Development of a Broadband Receiver for a Quadrupole Resonance (QR) Detection System
Open Access
- Author:
- Borda, Bianca
- Area of Honors:
- Electrical Engineering
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Jeffrey Louis Schiano, Thesis Supervisor
Julio Urbina, Thesis Honors Advisor - Keywords:
- Nuclear Quadrupole Resonance
Quadrupole Resonance Detection System - Abstract:
- This thesis designs a broadband receiver for quadrupole resonance (QR) detection systems. A QR detection system can reveal the presence of concealed materials such as explosives and narcotics. A QR system generates a series of radio-frequency (RF) pulses at a transition frequency of a target material, and if present, the target admits an RF signal at the transition frequency between the applied RF pulses. QR transition frequencies are unique to the target compound and range from about 400 kHz to 5 MHz. As the QR response is weak, conventional QR detection systems noise match an inductive sensor to a low-noise preamplifier. This approach has two d rawbacks. First, the noise-matching network must be re-tuned for each target frequency, thereby increasing the time to scan for multiple targets. Second, as the inductive sensor typically has a small real resistance, when in combination with the noise-matching network, a resonant circuit with a high-quality factor is formed. The applied RF pulses induce ringing in the tuned inductive sensor that introduces an undesirable dead time during reception of the QR response, as it is much smaller than the ringing amplitude. This thesis investigates an alternative broadband approach where the inductive sensor is connected to a broadband receiver that does not require tuning and which does not form a resonant circuit that can ring in response to RF pulses. While the predicted noise figure for the broadband receiver is larger than that of the noise-matched receiver, the reduction of dead time allows the spacing between RF pulses to be reduced. This in turn, increases the amplitude of the QR response, so that the measurement signal-to-noise ratio increases, despite the increase in receiver noise factor. Circuit simulations and a QR response simulation are used to predict the increase in measurement signal-to-noise ratio provided by the proposed broadband receiver design.