Wavsens LLC and the National Institute of Standards and Technology have created a way to use radio signals to create images and videos of hidden and mobile objects. Firefighters could use this to find escape routes and victims in buildings engulfed by smoke and fire. This technique could also track hypersonic things like missiles or space debris.
This new method, described in Nature Communications, could help to reduce injuries and deaths. The public safety community primarily aims to track and locate first responders indoors. The public safety community has a primary goal of monitoring first responders indoors.
Radio signals can penetrate almost any material, including concrete, drywall, wood, or glass because they are radio signals,” da Silva said. It’s cool because we can see behind walls, and it only takes a few microseconds to create an image frame. The sampling occurs at the speed and pace of light, so it is as fast as possible.
NIST imaging is a variation of radar. It sends an electromagnetic pulse and waits for reflections. The round-trip time is used to calculate the distance to a target. Multisite radar typically has one transmitter and multiple receivers that receive the echoes and triangulate them to locate an object.
“We used multisite radar, but in our case, we use many transmitters and only one receiver.” Da Silva stated. “This way, any reflection anywhere in space can be located and imaged.
Da Silva applied for a patent and recently left NIST to market the system named mWidar (microwave imaging detection, analysis, and ranging) through Wavsens LLC (Westminster, Colorado).
The NIST team demonstrated the technique in an anechoic chamber. It created images of a 3-D scene that involved a person behind drywall. The transmitter power was equal to 12 cellphones simultaneously sending signals to create images of the target at a distance of approximately 10 meters (30 feet) through the wallboard.
Da Silva stated that the current system could have a range of several kilometers. He said that the content could be extended with some improvements, but the transmitter power and receiver sensitivity limit it.
Transient rendering is a type of computational imaging that has been used as a tool for image reconstruction since 2008. It uses several signal measurements to reconstruct images from random patterns and correlations. This technique was previously used in communication coding, network management, machine learning, and other advanced forms of imaging.
Da Silva used signal processing and modeling techniques to create a mathematical formula for reconstructing images. Each transmitter emits a different type of random pulse pattern simultaneously. These interfere with each other’s pulses in time and space and provide enough information to create an image.
The transmitting antennas could operate at frequencies between 200 megahertz and ten gigahertz. This is the radio spectrum’s upper half, including microwaves. Two antennas were connected to a signal digitizer. The digitized data were transferred to a laptop to reconstruct the images and then uploaded to the graphics processing device.
NIST used this method to reconstruct a scene using 1.5 billion samples per second. This corresponds to the scene’s 366-kilohertz image frame rate (frames per sec). This is 100-1000 times faster than a smartphone’s video camera.
The NIST system produced 4096-pixel images using 12 antennas. This resolution is approximately 10 centimeters for a scene of 10 meters. This resolution is helpful for privacy or sensitive situations. The system could be upgraded to use existing technology, such as more transmitting antennas, faster random signal generators, and digitizers, improving the resolution.
Quantum entanglement could improve image quality in the future. This would allow radio signals to be interlinked and their properties to become interconnected. The trap can improve sensitivity. The sensitivity of radio-frequency quantum illumination systems could be increased.
This new imaging technology could transmit visible light rather than radio signals. Ultrafast lasers could increase image resolution, but they would not penetrate walls.
The new method could be used for imaging emergency conditions and space debris. It can also be used to measure shock wave velocity, a crucial metric for evaluating explosives.