Miniature Cryogenic Shutter Assembly Offers Major Innovations

infrared chip

The Naval Surface Warfare Center, Crane Division has developed a miniature cryogenic shutter assembly that allows small- and medium-format infrared cameras to perform high dynamic range or “superframe” imaging by providing an absolute “null” offset that could only previously be done by systems using more expensive and cumbersome external reference methods.

Crane’s miniature cryogenic shutter assembly is the only shutter in the market that can provide zero radiance referencing, create super-framed images, and be used in small- or medium-format cryogenically cooled infrared cameras. The miniature cryogenic shutter assembly’s zero radiance referencing allows real-time super-framing imaging. It is compatible with the standard format Dewar sensor assembly used in all small- and medium-sized cooled infrared cameras, and can be installed after-market in existing cameras (or can easily be added by the manufacturer of new cameras).

The miniature cryogenic shutter assembly could have applications in builders of super frame imagers known as high dynamic range imaging, tracking the location of missiles, laser applications, satellite applications, telescopes, night vision systems, and thermography.

Crane’s inventor, Eric Hillenbrand, faced challenging design restrictions when developing this innovative shutter. The shutter had to fit into a very tight space inside the camera or on the cooled sensor assembly, and had to be able to function mechanically in very low temperature (temperatures typically from 80.5 K or -314.5 °F).

Cooling is a necessary part of the process in the operation of the semiconductor materials used in a cooled infrared camera. Cooling down the image sensor in an infrared camera makes it much more sensitive, allowing the camera to see very faint sources of heat, such as in space, or allowing the camera to distinguish very small differences in temperature. Without cooling, the infrared camera’s sensors would be “blinded” by their own radiation. This is accomplished by using a technique called super-framing, whereby the camera overlays multiple images in real time. But before performing super-framing, the camera needs to start with a “black” image. This is where the miniature cryogenic shutter assembly comes into play—it allows the camera to easily take this “black” or zero radiance image, which then allows the camera to perform an “absolute measurement calibration.”

Developed for use by the military during the Korean War, infrared cameras are used in numerous situations for imaging heat, both in temperature or intensity. All objects give off black-body radiation as a part of their temperature. Black-body radiation is an opaque and non-reflective body. The higher the temperature, the more infrared radiation is released as black-body radiation. In much the same way an ordinary camera can detect visible light, an infrared camera can detect the black-body radiation any object releases, even in total darkness. The ability to take images in complete darkness is useful for rescue operations in smoke-filled buildings and underground. For taking temperature measurements, the warmest parts of the image are customarily colored white (brightest and warmest), intermediate temperatures are shown as red and yellow, and the coolest parts are shown as blue (dimmest and coolest).

For more information, email the Naval Surface Warfare Center, Crane Division.