Methods, systems, circuits and computer program products for determining polarization of a gas
A circuit for determining a polarization of a gas. The circuit includes a polarimetry circuit having an NMR coil that is configured to excite a polarized gas and that is responsive to an electromagnetic signal generated by the excited, polarized gas. The polarimetry circuit has a reproducible polarization measurement variability of less than about 2% when the NMR coil is exposed to a temperature in a range of about 0° C. to about 200° C.
1. A circuit for determining a polarization of a gas, comprising:
a polarimetry circuit having an NMR coil that is configured to excite a polarized gas and that is responsive to an electromagnetic signal generated by the excited, polarized gas, the polarimetry circuit having a reproducible polarization measurement variability of less than about 2% when the NMR coil is exposed to a temperature in a range of about 0° C. to about 200° C.
2. The circuit of claim 1 , wherein the polarimetry circuit has a reproducible polarization measurement variability of less than about 1% when the NMR coil is exposed to a temperature in a range of about 0° C. to about 200° C.
3. The circuit of claim 1 , wherein the circuit-to-circuit polarization measurement variability is less than about 3% when the NMR coil is exposed to a temperature in a range of about 0° C. to about 200° C.
4. The circuit of claim 1 , wherein the polarimetry circuit comprises:
an oscillator circuit comprising an NMR coil that is adjacent to an optical cell containing the polarized gas;
a pulse generator circuit that is configured to generate an electrical pulse that is transmitted to the optical cell through the NMR coil to excite the polarized gas;
a Q-reduction circuit that is independent of the pulse generator circuit and is configured to reduce oscillations in the oscillator circuit from the electrical pulse responsive to a control signal; and
a receive circuit that is responsive to an electrical signal induced in the oscillator circuit due to the electromagnetic signal generated by the excited, polarized gas.
5. The circuit of claim 4 , wherein the pulse generator circuit comprises:
a pair of diodes connected in anti-parallel and are placed in parallel with the oscillator circuit upon conclusion of the electrical pulse to limit a voltage drop across the oscillator circuit to a conduction voltage of one of the pair of diodes.
6. The circuit of claim 5 , wherein each of the pair of diodes has a leakage current associated therewith that is less than about 1 μA.
7. The circuit of claim 6 , wherein each of the pair of diodes has a leakage current associated therewith that is approximately 200 nA.
8. The circuit of claim 4 , wherein the Q-reduction circuit comprises a field effect transistor that is connected in parallel with the oscillator circuit.
9. The circuit of claim 8 , wherein the Q-reduction circuit further comprises:
a capacitor connected between a gate terminal of the field effect transistor and a reference potential;
an amplifier circuit having an input terminal that is coupled to the control signal;
a resistor connected between the gate terminal of the field effect transistor and an output terminal of an amplifier circuit; and
a diode connected in parallel with the resistor.
10. The circuit of claim 4 , wherein the oscillator circuit comprises:
a tuning capacitor; and
a resistor connected in series with the tuning capacitor, the resistor and the tuning capacitor connected in parallel with the NMR coil.
11. The circuit of claim 10 , wherein the tuning capacitor has a Q-value about 25 times the Q-value of the NMR coil.
12. The circuit of claim 10 , wherein the tuning capacitor has a Q-value greater than about 1000.
13. The circuit of claim 10 , wherein the oscillator circuit has a Q-value in a range of about 10 to about 30.
14. The circuit of claim 4 , wherein the receive circuit comprises:
an amplifier circuit having a gain that is proportional to a ratio of resistance values associated with a first resistor and a second resistor.
15. The circuit of claim 14 , wherein the first and the second resistors have about a 1% variability tolerance.
16. The circuit of claim 4 , wherein the NMR coil is a precision layer wound NMR coil.
17. The circuit of claim 4 , wherein a frequency of the electrical signal induced in the oscillator is associated with a frequency at which a Q-value of the NMR coil is substantially independent of temperature between about 30° C. and about 200° C.
18. The circuit of claim 4 , wherein the frequency of the electrical signal induced in the oscillator is about 61 kHz.
19. The circuit of claim 1 , wherein the gas comprises at least one of 129 Xe, 3 He, 13 C compounds, and 15 N compounds.