The tools used are monopole type or dipole type.

The monopole tools.

If the monopoles tools are used, the transmitters and receivers are multidirectional. The transmitter generates in the fluid a wave of compression which gives birth in the formation to a wave of compression (wave P) and a shear wave (wave S) to the angle-limits of the refraction. In practice the sonic log measures the transit time T, between two receivers. The system used can include several transmitters and receivers which enables us to eliminate most of the borehole effects and the off-centring of the tool.

Principle of sonic monopole probe

Picture and diagram of the sonic Mount Sopris probe