Bandwidth extension system using periodic switching
OwnerAlbert Macovskiinventor
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Abstract
In applications where a tuned coil is used as a receiving antenna, the coil's resistance can produce excessive noise. If a low-loss coil is used, such as with cooled or supercoductive wire, the resulting Q results in inadequate bandwidth. To provide the desired bandwidth without additional losses the coil and its tuning capacitor are periodically de-energized using one or two switches. This sets the signal to substantially zero where it starts again to build up, effectively widening the bandwidth. The resulting signal is synchronously detected to provide the in-phase and quadrature signals. In an NMR system this enables the performance to be limited by sample or object noise. In MRI systems using an oscillating readout bias, the shorting is timed with the transition of the bias waveform.
Claims19
In a method for receiving an electromagnetic field signal using a high-Q low-loss coil tuned with a capacitor to form a tuned circuit tuned to the frequency of the signal the steps of:
- periodically de-energizing the tuned circuit to substantially remove the signal whereby the effective bandwidth of the tuned circuit is substantially increased and;
- detecting the resulting signal.
Apparatus for receiving an electromagnetic field signal using a high-Q low-loss coil tuned with a capacitor to the frequency of the signal comprising:
- means for periodically de-energizing the coil and capacitor to substantially remove the signal whereby the effective bandwidth of the tuned circuit is substantially increased and;
- means for detecting the resulting signal.
In a method for receiving an NMR signal from precessing magnetic moments in an object using a high-Q coil as an antenna where the coil is tuned with a capacitor to the precession frequency of the magnetic moments the steps of:
- periodically de-energizing the high-Q coil and capacitor to effectively increase its bandwidth substantially without adding losses and;
- synchronously detecting the resulting signal to provide the complex amplitude of the NMR signal.
Dependencies are inferred from the claim text.