Guojin Feng

Infrared thermography for human skin temperature measurement, when calibrated with standard blackbodies, suffers from errors due to the mismatch in emissivity between a blackbody and human skin. This study introduces a novel calibration method utilizing a human skin-like gradient radiation source to enhance measurement accuracy. A custom radiation source with six temperature points and skin-like emissivity was developed. Thermal imagers were calibrated using this source, and their performance was compared against traditional blackbody calibration. The proposed method reduced the calibration error to 0.04 °C, a significant improvement over the 0.15 °C error obtained with blackbody calibration. Calibration with a skin-like radiation source proves superior to the blackbody method, enabling high-accuracy (less than 0.1 °C) human skin temperature measurement for improved fever screening.

To address the growing need for field calibration of the optical properties of pedestrian targets used in autonomous emergency braking (AEB) tests, a novel three-dimensional multi-faceted standard body (TDMFSB) was developed. A camera-based analytical algorithm was proposed to evaluate the bidirectional reflectance distribution function (BRDF) characteristics of pedestrian targets. Additionally, a field calibration method applied in AEB testing scenarios (CPFAO and CPLA protocols) on one new and one aged typical pedestrian target of the same type revealed a 21% decrease in the BRDF uniformity of the aged target compared to the new one, confirming optical degradation due to repeated “crash–scatter–reassembly” cycles. The surface wear of the aged target on the side facing the vehicle produced a smoother surface, increasing its BRDF magnitude by 25% compared to the new target and making it easily detectable by the vehicle’s perception system. This led to “reverse scoring,” a safety risk in performance evaluation, necessitating timely calibration of AEB pedestrian targets to ensure reliable test results. The findings provide valuable insights into the development of regulatory techniques, evaluation standards, and technical specifications for test targets and offer a practical path toward full-life-cycle traceability and quality control.

Measuring the emissivity of an infrared radiant sample with high accuracy is important. Previous studies reported on the multi- or two-temperature calibration methods, which used a reference blackbody (or blackbodies) to eliminate the background radiation, and assumed that the background radiation was independent of temperature. However, in practical measurements, this assumption does not hold. To solve the above problems, this study proposes a modified two-temperature calibration method and facility. The two temperature points are set in a certain small interval based on the proposed calculation method; based on the indication of the approximation that the emissivities of the sample and the background radiations remain the same at these two temperatures, the emissivities can be calculated with measurement signals at these two temperatures, and a reference blackbody is not needed. An experimental facility was built up and three samples with emissivities around 0.100, 0.500, and 0.900 were measured in (8~14) μm. The relative expanded uncertainties were 9.6%, 4.0%, and 1.5% at 60 °C, respectively, and 8.8%, 5.8%, and 1.2% at 85 °C (k = 2), respectively. The experimental results showed consistency with the results obtained using other methods, indicating the effectiveness of the developed method. The developed method might be suitable for samples whose emissivities are temperature insensitive.

The realization of the super black level diffuse reflectance scale of the National Institute of Metrology (NIM, China) is presented. Two facilities were used to achieve the reflectance scale under 0 d condition covering 0.0001–1.0 (absolute value), the first one based on the supercontinuum light source was used to realize the diffuse scale in the wavelength range 500 nm–2000 nm, while the other one based on QCL was applied for the mid infrared range from 7.5 μm to 10.6 μm. The relative expanded uncertainty (k = 2) of the reflectance scale was evaluated to be from 2.3% to 8.4% varying with range and wavelength in visible band to near infrared band while the reflectance is down to 0.0001. In the mid infrared band, the uncertainty of the reflectance scale was up to 8.9% while reflectance is 0.001, and up to 42.6% while reflectance is down to 0.0001. This low reflectance level scale can meet the calibration requirement of super black material or system such as carbon nanotube or blackbody.

Based on parallel light, a device for measuring sample emissivity under vacuum and low temperature was established. In this paper, a new emissivity measurement formula was designed, which replaces the derivation of Kirchhoff’s law of thermal radiation. The device is designed with a light-weight blackbody, an improved cooling speed, and an improved PID temperature control system to achieve a good temperature stability, close to 1 mK. The device is capable of measuring within a wavelength range of 4 μm to 16 μm. The results of the uncertainty assessment show that the uncertainty of the normal emissivity is better than 1.6% in the range of 4 μm to 7 μm, and better than 0.6% in the range of 7 μm to 14 μm (k = 1) at 0 °C.

为拓宽标准物质波段范围，采用物化性能稳定的掺杂有镨钕稀土元素的玻璃作为可见波长的标准物质的原材料，同时采用物化性能稳定的聚苯乙烯片（厚度1 mm）作为近红外波长的标准物质的原材料，利用二者互不影响的特点，并且将其叠加使用会拓展波段范围，由此研制了可见近红外波长标准物质。以F检验法对样品的均匀性进行了检验，用线性拟合法对样品的稳定性进行考察，通过溯源至国家基标准的方式解决了溯源性，确定了标准物质中的波段范围为430 nm～2 550 nm，不确定度为0.1 nm～1.0 nm。弥补了当前标准物质中波段范围覆盖太窄的缺陷。

In order to study the influence of different microstructures on the plane blackbody reflectance, 40 kinds of plane blackbody samples with surface microstructures composed of different cone gear types (square cone and circular cone), height and density were designed. The same process was adopted on the samples surface, and the same type of surface absorption coating was sprayed to reduce the surface reflection. The reflectance of the samples in the visible and near-infrared bands was measured by the spectrometer. The measurement results show that the microstructure can reduce the reflectance from 1.4% in the plane state to nearly 0.4%. When other conditions are consistent, the higher the height of the cone gear and the denser the cone gear, the lower the reflectance of the plane blackbody; different cone gear types have no significant effect on the reflectance; compared with the simulation value obtained by the Tracepro, the higher the height of the cone gear, the denser the cone gear surface, the greater the relative error, and the relative error is in the range of 10% ~ 65%.

Femtosecond (fs)-laser hyperdoped silicon has aroused great interest for applications in infrared photodetectors due to its special properties. Crystallinity and optical absorption influenced by co-hyperdoped nitrogen in surface microstructured silicon, prepared by fs-laser irradiation in gas mixture of SF₆/NF₃ and SF₆/N₂ were investigated. In both gas mixtures, nitrogen and sulfur were incorporated at average concentrations above 10¹⁹ atoms/cm³ in the 20–400 nm surface layer. Different crystallinity and optical absorption properties were observed for samples microstructured in the two gas mixtures. For samples prepared in SF₆/N₂, crystallinity and light absorption properties were similar to samples formed in SF₆. Significant differences were observed amongst samples formed in SF₆/NF₃, which possess higher crystallinity and strong sub-band gap absorption. The differing crystallinity and light absorption rates between the two types of nitrogen co-hyperdoped silicon were attributed to different nitrogen configurations in the doped layer. This was induced by fs-laser irradiating silicon in the two N-containing gas mixtures.

The infrared normal spectral emissivity of microstructured silicon prepared by femtosecond laser was measured for the middle infrared waveband at temperature range 200 to 400°C. Compared to that of flat silicon, emissivity was enhanced over the entire wavelength range. For a sample with different spike height, the max emissivity at a temperature of 300°C emissivity nearly reaches to 0.99 . Although the average emissivity is not very higher, it can be used stably at more wide temperature ranges. These results show the potential for microstructured silicon to be used as a flat blackbody source or silicon-based devices.