The SWEPT IMPACT SEISMIC TECHNIQUE (SIST) consists of producing seismic signals as controlled sequences of high voltage pulses. The low power of the individual pulses maintains a relatively high signal frequency content, while the energy is built up by using a long actuation time (20-30 s) for each record.
The SPH borehole piezoelectric sources are designed for investigation ranges of tens and hundreds meters and for depths of 1000 m and more. The seismic signals are produced by applying high voltage (6000 V) to a stack of piezoelectric crystals. The minimum borehole diameter is 56 mm for the SPH-52 and 64 mm for the SPH-64. The frequency band is 500 - 3500 Hz.
The tools consist of three modules connected by steel-armored cable: the power supply & controller (out-of-the-hole), the high voltage generator (out-of-the-hole or down-hole) and the piezoelectric actuator (down-hole) equipped with an acoustic impedance converter or a motor-driven sliding wedge clamping mechanism.
The downhole high voltage generator (vertical) and the piezoelectric actuator (on operator's shoulder) are shown below, while getting prepared for lowering in a deep hole.
 The SPH-64 piezoelectric source ready to be lowered in a deep hole |  detail of the acoustic impedance converter. |
 motor-driven sliding wedge clamping mechanism | |