title: Design and testing of a low impedance transceiver circuit for nitrogen-14 nuclear quadrupole resonance.
abstract: A low impedance transceiver circuit consisting of a transmit-receive switch circuit, a class-D amplifier and a transimpedance amplifier (TIA) was newly designed and tested for a nitrogen-14 NQR. An NQR signal at 1.37MHz from imidazole was successfully observed with the dead time of ~85µs under the high Q transmission (Q~120) and reception (Q~140). The noise performance of the low impedance TIA with an NQR probe was comparable with a commercial low noise 50Ω amplifier (voltage input noise: 0.25 nV/Hz) which was also connected to the probe. The protection voltage for the pre-amplifier using the low impedance transceiver was ~10 times smaller than that for the pre-amplifier using a 50Ω conventional transceiver, which is suitable for NQR remote sensing applications.
authors.affiliation: Department of Systems Innovation, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan. Electronic address: akaba@sup.ee.es.osaka-u.ac.jp.
authors.forename: Hideo
authors.initials: H
authors.lastname: Sato-Akaba
keywords: Class-D amplifier; Counterfeit medicines; Explosives; Illicit drugs; Nitrogen-14 nuclear quadrupole resonance; Non-invasive detection; Q switch; Transimpedance amplifier; Transmit-receiver switch circuit