Design And Experiment Of Flexural Low Frequency Monopole Acoustic Logging Transducer

The frequency of the monopole source is around 10 kHz commonly in Sonic logging.If the frequency of the acoustic emission transducer is controlled around 1kHz,we could detect the farther range.There is a tendency to reduce the frequency of monopole source.In order to reduce the frequency of monopole source in the limited borehole environment and instrument volume,a flexural monopole source transducer with low frequency is studied in this paper,which includes theoretical research and experimental research.The theoretical research is mainly in finite element analysis.The three-dimensional model of the flexural transducer is drawn by AutoCAD,and then the model is imported into the finite element simulation software ANSYS Workbench.Mode of vibration and frequency of flexural transducer got by modal analysis,the low frequency vibration and admittance curve of the flexural transducer got by harmonic response analysis.The experimental research is mainly in admittance measurement and directivity measurement of the flexural transducer.The frequency-admittance curve of the flexural transducer in air is measured by admittance tester.The flexural transducer is assembled and wrapped in a leather bag to measure the directivity in the water.The pumping signal is set according to the results of the finite element simulation.The theoretical analysis shows that the flexural transducer can vibrate in a monopole working mode when the frequency is 1108.4Hz.Using the square wave signal with width of 500 us to test the flexural transducer,it is found that the transducer has no directivity to meet the requirements of the low frequency monopole.The theoretical simulation of the flexural transducer admittance curve and the actual measurement curve are also in good agreement.