Microbolometer Array Research Articles

Non-Uniformity Correction in Microbolometer Array with Temperature Influence Compensation

Abstract In the article a non-uniformity correction method is presented which allows to compensate for the influence of detector’s temperature drift. For this purpose, dependency between output signal value and the temperature of the detector array was investigated. Additionally the influence of the temperature on the Offset and Gain coefficients was measured. Presented method utilizes estimated dependency between output signal of detectors and their temperature. In the presented method, the shutter is used for establishing signal reference. Thermoelectric cooler is used for changing the temperature of the detector array.

A Microbolometer Airborne Calibrated Infrared Radiometer: The Ball Experimental Sea Surface Temperature (BESST) Radiometer

A calibrated radiometer has been developed to enable the collection of accurate infrared measurements of sea surface temperature (SST) from unmanned aerial vehicles (UAVs). A key feature of this instrument is that in situ calibration is achieved with two built-in blackbodies (BBs). The instrument is designed so that the 2-D microbolometer array produces infrared images incremented as the aircraft travels, resulting in a well-calibrated strip of SST. Designed to be carried by medium-class UAVs, the Ball Experimental SST (BESST) instrument has been also successfully flown on manned aircraft. A recent intercalibration of BESST was carried out at the University of Miami using their National Institute of Standards and Technology traceable water-bath BB and a Fourier transform interferometer, the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI). The characterization of the BESST instrument with the Miami BB demonstrates the linearity and precision of the response of the microbolometer-based radiometer. Coincident measurements of SST from a nearby pier clearly demonstrated the excellent performance of the BESST instrument with a mean SST equal to that of the M-AERI and an RMS of 0.14 K very close to the microbolometer's advertised precision of 0.1 K. Cold calibration was not possible in Miami due to condensation, but a Ball BB was characterized relative to the Miami water-bath BB, and calibrations were made in Boulder at lower temperatures than were possible in Miami. The BESST instrument's performance remained linear, and the mean and RMS values did not change. UAV flights were conducted in summer/fall of 2013 over the Alaskan Arctic.

Combined holography and thermography in a single sensor through image-plane holography at thermal infrared wavelengths

Holographic interferometry in the thermal wavelengths range, combining a CO(2) laser and digital hologram recording with a microbolometer array based camera, allows simultaneously capturing temperature and surface shape information about objects. This is due to the fact that the holograms are affected by the thermal background emitted by objects at room temperature. We explain the setup and the processing of data which allows decoupling the two types of information. This natural data fusion can be advantageously used in a variety of nondestructive testing applications.

Experimental study of an uncooled microbolometer array for thermal mapping and spectroscopy of asteroids

We report on the experimental study of the imaging and spectroscopic capabilities of an uncooled microbolometer array for space missions to small bodies in the inner solar system. The selected Nano640E T M device manufactured by the ULIS company (Grenoble, France) has a format of 640x480 pixels and can measure temperatures down to at least 255 K, the lower limit reached in our tests. It has a Noise Equivalent Temperature Difference (NETD) of 40.9 ±4.5 mK (300 K, F/0.86) and the capability to produce excellent, radiometrically calibrated images with an error of the order of 1 to 5 K depending upon the number of calibration sources. Using a set of neutral density filters, we determined the signal-to-noise ratio (SNR) of a spectrum acquired by the detector, as a function of the scene temperature, wavelength and spectral resolution. Considering an asteroid at 1 AU from the Sun, an optical system at F/0.86, a spectral resolution of 0.3 μm and a scene temperature of >350 K, the resulting spectrum has sufficient SNR to properly identify the main mineralogical emission features. Our results show that uncooled microbolometer arrays are very promising to acquire calibrated thermal images and mid-infrared (8–14 μm) spectra of the surface of small bodies in the inner solar system.

Low-Cost and Modularized Test Bench for Focal Plane Array

In this paper, a low-cost and modularized test bench for microbolometric focal plane array is proposed. Based on the analysis of driving microbolometric focal plane array, we have set up the simple test bench. The test bench consists of four major modules: optical part, driving sequence timer, power supply and signal processing board, and data analyzer. Each module in the test bench is reconfigurable and the driving sequence timer is programmable in system. The proposed test bench is low-cost and has been applied to practical microbolometric focal plane arrays in our laboratory.

Quantum cascade laser-based hyperspectral imaging of biological tissue.

The spectroscopy of analyte-specific molecular vibrations in tissue thin sections has opened up a path toward histopathology without the need for tissue staining. However, biomedical vibrational imaging has not yet advanced from academic research to routine histopathology due to long acquisition times for the microscopic hyperspectral images and/or cost and availability of the necessary equipment. Here we show that the combination of a fast-tuning quantum cascade laser with a microbolometer array detector allows for a rapid image acquisition and bares the potential for substantial cost reduction. A 3.1 x 2.8 mm2 unstained thin section of mouse jejunum has been imaged in the 9.2 to 9.7 μm wavelength range (spectral resolution ~1 cm(-1)) within 5 min with diffraction limited spatial resolution. The comparison of this hyperspectral imaging approach with standard Fourier transform infrared imaging or mapping of the identical sample shows a reduction in acquisition time per wavenumber interval and image area by more than one or three orders of magnitude, respectively.

Terahertz holography for imaging amplitude and phase objects

A non-monochromatic THz Quantum Cascade Laser and an uncooled micro-bolometer array detector with VGA resolution are used in a beam-splitter free holographic set-up to measure amplitude and phase objects in transmission. Phase maps of the diffraction pattern are retrieved using the Fourier transform carrier fringe method; while a Fresnel-Kirchhoff back propagation algorithm is used to reconstruct the complex object image. A lateral resolution of 280 µm and a relative phase sensitivity of about 0.5 rad are estimated from reconstructed images of a metallic Siemens star and a polypropylene test structure, respectively. Simulations corroborate the experimental results.

Uncooled Microbolometer Infrared Focal Plane Array Without Substrate Temperature Stabilization

This paper presents a novel and compact compensation architecture for uncooled microbolometers without substrate temperature stabilization. The substrate temperature-induced nonuniformity and nonlinear resistance characteristics of the microbolometer array elements are investigated in detail. We propose an analytical model to identify the main nonideal effects and dispersion sources caused by the substrate temperature and their respective impacts on the uncooled microbolometers array. This proposed compensation approach is based on a differential current mirror readout architecture, which allows pixel response and offset correction to be performed as a function of the uncooled infrared focal plane array (IRFPA) sensor's operating temperature. An experimental FPA chip based on this approach has been designed and implemented on silicon using a 0.5- μm CMOS technology and surface micromachining process. The proposed architecture allows the microbolometer array nonuniformity control over a wider range of readout integrated circuits substrate temperatures while maintaining better than 63-mK noise equivalent temperature difference with f/1 optics. As a result of the elimination of the temperature stabilization requirement, the IRFPA turn-on time for high performance imaging can be greatly reduced. Power, volume, and weight of the IRFPA are also significantly reduced. This approach is ideally suited for high-volume, low-cost, low-power, and low-weight production applications.

Long-wave infrared digital holographic interferometry with diffuser or point source illuminations for measuring deformations of aspheric mirrors

Long-wave infrared digital holographic interferometry with CO2 laser and microbolometer arrays has been developed for testing the large deformations of space reflectors. The setup considered is a Mach–Zehnder, associated to the digital holography reconstruction of the wavefront in the inline configuration with phase shifting. Two possibilities exist for illuminating the tested reflector: either with a point source (similarly to classical interferometry) or an extended source (with a diffuser). This paper presents the development of a modular setup which allows comparing both in the case of a parabolic mirror.

High-speed CMOS readout integrated circuit for large-scale and high-resolution microbolometer array

A new CMOS readout integrated circuit (ROIC) for microbolometric focal plane array (FPA) is proposed in this paper. By applying multiple-module parallel working technique, the pixel readout speed of the CMOS ROIC can reach 10MHz, which is very suitable for large-scale microbolometer array. The CMOS ROIC of each parallel working module consists of three major parts: direct injection (DI) input circuits, column-shared integrating circuits, and common noise-suppressing circuits. The readout structure of the ROIC is simple because of the DI input, shared and common circuits, and this makes the ROIC satisfy the requirements of small-pixel microbolometric FPA. Furthermore, the voltage signals from different working modules can be output according to a certain order through a high-speed output circuit. An experimental readout chip based on the proposed ROIC has been designed and fabricated to verify its readout function and performance. The measurement results of the experimental readout chip have successfully proved that the proposed CMOS ROIC can be applied to high-speed, low-noise, large-scale and high-resolution microbolometric FPA.

A novel non-uniformity compensating method for microbolometric focal plane array

This paper describes a non-uniformity compensating method for microbolometric focal plane array. Through the analysis of the basic principle of conventional non-uniformity compensating methods for microbolometric focal plane array, we have pointed out their common fatal limitation unable to compensate the nonlinear non-uniformity of microbolometer array. Based on our previous constant power optimized bias, a novel and simple nonlinear non-uniformity compensating method for microbolometric focal plane array is proposed in this paper. The proposed compensating method is simply configured and can easily and effectively be utilized to compensate the nonlinear non-uniformity of microbolometer array.

A compact thermosonic inspection system for the inspection of composites

A portable thermosonic inspection system has been developed incorporating a miniature microbolometer array camera. The vibrations excited during a test are monitored using a high frequency microphone and assessed automatically to validate the test. An investigation of the correlation between thermosonic heating and vibration excitation energy in composites is presented. The system has been trialled on aerospace components containing impact damage.

Uncooled Microbolometer Arrays With High Responsivity Using Meshed Leg Structure

In this letter, a meshed leg structure is proposed for the first time to control the thermal conductivity in the uncooled microbolometer arrays without changing the fill factor. An amorphous silicon-based microbolometer was fabricated with 64 × 64 arrays with a 35 μm pixel pitch to verify the proposed design. The hole in the meshed leg was 0.7 × 0.7 μm2. The uniformity of the pixel resistance within the 64 × 64 arrays was below 2%. Self-heating and responsivity under infrared (IR) irradiation were investigated in three leg types: 1) type 1-normal leg structure; 2) type 2-meshed leg structure; and 3) type 3-metal extended leg structure. Comparison of the IR irradiation current showed the responsivity of the proposed structure (type 2) that was improved by four times over type 3. For the thermal noise equivalent temperature difference value, type 2 is 194 mK, which is much better than 384 mK of type 3.

Polymer composite based microbolometers

Abstract. This work focuses on the basic suitability assessment of polymeric materials and the corresponding technological methods for the production of infrared (micro-) bolometer arrays. The sensitive layer of the microbolometer arrays in question is composed of an electrically conductive polymer composite. Semi-conducting tellurium and vanadium dioxide, as well as metallic silver, are evaluated concerning their suitability as conductive filling agents. The composites with the semi-conducting filling agents display the higher temperature dependence of electrical resistance, while the silver composites exhibit better noise performance. The particle alignment – homogeneous and chain-shaped alike – within the polymer matrix is characterized regarding the composites' electrical properties. For the production of microbolometer arrays, a technology chain is introduced based on established coat-forming and structuring standard technologies from the field of polymer processing, which are suitable for the manufacture of a number of parallel structures. To realize the necessary thermal isolation of the sensitive area, all pixels are realized as self-supporting structures by means of the sacrificial layer method. Exemplarily, 2 × 2 arrays with the three filling agents were manufactured. The resulting sensor responsivities lie in the range of conventional microbolometers. Currently, the comparatively poor thermal isolation of the pixels and the high noise levels are limiting sensor quality. For the microbolometers produced, the thermal resolution limit referring to the temperature of the object to be detected (NETD) has been measured at 6.7 K in the superior sensitive composite layer filled with silver particles.

Experimental three-dimensional beam profiling and modeling of a terahertz beam generated from a two-color air plasma

We use a broadband microbolometer array to measure the full three-dimensional (3D) terahertz (THz) intensity profile emitted from a two-color femtosecond plasma and subsequently focused in a geometry useful for nonlinear spectroscopic investigations. Away from the immediate focal region we observe a sharp, conical intensity profile resembling a donut, and in the focal region the beam collapses to a central, Lorentz-shaped profile. The Lorentzian intensity profile in the focal region can be explained by considering the frequency-dependent spot size derived from measurements of the Gouy phase shift in the focal region, and the transition from the donut profile to a central peak is consistent with propagation of a Bessel–Gauss beam, as shown by simulations based on a recent transient photocurrent model (You et al 2012 Phys. Rev. Lett. 109 183902). We combine our measurements to the first full 3D visualization of the conical THz emission from the two-color plasma.

First approach for on-ground radiometric characterization of the new infrared sensor technology camera

The aim is to present a first approach for the on-ground radiometric characterization of the new infrared sensor technology (NIRST) instrument. NIRST is an infrared radiometer on board the SAC-D/Aquarius mission, launched on June 10, 2011. It is composed of a middle-wave infrared and a long-wave infrared camera, with three arrays of 512 microbolometers each, and has also a pointing Be mirror. In order to perform the on-ground radiometric characterization, several measurements are taken using blackbody sources. Aiming to obtain a set of absolute radiometric coefficients for each pixel of each microbolometer array, relating digital numbers and brightness temperature or its equivalent in radiated power, polynomial fits are performed. Interpixel characterization to obtain relative calibration coefficients is also performed, relating the counts of an arbitrary pixel to those of a reference pixel. The choice of polynomial order for both absolute and relative calibration functions, as well as the election of reference pixels, are analyzed. Finally, a pointing angle characterization is performed. This approach leads to high polynomial orders for both absolute and relative calibrations, indicating that a new approach for NIRST radiometric characterization is required to catch-up the nonlinearity.

Infrared Emissivity Measurements of Building and Civil Engineering Materials: A New Device for Measuring Emissivity

The knowledge of the infrared emissivity of materials used in buildings and civil engineering structures is useful for two specific approaches. First, quantitative diagnosis of buildings or civil engineering infrastructures by infrared thermography requires emissivity values in the spectral bandwidth of the camera used for measurements, in order to obtain accurate surface temperatures; for instance, emissivity in the band III domain is required when using cameras with uncooled detectors (such as micro-bolometer arrays). Second, setting up accurate thermal balances by numerical modeling requires the total emissivity value for a large wavelength domain; this is, for instance, the case for computing the road surface temperature to predict ice occurrence. Furthermore, periodical surveys of emissivity variations due to aging or soiling of surfaces could be useful in many situations such as thermal mapping of roads or building insulation diagnosis. The use of portable emissivity measurement devices is required for that purpose. A device using an indirect measurement method was previously developed in our lab; the method uses measurement of the reflectivity from a modulated IR source and requires calibration with a highly reflective surface. However, that device uses a low-frequency, thermal modulation well adapted to laboratory measurements but unfit for fast and in situ measurements. Therefore, a new, portable system which retains the principle of an indirect measurement but uses a faster-frequency, mechanical modulation more appropriate to outdoor measurements was developed. Both devices allow measurements in the broad \((1\,\upmu \)m to \(40\,\upmu \)m) and narrow \((8\,\upmu \)m to \(14\,\upmu \)m) bands. Experiments were performed on a large number of materials commonly used in buildings and civil engineering structures. The final objective of this work is to build a database of emissivity of these materials. A comparison of laboratory and on-site measurements of emissivity values obtained in both spectral bands will be presented along with an estimation and an analysis of measurement uncertainties.

Thermal-vision channel based on an uncooled array of microbolometers

This paper reports the development of a thermal-vision channel (device) based on an uncooled array of microbolometers, along with its features and characteristics. The channel can be used in portable devices or self-contained systems, such as unmanned aircraft and robotic complexes.

Mobile speckle interferometer in the long-wave infrared for aeronautical nondestructive testing in field conditions

We present the development of a speckle interferometer based on a CO 2 laser and using a thermal infrared camera based on an uncooled microbolometer array. It is intended to be used for monitoring deformations as well as detecting flaws in aeronautical composites, with a smaller sensitivity to displacement compared to an equivalent system using visible (VIS) lasers. Moreover the long wavelength allows working with such interferometers outside the laboratory. A mobile system has been developed on the basis of previous laboratory developments. Then it is validated in a variety of industrial nondestructive testing applications in field working conditions.

Nb5N6 microbolometer arrays for terahertz detection

A novel room-temperature microbolometer array chip consisting of an Nb5N6 thin film microbridge and a dipole planar antenna, which is used as a terahertz (THz) detector, is described in this paper. Due to the high-temperature coefficient of the resistance of the Nb5N6 thin film, which is as high as −0.7% K−1, such an antenna-coupled microbolometer is ideal for detecting signals in a frequency range from 0.22 THz to 0.33 THz. The dc responsivity, calculated from the measured I–V curve of the Nb5N6 microbolometer, is about −760 V/W at a bias current of 0.19 mA. A typical noise voltage as low as 10 nV/Hz1/2 yields a low noise equivalent power (NEP) of 1.3 × 10−11 W/Hz1/2 at a modulation frequency above 4 kHz, and the best RF responsivity, characterized using an infrared device measuring method, is about 580 V/W, with the corresponding NEP being 1.7 × 10−11 W/Hz1/2. In order to further test the performance of the Nb5N6 microbolometer, we construct a quasi-optical type receiver by attaching it to a hyperhemispherical silicon lens, and the result is that the best responsivity of the receiver is up to 320 V/W. This work could offer another way to develop a large scale focal-plane array in silicon using simple techniques and at low cost.