• Strobe light for 5G: Imaging system spot

    From ScienceDaily@1:317/3 to All on Fri Feb 4 21:30:46 2022
    Strobe light for 5G: Imaging system spotlights the tiny mechanical
    hearts at the core of every cellphone
    Movies of minuscule vibrations reveal how well 5G and other mobile
    networks are operating

    Date:
    February 4, 2022
    Source:
    National Institute of Standards and Technology (NIST)
    Summary:
    Researchers have developed an instrument to image the acoustic
    waves generated by micromechanical resonators over a wide range of
    frequencies and produce 'movies' of them with unprecedented detail.



    FULL STORY ========================================================================== Inside every cellphone lies a tiny mechanical heart, beating several
    billion times a second. These micromechanical resonators play an essential
    role in cellphone communication. Buffeted by the cacophony of radio
    frequencies in the airwaves, these resonators select just the right
    frequencies for transmitting and receiving signals between mobile devices.


    ==========================================================================
    With the growing importance of these resonators, scientists need
    a reliable and efficient way to make sure the devices are working
    properly. That's best accomplished by carefully studying the acoustic
    waves that the resonators generate.

    Now, researchers at the National Institute of Standards and Technology
    (NIST) and their colleagues have developed an instrument to image these acoustic waves over a wide range of frequencies and produce "movies"
    of them with unprecedented detail.

    The researchers measured acoustic vibrations as rapid as 12 gigahertz
    (GHz, or billions of cycles per second) and may be able to extend those measurements to 25 GHz, providing the necessary frequency coverage for
    5G communications as well as for potentially powerful future applications
    in quantum information.

    The challenge of measuring these acoustic vibrations is likely to increase
    as 5G networks dominate wireless communications, generating even tinier acoustic waves.

    The new NIST instrument captures these waves in action by relying on
    a device known as an optical interferometer. The illumination source
    for this interferometer, ordinarily a steady beam of laser light, is
    in this case a laser that pulses 50 million times a second, which is significantly slower than the vibrations being measured.



    ==========================================================================
    The laser interferometer compares two pulses of laser light that travel
    along different paths. One pulse travels through a microscope that
    focuses the laser light on a vibrating micromechanical resonator and
    is then reflected back. The other pulse acts as a reference, traveling
    along a path that is continually adjusted so that its length is within
    a micrometer (one millionth of a meter) of the distance traveled by the
    first pulse.

    When the two pulses meet, the light waves from each pulse overlap,
    creating an interference pattern -- a set of dark and light fringes
    where the waves cancel or reinforce one another. As subsequent laser
    pulses enter the interferometer, the interference pattern changes as
    the microresonator vibrates up and down.

    From the changing pattern of the fringes, researchers can measure the
    height (amplitude) and phase of the vibrations at the location of the
    laser spot on the micromechanical resonator.

    NIST researcher Jason Gorman and his colleagues deliberately chose a
    reference laser that pulses between 20 and 250 times more slowly than
    the frequency at which the micromechanical resonator vibrates. That
    strategy enabled the laser pulses illuminating the resonator to, in
    effect, slow down the acoustic vibrations, similar to the way that a
    strobe light appears to slow down dancers in a nightclub.

    The slowdown, which converts acoustic vibrations that oscillate at
    GHz frequencies to megahertz (MHz, millions of cycles per second),
    is important because the light detectors used by the NIST team operate
    much more precisely, with less noise, at these lower frequencies.

    "Moving to lower frequencies removes interference from communication
    signals typically found at microwave frequencies and allows us to use photodetectors with lower electrical noise," said Gorman.



    ==========================================================================
    Each pulse lasts only 120 femtoseconds (quadrillionths of a second),
    providing highly precise moment-to-moment information on the
    vibrations. The laser scans across the micromechanical resonator so
    that the amplitude and phase of the vibrations can be sampled across
    the entire surface of the vibrating device, producing high-resolution
    images over a wide range of microwave frequencies.

    By combining these measurements, averaged over many samples, the
    researchers can create three-dimensional movies of a microresonator's vibrational modes.

    Two types of microresonators were used in the study; one had dimensions
    of 12 micrometers (millionths of a meter) by 65 micrometers; the other
    measured 75 micrometers on a side -- about the width of a human hair.

    Not only can the images and movies reveal whether a micromechanical
    resonator is operating as expected, they can also indicate problem areas,
    such as places where acoustic energy is leaking out of the resonator. The
    leaks make resonators less efficient and lead to loss of information in
    quantum acoustic systems. By pinpointing problematic areas, the technique
    gives scientists the information they need to improve resonator design.

    In the Feb. 4, 2022, edition of Nature Communications, the researchers
    reported that they could image acoustic vibrations that have an amplitude (height) as small as 55 femtometers (quadrillionths of a meter), about one-five-hundredth the diameter of a hydrogen atom.

    Over the past decade, physicists have suggested that micromechanical
    resonators in this frequency range may also serve to store fragile quantum information and to transfer the data from one part of a quantum computer
    to another.

    Establishing an imaging system that can routinely measure micromechanical resonators for these applications will require further research. But
    the current study is already a milestone in assessing the ability of micromechanical resonators to accurately perform at the high frequencies
    that will be required for effective communication and for quantum
    computing in the near future, Gorman said.

    ========================================================================== Story Source: Materials provided by National_Institute_of_Standards_and_Technology_(NIST).

    Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Lei Shao, Vikrant J. Gokhale, Bo Peng, Penghui Song, Jingjie Cheng,
    Justin Kuo, Amit Lal, Wen-Ming Zhang, Jason J. Gorman. Femtometer-
    amplitude imaging of coherent super high frequency vibrations in
    micromechanical resonators. Nature Communications, 2022; 13 (1)
    DOI: 10.1038/s41467-022-28223-w ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/02/220204161713.htm

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