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Title Ultra Low Frequency Infrasonic Measurement System
Author Rasmussen, Per (G.R.A.S. Sound & Vibration)
Kinnerup, Rasmus Trock (Department of Electrical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Supervisor Knott, Arnold (Electronics, Department of Electrical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Thomsen, Ole Cornelius (Electronics, Department of Electrical Engineering, Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark)
Marbjerg, Kresten (G.R.A.S. Sound & Vibration)
Institution Technical University of Denmark, DTU, DK-2800 Kgs. Lyngby, Denmark
Thesis level Master's thesis
Year 2011
Abstract An infrasonic measurement system is built capable of sensing acoustic signals down to 10 mHz which is advantageous for measurements of wind farm noise or sonic boom shapers. The system consists of an electric preamplier built into a housing and a G.R.A.S. 40AZ 1 2 -inch prepolarized condenser microphone with a closed vent conguration. The total system has a dynamic range of 94 dB and a lower limiting -3 dB cuto frequency of 8 mHz. The preamplier connects the microphone signal directly to the input of an op-amp with an input resistance of 10 T , one of the industry's highest, which forms a high pass lter with the microphone capacitance of 20 pF. The bias current is supplied to the input node by two diode-connected FETs. The big challenge has been to sense the sound signal from the capacitive microphone with a high enough input impedance of the preamplier to avoid an inherent cuto of frequencies of interest. Being able to measure down to ultra low frequencies in the infrasonic frequency range will aid actors in the debate on wind turbine noise. Sonic booms from supersonic ights include frequencies down to 10 mHz and this measurement system will aid scientists trying to modify the N-shaped shock wave at high level which prohibits ights in land zones.
Pages 92
Fulltext
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Admin Creation date: 2011-10-20    Update date: 2011-10-20    Source: dtu    ID: 285801    Original MXD