Microbolometer Research Articles

Proposal for a protocol using an infrared microbolometer camera and wavelet analysis to study foot thermoregulation

ABSTRACT Here we propose a protocol to (i) generate skin temperature (SkT) oscillations on glabrous tissues (plantar foot) in healthy subjects under controlled clinical environment conditions; (ii) measure quantitative temperature fields with an inexpensive microbolometer (MB) infrared camera in a clinical environment; and (iii) quantify the characteristics of skin temperature (SkT) oscillations through spectral analysis. We paid particular attention to the metrology of thermal measurements, with a special bench, including four homemade black body reference areas. We propose a live calibration procedure using this setup while correcting the thermal drift. After all of these correction steps, the experimental thermal resolution (NETDexp) for the temporal variation in each pixel was about 25 mK. Finally, a movement removal procedure was also applied to the thermal images to avoid foot spatial movement over the 10-min observation period. Thermoregulation was stimulated by a 6-min walking exercise test on six volunteers and was then studied using three kinds of scalar indicators evaluated before and after exercise per thermal image pixel. We demonstrated that the 6-min walk exercise increased the thermoregulation activity beneath the plantar foot sole. Moreover, unlike manually placed local thermal probes, the indicator fields proposed in this paper allow the operator to select the exact thermoregulation activation locations and analyse the spatial distribution patterns at these locations.

Infrared Deflectometry for Slope Deformation Measurements

This paper presents an implementation of deflectometry in the infrared spectrum. Deflectometry consists in recording the specular image of a reference grid pattern onto the mirror-like surface of a test specimen. This technique has two main advantages, high sensitivity and direct measurement of surface slopes, which in the case of thin plate bending is only one spatial differentiation away from surface strains. The objective of imaging in the infrared spectrum is to mitigate the main limitation of deflectometry in the visible spectrum, which is to require an extremely smooth surface to provide dominant specular reflection. This paper explores IR deflectometry for the first time for deformation measurements. Two different infrared cameras were assessed for use in IR deflectometry, a short wave quantum detector one, and a long wave microbolometer (MB) array one. Different materials of varying surface roughness were imaged and it was verified that the Rayleigh criterion was appropriate to determine whether IR deflectometry was feasible on a given surface. With the MB camera, most off-the-shelf material surfaces proved reflective enough to perform IR deflectometry. Finally, several bending tests were performed on aluminium plates and the deformation fields were shown to compare remarkably well with finite element simulations. The experimental data were then used in the Virtual Fields Method (VFM) and the elastic stiffness components of aluminium were retrieved with excellent accuracy, further validating IR deflectometry.

Рынок неохлаждаемых микроболометров для ИК-камер: тенденции и перспективы

Основное увеличение объема выпускаемых тепловизионных ИК-систем связано с гражданским применением: термографией, охранным и пожарным наблюдением, персональными системами ночного видения и локальными рынками безопасности (муниципальными, частными и пр.).

Design and Simulation of Device-Level Vacuum-Packaged Microbolometer With Integrated Optical Filter

Design and Simulation of Device-Level Vacuum-Packaged Microbolometer With Integrated Optical Filter

Challenges in using an analog uncooled microbolometer thermal camera to measure crop temperature

Abstract: It has been long known that thermal imaging may be used to detect stress (e.g. water and nutrient deficiency) in growing crops. Developments in microbolometer thermal cameras, such as the introduction of imaging arrays that may operate without costly active temperature stabilization, have vitalized the interest in thermal imaging for crop measurements. In this study, we have focused on the challenges occurring when temperature stabilization is omitted, including the effects of focal-plane-array (FPA) temperature, camera settings and the environment in which the measurements are performed. Further, we have designed and tested models for providing thermal response from an analog LWIR video signal (typical output from low-cost microbolometer thermal cameras). Finally, we have illustrated and discussed challenges which typically occur under practical use of thermal imaging of crops, by means of three cereal showcases, including proximal and remotely based (UAV) data acquisition. The results showed that changing FPA temperature greatly affected the measurements, and that wind and irradiance also appeared to affect the temperature dynamics considerably. Further, we found that adequate settings of camera gain and offset were crucial for obtaining a reliable result. The model which was considered best in terms of transforming video signals into thermal response data included information on camera FPA temperature, and was based on a priori calibrations using a black-body radiation source under controlled conditions. Very good calibration (r2>0.99, RMSE=0.32°C, n=96) was obtained for a target temperature range of 15-35°C, covering typical daytime crop temperatures in the growing season. However, the three showcases illustrated, that under practical conditions, more factors than FPA temperature may need to be corrected for. In conclusion, this study shows that thermal data acquisition by means of an analog, uncooled thermal camera may represent a possible, cost-efficient method for the detection of crop stress, but appropriate corrections of disturbing factors are required in order to obtain sufficient accuracy. Keywords: analog thermal camera, uncooled microbolometer, canopy temperature, cereals, UAV DOI: 10.3965/j.ijabe.20140704.007 Citation: Kusnierek K, Korsaeth A. Challenges in using an analog uncooled microbolometer thermal camera to measure crop temperature. Int J Agric & Biol Eng, 2014; 7(4): 60－74.

Thin film uncooled microbolometers based on plasma deposited materials

We make a summary of our research and development efforts made about microbolometers (MBs) based on plasma-enhanced chemical vapor deposition (PECVD) materials, like noncrystalline semiconductors that provide high temperature coefficient of resistivity values, in conjunction with SiOx and SiNx dielectrics used for thermoisolation, which, together with micromachining, are paving new ways for fabrication of MBs, making them promising for 2D imagers in both infrared and tera-Hertz regions. We studied a-Si:H(B), a-Ge:H, a-GeSi:H, and polymorphous p-Ge:H, p-SiGe:H as thermosensing materials (TSMs) for MBs in “bridge” configuration with “planar” and “sandwich” electrodes. This allows placing the read-out circuitry under the bridge, improving use of pixel area. PECVD SiNx films were used as both a support layer and as a coating for improving the response for λ = 8–12 μm. 2D modeling revealed both linear and super linear response to IR intensity. Voltage responsivity RU = (1.2–7) × 105 V/W is observed in both “planar” and “sandwich” MBs. The latter shows current responsivity RI = 0.3–14 A/W higher by about three orders of magnitude than the former. A key issue for any detector is the detectivity. Different TSMs show different noise characteristics. Noise in “sandwich” MBs is several orders of magnitude higher than that in “planar” structures. The best parameters observed with TSM Ge-Si:H are: RU = 7.2 × 105 V/W, RI = 14 A/W voltage and current detectivities [Formula: see text] = 8 × 109 cm Hz1/2W−1 and [Formula: see text] = 4 × 109 cm Hz1/2W−1. Junction structures on top of the “bridge” are also discussed. Finally we describe some reported applications of MBs.

The Performance Modeling of a VGA Bolometer with Self-Aligned Structure

The performance modeling of a pitch VGA -bolometer with the self-aligned thermal resistor structure is carried out. The self-aligned thermal resistor can be utilized for the maximizing the thermal resistance and the fill factor of a bolometer, so the performance improvement can be expected. From the results of the performance modeling of the micro-bolometer with self-align thermal resistor for a pitch microbolometer designed with minimum feature size, the drastic improvements of NETD from 38.7 mK to 19.1 mK, responsivity of 1.9 times are expected with a self aligned thermal resistor structure. The main reason for the performance improvements with a self-aligned thermal resistor structure comes from the increasement of the thermal resistance.

Imaging of breast cancer with mid- and long-wave infrared camera

In this novel study the breasts of 15 women with palpable breast cancer were preoperatively imaged with three technically different infrared (IR) cameras—micro bolometer (MB), quantum well (QWIP) and photo voltaic (PV)—to compare their ability to differentiate breast cancer from normal tissue. The IR images were processed, the data for frequency analysis were collected from dynamic IR images by pixel-based analysis and from each image selectively windowed regional analysis was carried out, based on angiogenesis and nitric oxide production of cancer tissue causing vasomotor and cardiogenic frequency differences compared to normal tissue. Our results show that the GaAs QWIP camera and the InSb PV camera demonstrate the frequency difference between normal and cancerous breast tissue; the PV camera more clearly. With selected image processing operations more detailed frequency analyses could be applied to the suspicious area. The MB camera was not suitable for tissue differentiation, as the difference between noise and effective signal was unsatisfactory.

Superconducting microbolometer captures radiation

superconducting microbolometer captures radiation