Many people and many customers are not very clear why some thermal imager import certificates have to be approved by the Chinese Ministry of Commerce, Ministry of Commerce and Production of thermal imager, often to question, please look at the description of the web page.
In fact, if the uncooled thermal imager micro bolometer detector and frame rate greater than 9Hz, then it must be approved by China Ministry of Commerce and Production Department of Commerce before they can be exported.
A paradigm shift has occurred in the commercial infrared camera industry as a result of classified military thermal sensor development in the 1980’s. In the past most high performance infrared cameras used in commerce had photon-detection sensors that needed to be cooled to liquid nitrogen temperature (77K). Cryogenic coolers were used to cool the detectors requiring about 10 minutes turn-on time to achieve this very low temperature. New high performance cameras use thermal sensors that eliminate the need for cryo-coolers. Their turn-on time is 15 seconds or less.
Cryo-coolers are expensive and have wear-out issues. The elimination of the cryo-cooler and advances in electronics has made the cameras smaller, more reliable and less expensive.
热传感器
红外热传感器原理图如右图所示。A tiny thin plate (which I call a “platelet”) is made on a silicon wafer in a silicon foundry by a micro-machining process. The platelet is typically 50 m (microns) square by 0.5 m thick. Even smaller sizes are under development. Long thin support legs and a vacuum environment thermally isolates it from the substrate. Small thermal radiation from the target focused onto the platelet heats it. The higher the target temperature, the greater the focused radiation is and therefore the higher the platelet temperature.
The temperature of the platelet and therefore the intensity of the radiation can be measured by the change in resistance of an electrical resistor deposited on the platelet – the microbolometer sensor. It can be measured by a thermocouple with the hot junction on the platelet and the reference junction on the substrate – the thermoelectric sensor. Or it can be measured by an electrical capacitance effect – the pyroelectric sensor. The microbolometer was developed by Honeywell and is used in Infrared Solutions, Inc. cameras.
Technology micro bolometer
Individual sensor elements use the change in electrical resistance of a VOx resistor deposited onto the tiny “platelets” fabricated by silicon micro-machining in a silicon foundry. Incoming target radiation heats the VOx causing a change in electrical resistance, which is readout by measuring the resulting change in bias current. 80,000 and more sensors can be fabricated together into a two-dimensional array. The structure can be dimensioned to operate at 30 Hertz. That is, the thermal conductance of the isolating legs can be adjusted to match the time-constant for 30-hertz operation. An example of a microbolometer element is pictured below.
It consists of a two-layer structure. An interconnecting readout circuitry is applied to the silicon process wafer and then the microbolometer structure is built on top of the readout circuitry. First a pattern of islands _ wavelength thick are deposited on the readout circuitry. The islands are made of a material that can be selectively etched away later to form a bridge structure. Three layers – silicon nitride, vanadium oxide, and silicon nitride – are deposited over the sacrificial islands. The sacrificial islands are then etched away leaving the thermally isolated bridge structure of vanadium oxide. A photo of an early Honeywell microbolometer element is shown in the picture below followed by a photo of one corner of a 320 by 240 microbolometer array
Now most thermal imager manufacturers use 320x240 pixels miniature heat radiometer detector array. However, there is still a very superior alternative products -160x120 array detector, although small array, but to create a thermal imager prices are much lower price. More Far more arrays can be produced on a single wafer and the yield is higher for the smaller array. In addition, one of the most expensive components of an infrared camera is the lens and its cost is proportional to the array size.
The only advantage of the larger array is field of view (FOV). With the same f# and focal length lens and the same detector size, a camera with 320 by 240 or 160 by 120 will have identical spatial resolution. But the target size for a fixed distance between the camera and target will be twice as large in both dimensions for the camera with the larger array. For many commercial applications the cost savings of the smaller array size over shadows the advantage of a larger FOV.
Some historical facts
in the 1980s, the US Department of Defense to many Honeywell and Texas Instruments (TI) 2 large companies secret contract to develop uncooled infrared sensor technology. A sensor may military uses require very short time to work. These two programs are very successful, TI has developed a pyroelectric sensor, Honeywell has developed a micro-bolometer (miniature thermal radiometer).
1992年美国政府为商用产品从机密表中删除了红外技术的应用一项，但保留了对技术的控制。TI公司利用它们的传感器技术开发出了商用热像仪，Honeywell则开始向其它公司发放许可证允许他们使用微型测热辐射仪技术。
最初有4个公司购买了微型测热辐射仪使用证书。Loral公司收购了Honeywell的 光电部门（Electro Optics Division），获得了一个使用证书。Santa Barbara Research是Hughes, Amber Engineering的一个部门, 与Amber Engineering及Rockwell也都购买了使用证书。所有这4个证书也都曾经转手过，而且有些还不止一次。Loral后来被Lockheed Martin收购， Lockheed Martin后来将微型测热辐射仪机构应用到他们的Sanders运作中，而这个项目后来又被英国航天航空（British Aerospace）收购。Raytheon （雷神）则从Hughes收购了Santa Barbara Research并收购了Amber Engineering。波音公司收购了Rockwell的红外机构，几年以后又把它卖给了DRS技术公司。所以最初的4个有证书的公司目前变成了3个：英国航天航空（British Aerospace）, Raytheon（雷神）和DRS技术公司（DRS Technologies）。
有3个另外的公司也购买了使用证书，分别是Indigo Systems, InfraredVision技术公司以及最新购买的公司NEC。除了这6个公司，Institut National d’Optique (INO), 有有限使用的证书。
Thermal imager technology
in the past using multiple infrared imaging sensors made of special materials, these materials require special cooling with liquid nitrogen, it can be cooled to a temperature of -320 ℉ (-195 ℃). Technological breakthroughs in this area because of military research and development achievements, making the production uncooled, high-performance measurement and sensing infrared energy sensor possible. This stimulation of new non-commercial use under refrigeration technology, making use of infrared technology reveals huge opportunity.
这种非制冷技术也使得开发新型、低成本、易操作的2维探测器红外成像设备成为可能。这种红外成像设备，如都泰成像红外系统公司的便携式热像仪MIDAS 320L或PYROVIEW 320/380/640N等设备，可以立即“看到”整个景色，可以在视频设备中产生实时的图像