Book contents
- Frontmatter
- Contents
- List of contributors
- Preface
- Introduction
- PART I AN INTRODUCTION TO GRAVITATIONAL WAVES AND METHODS FOR THEIR DETECTION
- PART II GRAVITATIONAL WAVE DETECTORS
- 4 Resonant-bar detectors
- 5 Gravity wave dewars
- 6 Internal friction in high Q materials
- 7 Motion amplifiers and passive transducers
- 8 Parametric transducers
- 9 Detection of continuous waves
- 10 Data analysis and algorithms for gravitational wave antennas
- PART III LASER INTERFEROMETER ANTENNAS
- Index
8 - Parametric transducers
Published online by Cambridge University Press: 18 December 2009
- Frontmatter
- Contents
- List of contributors
- Preface
- Introduction
- PART I AN INTRODUCTION TO GRAVITATIONAL WAVES AND METHODS FOR THEIR DETECTION
- PART II GRAVITATIONAL WAVE DETECTORS
- 4 Resonant-bar detectors
- 5 Gravity wave dewars
- 6 Internal friction in high Q materials
- 7 Motion amplifiers and passive transducers
- 8 Parametric transducers
- 9 Detection of continuous waves
- 10 Data analysis and algorithms for gravitational wave antennas
- PART III LASER INTERFEROMETER ANTENNAS
- Index
Summary
Introduction
To be able to detect gravitational radiation, resonant mass antennae must achieve a dimensionless strain sensitivity of ∼10–19–10–20 (Thorne, 1987). Such a high sensitivity can only be obtained by the use of well isolated, massive, high acoustic Q antennae which are cooled to liquid-helium temperatures, and use ‘quantum limited” transducers to read out the antenna's vibrations. Modern resonant mass antennae generally consist of a high Q cylindrical bar to which is attached one or more smaller masses which are resonant at the antenna frequency, to form a two-mode or multi-mode antenna (see Richard and Folkner's chapter 7). The coupled resonators mechanically amplify the bar's vibrations thereby reducing the effect of transducer wideband noise. It is important that the acoustic Q of the entire antenna be high so as to minimise noise due to Brownian motion of the masses.
Initially, resonant mass antennae used passive PZT crystal transducers which were mounted near or around the girth of the bar. These were subsequently superseded by passive, modulated inductance and capacitance transducers which have proven to be much more sensitive, and are still being developed (see chapter 7). More recently, several groups have started to investigate another class of transducers: the parametric or active transducer (Bordoni et al., 1986; Braginsky, Panov and Popel'nyuk, 1981; Oelfke and Hamilton, 1983; Tsubono, Ohashi and Hirakawa, 1986; Veitch et al., 1987). This type of transducer differs from passive transducers in that it requires an external power source (a pump oscillator), and it has intrinsic power gain.
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- The Detection of Gravitational Waves , pp. 186 - 225Publisher: Cambridge University PressPrint publication year: 1991
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