Parametric Motion Transducer for Gravitational Wave Detectors.

We designed, constructed, and tested (using two different low phase noise electrical pump generators) a cryogenic double-resonant parabridge motion transducer made out of niobium, whose electrical output was amplified by a two stage MESFET cryogenic amplifier. Most of the experimental results agreed well with the theoretical models, and we successfully measured the mechanical Brownian motion of this transducer. We were able to adjust the two electrical bridge resonant frequencies on top of each other at the pump frequency, allowing us to obtain an electromechanical coupling as high as 0.054. This high coupling, corresponding to an rms electric field strength of 1.79 $\times$ 10\sp5 V/m across the capacitor plates, is the highest measured so far for this class of transducers. In one case, we observed a dip in the electrical noise spectrum near the mechanical resonant frequency due to destructive interference between this noise and its reflection from the mechanical resonator. At the bottom of this dip, we measured, for this transducer, an equivalent displacement noise of 4 $\times$ 10\sp{-16} m/$\sqrt{\rm Hz}$ with a systematic error of less than 10%. This measured equivalent displacement noise allows this parametric transducer to detect accelerations of 1.4 $\times$ 10\sp{-8} m/s\sp2 at 929 Hz in a one Hz bandwidth. If coupled to the LSU gravitational wave antenna, a 2.3 $\times$ 10\sp3 kg aluminum bar, this transducer resonator of 0.27 kg would detect gravitational wave strains (h) as small as 6 $\times$ 10\sp{-18}. A large improvement can be achieved if we manage to obtain 50 V\sb{\rm peak} across the transducer\u27s capacitor plates with a 5 MHz crystal oscillator. In this case, we would reach an equivalent displacement noise of 2 $\times$ 10\sp{-17} m/$\sqrt{\rm Hz}$, corresponding to h $\sim$ 3 $\times$ 10\sp{-19}. Further improvement could be obtained by the use of a DC SQUID preamplifier

Can lightning be a noise source for a spherical gravitational wave antenna?

The detection of gravitational waves is a very active research field at the moment. In Brazil the gravitational wave detector is called Mario SCHENBERG. Due to its high sensitivity it is necessary to model mathematically all known noise sources so that digital filters can be developed that maximize the signal-to-noise ratio. One of the noise sources that must be considered are the disturbances caused by electromagnetic pulses due to lightning close to the experiment. Such disturbances may influence the vibrations of the antenna's normal modes and mask possible gravitational wave signals. In this work we model the interaction between lightning and SCHENBERG antenna and calculate the intensity of the noise due to a close lightning stroke in the detected signal. We find that the noise generated does not disturb the experiment significantly.Comment: 5 pages, 6 figure

The Past, Present and Future of the Resonant-Mass Gravitational Wave Detectors

Resonant-mass gravitational waves detectors are reviewed from the concept of gravitational waves and its mathematical derivation, using Einstein's general relativity, to the present status of bars and spherical detectors, and their prospects for the future, which include dual detectors and spheres with non-resonant transducers. The review covers not only the technical aspects of detectors and the science that will be done, but also analyses the subject in a historic perspective, covering the various detection efforts over four decades, starting from Weber's pioneering work.Comment: 49 pages, 45 figures, invited review article, which will be published at Research in Astronomy and Astrophysics (RAA

The Schenberg spherical gravitational wave detector: the first commissioning runs

Here we present a status report of the first spherical antenna project equipped with a set of parametric transducers for gravitational detection. The Mario Schenberg, as it is called, started its commissioning phase at the Physics Institute of the University of Sao Paulo, in September 2006, under the full support of FAPESP. We have been testing the three preliminary parametric transducer systems in order to prepare the detector for the next cryogenic run, when it will be calibrated. We are also developing sapphire oscillators that will replace the current ones thereby providing better performance. We also plan to install eight transducers in the near future, six of which are of the two-mode type and arranged according to the truncated icosahedron configuration. The other two, which will be placed close to the sphere equator, will be mechanically non-resonant. In doing so, we want to verify that if the Schenberg antenna can become a wideband gravitational wave detector through the use of an ultra-high sensitivity non-resonant transducer constructed using the recent achievements of nanotechnology