---------- Forwarded message ---------- Date: Fri, 12 Jan 2001 13:50:22 -0500 (EST) From: AIP listserver <physnews@aip.org> To: physnews-mailing@aip.org Subject: update.520 PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 520 January 12, 2001 by Phillip F. Schewe, James Riordon, and Ben Stein PLANETARY OCTAVE. Johannes Kepler succeeded in [ SSZ: Text deleted ] TILTING AT OPTICAL WINDMILLS. One of the greatest challenges facing engineers who design tiny microelectromechanical systems (MEMS) is finding ways to power machines that often measure only microns across. The answer, it seems, may be blowing in the optical wind. Researchers at the Hungarian Academy of Sciences have built resin-based structures that operate on principles similar to those that propel windmills. Rather than extracting energy from wind, however, the new devices are driven by beams of light. In one demonstration of the potential for light-powered machinery, an optical vane turned a series of interlinked cogwheels, each only 5 microns in diameter. The researchers (P�l Ormos, pali@everx.szbk.u-szeged.hu, 36-62-433-465) manufactured various shapes for their devices, including helixes and propellers, by curing resin with focused laser light. A particularly promising structure that resembles a common lawn sprinkler (see figure at http://www.aip.org/physnews/graphics) spins at several revolutions per second when illuminated by a 20 milliwatt laser beam. In addition to providing torque to miniature gears, pumps, and other micro-machines, the light-powered rotors could be used to measure fluid properties on micrometer scales. Alternatively, it may be possible to study the mechanical properties of certain molecules, such as proteins or DNA, by fixing one end to a surface, attaching a rotor to the other end, and using light to apply a twisting force. (P�ter Galajda; P�l Ormos, Applied Physics Letters, 8 January 2001.) ARRAYS OF LOW-TEMPERATURE SENSORS can now be serviced by a single SQUID detector operating in a multiplex mode for the first time. A SQUID, short for superconducting quantum interference device, can detect very small magnetic fields in the following way: a SQUID circuit consists basically of a superconducting loop interrupted at two points by a thin insulator gap through which pairs (Cooper pairs) of electrons must tunnel (that is, in their wavelike capacity the electrons can pass through an otherwise forbidden zone) to maintain a flowing current. This whole process is sensitive to any magnetic flux threading the circuit. The addition of more flux will cause a slight voltage increase across the gap. Thus a SQUID operates as a flux-to-voltage converter, but can also be used to read small currents. Physicists at UC Berkeley (contact Jongsoo Yoon, 510-642-8809, yoon@cfpa.berkeley.edu) have now developed a SQUID-based multiplexer which can interrogate arrays of many low-temperature sensors all at once. This makes possible arrays of a thousand or more sensors for magnetoencephalography (which maps magnetic fields from brain activity) and arrays of several thousands of a voltage-biased superconducting bolometers, or VSBs, employing tens of multiplexers. Such large VSB arrays are being developed for the next generation of spacecraft-based astronomical observations to detect radiation from interstellar dust and to explore the earliest history of the Universe by measuring the cosmic microwave background radiation. The multiplexer is also useful for arrays of sensors for the detection of ultraviolet light and X-rays.(Yoon et al., Applied Physics Letters, 15 January 2000.) CORRECTION. The correct acronym for the rainfall measuring satellite (Update 518) is TRMM (not TRIM), and its correct website is http://trmm.gsfc.nasa.gov/