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Abandoned landmines and terrorist bomb attacks are severe issues threatening our society. These issues necessitate the development of prompt and accurate explosive detection systems. The detection mechanisms commonly-used nowadays usually search for explosive containers, which suffer numerous false alarms caused by external detection circumstance changes. Alternatively, explosive substances inside the bombs and landmines can be detected by means of biology, chemistry and physics techniques. Nuclear Quadrupole Resonance (NQR) detection technology has proven to be a highly effective solution for detecting explosives unambiguously.
In this work, a portable NQR-based explosive detection system that employs state-of-the-art semiconductor technologies is presented. This system consists of a transmitter section, an NQR probe, an RFI probe, a receiver section and auxiliary modules. In the transmitter section, a novel Class-D power amplifier (PA) with fast-start fast-stop functions is proposed. The receiver section consists of low-noise amplifiers (LNAs), an adaptive filter for RFI mitigation, and an advanced DSP platform for NQR signal processing. The LNA is based on an infinite input impedance power matching scheme, which improves the noise factor and simplifies the circuit structure. A Continuous Time Least Mean Square (CTLMS) adaptive filter is employed to mitigate RFI in the analog domain, and a new weight-updating circuit with DC offset cancellation is included in this adaptive filter. Between the transmitter and the receiver sections, a power multiplexing scheme is designed in order to use a single NQR probe for both transmitting and receiving. A PIN diode based RF switch provides high isolation during transmitting and low signal attenuation during receiving.
A customized mixed-signal integrated circuit (IC) is fabricated in 0.18um RF CMOS process, which contains the LNAs, adaptive filter and micro controller unit (MCU). The MCU performs the logic control of the whole system. The proposed NQR-based explosive detection system is implemented at board level with the prototype system successfully established. Detection of chemical samples, hexamethylenetetramine (HMT) and Urea, are performed on the prototype system. Test results show the effectiveness of the proposed solution as well as the compact size and low power consumption of the system.
Adviser: Sina Balkir