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View Diary: Overnight News Digest 02/08/2013 (57 comments)

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  •  government & culture - cloaking submarines (9+ / 0-)

    KK: Can you provide a summary of the theoretical principle behind your research on a technique for manipulating heat?

    MM: Both heat and sound are atomic vibrations transmitted through matter. One of the main differences, however, is that sound vibrates at low-frequencies (~kHz) and travels large distances, while heat vibrates at high-frequencies (~THz) and travels short distances. In addition, heat is made of a relatively large range of frequencies. The theoretical principle behind the research is that, if we suppress the high-frequency vibrations that contribute to heat transfer, the remaining lower frequency vibrations can be treated like sound. This result can have a significant impact for thermal management as materials and devices already developed to manipulate sound (e.g., phononic crystals) could be now employed to control heat.

    Metamaterial acoustic cloak

    A laboratory metamaterial device that is applicable to ultra-sound waves has been demonstrated in January 2011. It can be applied to sound wavelengths from 40 to 80 kHz.

    The metamaterial acoustic cloak is designed to hide objects sumberged in water. The metamaterial cloaking mechanism bends and twists sound waves by intentional design.

    The cloaking mechanism consists of 16 concentric rings in a cylindrical configuration, and each ring with acoustic circuits. It is intentionally designed to guide sound waves, in two dimensions. The first microwave metamaterial cloak guided electromagnetic waves in two dimensions.

    Each ring has a different index of refraction. This causes sound waves to vary their speed from ring to ring. "The sound waves propagate around the outer ring, guided by the channels in the circuits, which bend the waves to wrap them around the outer layers of the cloak".

    This device has been described as an array of cavities which actually slow the speed of the propagating sound waves. An experimental cylinder was submerged in tank, and then it disappeared from sonar. Other objects of various shape and density were also hidden from the sonar. The acoustic cloak demonstrated effectiveness for the sound wavelengths of 40 kHz to 80 kHz
    Phononic crystal

    Nelson, Bryn (January 19, 2011). "New metamaterial could render submarines invisible to sonar". Defense Update. Retrieved 2011-01-31.

    New Meta-Material Could Render Submarines Invisible to Sonar Detection

    A research team from the University of Illinois, led by mechanical science and engineering professor Nicholas Fang, have demonstrated a technology that renders underwater objects invisible to sonar and other ultrasound waves.

    This kind of an ‘acoustic cloak’ could be used in the future to mask submarines from enemy sonars.

    The Enterprise ncc1701d uses a cloaking device for the first time to get out of a bad situation.

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