through the mutual conversion of electric field energy and magnetic field energy, the process oscillates freely, and an amplifier circuit with positive feedback is needed to maintain the oscillation. Because the parameters of the auxiliary devices can't be exactly the same, the states of the two auxiliary samplers change at the moment of power-on, and this change is more and more intense due to the positive feedback, which leads to a transient state. During the transient state, another auxiliary sampler is turned on or off after being gradually charged by the capacitor, and the state is reversed to reach another transient state. Therefore, the particle size range it collects is naturally wider than that of a single stage, which is unmatched by some single-stage soil bulk density samplers. The circular nozzle of the sampler for measuring soil bulk density has higher sampling efficiency than the slit equal nozzle. When sampling, the relative humidity increases step by step, which is very beneficial to fragile pathogenic microorganisms.