Seismic vibrator with adjustable resonance frequency

A seismic vibrator configured to be operated at or close to resonance, the seismic vibrator comprising:

• a baseplate;
• a reaction mass coupled to the baseplate via an elastic coupling mechanism that includes springs fixedly attached to the baseplate;
• and
• a frequency-adjusting system, FAS, that includes a continuously variable transmission, CVT, connected to at least one of the springs, the FAS being configured to change an equivalent spring rate of the springs by changing a CVT's drive ratio to make a natural frequency of the elastic coupling mechanism match an actuating frequency of the reaction mass.

A frequency-adjusting system, FAS, configured to adjust a natural frequency of an elastic coupling mechanism and a reaction mass coupled to a baseplate, the elastic coupling mechanism including a top chamber and a bottom chamber formed inside a cavity of the reaction mass, wherein the top chamber is separated by the bottom chamber by a piston, the FAS comprising:

• a controller configured to calculate pressure and/or gas volume values of the top chamber and of the bottom chamber, the calculated pressure and/or volume values corresponding to target values needed to realize a desired natural frequency;
• accumulators and valves receiving commands from the controller to independently achieve the calculated pressure and/or volume values in the top chamber and the bottom chamber, and
• an actuator configured to displace the reaction mass with an actuating frequency, the actuator including a top chamber and a bottom chamber formed inside a second cavity of the reaction mass, and a second piston configured to slide inside the second cavity and separating the top chamber from the bottom chamber,
• wherein the controller outputs the commands causing instantaneous pressures and volumes of the top chamber and of the bottom chamber to have the calculated pressure and volume values thereby making the natural frequency to be substantially equal to an actuation frequency applied to the reaction mass.

A method of operating a vibrator having a reaction mass attached to a baseplate via an elastic coupling mechanism including a top chamber and a bottom chamber formed inside a cavity of the reaction mass, a piston configured to slide inside the cavity separating the top chamber from the bottom chamber, which is below the top chamber, the method comprising:

• obtaining an actuating frequency versus time profile;
• independently calculating values of one or more pressure and/or volume in the top chamber and the bottom chamber determining a natural frequency of the elastic coupling mechanism and the reaction mass so that the natural frequency matches frequency values of the actuating frequency in the actuating frequency versus time profile;
• displacing with an actuator the reaction mass with an actuating frequency, the actuator including a top chamber and a bottom chamber formed inside a second cavity of the reaction mass, and a second piston configured to slide inside the second cavity and separating the top chamber from the bottom chamber;
• and
• adjusting the one or more of the pressure and/or volume in the top chamber and/or the bottom chamber using the calculated values while the reaction mass is actuated according to the actuating frequency versus time profile.