Accurate calibration technique for a resonant-mass gravitational wave detector

Abstract

The methodology for accurately calibrating the Niobe resonant-mass gravitational wave detector is presented. The transducer is based on a low noise resonant microwave cavity transducer that converts the displacement of the resonating mass to microwave energy. The calibration technique consists of a one off measurement of the microwave frequency versus resonant-mass displacement characteristic. To measure this accurately, known static forces were applied to the resonant mass and the change in the transducer microwave frequency was recorded. With the aid of finite element analysis and accurate measurements of the resonant-mass characteristics, the deflection due to the known force was calculated. The calculated deflections were verified coarsely with measurements from a calibrated linear variable differential transformer. Typically, the detector operates with a 1 mK noise temperature. A best noise temperature of 890 μK between 1300 and 2000 Universal Time Coordinate (UTC) for day 60 in 1997 is reported. The transducer has been upgraded with a new microwave amplifier, which has a measured electronic noise floor 40 dB lower than the previous amplifier, which is only 10 dB above the quantum limit.

Measurement of the strain-induced coefficient of permittivity of sapphire using whispering gallery modes excited in a high-Qacoustic sapphire oscillator

“…The signal was then mixed with a phase shifted portion of carrier signal which was adjusted such that the system was phase sensitive. The absolute value of df/dz cannot be measured directly without using a detailed calibration method for a parametric transducer [12,13]. However, we have verified the mode shape calculations by taking relative measurements of the magnitudes of df/dz's between modes with respect to the TM 14,1,δ mode.…”

A method for detecting gravitational waves coincident with gamma-ray bursts

“…Quantitatively, we see that the quasar models have comparative signal level with the star formation models and so we find that the signal seen at the bar detector is reasonably insensitive to the redshift and source model. We may compare the results in Figs 2 to 6 with the sensitivity curves provided by Tobar et al (1995) for the NIOBE bar detector. The sensitivity curves show that, within the two resonance bands, the rms noise reaches a level of ,2 and ,7 Â 10 220 Y for the plus and minus mode respectively.…”

“…However, the improvements to NIOBE will result in an order of magnitude sensitivity gain. The bandwidth will also increase by a factor 50X0a2 Â 0X3 83X Tobar & Blair (1995) and Tobar (1997) report that, to a good approximation, h G Df p for Df the bandwidth of the detector. That is, from equation (8), a linear change in the cross-section of the bar, S n H 0 , corresponds to a change in h G S n H 0 q X We can therefore find an optimistic estimate of the number of bursts, N b , required for us to achieve a SNR ,1,…”

“…Near the resonance frequency, bar detectors are capable of reaching sensitivities of ,10 219 ±10 218 (e.g. Tobar et al 1995) and future sensitivities are expected to reach ,10 220 (e.g. Tobar et al 1998).…”

Reentrant cavities as electromechanical transducers

“…12 Scaled up by a factor of 10 for ease of machining and testing at early stages of the design, the cavities we have examined are developmental replicas of electromechanical transducers to be instrumented in a resonant mass gravitational wave antenna, the Schenberg detector, under development at the National Institute for Space Research. 13 Specific requirements for the tuning coefficient in this kind of detector is placed by the sources of noise, which may be divided in two groups, 14,15 namely, narrow-and broad-band noises. Narrowband-noise is characterized by fluctuations due to the back action effect from the pump oscillator and goes up with the square of the sensitivity ⌬ f 0 /⌬d.…”