Development of Method for Suppression of Transient Processes in Large Power NQR Sensor

An inherently low signal-to-noise ratio of the NQR technique limits the application of this technique to the cases where the detection of large quantities of nitrogen-based substances is required (e.g., bombs placed under a road or in a vehicle). NQR detection of nitrogen-based substances at a distance or in a partially shielded volume faces the problem of manipulation with high excitation powers. To achieve the high signal-to-noise ratio (SNR), required for reliable detection of NQR signals, the quality factor (Q) of the resonant circuit should be as high as possible. However, the high Q-factor leads to a prolongation of the transient process in the resonant LC circuit, because after the application of powerful RF excitation pulses, unwanted oscillations occur in the RF probe, which should be suppressed before the registration of an NQR signal. This paper presents a method for the suppression of transient processes in a nuclear quadrupole resonance RF sensor. Operation of the device in the low-frequency range of 0.5–1MHz and RF pulse powers up to 4kW is considered. The design allows operation with a high-quality (≥200) resonant circuit and high voltages (several kilovolts) in the sensor. If necessary, the circuit can be easily scaled to higher voltages or currents in the resonant circuit.