Patent ID: 7109714

Claim:
An apparatus for changing the Q-factor of a probe, having an impedance that can be varied to achieve a Q-factor of minimal orders of magnitude and a Q-factor of high orders of magnitude, for irradiating a sample with RF energy during transmitting periods and detecting an NQR or NMR signal emitted from a substance contained within the sample from a signal received by the probe during receiving periods, the apparatus comprising: Q-factor setting circuit for setting the Q-factor of a probe from minimal orders of magnitude to high orders of magnitude; Q-factor changing circuit having low reactance for actively changing the Q-factor of the probe without injecting a parasitic charge therein; and control circuit to control said Q-factor changing circuit so as to change the Q-factor of the probe in accordance with said Q-factor setting circuit to: (i) an optimal level during a prescribed transmitting period of an RF pulse for irradiating the sample with said RF energy; (ii) a minimal level during a prescribed recovery period immediately following said transmitting period to rapidly dampen transient signals from the probe; and (iii) a maximal level during a prescribed receiving period for detecting an NQR or NMR signal from the target substance if present, immediately following the recovery period; said optimal level being: (a) sufficiently low to reduce said prescribed recovery period to a period in which said transient signals may be dampened and to develop the leading edge of the pulse envelope of said RF pulse during said transmitting period; and (b) sufficiently high to reduce the bandwidth of said RF pulse during said transmitting period and so mitigate the power expended in amplifying the pulse envelope over the bandwidth; and said maximal level being sufficiently high for the probe to receive a signal during the receiving period, after the recovery period, to enable an NQR or NMR signal emitted from a substance within the sample to be detected; wherein said control circuit is adapted to control said Q-factor changing circuit in accordance with said Q-factor setting circuit to actively step the impedance of the probe down in a plurality of stages after said transmitting period for some period of time during the recovery period to provide the requisite minimal level of the Q-factor for the probe.