• [KB6NU] NIST Method Uses Radio Signals to Image Hidden and Speeding Obj

    From KB6NU via rec.radio.amateur.moderat@21:1/5 to All on Fri Jun 25 12:53:02 2021
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    NIST Method Uses Radio Signals to Image Hidden and Speeding Objects

    Posted: 25 Jun 2021 08:22 AM PDT http://feedproxy.google.com/~r/kb6nu/tVpu/~3/x6nboGY1m_0/?utm_source=feedburner&utm_medium=email


    People often ask me what good an amateur radio license is. Well,
    increasingly our technology is using wireless communications, i.e. radio.
    Radio waves are also being used in other innovative ways, as seen below in
    this June 25, 2021 NIST report. Being an amateur radio operator can help
    one learn the skills necessary to be a part of this kind of research and development.Dan

    Illustration of the lab setup for m-Widar, with transmitters and receiver
    at left and person behind wallboard at right. Inset at lower right shows
    the corresponding image produced by the instrument. Credit: NIST

    Researchers at the National Institute of Standards and Technology (NIST)
    and Wavsens LLC have developed a method for using radio signals to create real-time images and videos of hidden and moving objects, which could help firefighters find escape routes or victims inside buildings filled with
    fire and smoke. The technique could also help track hypersonic  objects
    such as missiles and space debris.

    The new method, described June 25 in Nature Communications, could provide critical information to help reduce deaths and injuries. Locating and
    tracking first responders indoors is a prime goal for the public safety community. Hundreds of thousands of pieces of orbiting space junk are considered dangerous to humans and spacecraft.

    “Our system allows real-time imaging around corners and through walls and tracking of fast-moving objects such as millimeter-sized space debris
    flying at 10 kilometers per second, more than 20,000 miles per hour, all
    from standoff distances,” said physicist Fabio da Silva, who led the development of the system while working at NIST.

    “Because we use radio signals, they go through almost everything, like concrete, drywall, wood and glass,” da Silva added. “It’s pretty cool because not only can we look behind walls, but it takes only a few
    microseconds of data to make an image frame. The sampling happens at the
    speed of light, as fast as physically possible.”


    This demonstration of the m-Widar (micro-Wave image detection, analysis and ranging) system shows, in the video on the left, a person walking and later crouching and lying down in an anechoic chamber. The transmitters and
    receiver are in a vertical line on the right side of the chamber. The
    second video on the right shows the instrument’s view of the same scene. About 21 seconds into the video, a wallboard is inserted between the person
    and the instrument in the anechoic chamber, to show that m-Widar can “see” through walls. Credit: NIST

    The NIST imaging method is a variation on radar, which sends an
    electromagnetic pulse, waits for the reflections, and measures the
    round-trip time to determine distance to a target. Multisite radar usually
    has one transmitter and several receivers that receive echoes and
    triangulate them to locate an object.

    “We exploited the multisite radar concept but in our case use lots of transmitters and one receiver,” da Silva said. “That way, anything that reflects anywhere in space, we are able to locate and image.”

    Da Silva has applied for a patent, and he recently left NIST to
    commercialize the system under the name m-Widar (microwave image detection, analysis and ranging) through a startup company, Wavsens LLC (Westminster, Colorado).

    The NIST team demonstrated the technique in an anechoic (non-echoing)
    chamber, making images of a 3D scene involving a person moving behind
    drywall. The transmitter power was equivalent to 12 cellphones sending
    signals simultaneously to create images of the target from a distance of
    about 10 meters (30 feet) through the wallboard.

    Da Silva said the current system has a potential range of up to several kilometers. With some improvements the range could be much farther, limited only by transmitter power and receiver sensitivity, he said.

    The basic technique is a form of computational imaging known as transient rendering, which has been around as an image reconstruction tool since
    2008. The idea is to use a small sample of signal measurements to
    reconstruct images based on random patterns and correlations. The technique
    has previously been used in communications coding and network management, machine learning and some advanced forms of imaging.

    Da Silva combined signal processing and modeling techniques from other
    fields to create a new mathematical formula to reconstruct images. Each transmitter emits different pulse patterns simultaneously, in a specific
    type of random sequence, which interfere in space and time with the pulses
    from the other transmitters and produce enough information to build an
    image.

    The transmitting antennas operated at frequencies from 200 megahertz to 10 gigahertz, roughly the upper half of the radio spectrum, which includes microwaves. The receiver consisted of two antennas connected to a signal digitizer. The digitized data were transferred to a laptop computer and uploaded to the graphics processing unit to reconstruct the images.

    The NIST team used the method to reconstruct a scene with 1.5 billion
    samples per second, a corresponding image frame rate of 366 kilohertz
    (frames per second). By comparison, this is about 100 to 1,000 times more frames per second than a cellphone video camera.

    With 12 antennas, the NIST system generated 4096-pixel images, with a resolution of about 10 centimeters across a 10-meter scene. This image resolution can be useful when sensitivity or privacy is a concern. However,
    the resolution could be improved by upgrading the system using existing technology, including more transmitting antennas and faster random signal generators and digitizers.

    Da Silva explains the imaging process like this: To image a building, the actual volume of interest is much smaller than the volume of the building itself because it’s mostly empty space with sparse stuff in it. To locate a person, you would divide the building into a matrix of cubes. Ordinarily,
    you would transmit radio signals to each cube individually and analyze the reflections, which is very time consuming. By contrast, the NIST method
    probes all cubes at the same time and uses the return echo from, say, 10
    out of 100 cubes to calculate where the person is. All transmissions will return an image, with the signals forming a pattern and the empty cubes dropping out.

    In the future, the images could be improved by using quantum entanglement,
    in which the properties of individual radio signals would become
    interlinked. Entanglement can improve sensitivity. Radio-frequency quantum illumination schemes could increase reception sensitivity.

    The new imaging technique could also be adapted to transmit visible light instead of radio signals — ultrafast lasers could boost image resolution
    but would lose the capability to penetrate walls — or sound waves used for sonar and ultrasound imaging applications.

    In addition to imaging of emergency conditions and space debris, the new
    method might also be used to measure the velocity of shock waves, a key
    metric for evaluating explosives, and to monitor vital signs such as heart
    rate and respiration, da Silva said.

    This work was funded in part by the Public Safety Trust Fund, which
    provides funding to organizations across NIST leveraging NIST expertise in communications, cybersecurity, manufacturing and sensors for research on critical, lifesaving technologies for first responders.


    Paper: F.C.S. da Silva, A.B. Kos, G.E. Antonucci, J.B. Coder, C.W. Nelson
    and A. Hati. Continuous Capture Microwave Imaging. Nature Communications. Published online June 25, 2021. DOI: 10.1038/s41467-021-24219-0

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