RF probe recovery time reduction with a novel active ringing suppression circuit

A simple Q-damper device for active probe recovery time reduction is introduced along with a straightforward technique for the circuit's component value optimization. The device is inductively coupled to a probe through a coupling transformer positioned away from the main coil, which makes the design independent of the coil type being used. The Q-damper is a tuned circuit, which is resonant at the same frequency as the probe and can be actively interrupted. When the circuit is interrupted, it is detuned and, thereby, is uncoupled from the probe, which operates normally. Turning the device on leads to re-coupling of the circuits and causes splitting of the probe's resonance line, which can be observed through its drive port. A resistance of an appropriate value is introduced into the Q-damper circuit, resulting in smoothing of the resonance splitting into one broad line, representing the coupled system's low-Q state, in which the energy stored in the main coil is efficiently dissipated. The circuit's component values are optimized by monitoring the shape of this low-Q state. Probe recovery time reduction by, approximately, an order of magnitude has been obtained with this device. Application of the device during an NQR experiment led to an increase in the signal-to-noise ratio by a factor of 4.9.Fil: Peshkovsky, Alexey S.. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; ArgentinaFil: Forguez, J.. No especifíca;Fil: Cerioni, Lucas Matias Ceferino. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pusiol, Daniel Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Influence of solvent properties on the electrical response of poly(vinylidene fluoride)/NaY composites

Different solvents were used for the preparation of poly(vinylidene fluoride), PVDF, and NaY zeolite composites by solvent casting and melt crystallization. Solvents like N,N-dimethylformamide (DMF) and dimethylsulphoxide (DMSO) and triethyl phosphate (TEP) were chosen as they present different dielectric constants and can be encapsulated in the porous structure of NaY zeolite introduced in the PVDF/zeolite composites. The solvent molecules encapsulated induce variations in the dielectric response of the composite films according to the solvent dielectric constant. In this way, the solvent with the higher dielectric constant, DMSO, results in the composite with higher dielectric constant, while the opposite happens with TEP. The solvent molecules modify the distribution of intra zeolite cations increasing the dielectric constant of the composite. The zeolite also contribute to the increase of the d.c. conductivity, which is characterized by a double regime indicated by a breaking voltage, which value decreases when the dielectric constant of the solvent increases.This work is supported by the Center of Physics and by the Center of Chemistry and is funded by FEDER funds through the "Programa Operacional Factores de Competitividade – COMPETE" and by national funds by FCT- Fundação para a Ciência e a Tecnologia, project references NANO/NMed-SD/0156/2007, PTDC/CTM-NAN/112574/2009, PEST-C/FIS/UI607/2011 and PEst-C/QUI/UI0686/2011. ACL thanks the FCT for the grant SFRH/BD/62507/2009. The authors also thank support from the COST Action MP1003, the ‘European Scientific Network for Artificial Muscles’ (ESNAM)