Apparatus and method for increasing the sensitivity of a nuclear magnetic resonance probe

Claim 2

A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising: a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen; a tuning circuit element connected to the sample coil, the sample coil and tuning circuit element substantially forming a resonant circuit tuned to a selected Larmor frequency; and a balanced impedance circuit means connected to the sample coil and tuning circuit element for controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground.

Claim 3

The nuclear magnetic resonance probe circuit of claim 1 wherein the tuning circuit element comprises a tuning capacitor and the balanced impedance circuit means comprises a balanced impedance matching capacitance connected in series circuit with the sample coil for balancing the voltage across the sample coil.

Claim 4

The nuclear magnetic resonance probe circuit of claim 2 wherein the balanced impedance matching capacitance comprises a first impedance matching capacitor connected between the sample coil and an ungrounded output terminal and a second impedance matching capacitor connected between the sample coil and a grounded output terminal, the first impedance matching capacitor and the second impedance matching capacitor each having a capacitance which is approximately twice the capacitance of the tuning capacitor.

Claim 5

The nuclear magnetic resonance probe circuit of claim 1 wherein the selected Larmor frequency is approximately 100 MHz and the sample coil has a nominal inductance of approximately 100 nanohenries.

Claim 6

A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising: a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen; a tuning capacitor connected to the sample coil, the sample coil and tuning capacitor substantially forming a resonant circuit tuned to a selected Larmor frequency; a first impedance matching capacitor connected between the sample coil and an ungrounded output terminal; and a second impedance matching capacitor connected between the sample coil and a grounded output terminal; the sample coil being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals; the first and second impedance matching capacitors controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground.

Claim 7

A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising: a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen; a tuning capacitor connected to the sample coil, the sample coil and tuning capacitor substantially forming a resonant circuit tuned to a selected Larmor frequency; a first impedance matching capacitor connected between the sample coil and an ungrounded output terminal; and a second impedance matching capacitor connected between the sample coil and a grounded output terminal; the sample coil being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals; the first and second impedance matching capacitors controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground.

Claim 8

The nuclear magnetic resonance probe circuit of claim 5 wherein the tuning capacitor is connected in parallel circuit with the sample coil.

Claim 9

The nuclear magnetic resonance probe circuit of claim 6 wherein the tuning capacitor is positioned in close proximity to the specimen.

Claim 10

The nuclear magnetic resonance probe circuit of claim 5 wherein the tuning capacitor is connected between the grounded output terminal and a first junction, where the first impedance matching capacitor is connected to the sample coil, and wherein the second impedance matching capacitor is connected between the sample coil and a second junction, where the tuning capacitor is connected to the grounded output terminal.

Claim 11

The nuclear magnetic resonance probe circuit of claim 8, further comprising an additional capacitor connected in parallel circuit with the sample coil, the parallel circuit formed by the sample coil and additional capacitor being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and ground output terminals.

Claim 12

The nuclear magnetic resonance probe circuit of claim 9 wherein the second impedance matching capacitor and the additional capacitor are positioned in close proximity to the specimen.

Claim 13

The nuclear magnetic resonance probe circuit of claim 5 wherein the tuning capacitor is adjustable for tuning the resonant circuit formed substantially by the sample coil and tuning capacitor to a selected Larmor frequency.

Claim 14

The nuclear magnetic resonance probe circuit of claim 8 wherein the tuning capacitor is adjustable for tuning the resonant circuit formed substantially by the sample coil and tuning capacitor to a selected Larmor frequency.

Claim 15

The nuclear magnetic resonance probe circuit of claim 5 wherein at least one of the first and second impedance matching capacitors is adjustable for matching the impedance across the ungrounded and grounded output terminals to a predetermined impedance.

Claim 16

The nuclear magnetic resonance probe circuit of claim 13 wherein the predetermined impedance is approximately 50 ohms.

Claim 17

The nuclear magnetic resonance probe circuit of claim 5 wherein the first impedance matching capacitor and the second impedance matching capacitor each have a capacitance which is approximately twice the capacitance of the tuning capacitor.

Claim 18

The nuclear magnetic resonance probe circuit of claim 5 wherein the selected Larmor frequency is approximately 100 MHz and the sample coil has a nominal inductance of approximately 100 nanohenries.

Claim 19

A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising: a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen, the sample coil being connected between a first node and a second node; a tuning capacitor connected between the first and second nodes, the sample coil and tuning capacitor substantially forming a parallel resonant circuit resonant at a selected Larmor frequency; a first impedance matching capacitor connected between the first node and an underground output terminal; and a second impedance matching capacitor connected between the second node and a grounded output terminal; the parallel resonant circuit formed substantially by the sample coil and tuning capacitor being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals; the first and second impedance matching capacitors controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground.

Claim 20

A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising: a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen, the sample coil being connected between a first node and a second node; a tuning capacitor connected between the first and second nodes, the sample coil and tuning capacitor substantially forming a parallel resonant circuit resonant at a selected Larmor frequency; a first impedance matching capacitor connected between the first node and an underground output terminal; and a second impedance matching capacitor connected between the second node and a grounded output terminal; the parallel resonant circuit formed substantially by the sample coil and tuning capacitor being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals; the first and second impedance matching capacitors controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground.

Claim 21

The nuclear magnetic resonance probe circuit of claim 17 wherein the tuning capacitor is positioned in close proximity to the specimen.

Claim 22

The nuclear magnetic resonance probe circuit of claim 17 wherein the tuning capacitor is adjustable for tuning the parallel resonant circuit formed substantially by the sample coil and tuning capacitor to a selected Larmor frequency.

Claim 23

The nuclear magnetic resonance probe circuit of claim 17 wherein at least one of the first and second impedance matching capacitors is adjustable for matching the impedance across the grounded and ungrounded output terminals to a predetermined impedance.

Claim 24

The nuclear magnetic resonance probe circuit of claim 20 wherein the predetermined impedance is approximately 50 ohms.

Claim 25

The nuclear magnetic resonance probe circuit of claim 17 wherein the first impedance matching capacitor and the second impedance matching capacitor each have a capacitance which is approximately twice the capacitance of the tuning capacitor.

Claim 26

The nuclear magnetic resonance probe circuit of claim 17 wherein the selected larmor frequency is approximately 100 MHz and the sample coil has a nominal inductance of approximately 100 nanohenries.

Claim 27

A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising: a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen, the sample coil being connected between a first node and a second node; a tuning capacitor connected between the first node and a grounded output terminal, the sample coil and tuning capacitor substantially forming a parallel resonant circuit resonant at a selected Larmor frequency; a first impedance matching capacitor connected between the first node and an ungrounded output terminal; and a second impedance matching capacitor connected between the second node and the grounded output terminal; the sample coil being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals; the first and second impedance matching capacitors controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground.

Claim 28

A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising: a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen, the sample coil being connected between a first node and a second node; a tuning capacitor connected between the first node and a grounded output terminal, the sample coil and tuning capacitor substantially forming a parallel resonant circuit resonant at a selected Larmor frequency; a first impedance matching capacitor connected between the first node and an ungrounded output terminal; and a second impedance matching capacitor connected between the second node and the grounded output terminal; the sample coil being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals; the first and second impedance matching capacitors controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground.

Claim 29

The nuclear magnetic resonance probe circuit of claim 24, further comprising an additional capacitor connected in parallel circuit with the sample coil between the first and second nodes, the parallel circuit formed by the sample coil and additional capacitor being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals.

Claim 30

The nuclear magnetic resonance probe circuit of claim 25 wherein the second impedance matching capacitor and the additional capacitor are positioned in close proximity to the specimen.

Claim 31

The nuclear magnetic resonance probe circuit of claim 24 wherein the tuning capacitor is adjustable for tuning the parallel resonant circuit formed substantially by the sample coil and tuning capacitor to a selected Larmor frequency.

Claim 32

The nuclear magnetic resonance probe circuit of claim 24 wherein at least one of the first and second impedance matching capacitors is adjustable for matching the impedance across the grounded and ungrounded output terminals to a predetermined impedance.

Claim 33

The nuclear magnetic resonance probe circuit of claim 28 wherein the predetermined impedance is approximately 50 ohms.

Claim 34

The nuclear magnetic resonance probe circuit of claim 24 wherein the first impedance matching capacitor and the second impedance matching capacitor each have a capacitance which is approximately twice the capacitance of the tuning capacitor.

Claim 35

The nuclear magnetic resonance probe circuit of claim 24 wherein the selected Larmor frequency is approximately 100 MHz and the sample coil has a nominal inductance of approximately 100 nanohenries.

Claim 38

The method of claim 32 wherein the tuning circuit element comprises a tuning capacitor and the balanced impedance circuit means comprises a balanced impedance matching capacitance for balancing the voltage across the sample coil.

Claim 39

The method of claim 33 wherein the balanced impedance matching capacitance comprises a first impedance matching capacitor connected between the sample coil and an ungrounded output terminal and a second impedance matching capacitor connected between the sample coil and a grounded output terminal, the sample being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals, the first impedance matching capacitor and the second impedance matching capacitor each having a capacitance which is approximately twice the capacitance of the tuning capacitor.

Claim 40

The method of claim 32 wherein the selected Larmor frequency is approximately 100 MHz and the sample coil has a nominal inductance of approximately 100 nanohenries.

Claim 43

The method of claim 36 wherein the tuning capacitor is connected in parallel circuit with the sample coil.

Claim 44

The method of claim 37, further comprising the step of positioning the tuning capacitor in close proximity to the specimen.

Claim 45

The method of claim 36 wherein the first impedance matching capacitor is inserted between the ungrounded output terminal and a first junction, where the tuning capacitor is connected to the sample coil, and wherein the second impedance matching capacitor is inserted between the sample coil and a second junction, where the tuning capacitor is connected to the grounded output terminal.

Claim 46

The method of claim 36 wherein the tuning capacitor is adjustable for tuning the resonant circuit formed substantially by the sample coil and tuning capacitor to a selected Larmor frequency, further comprising the step of adjusting the tuning capacitor for tuning the resonant circuit formed substantially by the sample coil and tuning capacitor to the selected Larmor frequency.

Claim 47

The method of claim 39 wherein the tuning capacitor is adjustable for tuning the resonant circuit formed substantially by the sample coil and tuning capacitor to a selected Larmor frequency, further comprising the step of adjusting the tuning capacitor for tuning the resonant circuit formed substantially by the sample coil and tuning capacitor to the selected Larmor frequency.

Claim 48

The method of claim 36 wherein at least one of the first and second impedance matching capacitors is adjustable for matching the impedance across the ungrounded and grounded output terminals to a predetermined impedance, further comprising the step of adjusting the at least one of the first and second impedance matching capacitors for matching the impedance across the ungrounded and grounded output terminals to the predetermined impedance.

Claim 49

The method of claim 42 wherein the predetermined impedance is approximately 50 ohms.

Claim 50

The method of claim 36 wherein the first impedance matching capacitor and the second impedance matching capacitor each have a capacitance which is approximately twice the capacitance of the tuning capacitor.

Claim 51

The method of claim 36 wherein the selected Larmor frequency is approximately 100 MHz and the sample coil has a nominal inductance of approximately 100 nanohenries.