Detection of Quadrupole Resonance Signals in the Presence of a Deterministic Sinusoidal Disturbance: A Comparison of Signal Averaging and Pseudo-Random Sequence Modulation
Open Access
Author:
Yu, Cathy
Area of Honors:
Electrical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Jeffrey Louis Schiano, Thesis Supervisor John Douglas Mitchell, Thesis Honors Advisor
Keywords:
QR explosive detection
Abstract:
Quadrupole resonance (QR) is a radio frequency (RF) spectroscopy technique that provides a means to non-invasively detect concealed explosives. Applications include inspecting luggage and shoes at aviation security checkpoints. Significant advantages of QR detection systems include the use of non-ionizing radiation and the ability to identify specific explosives, for example, RDX and PETN. The main disadvantage is a small measurement signal-to-noise ratio (SNR) resulting from an inherently small signal amplitude and the presence of RF interference.
This thesis focuses on the detection of QR signals from the explosives PETN and TNT, whose spectral locus is overlapped by AM broadcast stations. Previous research shows that the worst case scenario occurs when the AM broadcast signal derives from a deterministic sinusoidal modulation signal. Unlike the case for uncorrelated thermal noise, signal averaging is not as effective at eliminating the interfering AM signal. This thesis builds upon earlier work where the QR signal is modulated so that it can be distinguished from the RF interference. In specific, for an AM signal using a deterministic modulating signal, this thesis compares the ability of signal averaging and that of QR signal modulation in reducing the effect of AM broadcast interference. Based on analytical analysis and computer simulations, it is shown that modulation of QR signal phase is no more effective than signal averaging in reducing the effect of AM broadcast interference.
