An onboard combustion-gas-powered engine supplies power to a paintball marker or other projectile launcher by generating gas pressure pulses for propelling paintballs and other projectiles. The heat exchanger may comprise at least one hollow body that has a wall with an exterior surface and an interior surface, a first opening at a first end of the at least one hollow body, a second opening at a second end of the at least one hollow body. The inducing electrode is disposed on the first substrate. If desired the direct reconstruction process may be iterated a set number of times or until a desired threshold criteria is met, such as regarding image quality. Additionally, a plurality of circular conductive rings may be included in the RF sensor to generate a signal representing the voltage of the conductor.