, however, has strong wavelength dependence, which limits their functionality to a specific spectral range. Here, a multispectral hierarchical metamaterial (MHM) with broadband microwave absorption, gradient infrared (IR) emissivity, and high visible transparency is proposed. The MHM design entails the integration of two distinct functional layers: the infrared camouflage layer (IRCL) and the radar absorbing layer (RAL). Specifically, leveraging the low‐pass and high‐impedance properties of capacitive frequency selective surfaces and adjustable filling ratio of low IR radiation materials, the IRCL achieves simultaneous high microwave transmission and gradient IR emissivity designs (emissivity gradients > 0.15 at 3–5 and 8–14 µm). The RAL achieves broadband microwave absorption across radar C, X, Ku, and Ka bands through a circuit‐analog absorber designed with lossy materials. Furthermore, prioritizing materials with high transparency enhances the average optical transmittance (>61.8%) of MHM in 380–760 nm. These distinctive features underscore the potential of the proposed MHM for advanced applications in camouflage and stealth technologies.

Multi-band microbolometer in CMOS technology

Multi-spectral imaging enhances the information diversity of the object with complex, expensive, and low integrated components. Here, we demonstrated an antenna-coupled microbolometric detector in complementary metal-oxide-semiconductor (CMOS) technology, utilizing SiO2 absorption and L-shaped fractal antenna to achieve multi-band detection from infrared (IR) to terahertz (THz). Experimental results demonstrate that the detector can achieve high sensitivity detection in both THz and IR bands, with the maximum detectivity of 5 (108 cm·Hz1/2/W @305 GHz and 7 (108 cm·Hz1/2/W @8.55 µm, respectively. The presented multi-spectral detector is easily implementable in integrated circuit process, conducive to high-density, low-cost, and high-performance array imaging.

Ultrawide Spectra Camouflage Coatings from Metallic Flake Powder.

Ultrawide-spectra-compatible camouflage materials are imperative for military science and national security due to the continuous advancement of various sophisticated multispectral detectors. However, ultrawide spectra camouflage still has challenges, as the spectral requirements for different bands are disparate and even conflicting. This work demonstrates an ultrawide spectra camouflage material compatible with visible (VIS, 400-800 nm), infrared (IR, 3-5 and 8-14 μm), and microwave (S-Ku bands, 2-12 GHz). The carbon nanotubes adsorbed on porous anodic alumina/aluminum flake powder (CNTs@PAA/AFP) material for ultrawide spectra camouflage is composed of bioinspired porous alumina surface layers for low visible reflection and aluminum flake powder substrate for low infrared emissivity, while the surface of the porous alumina layers is loaded with carbon nanotubes for microwave absorption. Compared with previous low-emissivity materials, CNTs@PAA/AFP has omnidirectional low reflectance (Ravg = 0.29) and high gray scale (72%) in the visible band. Further, it exhibits low emissivity (ε3-5μm = 0.15 and ε8-14μm = 0.18) in the dual infrared atmospheric window, which reduces the infrared lock-on range by 59.6%/49.8% in the mid/far-infrared band at high temperatures (573 K). The infrared camouflage performance calculated from the radiation temperature of CNTs@PAA/AFP coatings is enhanced to over 65%, which is at least 4 times greater than that of its substrate. In addition, the CNTs@PAA/AFP coating achieves high microwave absorption (RLmin = -42.46 dB) and an effective absorption bandwidth (EAB = 7.43 GHz) in the microwave band (S-Ku bands) due to the enhancement of interfacial polarization and conductive losses. This study may introduce new insight and feasible methods for multispectral manipulation, electromagnetic signal processing, and thermal management via bioinspired structural design and fabrication.

Pixel-integrated Mie metasurface long-wave multispectral type II superlattice detector

Dynamic multispectral imaging finds extensive applications in acquiring multidimensional information. The integration of high-performance, dynamic, and long-wavelength multispectral detectors at the pixel level is highly desirable across various applications. However, the development of such detector faces enormous challenges due to the fundamental material and optical system limitations. In this work, we present a pixel-integrated long-wavelength multispectral type II superlattice detector based Mie dielectric metasurface (Mie-multispectral detector) realized by integrating a graphene-assisted depletion Mie metasurface structure (GAMS). The GAMS is featured with a single-layer graphene and electrically gated tuned Mie dielectric grating. This pixel-integrated multispectral detector allows for 340 nm electrical dynamic tuning and D* value of 5 × 1010 Jones. The Mie-multispectral detector offers potential solutions in space exploration, pollutant retrieval, and other relevant fields.

A Multi-Dimensional Feature Fusion Recognition Method for Space Infrared Dim Targets Based on Fuzzy Comprehensive with Spatio-Temporal Correlation

Space infrared (IR) target recognition has always been a key issue in the field of space technology. The imaging distance is long, the target is weak, and the feature discrimination is low, making it difficult to distinguish between high-threat targets and decoys. However, most existing methods ignore the fuzziness of multi-dimensional features, and their performance mainly depends on the accuracy of feature extraction, with certain limitations in handling uncertainty and noise. This article proposes a space IR dim target fusion recognition method, which is based on fuzzy comprehensive of spatio-temporal correlation. First, we obtained multi-dimensional IR features of the target through multi-time and multi-spectral detectors, then we established and calculated the adaptive fuzzy-membership function of the features. Next, we applied the entropy weight method to ascertain the objective fusion weights of each feature and computed the spatially fuzzified fusion judgments for the targets. Finally, the fuzzy comprehensive function was used to perform temporal recursive judgment, and the ultimate fusion recognition result was obtained by integrating the results of each temporal recursive judgment. The simulation and comparative experimental results indicate that the proposed method improved the accuracy and robustness of IR dim target recognition in complex environments. Under ideal conditions, it can achieve an accuracy of 88.0% and a recall of 97.5% for the real target. In addition, this article also analyzes the impact of fusion feature combinations, fusion frame counts, different feature extraction errors, and feature database size on recognition performance. The research in this article can enable space-based IR detection systems to make more accurate and stable decisions, promoting defense capabilities and ensuring space security.

Multispectral Invisible Coating: Laminated Visible-Thermal Physical Attack against Multispectral Object Detectors Using Transparent Low-E Films

Multispectral object detection plays a vital role in safety-critical vision systems that require an around-the-clock operation and encounter dynamic real-world situations(e.g., self-driving cars and autonomous surveillance systems). Despite its crucial competence in safety-related applications, its security against physical attacks is severely understudied. We investigate the vulnerability of multispectral detectors against physical attacks by proposing a new physical method: Multispectral Invisible Coating. Utilizing transparent Low-e films, we realize a laminated visible-thermal physical attack by attaching Low-e films over a visible attack printing. Moreover, we apply our physical method to manufacture a Multispectral Invisible Suit that hides persons from the multiple view angles of Multispectral detectors. To simulate our attack under various surveillance scenes, we constructed a large-scale multispectral pedestrian dataset which we will release in public. Extensive experiments show that our proposed method effectively attacks the state-of-the-art multispectral detector both in the digital space and the physical world.

Reconfigurable mechano-responsive soft film for adaptive visible and infrared dual-band camouflage.

Learning from nature in terms of the camouflage used by species has enabled the continuous development of camouflage technologies for the visible to mid-infrared bands to prevent objects from being detected by sophisticated multispectral detectors, thereby avoiding potential threats. However, achieving visible and infrared dual-band camouflage without destructive interference while also realizing rapidly responsive adaptivity to the varying background remains challenging for high-demand camouflage systems. Here, we report a reconfigurable mechano-responsive soft film for dual-band camouflage. Its modulation ranges for visible transmittance and longwave infrared emittance can be up to 66.3% and 21%, respectively. Rigorous optical simulations are performed to elucidate the modulation mechanism of dual-band camouflage and identify the optimal wrinkles required to achieve the goal. The broadband modulation capability (figure of merit) of the camouflage film can be as high as 2.91. Other advantages, such as simple fabrication and a fast response, make this film a potential candidate for dual-band camouflage that can adapt to diverse environments.

Recent Progress on Wavelength-Selective Perovskite Photodetectors for Image Sensing.

Spectral sensing plays a crucial part in imaging technologies, optical communication, and other fields. However, complicated optical elements, such as prisms, interferometric filters, and diffraction grating, are required for commercial multispectral detectors, which hampers their advance toward miniaturization and integration. In recent years, metal halide perovskites have been emerging for optical-component-free wavelength-selective photodetectors (PDs) because of their continuously tunable bandgap, fascinating optoelectronic properties, and simple preparation processes. In this review, recent advances in wavelength-selective perovskite PDs, including narrowband PDs, dual-band PDs, multispectral-recognizable PDs, and X-ray PDs, are highlighted, with an emphasis on device structure designs, working mechanisms, and optoelectronic performances. Meanwhile, the applications of wavelength-selective PDs in image sensing for single-/dual-color imaging, full-color imaging, and X-ray imaging are introduced. Finally, the remaining challenges and perspectives in this emerging field are presented.

Large‐Area and Flexible Plasmonic Metasurface for Laser–Infrared Compatible Camouflage

AbstractDue to interminable surveillance and reconnaissance through various sophisticated multispectral detectors, the need for multispectral compatible camouflage is now more than ever. Here, a flexible plasmonic metasurface is proposed to simultaneously realize low reflection at representative lasers (i.e., 1.06, 1.55, and 10.6 µm) and low emission in the atmosphere windows of both 3–5 and 8–14 µm. High absorption for both 1.06 and 1.55 µm lasers is realized by the destructive‐interference design of the multilayer Au/Ge/Ti/Ge films, while low reflection for the 10.6 µm laser results from the coding metasurface design, and low emission is attributed to ultrahigh reflection of the continuous Au/Ge/Ti/Ge films in the atmosphere windows. As a proof of concept, a flexible metasurface sample (10 cm × 10 cm) is prepared by the soft‐lithography technology. The measured specular reflectivities are 0.017, 0.13, and 0.17 at wavelengths 1.06, 1.55, and 10.6 µm, respectively. Meanwhile, the average emissivities are 0.19 and 0.11 in 3–5 and 8–14 µm, respectively. Additionally, the flexible metasurface also exhibits integrated advantages including easy mass fabrication, good mechanical flexibility and robustness, super‐hydrophobic characteristic, unambiguously demonstrating the success of the design strategy for promoting multispectral compatible camouflage.

Flexible Miniaturized Multispectral Detector Derived from Blade-Coated Organic Narrowband Response Unit Array.

Multispectral sensing is extremely desired in intelligent systems, e.g., autonomous vehicles, encrypted information communication, and health biometric monitoring, due to its highly sensitive spectral discrimination ability. Nevertheless, rigid bulky optics and delicate optical paths in devices significantly increase their complexity and size, which subsequently impede their integration in smart optoelectronic chips for universal applications. In this work, a filterless miniaturized multispectral photodetector is realized with an organic narrowband response unit array. With the manipulation of Frenkel exciton dissociation in active layers, a series of narrowband organic sensing units with full-width-at-half-maximum (fwhm) narrowing to ∼50 nm are achieved from 700 to 1050 nm with a laudable performance of responsivity of over 60 mA/W, -3 dB bandwidth over 10 kHz, linear dynamic range (LDR) reaching ∼120 dB, and a low noise current of less than 4 × 10-14 A·Hz-0.5. Furthermore, a 6 × 8 multispectral sensing array on a flexible substrate was fabricated with blade-coating. Assisted by a computational process, we successfully demonstrate the spectral recognition with a resolution of ∼50 nm and a mismatch of ∼10 nm. Finally, the function of matter identification is successfully achieved with our multispectral detector array.

Smart coating textiles for visible and infrared camouflage with photochromism and tunable emissivity

The development of sophisticated multispectral detectors leads to the failure of camouflage technology limited to a specific spectrum, which pushes the exploration of multispectral camouflage materials. However, one of the great challenges in multispectral camouflage is to attain compatibility. This work reports the smart coating textile with tunable infrared radiation characteristics and the capability of stimuli-responsive isomerization, for visible and infrared camouflage. The molecular interactions and synergistic effects of designed polyurethane and chromogen within the composite coating, pave the way for the compatibility of infrared and visible dual camouflage. We demonstrate that the smart coating textile has a controllable infrared emissivity ranging from 0.77 to 0.94. Moreover, the coating textile exhibits adaptively color-changing behavior in response to environmental changes. These coating textiles are characterized by low cost, good durability, stable performance, as well as infrared and visible compatible camouflage. We expect this work may inspire and promote the development of multispectral compatible camouflage materials.

ADJUST: a dictionary-based joint reconstruction and unmixing method for spectral tomography

Advances in multi-spectral detectors are causing a paradigm shift in x-ray computed tomography (CT). Spectral information acquired from these detectors can be used to extract volumetric material composition maps of the object of interest. If the materials and their spectral responses are known a priori, the image reconstruction step is rather straightforward. If they are not known, however, the maps as well as the responses need to be estimated jointly. A conventional workflow in spectral CT involves performing volume reconstruction followed by material decomposition, or vice versa. However, these methods inherently suffer from the ill-posedness of the joint reconstruction problem. To resolve this issue, we propose ‘A Dictionary-based Joint reconstruction and Unmixing method for Spectral Tomography’ (ADJUST). Our formulation relies on forming a dictionary of spectral signatures of materials common in CT and prior knowledge of the number of materials present in an object. In particular, we decompose the spectral volume linearly in terms of spatial material maps, a spectral dictionary, and the indicator of materials for the dictionary elements. We propose a memory-efficient accelerated alternating proximal gradient method to find an approximate solution to the resulting bi-convex problem. From numerical demonstrations on several synthetic phantoms, we observe that ADJUST performs exceedingly well compared to other state-of-the-art methods. Additionally, we address the robustness of ADJUST against limited and noisy measurement patterns. The demonstration of the proposed approach on a spectral micro-CT dataset shows its potential for real-world applications. Code is available at https://github.com/mzeegers/ADJUST.

Noise-aware deep learning algorithm for one-stage multispectral pedestrian detection

Multispectral pedestrian detection has gained momentum in the research literature with its wide range of applications in car safety, video surveillance, and robotics. We introduce a noise-aware multispectral detector, called NAMPD, that is based on the one-stage YOLOv4 to produce fast and accurate detection. NAMPD merges the color and thermal streams at the decision level by a weighted sum, where the weight is computed using both the noise level and average luminance of a given image pair. We show that the noise level provides a distinction between nighttime and daytime and can be utilized to improve the detection performance. Experiments are carried out on the sanitized KAIST dataset. They demonstrate that NAMPD is able to achieve a log-average miss rate of 4.25%, which is better than that of the conventional IAF R-CNN, cross-modality interactive attention network, MSDS-RCNN, and MCFF. This mechanism can operate at a speed of 15 fps on the general GPU 1080 Ti, and, thus, is a viable option to be deployed in practical pedestrian detection systems.

Multispectral Superconducting Nanowire Single-Photon Detector Based on Thickness-Modulated Optical Film Stack

We report on a multispectral superconducting nanowire single-photon detector based on a thickness-modulated optical film stack. This unique optical film structure provides a modulated reflection bands used for single-photon detection in well-separated multiple wavelength ranges. The fabricated detector shows four detection bands with the system detection efficiencies of 76.2%, 76.9%, 81.3%, and 85.0% at the wavelengths of 505, 610, 1030, and 1550 nm, respectively. A 4-pixel multispectral detector array is then demonstrated, and a photon flux reconstruction experiment is performed to reconstruct the photon flux at the wavelengths of interest. The present multispectral detector enriches the available optical architectures and may have interesting multispectral applications such as multispectral ranging or imaging.

Vertical artifacts in high-resolution WorldView-2 and WorldView-3 satellite imagery of aquatic systems

ABSTRACT Satellite image artefacts are features that appear in an image but not in the original imaged object and can negatively impact the interpretation of satellite data. Vertical artefacts are linear features oriented in the along-track direction of an image system and can present as either banding or striping; banding are features with a consistent width, and striping are features with inconsistent widths. This study used high-resolution data from DigitalGlobeʻs (now Maxar) WorldView-3 satellite collected at Lake Okeechobee, Florida (FL), on 30 August 2017. This study investigated the impact of vertical artefacts on both at-sensor radiance and a spectral index for an aquatic target as WorldView-3 was primarily designed as a land sensor. At-sensor radiance measured by six of WorldView-3ʻs eight spectral bands exhibited banding, more specifically referred to as non-uniformity, at a width corresponding to the multispectral detector sub-arrays that comprise the WorldView-3 focal plane. At-sensor radiance measured by the remaining two spectral bands, red and near-infrared (NIR) #1, exhibited striping. Striping in these spectral bands can be attributed to their time delay integration (TDI) settings at the time of image acquisition, which were optimized for land. The impact of vertical striping on a spectral index leveraging the red, red edge, and NIR spectral bands—referred to here as the NIR maximum chlorophyll index (MCINIR)—was investigated. Temporally similar imagery from the European Space Agencyʻs Sentinel-3 and Sentinel-2 satellites were used as baseline references of expected chlorophyll values across Lake Okeechobee as neither Sentinel-3 nor Sentinel-2 imagery showed striping. Striping was highly prominent in the MCINIR product generated using WorldView-3 imagery, as noise in the at-sensor radiance exceeded any signal of chlorophyll in the image. Adjusting the image acquisition parameters for future tasking of WorldView-3 or the functionally similar WorldView-2 satellite may alleviate these artefacts. To test this, an additional WorldView-3 image was acquired at Lake Okeechobee, FL, on 26 May 2021 in which the TDI settings and scan line rate were adjusted to improve the signal-to-noise ratio. While some evidence of non-uniformity remained, striping was no longer noticeable in the MCINIR product. Future image tasking over aquatic targets should employ these updated image acquisition parameters. Since the red and NIR #1 spectral bands are critical for inland and coastal water applications, archived images not collected using these updated settings may be limited in their potential for analysis of aquatic variables that require these two spectral bands to derive.

Miniaturized Multispectral Detector Derived from Gradient Response Units on Single MAPbX3 Microwire

AbstractMiniaturized multispectral detectors are urgently desired given the unprecedented prosperity of smart optoelectronic chips for integrated functions including communication, imaging, scientific analysis, etc. However, multispectral detectors require complicated prism optics or interference/interferometric filters for spectral recognition, which hampers the miniaturization and their subsequent integration in photonic integrated circuits. In this work, inspired by the advance of computational imaging, optical‐component‐free miniaturized multispectral detector on 4 mm gradient bandgap MAPbX3 microwire with a diameter of 30 µm, is reported. With accurate composition engineering, halide ions in MAPbX3 microwire vary from Cl to I giving in the gradual variation of optical bandgap from 2.96 to 1.68 eV along axis. The sensing units on MAPbX3 microwire offer the response edge ranging from 450 to 790 nm with the responsivity over 20 mA W−1, −3dB width over 450 Hz, LDR of ≈60 dB, and a noise current less than ≈1.4 × 10−12 A Hz−0.5. As a result, the derived miniaturized detector achieves the function of multispectral sensing and discrimination with spectral resolution of ≈25 nm and mismatch of ≈10 nm. Finally, the proof‐of‐concept colorful imaging is successfully conducted with the miniaturized multispectral detector to further confirm its application in spectral recognition.

On-chip short-wave infrared multispectral detector based on integrated Fabry–Perot microcavities array

We demonstrate an ultra-compact short-wave infrared (SWIR) multispectral detector chip by monolithically integrating the narrowband Fabry–Perot microcavities array with the InGaAs detector focal plane array. A 16-channel SWIR multispectral detector has been fabricated for demonstration. Sixteen different narrowband response spectra are acquired on a 64×64 pixels detector chip by four times combinatorial etching processes. The peak of the response spectra varies from 1450 to 1666 nm with full width at half-maximum of 24 nm on average. The size of the SWIR multispectral detection system is remarkably reduced to a 2 mm2 detector chip.

Ferroelectric superdomain controlled graphene plasmon for tunable mid-infrared photodetector with dual-band spectral selectivity

Dual-band infrared photodetectors (DBIPs) can discriminate desired signals from complex scenes and thus are highly expected for threat-warning, remote sensing, and astronomy applications. Conventional DBIPs with high performances are, however, typically based on semiconductor thin films, but remain the challenges of expensive growth and cooling requirements. Here, we report a room-temperature graphene plasmonic photodetector with tunable dual-band infrared spectral selectivity driven by ferroelectric superdomain. The periodic ferroelectric polarization array with nanoscale ring shapes provides an ultrahigh electrostatic field for spatially doping of monolayer graphene to desired patterns, and is further used to excite and confine intrinsic graphene plasmons. Our devices exhibit tunable resonance photoresponse in both two bands of 3.7–16.3 μm and 15.1–52.1 μm. The numerical calculations show that our devices own ultrahigh responsivities of 667–1080 A W−1 at room temperature in the range of 5–50 μm. Our devices make possible the applications of the infrared imaging system and both stationary and motion states of objects detection. These investigations provide a novel approach for advanced infrared system construction by employing a simple, low-cost, uncooled multispectral detectors array.