Open Access
Add to BibSonomy
Abstract
We present a large-area perfect blackbody sheet, which would offer a planar standard radiator for high-precision thermal imager calibration. Polydimethylsiloxane (PDMS) sheets with nano-precision surface micro-cavity structures achieve both ultra-low reflectance (ultra-high emissivity close to unity) over the thermal infrared wavelengths and high durability to mechanical contact. The investigation on the geometrical parameters of the conical micro-cavities, that is, radii and aspect ratios (ratio of height to radius), confirmed that the PDMS blackbody sheet with a micro-cavity radius of ∼6 µm and an aspect ratio of ∼4 exhibits the optimum hemispherical reflectance of less than 0.002 (emissivity of higher than 0.998) at the thermal infrared wavelengths (6–15 µm). Furthermore, the large-area PDMS blackbody sheet of 100 mm × 80 mm maintained an excellent in-plane uniformity of the emissivity. This unprecedented large-area perfect blackbody conforms to the International Electrotechnical Commission (IEC) standard recommendation regarding thermal imager calibration for fever screening in terms of the emissivity performance.
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Thermal imagers such as infrared thermography devices enable us to visualize the radiation temperature map of target objects at near room temperature by detecting thermal infrared of typically 7–14 µm in wavelength. Recent uncooled infrared two-dimensional sensor technology such as microbolometer arrays with higher resolution, smaller size, and lower price, has advanced the applications of thermal imagers in various fields: fever screening and disease diagnosis, land and sea surface temperature measurement in earth observation, landslide mapping and volcanic activity observation for disaster prevention, and building diagnosis and equipment inspection for condition monitoring [1–9]. In particular, medical application and earth observation often require precise radiation temperature measurement: for example, sea surface temperature measurement for climate variable datasets or fever screening thermographs requires 0.1 K of accuracy or stability [4,10–13]. Recent thermal imagers potentially have such capability, however, measured temperature values are usually unstable without monitoring a reference. A planar blackbody source is used as the reference to accommodate an imager making two-dimensional measurements. To achieve an accurate calibration, the emissivity of the planar blackbody should be close to unity. Indeed, the International Electrotechnical Commission (IEC) standard regarding thermographic fever screening recommends emissivity of ≥0.998 for the calibrator [12,13]. However, most of the commercially available planar blackbody sources have an insufficient emissivity of 0.95–0.98 [12,14].
High emissivity means low reflectance for opaque materials because the sum of the reflectance, absorptance, and transmittance is unity and the absorptance is equal to emissivity according to Kirchhoff's law. To conform to the IEC standard [13], opaque materials with a reflectance of less than 0.002 should be used. One of the strategies to achieve such an ultra-low reflectance is the suppression of Fresnel reflection [15–19]. According to the effective medium theory [20], the porous surface structure of nanometer size and low density makes the effective refractive index of the material surface close to the ambient refractive index, reducing the Fresnel reflection. A typical example of such porous ultra-low reflectance materials includes vertically aligned carbon nanotubes (VACNTs), but they are limited to non-contact, closed-environment applications due to the fragility of their porous surface structure [15,16,21]. Therefore, surface durability should be pursued for use in consumer products. To this end, we have recently developed a perfect blackbody sheet from polydimethylsiloxane (PDMS), based on a simple cavity blackbody strategy rather than the low-density porous structures, to achieve both ultra-low reflectance and contact durability (Fig. 1(a)) [22]. The PDMS blackbody sheet has a fine structure filled with micro-cavity blackbodies all over the surface (Fig. 1(b)). These microstructures can be produced by a replica molding process. The mold, which is made of a poly allyl diglycol carbonate (CR-39, in trade name) substrate, has conical micro etch pits formed via ion track etching technique [23]. PDMS absorbs mid-infrared due to many vibration modes of a polymer framework. Furthermore, the micro-cavity blackbody structure enhances infrared light absorption via multiple reflections, reducing the net reflectance extremely (Fig. 1(c)). Indeed, the PDMS blackbody sheet exhibited a hemispherical reflectance of less than 0.002 in the wavelengths of 6–15 µm [22].
Fig. 1. (a) Photograph of our PDMS blackbody sheet and (b) scanning electron microscope image of the blackbody sheet surface. (c) The precise micro-cavity structure on the blackbody sheet surface reduces net reflectance via multiple reflections.
In this study, we investigated the performance of our PDMS blackbody sheet as a promising candidate for the reference planar blackbody source to calibrate a thermal imager in the field. We experimentally determined the optimum geometry of the surface micro-cavities: a radius and aspect ratio, along with a review of the theoretical simulation in previous studies. Then, we fabricated a PDMS blackbody sheet of a large area to meet the requirement for the calibration source. We successfully confirmed that our large-area PDMS blackbody sheet exhibited the ultra-low reflectance of <0.002 (close-to-unity emissivity of >0.998) and the excellent in-plane uniformity, which conform to the IEC document recommendation.
2. Experiments
2.1 Fabrication of PDMS blackbody sheets
Figure 2 shows a fabrication procedure of a PDMS blackbody sheet. The PDMS blackbody sheets with a conical spike-type microstructure were fabricated by a replica molding process using templates made by ion track etching as in the previous paper [22]. Substrates of CR-39 (BARYOTRAK, Fukuvi Chemical Industry Co., Ltd, Japan) with 0.8 mm thick were used as a template material. The substrate cut to 100 mm × 100 mm was set in the ion irradiation chamber of an azimuthally varying field cyclotron at the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) facility of National Institutes for Quantum and Radiological Science and Technology (QST) (Fig. 2(a)). The chamber was evacuated to 10−3 Pa. Neon or oxygen ions with energy in the range from 200–335 MeV were irradiated onto the CR-39 substrate. The ion irradiation areal density was the order of 105–106 ions cm-2. The irradiated substrates were cut into small pieces or 100 mm × 80 mm, and then etched in a 6.4 mol L-1 NaOH aqueous solution at 70 °C for 10–20 h (Fig. 2(b)). One conical micro-pit is formed for each ion track. By proceeding with the etching, the micro-pits were grown until the pit openings filled the entire surface of the substrate. The ion irradiation areal density determines the average radius of the pit. The ion species and their energies affect the damage density on the polymer molecule bonds in the substrate and determine the track etching rate while bulk etching rate is maintained. Therefore, the pit radius and aspect ratio (ratio of pit depth to radius) formed on the CR-39 substrate can be controlled by adjusting ion irradiation areal density, ion species and energy. The etched CR-39 substrates were washed in pure water and dried to be used as molds for the blackbody sheets fabrication.
Fig. 2. Fabrication procedure of a PDMS blackbody sheet. (a) CR-39 is irradiated with the ion beam. (b) Irradiated CR-39 is etched in a NaOH aqueous solution. (c) A PDMS prepolymer is poured onto the CR-39 mold. (d) Cured PDMS is peeled off from the CR-39 mold.
PDMS prepolymer (SIM-360, Shin-Etsu Chemical Co., Ltd, Japan) was mixed with a curing agent (CAT-360, Shin-Etsu Chemical Co., Ltd, Japan) in a weight ratio of 10:1, and subsequently degassed in a vacuum desiccator. The mixed prepolymer was poured on the CR-39 mold to a thickness of approximately 1 mm (Fig. 2(c)) and then left to cure at room temperature for one day. The cured PDMS with the inverted microstructural surface of the mold was peeled off from the CR-39 mold to obtain a PDMS blackbody sheet (Fig. 2(d)).
2.2 Geometry characterization of surface microstructure
The definitions of the surface microstructure geometries in this study are schematically shown in Fig. 3. The radius and height of the conical spike on a PDMS blackbody sheet are defined as r and h, respectively. The ratio is defined as the aspect ratio a. The r and a can be determined by using the corresponding CR-39 mold because these values are nearly identical with the opening radius and aspect ratio of the conical pit on the CR-39 mold. In this study, we determined r as the average radius of the opening derived from the average area of each pit, that is, the reciprocal of the ion irradiation areal density on the CR-39 substrate. The aspect ratio a was determined as the cotangent of the half apex angle of the conical pit, which was measured on a cross-sectional image of the CR-39 mold observed by an optical microscope.
Fig. 3. Parameters of the surface microstructure of the PDMS blackbody sheet. The r and h are the radius and height of the conical spike, respectively. The aspect ratio a is defined by ${h / r}$. The conical spike of the PDMS blackbody sheet is an inverted replica of the conical pit of the corresponding CR-39 mold.
2.3 Optical characterization
The hemispherical reflectance of a PDMS blackbody sheet and the corresponding CR-39 mold was measured at the wavelengths of 2.5–15 µm using a Fourier transform infrared (FTIR) spectrometer (FT/IR-6300typeA FTIR spectrometer, JASCO Co., Japan). The FTIR spectrometer is equipped with a 3-inch diffusive gold integrating sphere and liquid nitrogen-cooled mercury cadmium telluride detector option (IntegratIR, PIKE Technologies, USA). The sample port size of the integrating sphere was approximately 1 inch. The sample hemispherical reflectance was determined by comparison to the reflectance standard from diffusible gold (Infragold, Labsphere, USA). The measurement of the hemispherical reflectance followed the procedure described in the previous paper [22]. Detector linearity has been confirmed at the measured reflectance level. Measurements were performed by taking into account the throughput of the integrating sphere and the baseline signal. The typical uncertainty (95% confidence level) of the hemispherical reflectance measurement is estimated to be 0.0005 at a wavelength of 10 µm. To determine the uniformity of a large-area PDMS blackbody sheet of 100 mm × 80 mm, the hemispherical reflectance was measured at six separate positions on the surface. To evaluate the thermal image of the large-area PDMS blackbody sheet, a thermal imager (FLIR E60, FLIR Systems, Inc., USA) was used. The detection wavelength range of the thermal imager was 7.5–13 µm. The emissivity setting of the thermal imager was set to 1.00. The sheet was placed on an aluminum plate, and only one end of the plate was fixed with a vise. The sheet was placed in a temperature-controlled room at 22 °C to 23 °C and imaged with the thermal imager after aging for ∼1 h.
3. Results and discussion
3.1 Reflectance depending on surface microstructure geometry
The reflectance of the PDMS blackbody sheet was evaluated in terms of the dependence on surface conical microstructure geometry, particularly radius and aspect ratio, to establish the conditions to achieve the desirable emissivity of >0.998 for a planar blackbody calibrator. Although we mainly focused on the PDMS blackbody sheet, the reflectance of the corresponding CR-39 mold was investigated together because CR-39 is also a good mid-infrared absorber. Figure 4(a) and 4(b) show the hemispherical reflectance of PDMS blackbody sheets and that of their molds, respectively. In this case, the aspect ratio a was a nearly fixed value of ∼2.9 and the radii r were 3.6 µm and 6.3 µm. The reflectance for the unprocessed flat samples is also shown together in the same graph. The reflectance of the PDMS blackbody sheets was less than 0.004 at wavelengths above 6 µm. PDMS became transmissive at some wavelengths below 6 µm (shaded bands in the graph), where the high reflectance was observed due to Fresnel reflection from an interface between at the back of the sheet and air. The reflectance in the shaded band is not discussed further because the band is out of the measurement range of a thermal imager for around room temperature. The reflectance of the PDMS blackbody sheets was reduced to less than one-tenth that of flat PDMS due to the micro-cavity structure of the sheets. The sharp fluctuation of reflectance due to intrinsic anomalous dispersion of PDMS was observed at some wavelengths. Typical anomalous dispersions observed at approximately 8 µm, 10 µm, and 12 µm are attributed to CH3 symmetric bending vibration in Si–CH3, stretching vibration of Si–O–Si, and CH3 rocking vibration in Si–CH3, respectively [24–26]. The decreasing reflectance with increasing r was observed, as previously predicted by numerical simulation [22,27]. Similar trends were also observed for the corresponding CR-39 molds as shown in Fig. 4(b). The change in reflectance depending on the r was larger for the pit-type microstructure (the CR-39 molds) than the spike-type microstructure (the PDMS blackbody sheets). This difference between pit and spike was also shown in numerical simulation at $a$∼5 [21], while the discussion is not simple due to different materials. Another r dependence of the reflectance was also investigated with a nearly fixed aspect ratio a ∼3.5 as shown in Fig. 4(c) and 4(d). The reflectance of both the PDMS blackbody sheet and the CR-39 mold decreased with increasing radius, and this trend was more apparent for pit-type microstructure and at longer wavelengths, as same as in the case of a ∼2.9. Notably, these PDMS blackbody sheets of both samples in Fig. 4(c) exhibited the ultra-low reflectance of less than 0.002 at the wavelengths of 6–15 µm, and mostly less than 0.001. The peak at a wavelength of 8 µm was considerably reduced and unrecognized anymore. This level is already enough low reflectance for a reference planar blackbody source. Until our development, such a planar blackbody has never existed other than VACNTs.
Fig. 4. Hemispherical reflectance of (a)(c) PDMS blackbody sheets and (b)(d) the corresponding CR-39 molds. The reflectance for (a)(b) radius r of 3.6 µm and 6.3 µm at the nearly fixed aspect ratio a of ∼2.9, and for (c)(d) radius r of 4.6 µm and 6.6 µm at the nearly fixed aspect ratio a of ∼3.5. The hemispherical reflectance of unprocessed flat samples is also shown in each figure. The shaded bands indicate wavelengths at which the PDMS blackbody sheet becomes transmissive.
As shown in Fig. 4, not only the radius r but also the aspect ratio a seems to have a large effect on the reflectance. Then the influence of the aspect ratio a on the reflectance was investigated with a fixed radius r. Figure 5 shows the hemispherical reflectance of PDMS blackbody sheets and the corresponding CR-39 molds when a is 2.9 or 3.6 with a nealy fixed r of ∼6.4 µm. The reflectance of both samples decreased with increasing the aspect ratio a. This trend was also consistent with the numerical simulation [22,27]. Increasing the aspect ratio a with the same radius means that the wall angle of the micro-cavity becomes steeper and the cavity length becomes longer. They are synonymous with that the possibility of reflected light toward the bottom of the cavity increases and the area of the cavity wall increases. The effect of multiple reflections is consequently enhanced, which applies to both the spike-type blackbody sheet and the pit-type mold.
Fig. 5. Hemispherical reflectance of (a) PDMS blackbody sheets and (b) the corresponding CR-39 molds with the aspect ratio a of 2.9 and 3.6 and the nearly fixed radius r of ∼6.4 µm. The hemispherical reflectance of unprocessed flat samples is also shown in each figure. The data shown by the green and purple lines are the same as those in Fig. 4. The shaded bands indicate wavelengths at which the PDMS blackbody sheet becomes transmissive.
According to the above results, it was experimentally confirmed that the reflectance decreases with increasing the radius $r$ and the aspect ratio a. Then we investigated the optimum conditions of the radius r and aspect ratio a to establish extremely low reflectance (<0.002). Figure 6 shows the hemispherical reflectance of the samples with $r$ = 4.6 µm, $a$ = 3.4 (condition I), with $r$ = 6.6 µm, $a$ = 3.6 (condition II), and with $r$ = 5.3 µm, $a$ = 4.0 (condition III). Under these conditions, the hemispherical reflectance of <0.002 at wavelengths of 6–15 µm was achieved in the PDMS blackbody sheet. Note that condition III has a smaller r but larger a than condition II. The trend of reflectance was III < II < I, whereas the change in reflectance depending on the conditions was smaller in the PDMS blackbody sheet (spike-type) than in the corresponding CR-39 mold (pit-type). In the case of the PDMS blackbody sheet at the condition I, the reflectance slightly exceeded 0.001 at the wavelengths of 9–10 µm and 12–13 µm (at around anomalous dispersion). Probably, the condition I represents the lower limit of r and a for achieving the target mid-infrared reflectance of <0.002. To stably realize the reflectance of enough less than 0.002 in the PDMS blackbody sheet, it can be concluded that the optimum condition of r and a is approximately 6 µm and 4, respectively.
Fig. 6. Hemispherical reflectance of (a) PDMS blackbody sheets and (b) the corresponding CR-39 molds with the radius $r$ = 4.6–6.6 µm and the aspect ratio $a$ = 3.4–4.0. The data of red and purple lines are the same as the data in Fig. 4. The gray shaded bands indicate wavelengths at which the PDMS blackbody sheet becomes transmissive.
3.2 In-plane uniformity of reflectance in large-area blackbody sheet
Based on the optimum microstructure mentioned above, a large-area PDMS blackbody sheet of 100 mm × 80 mm was fabricated to meet the demand for a planar blackbody source (Fig. 7). The fabricated micro-spike structure has 5.3 µm for r and 4.0 for a.
Along with the emissivity, the in-plane uniformity is also one of the most important parameters for a planar blackbody source. To examine the uniformity, the reflectance of the PDMS blackbody sheet was measured at six separate areas as shown in Fig. 8(a). The reflectance at all the separated area was less than 0.002 at wavelengths of 6–15 µm, and mostly well below 0.001, as expected from the microstructure geometry. The measurement results at the six areas showed almost the same values at the wavelengths of 6–15 µm. The standard deviation of the reflectance at the six areas was less than 0.001 at the wavelengths of 6–15 µm, as shown in Fig. 8(b). Although the measured reflectance was an average value within the area of sample port of one inch in diameter, the reflectance was found to be uniform over a wide area of the 100 mm × 80 mm sheet surface. This performance is due to the high uniformity of materials and processing techniques: CR-39 for a master mold and PDMS for a replica, and techniques of ion track etching. In this way, the large-area blackbody sheet that has not only high emissivity but also extremely high uniformity was successfully produced. There is also an advantage that mass production is considered possible by replica molding. Furthermore, the PDMS blackbody sheet is durable and has heat resistance [22], which is advantageous as a reference standard for the field use.
Fig. 8. (a) Hemispherical reflectance and (b) its standard deviation at six measurement areas on the large-area PDMS blackbody sheet. The shaded bands indicate wavelengths at which the PDMS blackbody sheet becomes transmissive. The inset photograph is the measured sample and the dotted circles indicate the six measurement areas.
We demonstrated the possibility of thermal imager calibration with our PDMS blackbody sheet. A thermal image of the large-area PDMS blackbody sheet was obtained at room temperature (Fig. 9). As shown in Fig. 9(a), the blackbody sheet was placed on an aluminum plate with the thermal imager facing it. Figure 9(b) shows the thermal image, in which the blackbody sheet is shown in the area surrounded by the dashed line, and the underlying aluminum plate is shown around it. The higher temperature parts in the lower and right of the image correspond to the reflected images of the warmed thermal imager and the cable connected to it, respectively. The reflected images were not observed on the place of the PDMS blackbody sheet, thanks to its ultra-low reflectance. Although the sheet temperature appeared almost uniform, vertical streak patterns were observed. The same pattern was observed even when the sheet or the imager was rotated and thus is attributed to the non-uniformity of the thermal imager, not of the blackbody sheet. The thermal image of large-area PDMS blackbody sheets perceives such a slight non-uniformity of the imager, indicating that the blackbody sheets can evaluate properties of thermal imagers in detail. In this case, the difference between the maximum and minimum temperature readings of each pixel was ∼0.6 K within the area of the blackbody sheet. When the thermal image of the blackbody sheet was segmented by 396 areas corresponding to ∼4.2 mm square including 11 × 11 pixels, the average temperature reading of each segmented area was within 22.8 °C to 22.9 °C (ΔT∼0.14 K). This result includes not only the non-uniformity of the thermal imager reading but possibly also the non-uniformity of emissivity and temperature distribution of the blackbody sheet. However, the ΔT value is close to those required by the IEC standard for fever screening thermography. Note that Fig. 9(b) is a qualitative demonstration regarding the uniformity of the emissivity of the blackbody sheet; when the surroundings of an object are at room temperature, the thermal image of the object at the same room temperature will appear uniform regardless of the actual emissivity of the object. Figure 9(b) does show the lack of any superimposed image of the higher temperature imager itself and its holder. However, it is still necessary to investigate the uniform infrared radiation from the blackbody sheet when mounted as a reference blackbody source and set to other predetermined temperatures near body temperature.
Fig. 9. (a) Layout of thermal image acquisition of the large-area PDMS blackbody sheet on an aluminum plate. (b) Thermal image of the 100 mm × 80 mm large-area PDMS blackbody sheet on the aluminum plate as shown in the dashed rectangular area. The aluminum plate is shown around the blackbody sheet.
4. Conclusion
The present study was designed to determine the feasibility of the application of the PDMS blackbody sheet towards thermal imager calibration. The effect of the surface microstructure geometry of the PDMS blackbody sheet on its emissivity was investigated. The reflectance decreased with increasing the radius and the aspect ratio of the conical micro-spikes of the PDMS blackbody sheet. To achieve the reflectance of less than 0.002 (the emissivity of higher than 0.998) at the wavelengths of 7–14 µm (the typical detection band of infrared thermal imager), the optimum radius and aspect ratio of the micro-spikes were approximately 6 µm and 4, respectively. Under these conditions, a large-area PDMS blackbody sheet of 100 mm × 80 mm was fabricated, and the in-plane uniformity of the reflectance was evaluated. The hemispherical reflectance at the six separated areas on the sheet was less than 0.002 at the wavelengths of 6–15 µm, and the standard deviation of the reflectance was less than 0.001. This means that the in-plane emissivity is higher than 0.998 and uniform, which conforms to the IEC document recommendation regarding thermal imager calibration for fever screening. Such a large-area planar blackbody has never existed other than our PDMS blackbody sheet or VACNTs.
The excellent emissivity performance of the large-area perfect PDMS blackbody sheet at room temperature is a milestone for application to thermal imager calibrators. The PDMS blackbody sheet, which has contact durability and heat resistance, will greatly ease the limitation on the operating environment. Additionally, the fact that the PDMS blackbody sheet can be produced by the replica molding process is excellent from a viewpoint of mass productivity. We believe that the PDMS blackbody sheet is a promising candidate material for the reference planar blackbody in a calibrator of thermal imager for universal users. Further study of the PDMS blackbody sheet is needed on the reflectance or emissivity at other temperatures and control of the sheet temperature.
Funding
Japan Society for the Promotion of Science (JP18K11940).
Acknowledgements
The ion beam irradiation experiment was conducted at Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) of National Institutes for Quantum and Radiological Science and Technology (QST), Takasaki, Japan, which was supported by the Inter-University Program for the Joint Use of JAEA/QST Facilities (proposal no. 20006).
Disclosures
Corresponding author (K.A.) is an inventor on a patent application related to this work, filed by National Institute of Advanced Industrial Science and Technology, Japan (patent publication number: WO/2019/087439). The other authors have no conflicts of interest, financial or otherwise.
References
1. B. B. Lahiri, S. Bagavathiappan, T. Jayakumar, and J. Philip, “Medical applications of infrared thermography: A review,” Infrared Phys. Technol. 55(4), 221–235 (2012). [CrossRef]
2. D. Bitar, A. Goubar, and J. C. Desenclos, “International travels and fever screening during epidemics: a literature review on the effectiveness and potential use of non-contact infrared thermometers,” Euro Surveill. 14(6), 19115 (2009).
3. P. J. Minnett and I. J. Barton, “Remote Sensing of the Earth’s Surface Temperature,” Exp. Methods Phys. Sci. 43(C), 333–391 (2010). [CrossRef]
4. J. A. Sobrino, F. Del Frate, M. Drusch, J. C. Jimenez-Munoz, P. Manunta, and A. Regan, “Review of Thermal Infrared Applications and Requirements for Future High-Resolution Sensors,” IEEE Trans. Geosci. Remote Sens. 54(5), 2963–2972 (2016). [CrossRef]
5. F. Amon and C. Pearson, “Thermal Imaging in Firefighting and Thermography Applications,” Exp. Methods Phys. Sci. 43(C), 279–331 (2010). [CrossRef]
6. W. Frodella, G. Gigli, S. Morelli, L. Lombardi, and N. Casagli, “Landslide Mapping and Characterization through Infrared Thermography (IRT): Suggestions for a Methodological Approach from Some Case Studies,” Remote Sens. 9(12), 1281 (2017). [CrossRef]
7. L. Spampinato, S. Calvari, C. Oppenheimer, and E. Boschi, “Volcano surveillance using infrared cameras,” Earth-Sci. Rev. 106(1-2), 63–91 (2011). [CrossRef]
8. A. Kylili, P. A. Fokaides, P. Christou, and S. A. Kalogirou, “Infrared thermography (IRT) applications for building diagnostics: A review,” Appl. Energy 134, 531–549 (2014). [CrossRef]
9. S. Bagavathiappan, B. B. Lahiri, T. Saravanan, J. Philip, and T. Jayakumar, “Infrared thermography for condition monitoring – A review,” Infrared Phys. Technol. 60, 35–55 (2013). [CrossRef]
10. G. Ohring, B. Wielicki, R. Spencer, B. Emery, and R. Datla, “Satellite Instrument Calibration for Measuring Global Climate Change: Report of a Workshop,” Bull. Am. Meteorol. Soc. 86(9), 1303–1314 (2005). [CrossRef]
11. J. J. Butler, B. Carol Johnson, and R. A. Barnes, “10. The Calibration and Characterization of Earth Remote Sensing and Environmental Monitoring Instruments,” Exp. Methods Phys. Sci. 41(C), 453–534 (2005). [CrossRef]
12. P. Ghassemi, T. J. Pfefer, J. P. Casamento, R. Simpson, and Q. Wang, “Best practices for standardized performance testing of infrared thermographs intended for fever screening,” PLoS One 13(9), e0203302 (2018). [CrossRef]
13. IEC/ISO, “IEC 80601-2-59:2017 Medical electrical equipment — Part 2-59: Particular requirements for the basic safety and essential performance of screening thermographs for human febrile temperature screening,” (2017).
14. Y. Yamada and J. Ishii, “Toward Reliable Industrial Radiation Thermometry,” Int. J. Thermophys. 36(8), 1699–1712 (2015). [CrossRef]
15. K. Mizuno, J. Ishii, H. Kishida, Y. Hayamizu, S. Yasuda, D. N. Futaba, M. Yumura, and K. Hata, “A black body absorber from vertically aligned single-walled carbon nanotubes,” Proc. Natl. Acad. Sci. 106(15), 6044–6047 (2009). [CrossRef]
16. J. Lehman, C. Yung, N. Tomlin, D. Conklin, and M. Stephens, “Carbon nanotube-based black coatings,” Appl. Phys. Rev. 5(1), 011103 (2018). [CrossRef]
17. J. Guo, D. Li, H. Zhao, W. Zou, Z. Yang, Z. Qian, S. Yang, M. Yang, N. Zhao, and J. Xu, “Cast-and-Use Super Black Coating Based on Polymer-Derived Hierarchical Porous Carbon Spheres,” ACS Appl. Mater. Interfaces 11(17), 15945–15951 (2019). [CrossRef]
18. Y. F. Huang, S. Chattopadhyay, Y. J. Jen, C. Y. Peng, T. A. Liu, Y. K. Hsu, C. L. Pan, H. C. Lo, C. H. Hsu, Y. H. Chang, C. S. Lee, K. H. Chen, and L. C. Chen, “Improved broadband and quasi-omnidirectional anti-reflection properties with biomimetic silicon nanostructures,” Nat. Nanotechnol. 2(12), 770–774 (2007). [CrossRef]
19. W. R. Johnson, Y. Y. Karl, and S. J. Hook, “Black silicon blackbody calibration,” U.S. patent 10371579 (2019).
20. F. J. García-Vidal, J. M. Pitarke, and J. B. Pendry, “Effective Medium Theory of the Optical Properties of Aligned Carbon Nanotubes,” Phys. Rev. Lett. 78(22), 4289–4292 (1997). [CrossRef]
21. E. Theocharous, C. J. Chunnilall, R. Mole, D. Gibbs, N. Fox, N. Shang, G. Howlett, B. Jensen, R. Taylor, J. R. Reveles, O. B. Harris, and N. Ahmed, “The partial space qualification of a vertically aligned carbon nanotube coating on aluminium substrates for EO applications,” Opt. Express 22(6), 7290–7307 (2014). [CrossRef]
22. K. Amemiya, H. Koshikawa, M. Imbe, T. Yamaki, and H. Shitomi, “Perfect blackbody sheets from nano-precision microtextured elastomers for light and thermal radiation management,” J. Mater. Chem. C 7(18), 5418–5425 (2019). [CrossRef]
23. K. Amemiya, H. Koshikawa, T. Yamaki, Y. Maekawa, H. Shitomi, T. Numata, K. Kinoshita, M. Tanabe, and D. Fukuda, “Fabrication of hard-coated optical absorbers with microstructured surfaces using etched ion tracks: Toward broadband ultra-low reflectance,” Nucl. Instrum. Methods Phys. Res., Sect. B 356-357, 154–159 (2015). [CrossRef]
24. J. J. H. Lancastre, N. Fernandes, F. M. A. Margaça, I. M. Miranda Salvado, L. M. Ferreira, A. N. Falcão, and M. H. Casimiro, “Study of PDMS conformation in PDMS-based hybrid materials prepared by gamma irradiation,” Radiat. Phys. Chem. 81(9), 1336–1340 (2012). [CrossRef]
25. L. M. Johnson, L. Gao, C. Shields IV, M. Smith, K. Efimenko, K. Cushing, J. Genzer, and G. P. López, “Elastomeric microparticles for acoustic mediated bioseparations,” J. Nanobiotechnol. 11(1), 22 (2013). [CrossRef]
26. J. Lee, J. Kim, H. Kim, Y. M. Bae, K.-H. Lee, and H. J. Cho, “Effect of thermal treatment on the chemical resistance of polydimethylsiloxane for microfluidic devices,” J. Micromech. Microeng. 23(3), 035007 (2013). [CrossRef]
27. A. Deinega, I. Valuev, B. Potapkin, and Y. Lozovik, “Minimizing light reflection from dielectric textured surfaces,” J. Opt. Soc. Am. A 28(5), 770–777 (2011). [CrossRef]
