Development of a flextensional transducer for high resolution seismic imaging

Piezoelectric transducers are considered as potential sources for geophysical applications such as 4D monitoring or shallow subsurface survey, which require high repeatability and precise control of the emitted signal. However, the use of piezoelectric sources is limited by their low power and narrow bandwidth. Flextensional transducers are compact, high power, low frequency, wide-band projectors used in underwater acoustics. The design, fabrication and test of a flextensional transducer for high resolution seismic imaging are presented in this paper. Circuit modeling is used to discuss the general properties of piezoelectric sources radiating in the ground. Finite element simulations (ATILA code) are conducted to design a wide band 500–1500 Hz flextensional transducer. On-site tests are performed for a typical configuration of shallow subsurface survey. The prototype transducer is compared to a weight drop which constitutes a well-known seismic source. By taking advantage of the source repeatability and using specific signal processing, it is found that the flextensional transducer is equivalent to weight drop ranging from 300 to 1300 J. Bandwidth is increased by 200 to 300%, leading to a significant improvement of image resolution.