Uncooled Infrared Imaging System Research Articles

Multi-scale thermal radiation effects correction via a fast surface fitting with Chebyshev polynomials.

In an uncooled infrared imaging system, thermal radiation effects are caused by the heat source from the target or the detection window, which affects the ability of target detection, tracking, and recognition seriously. To address this problem, a multi-scale correction method via a fast surface fitting with Chebyshev polynomials is proposed. A high-precision Chebyshev polynomial surface fitting is introduced into thermal radiation bias field estimation for the first time, to the best of our knowledge. The surface fitting in the gradient domain is added to the thermal radiation effects correction model as a regularization term, which overcomes the ill-posed matrix problem of high-order bivariate polynomials surface fitting, and achieves higher accuracy under the same order. Additionally, a multi-scale iterative strategy and vector representation are adopted to speed up the iterative optimization and surface fitting, respectively. Vector representation greatly reduces the number of basis function calls and achieves fast surface fitting. In addition, split Bregman optimization is used to solve the minimization problem of the correction model, which decomposes the multivariable optimization problem into multiple univariate optimization sub-problems. The experimental results of simulated and real degraded images demonstrate that our proposed method performs favorably against the state of the art in thermal radiation effects correction.

Design of low noise electrical system for uncooled long wave infrared imaging

The research and design of low-noise imaging circuit is of great significance to enhance the imaging quality of the detector. To improve the imaging quality of an uncooled infrared imaging system, a low noise imaging circuit is designed. The generation scheme of bias voltage is emphasized, and the design methods of timing drive module and ADC conversion module are briefly described. A filter with a pass-band cutoff frequency of 1 Hz is designed at the bias voltage output to filter out high-frequency noise. The experimental results show that the precision of bias voltage is over 98% and the RMS noise of bias voltage below 1kHz is 1.4uV. The feasibility of other modules is verified by simulation and experiment.

Single-frame-based column fixed-pattern noise correction in an uncooled infrared imaging system based on weighted least squares.

Uncooled infrared images typically suffer from column fixed-pattern noise (FPN), which is introduced by the non-uniformity of the column-parallel readout circuit. It is a challenging task to remove column FPN without introducing stripe artifacts near strong vertical edges. In this paper, we introduce a novel single-frame-based algorithm to accurately correct column FPN. The algorithm contains two 1D filters. First, a 1D weighted least-squares filter is applied to perform edge-preserving filtering in the horizontal direction to obtain a coarse estimation of the clear scene. Then, a local weighted ridge regression is performed between the horizontal smoothed image and the raw infrared image in vertical direction to refine this estimation. Through an analysis on the cause of stripe artifacts, the proposed non-uniformity correction (NUC) algorithm is proved to be effective in eliminating this problem. The performance of our proposed algorithm is thoroughly investigated and compared to four state-of-the-art single-frame-based destriping methods using both simulated and real experiments.

Infrared Stripe Correction Algorithm Based on Wavelet Analysis and Gradient Equalization

In the uncooled infrared imaging systems, owing to the non-uniformity of the amplifier in the readout circuit, the infrared image has obvious stripe noise, which greatly affects its quality. In this study, the generation mechanism of stripe noise is analyzed, and a new stripe correction algorithm based on wavelet analysis and gradient equalization is proposed, according to the single-direction distribution of the fixed image noise of infrared focal plane array. The raw infrared image is transformed by a wavelet transform, and the cumulative histogram of the vertical component is convolved by a Gaussian operator with a one-dimensional matrix, in order to achieve gradient equalization in the horizontal direction. In addition, the stripe noise is further separated from the edge texture by a guided filter. The algorithm is verified by simulating noised image and real infrared image, and the comparison experiment and qualitative and quantitative analysis with the current advanced algorithm show that the correction result of the algorithm in this paper is not only mild in visual effect, but also that the structural similarity (SSIM) and peak signal-to-noise ratio (PSNR) indexes can get the best result. It is shown that this algorithm can effectively remove stripe noise without losing details, and the correction performance of this method is better than the most advanced method.

Bioinspired infrared detection using thermoresponsive hydrogel nanoparticles

Abstract The development of high performance uncooled infrared (IR) detection and imaging systems will greatly expand the application of IR technology in broad areas such as transportation, environmental monitoring, and medical care. Inspired by the superior IR detection capability of beetle Melanophila acuminata, we explored the potential use of hydrogel nanoparticles (NPs) in uncooled IR detection system. In the system, the absorption of the incoming IR radiation by the temperature-sensitive hydrogel NPs, together with water, induces the volume change of the hydrogel NPs, similar to the volume change of the biofluid inside the sensillae receptors in M. acuminata caused by the IR radiation. This volume change results in the change of optical readout (transmittance in this study) in visible range and provides the sensitive detection of the IR radiation. In this work, poly(N-isopropylacrylamide-co-acrylic acid) (poly(NIPAM-co-AAc)) copolymer NPs with different sizes were synthesized and their IR sensing performances were studied in detail. The correlation between the NP size and concentration and the IR sensing property was also discussed in the paper. This work helps enhance the understanding of the response of hydrogel NPs under IR radiation, and offers a potential material system for uncooled IR detection that is inspired by M. acuminata. The direct use of transmittance of the NP solution as the readout for IR detection also provides a simple and sensitive IR detection approach for low cost and portable industrial applications.

Image quality improvement by the structured light illumination method in an optical readout cantilever array infrared imaging system.

The structured light illumination method is applied in an optical readout uncooled infrared imaging system to improve the IR image quality. The unavoidable nonuniform distribution of the initial bending angles of the bimaterial cantilever pixels in the focal plane array (FPA) can be well compensated by this method. An ordinary projector is used to generate structured lights of different intensity distribution. The projected light is divided into patches of rectangular regions, and the brightness of each region can be set automatically according to the deflection angles of the FPA and the light intensity focused on the imaging plane. By this method, the FPA image on the CCD plane can be much more uniform and the image quality of the IR target improved significantly. A comparative experiment is designed to verify the effectiveness. The theoretical analysis and experimental results show that the proposed structured light illumination method outperforms the conventional one, especially when it is difficult to perfect the FPA fabrication.

Method for Uncooled Infrared Image Processing

Uncooled infrared imaging system has been increasingly applied in both the national defense and various fields of national economy. Such popularity is attributed to many of its advantages, including small size, light weight, low energy-consumption and superior portability. However, as limited by the structure and the material of infrared detector and the manufacturing techniques, infrared images are plagued with low resolution and poor image quality. This paper mainly studies the uncooled infrared image processing based on the gray levels partition processing, gray levels stretching and histogram modification, it aims to enhance the visual effect of infrared image.

Short-wave infrared, medium-wave infrared, and long-wave infrared imaging study for optical readout microcantilever array infrared sensing system

We aim to study the short-wave infrared (SWIR), medium-wave infrared (MWIR), and long-wave infrared (LWIR) imaging ability based on optical readout bimaterial microcantilever focal plane array (FPA) uncooled infrared imaging system. First, the principle of the bimaterial microcantilever sensing and the fabrication of the microcantilever array are introduced. Second, the optical-thermal-mechanical sensing theories based on the FPA are given. Finally, an optical readout microcantilever FPA infrared imaging system is developed for SWIR, MWIR, and LWIR imaging experiments. The experimental results show that the system can acquire the clear images of the SWIR, MWIR, and LWIR targets.

Equivalent circuit model of the substrate-free focal plane array based on the optical readout uncooled infrared imaging system

与传统的有基底FPA(焦平面阵列)相比, 基于全镂空支撑框架结构的新型无基底FPA在热学特性上存在显著差异, 传统的基于恒温基底假设的热学分析模型不再适用, 因此, 通过电学比拟方法, 将无基底FPA的热响应特性等效为电学模型.通过该模型, 进一步分析了无基底FPA在非真空环境下的热学性能, 分析表明: 该无基底FPA具有在大气压下优良的红外成像性能, 其NETD(噪声等效温度差)值仅比真空环境下增加了数倍.;Thermal characteristics of new substrate-free FPA (focal plane array) with full hollow supporting frame structure are very different from that of traditional substrate FPA. The thermal analysis model which based on temperature-constant substrate assumption is not efficient any more. Therefore, an equivalent circuit model was presented to analyze the thermal response characteristics of substrate-free FPA with electrics and holistic approach. According to this model, the thermal characteristics of substrate-free FPA under non-vacuum environment were analyzed. The result shows that, the substrate-free FPA has excellent infrared imaging performances under atmospheric pressure, while its NETD (noise equivalent temperature difference) is just increased several times than in the vacuum environment.

Performance analysis of the substrate-free focal plane array in infrared imaging

Based on the proposed optical readout uncooled infrared (IR) imaging system，several batches of the substrate-free focal plane array (FPA) with different pitches have been successively fabricated，and by using these fabricated FPAs，the thermal images were obtained at room temperature. However，the theoretical analysis indicates that the deviation between the theoretical model assuming constant temperature of the supporting frames of the FPAs and the experimental results gradually increases with the decreasing pitch size of from 200μm to 60μm. Based on the finite element method，the thermal characteristic of those FPAs was simulated and the reason for the deviation is found to be that the temperature-constant assumption is not quite appropriate for the substrate-free FPA，and the absorption of the thermal radiation will obviously result in the temperature rise of the supporting frame，which would increase the temperature of the adjacent pixels. The imaging performance of the substrate-free FPA is also analyzed. Compared with the substrate FPA with the same pitch, the thermal detection sensitivity of the substrate-free FPA with 60μm pitch increases by about one order of magnitude.

An Optical Readout Method Based Uncooled Infrared Imaging System

This paper presents an optical readout method based uncooled infrared imaging system that contains an optical read-out section and a bi-material micro-cantilever arrays (BMCA) detector. The optical read-out section is based on incoherent light spatial filter technique. The read-out section converts the deflection angles of BMCA caused by absorption of infrared (IR) radiation to a visible image through optical filtering operation of the BMCA with a knife-edge filter. A spatial mathematical model is presented to describe the read-out method and its validity is proved. The IR image of a person’s hand obtained through the using of the 100 × 100 BMCA and the 12-bit A/D quantizer demonstrates the ability of the system to create image. The performance test shows that the average Noise-equivalent temperature difference (NETD) of the imaging system can arrive at about 183mK with some areas having a NETD as low as 78mK.

The pressure-dependent performance of a substrate-free focal plane array in an uncooled infrared imaging system

Uncooled focal plane arrays (FPAs) are being developed for a wide range of infrared imaging applications. A substrate-free FPA for optical readout infrared imaging is fabricated with a pixel pitch of 120 μm. The pressure dependences of thermal conductance of a FPA with/without substrate are studied by modeling analysis. Infrared imaging experiments are performed to validate the modeling analysis. At atmospheric pressure the total thermal conductance of the substrate-free FPA is only 1/1000 time of the traditional FPA which has a 2 μm air gap between the cantilever beam and the substrate. Room temperature object’s thermal images are obtained even if the FPA is placed in the atmosphere. The air conductance of a substrate-free FPA at atmospheric pressure could be as small as that of a traditional FPA with a substrate in high vacuum (about 1 Pa). The experimental result also shows that the system noise keeps almost unchanged with the pressure. These characters will decrease the vacuum packaging request of the FPA and should be valuable for practical applications.

Design of a Novel Substrate-Free Double-Layer-Cantilever FPA Applied for Uncooled Optical-Readable Infrared Imaging System

This paper describes the design and performances of a novel focal-plane array (FPA) containing pixels of double bimaterial-layer cantilevers without silicon (Si) substrate for being applied in the uncooled optical-readable infrared (IR) imaging system. The top layer of the cantilever pixels is made of two materials with large mismatching thermal expansion coefficients: silicon nitride (SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) and gold (Au), which convert IR heat into mechanical deflection. The bottom layer is SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> cantilever, which partially serves thermal isolation legs. The top and bottom pads form the resonant cavity, which can dramatically enhance the absorption of incident IR irradiation, and the substrate-free configuration enables reducing the loss of incident IR energy. Responding to the IR source with spectral range from 8 to 14 mum, the IR imaging system may receive an IR images through visible optical readout method. A thermal-mechanical model for such cantilever microstructure is proposed, and the thermal and thermal-mechanical coupling field characteristics of the cantilever microstructure are optimized through numerical analysis method and simulation by using the finite-element method. The thermal-mechanical deflection simulated is 7.2 mum/K, generally in good agreement with what the thermal-mechanical model and numerical analysis forecast. The analysis suggests that the detection resolution of current design is 0.03 K, whereas the noise analysis from FPA indicates the current resolution to be around 100 muK and the limit noise-equivalent temperature difference (NETD) of the IR imaging system can reach to 7 mK.

Failure analysis of uncooled infrared focal plane array under a high-g inertial load

This paper describes the failure analysis of an uncooled infrared focal plane array (IRFPA) under a high-g inertial load system using finite element simulation and experimental validation methods. The uncooled IRFPA, responding to a source of infrared (IR) radiation with spectral range from 8 µm to 14 µm, is a cantilever array, which consists of two materials with mismatched thermal expansion coefficients. The radiance distribution of the IR source could be obtained by measuring the thermal–mechanical rotation angle distribution of every pixel in the cantilever array using a visible optical readout method. Based on this principle, room-temperature infrared imaging was developed under a static gravity environment, as described in our previous paper (Li C et al 2006 Meas. Sci. Technol. 17 1981–6). But under a dynamic inertial load, the rotation angle of every pixel includes not only the thermal–mechanical part but also a part induced by the inertial load. In the elastic deformation range, with a linearly increasing acceleration, the deformation angle induced by the inertial load increases linearly, which is validated by finite element simulation. This linear change in deformation, which can be subtracted from the total rotation angle in the optical readout using certain arithmetic, will not influence the imaging result. It is noteworthy that failure stress will occur when the deformation angle induced by the inertial load moves into the plastic deformation range, and the optical readout cannot image the IR object. Through finite element simulation the critical load resulting in IRFPA failure is 2715g, and this can be validated through impact using a Hopkinson bar after the IRFPA is placed in vacuum. By finite element simulation, the initial IRFPA surface profile without IR radiance after the 2715g load showed a conicoid characteristic. Simulation of the failure analysis of the uncooled IRFPA under 2715g acceleration predicts the military application of IRFPAs for an uncooled infrared imaging system in the high-g tactical range.

Optomechanical uncooled infrared imaging system: design, microfabrication, and performance

This paper presents the design, fabrication and performance of an uncooled micro-optomechanical infrared (IR) imaging system consisting of a focal-plane array (FPA) containing bi-material cantilever pixels made of silicon nitride (SiNx) and gold (Au), which serve as infrared absorbers and thermomechanical transducers. Based on wave optics, a visible optical readout system is designed to simultaneously measure the deflections of all the cantilever beams in the FPA and project the visible deflection map onto a visible charge-coupled device (CCD) imager. The IR imaging results suggest that the detection resolution of current design is 3-5 K, whereas noise analysis indicates the current resolution to be around 1 K. The noise analysis also shows that the theoretical noise-equivalent temperature difference (NETD) of the system can be below 3 mK.

Uncooled IR imaging array based on quartz microresonators

A quartz crystal resonator's resonance frequency is sensitive to temperature. This sensitivity has been exploited in the past in thermometers made of single, macroscopic quartz resonators that can accurately detect temperature changes of /spl mu/K. Using semiconductor microfabrication techniques, it is now possible to fabricate a large number of microresonators from a single quartz wafer. It is shown that combining the small thermal mass and high thermal isolation capability of such microresonators, the steep frequency versus temperature characteristics of resonators made of certain cuts of quartz and the low-noise characteristics of quartz crystal oscillators can result in high-performance infrared (IR) sensors and sensor arrays. In a microresonator sensor, the temperature change produced by the absorption of IR energy results in a frequency change that can be measured with a resolution that corresponds to a change in the resonator's temperature of less than a /spl mu/K. Calculation shows that an array of microresonators in the 200 MHz-1 GHz range can be the basis of an uncooled IR imaging system with a noise equivalent temperature difference, NETD, of <0.01 K. The design and fabrication problems to be overcome before such microresonator arrays can be realized are discussed.

Midinfrared modulation through the use of field-induced scattering in ferroelectric liquid crystals

The feasibility of the use of modulation devices based on field-induced transient scattering in ferroelectric liquid crystals (LC) to replace mechanical choppers used in uncooled infrared-imaging systems was investigated. Devices fabricated with ITO-coated ZnSe substrates and a ferroelectric LC path length of 25 µm were able to modulate optical radiation by transient forward scattering at rates approaching 20 kHz. Through the use of a commercial arbitrary waveform generator and associated PC-based software, drive waveforms were developed that produced a variable, square-wave optical-modulation pattern by the extension of the duration of the scattering state to periods ranging from hundreds of microseconds to milliseconds. The ability of these extended-scattering-mode (ESM) devices to modulate radiation in both the visible and midinfrared regions was verified in a simple experiment through the use of a Fourier-transform infrared spectrometer, in which an unoptimized ESM device displayed a 40% modulation dep th for IR radiation in the 8-12-µm region.