Monolithic folded pendulum accelerometers for seismic monitoring and active isolation systems

A new class of very low noise low-frequency force-balance accelerometers is presented. The device has been designed for advanced mirror isolation systems of interferometric gravitational wave detectors. The accelerometer consists of a small monolithic folded pendulum with 2 s of natural period and an in-vacuum mechanical quality factor of 3000. The folded pendulum geometry, combined with the monolithic design, allows a unique 0.01% cross-axis residual coupling. Equipped with a high-resolution capacitance position sensor, it is capable of a noise-equivalent inertial displacement of 1-nm root mean square integrated over all the frequencies above 0.01 Hz. The main features of this new accelerometer are here reviewed. New possible applications of monolithic folded pendula in geophysical instrumentation are discussed

Monolithic folded pendulum accelerometers for seismic monitoring and active isolation systems

A new class of very low noise low-frequency force-balance accelerometers is presented. The device has been designed for advanced mirror isolation systems of interferometric gravitational wave detectors. The accelerometer consists of a small monolithic folded pendulum with 2 s of natural period and an in-vacuum mechanical quality factor of 3000. The folded pendulum geometry, combined with the monolithic design, allows a unique 0.01% cross-axis residual coupling. Equipped with a high-resolution capacitance position sensor, it is capable of a noise-equivalent inertial displacement of 1-nm root mean square integrated over all the frequencies above 0.01 Hz. The main features of this new accelerometer are here reviewed. New possible applications of monolithic folded pendula in geophysical instrumentation are discussed

Quantum theory of fluctuations in a cold damped accelerometer

We present a quantum network approach to real high sensitivity measurements. Thermal and quantum fluctuations due to active as well as passive elements are taken into account. The method is applied to the analysis of the capacitive accelerometer using the cold damping technique, developed for fundamental physics in space by ONERA and the ultimate limits of this instrument are discussed. It is confirmed in this quantum analysis that the cold damping technique allows one to control efficiently the test mass motion without degrading the noise level.Comment: 10 pages, 6 figures, RevTeX; Minor change

Inertial control of the mirror suspensions of the VIRGO interferometer for gravitational wave detection

In order to achieve full detection sensitivity at low frequencies, the mirrors of interferometric gravitational wave detectors must be isolated from seismic noise. The VIRGO vibration isolator, called 'superattenuator', is fully effective at frequencies above 4 Hz. Nevertheless, the residual motion of the mirror at the mechanical resonant frequencies of the system are too large for the interferometer locking system and must be damped. A multidimensional feedback system, using inertial sensors and digital processing, has been designed for this purpose. An experimental procedure for determining the feedback control of the system has been defined. In this paper a full description of the system is given and experimental results are presented.Comment: 17 pages, 11 figures, accepted for publication on Review of Scientific Instrument

Research on gravitational mass sensors Quarterly progress report no. 1, 15 Oct. 1964 - 14 Jan. 1965

Lunar orbiter and deep space probe gravitational sensor for determining mass distribution of moon and asteroid

Field tests of a portable MEMS gravimeter

Gravimeters are used to measure density anomalies under the ground. They are applied in many different fields from volcanology to oil and gas exploration, but present commercial systems are costly and massive. A new type of gravity sensor has been developed that utilises the same fabrication methods as those used to make mobile phone accelerometers. In this study, we describe the first results of a field-portable microelectromechanical system (MEMS) gravimeter. The stability of the gravimeter is demonstrated through undertaking a multi-day measurement with a standard deviation of 5.58 × 10−6 ms−2 . It is then demonstrated that a change in gravitational acceleration of 4.5 × 10−5 ms−2 can be measured as the device is moved between the top and the bottom of a 20.7 m lift shaft with a signal-to-noise ratio (SNR) of 14.25. Finally, the device is demonstrated to be stable in a more harsh environment: a 4.5 × 10−4 ms−2 gravity variation is measured between the top and bottom of a 275-m hill with an SNR of 15.88. These initial field-tests are an important step towards a chip-sized gravity senso

Inertial Control of the VIRGO Superattenuator

The VIRGO superattenuator (SA) is effective in depressing the seismic noise below the thermal noise level above 4 Hz. On the other hand, the residual mirror motion associated to the SA normal modes can saturate the dynamics of the interferometer locking system. This motion is reduced implementing a wideband (DC-5 Hz) multidimensional control (the so called inertial damping) which makes use of both accelerometers and position sensors and of a DSP system. Feedback forces are exerted by coil-magnet actuators on the top of the inverted pendulum. The inertial damping is successful in reducing the mirror motion within the requirements. The results are presented.Comment: 7 pages, 6 figures, Talk at the 3rd Amaldi Conference on Gravitational Waves Experiment, Caltech, Pasadena, 12-16 July 199

Analysis Of The Suspension Beam In Accelerometer For Stiffness Constant And Resonant Frequency By Using Analytical And Numerical Investigation

Mikro-meterpecut yang digunakan dalam pelbagai penerapan hanya akan tercapai dengan jayanya sekiranya keperluan frekuensi resonans dan kepekaan dapat dipenuhi dan konsisten. A successful and consistent performance of micro-accelerometer which has been applied in various applications can only be achieved when the resonant frequency and the sensitivity requirement are fulfilled