Transfer functions of geophones and accelerometers and their effects on frequency content and wavelets
Michael S. Hons, Robert R. Stewart
Transfer functions for geophone and accelerometer transducers are derived. The mechanical deflection within the sensor and how that deflection is transformed into an electrical signal are both important in the derivation of transfer functions. For both transducers the output to the digitizer is the double time derivative of the ground displacement. Due to interactions of the mechanical system and the transducer, a geophone transducer reduces amplitude and adds phase lag to low frequencies. Wavelets calculated from the amplitude and phase spectra of the transducer transfer functions are shown. Next an input zero-phase wavelet is examined to find the differences resulting from its transformation by the transducers. Accelerometer transducers are found to produce negligible changes to the waveform, and the ground motion can be recovered through a double integration.