SUPERCONDUCTING SEISMOMETERS

WE PROPOSE TO DEVELOP A SUPERCONDUCTING SEISMOMETER WHICH WILL RESOLVE GROUND NOISE AT FREQUENCIES OF 100 HERTZ AND HIGHER. THE NEW INSTRUMENT WILL HAVE IMPROVED LINEARITY, WILL HAVE A DYNAMIC RANGE OF 140 DB OR MORE, AND WILL MAINTAIN HIGH SENSITIVITY OVER A BROAD RANGE OF FREQUENCIES. THE NEW SEISMOMETER WILL USE A SQUID SENSOR TODETECT DISPLACEMENTS OF A MAGNETICALLY SUSPENDED SUPERCONDUCTING SPHERE. THE RESOLUTION OF THIS INSTRUMENT IS ENHANCED BY THE SENSITIVITY OF THE SQUID AND BY THE REDUCED BROWNIAN MOTION OF THE SUSPENDED SPHERE. THE LINEARITY, DYNAMIC RANGE, AND FREQUENCY BAND ARE ENHANCED BYTHE INHERENT PROPERTIES OF THE SENSOR, BY THE STABILITY OF PERSISTENT FIELDS IN SUPERCONDUCTING MAGNETS, AND BY THE FACILITY WITH WHICH THE POTENTIAL ENERGY SURFACE OF THE SUSPENDED MASS CAN BE CONTROLLED. THE SUPERCONDUCTING SEISMOMETER WILL HAVE FEW MOVING PARTS AND WILL LEND ITSELF TO MINIATURIZATION. THE INITIAL VERSIONS WILL REQUIRE COOLING TO A FEW DEGREES KELVIN, BUT LATER VERSIONS MAY BE BASED ON HIGH-TEMPERATURE SUPERCONDUCTIVITY.