Resonance detector

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A resonance detector is a type of gravitational wave detector that was used in the 1960s and 1970s to attempt to detect such waves. These detectors are also called Weber bars after Joseph Weber , who proposed this type of detector and who carried out the first such tests at the University of Maryland, College Park .

The main element of the detector is an oscillating test mass, the resonator . In the first experiments, resonators were aluminum cylinders with diameters of approx. 20 cm to approx. 1 m and lengths of approx. 1–2 m, later plates were also used. It was assumed that gravitational waves can cause these masses to vibrate and, due to the excessive resonance, even very small signals can be made measurable. The disadvantage of this concept is that such a resonator only responds to the components of the gravitational wave signal that are close to the natural oscillation frequency ( natural frequency ) of the resonator.

The resonator was suspended in a node of the vibration mode used ; the longitudinal vibration of the cylinders was measured, which has its node surface in the cylinder center . The suspension was carried out in such a way that vibrations from the environment were transmitted to the resonator as little as possible. Therefore, the interfering signal from the detectors was essentially limited by the thermal noise; this corresponds to a vibration amplitude in the range of 10 −16  m . The resonance frequencies of the detectors were between 60 and 1660 Hertz .

Weber's first reports in 1968 and 1969 that gravitational waves were actually detected at the same time (in coincidence) with two independent resonance detectors at a great distance are probably due to interfering influences that were not recognized as such due to insufficient analysis of the data. In later tests in various institutions, no gravitational waves could be detected despite the higher sensitivity. Attempts to detect gravitational waves from this source with a resonance detector tuned to twice the speed of the pulsar in the Crab Nebula were also unsuccessful.

literature

  • J. Weber: Gravitational Radiation . In: Physical Review Letters . Volume 18, Issue 13, 1967, pp. 498-501.
  • J. Weber: Gravitational Wave Detector Events . In: Physical Review Letters . Volume 20, Issue 23, 1968, pp. 1307-1308.
  • J. Weber: Evidence for Discovery of Gravitational Radiation . In: Physical Review Letters . Volume 22, Issue 24, 1969, pp. 1320-1324.
  • Hiromasa Hirakawa, Kimio Tsubono, Masa-Katsu Fujimoto: Search for gravitational radiation from the Crab pulsar . In: Physical Review D . Volume 17, 1978, pp. 1919-1923.
  • James L. Levine: Early Gravity-Wave Detection Experiments, 1960-1975 . In: Physics in Perspective . Volume 6, 2004, pp. 42-75.
  • David Lindley: A Fleeting Detection of Gravitational Waves . American Physical Society Focus, December 22, 2005. ( online )