The Mario Schenberg gravitational wave detector has been constructed at its site in the Physics Institute of the University of São Paulo as programmed by the Brazilian Graviton Project, under the full support of FAPESP (the São Paulo State Foundation for Research Support). We are preparing it for a first commissioning run of the spherical antenna at 4.2 K with three parametric transducers and an initial target sensitivity of h ∼ 2 × 10−21 Hz−1/2 in a 60 Hz bandwidth around 3.2 kHz. Here we present the status of this project.

"Mario Schenberg" is a spherical gravitational wave (GW) detector that will be part of a GW detection array of two detectors. Another one is been built in The Netherlands. Spherical gravitational wave detector is a resonant-mass detector, which signal comes when the GW passes through and causes vibrations in a spherical mass. The resonant frequencies of this array will be around 3.2 kHz with a bandwidth of about 200 Hz. This range of frequencies is new in a fi eld where the typical frequencies lay below 1 kHz, making the transducer development some more complex. In this work we made a series of fi ne element studies in sphere coupled to a resonant mushroom shape resonator that will work as a mechanical impedance matcher between the sphere and the transducer. We describe the search for a shape in the impedance matcher that will improve the performance of the detector.

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The resonant-mass gravitational wave detector SCHENBERG was designed by the Brazilian group Graviton to be sensitive to a central frequency nearing 3200 Hz and a bandwidth of 200 Hz. It has a spherical antenna weighing 1150 kg that is connected to the outer environment by a suspension system designed to attenuate local noise due to seism as well as other sources. Should a gravitational wave pass by the detector, the antenna is expected to vibrate. This motion will be monitored by six parametric transducers whose output signals will be digitally analyzed. In order to improve the sensitivity of the detector, it must be cooled down to the lowest possible temperature, and for this purpose a dilution refrigerator is planned to be implemented in the detector. It is known that such device produces vibration when operational, consequently introducing noise in the system. Using the finite elements method, this work investigates thermal connections between the dilution refrigerator and the sphere suspension that allow the detector to operate within its projected sensitivity. The finite elements method showed an attenuation of 240dB in the best-valued thermal connection.

In order to investigate the speed of gravitational signals travelling in air or through a different medium two experiments were designed. One of the experiments contains 2 masses rotating at very high speed and in the other experiment a sapphire bar will vibrate, in both cases they will emit a periodic tidal gravitational signal and one sapphire device that behaves as a detector, which are suspended in vacuum and cooled down to 4.2 K will act as a detector. The vibrational amplitude of the sapphire detector device is measured by an microwave signal with ultralow phase-noise that uses resonance in the whispering gallery modes inside the detector device. Sapphire has a quite high mechanical Q and electrical Q which implies a very narrow detection band thus reducing the detection sensitivity. A new detector shape for the detector device is presented in this work, yielding a detection band of about half of the device vibrational frequency. With the aid of a Finite Element Program the normal mode frequencies of the detector can be calculated with high precision. The results show a similar expected sensitivity between the two experimental setup, but the experiment with the vibration masses is more stable in frequency then it is chosen for the experimental setup to measure the speed of gravity in short distances. Then a more precise analysis is made with this experiment reaching a signal-noise ratio of 10 at a frequency of 5000 Hz.

SCHENBERG is a resonant-mass gravitational wave detector built in Brazil. Its spherical antenna, weighting 1.15 t, is connected to the outside world by a suspension system whose main function is to attenuate the external seismic noise. In this work, we report how the system was modeled using finite elements method. The model was validated on experimental data. The simulation showed that the attenuation obtained is of the order of 260 dB, which is sufficient for decreasing the seismic noise below the level of the thermal noise of the detector operating at 50 mK.

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Ao meu orientador Prof. Dr. Carlos Frajuca, pela oportunidade em pesquisar em uma área tão importante e pela atenção e incentivo. Aos professores do IFUSP, em especial aos professores Profs. Drs. Emerson José Veloso de Passos, Josif Frenkel, Élcio Abdala e Iberê Luiz Caldas, com os quais tive a chance de aprender e a honra de conviver. Aos Profs. Dr. Odylio D. Aguiar e Dr. Nei F. Oliveira Jr. pela luta contagiante em favor da ciência. A Profa. Dra. Nadja Magalhães pelo apoio e estímulo. Aos Dr Xavier Pierre Marie Gratens e Me. Sérgio Turano de Souza por sempre compartilhar as informações que dispunham. Aos colegas do projeto Gráviton pela colaboração sempre que esta foi necessária. Aos familiares pelo apoio e compreensão nas minhas ausências, em especial à minha esposa e meu filho. Aos Sr.