lecture 2: instrumentation - spin dynamics
TRANSCRIPT
CHEM-6154 Lecture 2: Instrumentation |
Lecture 2: InstrumentationCHEM 6154 – Nuclear Magnetic Resonance
Marcel Utz
January 26, 2020
CHEM-6154 Lecture 2: Instrumentation |
2 | Learning Goals for Today
In this lecture, we will:
É Examine the hardware necessary for NMR Spectroscopy
At the end, you will
É Understand how RF signals are generated, transmitted, and processed;
É Appreciate the technical requirements for NMR magnets;
CHEM-6154 Lecture 2: Instrumentation |
2 | Learning Goals for Today
In this lecture, we will:É Examine the hardware necessary for NMR Spectroscopy
At the end, you will
É Understand how RF signals are generated, transmitted, and processed;
É Appreciate the technical requirements for NMR magnets;
CHEM-6154 Lecture 2: Instrumentation |
2 | Learning Goals for Today
In this lecture, we will:É Examine the hardware necessary for NMR Spectroscopy
At the end, you will
É Understand how RF signals are generated, transmitted, and processed;
É Appreciate the technical requirements for NMR magnets;
CHEM-6154 Lecture 2: Instrumentation |
2 | Learning Goals for Today
In this lecture, we will:É Examine the hardware necessary for NMR Spectroscopy
At the end, you willÉ Understand how RF signals are generated, transmitted, and processed;
É Appreciate the technical requirements for NMR magnets;
CHEM-6154 Lecture 2: Instrumentation |
2 | Learning Goals for Today
In this lecture, we will:É Examine the hardware necessary for NMR Spectroscopy
At the end, you willÉ Understand how RF signals are generated, transmitted, and processed;
É Appreciate the technical requirements for NMR magnets;
CHEM-6154 Lecture 2: Instrumentation | Outline
3 | Outline
Overview
Magnets
Probes and Detectors
RF Signals
Detection and Data Processing
Recapitulation
CHEM-6154 Lecture 2: Instrumentation | Overview
4 | Block Diagram
Synth 1 Modulator 1 T1
PReceiverADC
B1
CHEM-6154 Lecture 2: Instrumentation | Magnets
5 | NMR Magnets
Coil
Bore
He Dewar
He fill port
LN2 fill port
Vacuum portVacuum port
NMR Cryomagnets
contain a superconducting coil which carries a persistent current. The magnetic fieldsgenerated vary between 5 T and 25 T. The stored field energy is of the order of 50 . . . 100 MJ,similar to that stored in the fully charged battery of an electric car.
CHEM-6154 Lecture 2: Instrumentation | Magnets
6 | Superconducting Wire
T
R
R ∼ T 3
R = 0
Tc
T
B
Tc
Bc 2
Bc 1
NMR Magnet
CHEM-6154 Lecture 2: Instrumentation | Magnets
6 | Superconducting Wire
T
R
R ∼ T 3
R = 0
Tc
T
B
Tc
Bc 2
Bc 1
NMR Magnet
CHEM-6154 Lecture 2: Instrumentation | Magnets
6 | Superconducting Wire
T
R
R ∼ T 3
R = 0
Tc
T
B
Tc
Bc 2
Bc 1
NMR Magnet
CHEM-6154 Lecture 2: Instrumentation | Magnets
6 | Superconducting Wire
T
R
R ∼ T 3
R = 0
Tc
T
B
Tc
Bc 2
Bc 1
NMR Magnet
CHEM-6154 Lecture 2: Instrumentation | Magnets
6 | Superconducting Wire
T
R
R ∼ T 3
R = 0
Tc
T
B
Tc
Bc 2
Bc 1
NMR Magnet
CHEM-6154 Lecture 2: Instrumentation | Magnets
7 | Superconductor Metallurgy
Nb3SnTc = 18 K, Bc 2 = 30 T, Bc 1 = 19 mTA15 crystal structureExtremely brittle
CHEM-6154 Lecture 2: Instrumentation | Magnets
8 | Cryostat
QuenchNMR magnets can contain several 100L of liquid He. Loss of Dewar vacuum or exposure toferromagnetic objects can lead to a runaway loss of superconductivity. Beware: Asphyxiationhazard!
CHEM-6154 Lecture 2: Instrumentation | Magnets
8 | Cryostat
QuenchNMR magnets can contain several 100L of liquid He. Loss of Dewar vacuum or exposure toferromagnetic objects can lead to a runaway loss of superconductivity. Beware: Asphyxiationhazard!
CHEM-6154 Lecture 2: Instrumentation | Probes and Detectors
9 | NMR Probe
13C Coil1H Coil
Tuning Cap
CHEM-6154 Lecture 2: Instrumentation | Probes and Detectors
10 | B1 Homogeneity
Probe Quality
É Efficiency (B1/p
P ) (Determines sensitivity)
É B0 homogeneity (resolution!)
É B1 homogeneity (enables complex pulse sequencees)
É Channel separation (enables high-power decoupling)
Nutation Experiment:
Exc. Pulse [µs]0 10 20 30 40 50 60 70 80 90
CHEM-6154 Lecture 2: Instrumentation | Probes and Detectors
10 | B1 Homogeneity
Probe Quality
É Efficiency (B1/p
P ) (Determines sensitivity)
É B0 homogeneity (resolution!)
É B1 homogeneity (enables complex pulse sequencees)
É Channel separation (enables high-power decoupling)
Nutation Experiment:
Exc. Pulse [µs]0 10 20 30 40 50 60 70 80 90
A90/A810 = 30%: Poor homogeneity
CHEM-6154 Lecture 2: Instrumentation | Probes and Detectors
10 | B1 Homogeneity
Probe Quality
É Efficiency (B1/p
P ) (Determines sensitivity)
É B0 homogeneity (resolution!)
É B1 homogeneity (enables complex pulse sequencees)
É Channel separation (enables high-power decoupling)
Nutation Experiment:
Exc. Pulse [µs]0 10 20 30 40 50 60 70 80 90
A90/A810 = 85%: Good homogeneity
CHEM-6154 Lecture 2: Instrumentation | RF Signals
11 | Transmission Lines
Electric fieldMagnetic field
x
U , I
x
U , I
I0
U0
λ
Z = |U0||I0|
λ= cν ≈
200 MHz·mν
CHEM-6154 Lecture 2: Instrumentation | RF Signals
11 | Transmission Lines
Electric fieldMagnetic field
x
U , I
x
U , I
I0
U0
λ
Z = |U0||I0|
λ= cν ≈
200 MHz·mν
CHEM-6154 Lecture 2: Instrumentation | RF Signals
11 | Transmission Lines
Electric fieldMagnetic field
x
U , I
x
U , I
I0
U0
λ
Z = |U0||I0|
λ= cν ≈
200 MHz·mν
CHEM-6154 Lecture 2: Instrumentation | RF Signals
11 | Transmission Lines
Electric field
Magnetic field
x
U , I
x
U , I
I0
U0
λ
Z = |U0||I0|
λ= cν ≈
200 MHz·mν
CHEM-6154 Lecture 2: Instrumentation | RF Signals
11 | Transmission Lines
Electric fieldMagnetic field
x
U , I
x
U , I
I0
U0
λ
Z = |U0||I0|
λ= cν ≈
200 MHz·mν
CHEM-6154 Lecture 2: Instrumentation | RF Signals
11 | Transmission Lines
Electric fieldMagnetic field
x
U , I
x
U , I
I0
U0
λ
Z = |U0||I0|
λ= cν ≈
200 MHz·mν
CHEM-6154 Lecture 2: Instrumentation | RF Signals
11 | Transmission Lines
Electric fieldMagnetic field
x
U , I
x
U , I
I0
U0
λ
Z = |U0||I0|
λ= cν ≈
200 MHz·mν
CHEM-6154 Lecture 2: Instrumentation | RF Signals
11 | Transmission Lines
Electric fieldMagnetic field
x
U , I
x
U , I
I0
U0
λ
Z = |U0||I0|
λ= cν ≈
200 MHz·mν
CHEM-6154 Lecture 2: Instrumentation | RF Signals
12 | RF Pulses
Reference signal (“Carrier”)
x -pulse
duration
amplitude
y -pulse
phase
−x -pulse
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
13 | Block Diagram
Synth 1 Modulator 1 T1
PReceiverADC
B1
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
14 | Detection and Demodulation
2 cosαt cosβ t = cos(αt +β t ) + cos(αt −β t )
Mixing
Before digitisation, RF signals are demodulated by mixing with the carrier at frequencyω0.This produces a signal that contains sum and difference components.
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
Original signal
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
After mixing
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
After low-pass filter
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
14 | Detection and Demodulation
2 cosαt cosβ t = cos(αt +β t ) + cos(αt −β t )
Mixing
Before digitisation, RF signals are demodulated by mixing with the carrier at frequencyω0.This produces a signal that contains sum and difference components.
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
Original signal
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
After mixing
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
After low-pass filter
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
14 | Detection and Demodulation
2 cosαt cosβ t = cos(αt +β t ) + cos(αt −β t )
Mixing
Before digitisation, RF signals are demodulated by mixing with the carrier at frequencyω0.This produces a signal that contains sum and difference components.
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
Original signal
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
After mixing
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
After low-pass filter
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
14 | Detection and Demodulation
2 cosαt cosβ t = cos(αt +β t ) + cos(αt −β t )
Mixing
Before digitisation, RF signals are demodulated by mixing with the carrier at frequencyω0.This produces a signal that contains sum and difference components.
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
Original signal
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
After mixing
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
After low-pass filter
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
14 | Detection and Demodulation
2 cosαt cosβ t = cos(αt +β t ) + cos(αt −β t )
Mixing
Before digitisation, RF signals are demodulated by mixing with the carrier at frequencyω0.This produces a signal that contains sum and difference components.
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
Original signal
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
After mixing
5 10 15 20t
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1SHtL
After low-pass filter
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
15 | Quadrature Detection
NMR Signal
Carrier (sin)
M
Carrier (cos)M
ω
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
15 | Quadrature Detection
NMR Signal
Carrier (sin)
M
Carrier (cos)M
ω
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
15 | Quadrature Detection
NMR Signal
Carrier (sin)
M
Carrier (cos)M
ω
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
15 | Quadrature Detection
NMR Signal
Carrier (sin)
M
Carrier (cos)M
ω
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
15 | Quadrature Detection
NMR Signal
Carrier (sin)
M
Carrier (cos)M
ω
CHEM-6154 Lecture 2: Instrumentation | Detection and Data Processing
15 | Quadrature Detection
NMR Signal
Carrier (sin)
M
Carrier (cos)M
ω
CHEM-6154 Lecture 2: Instrumentation | Recapitulation
16 | Recapitulation
Take-home messages from today:
É NMR magnets are based on low-Tc superconductors, and require cooling with liquid He;
É The quality of the NMR probe is crucial for sensitivity and resolution;
É Coaxial cables are conduits for electromagnetic radiation. They are characterised by theirwave impedance Z (typically 50 Ω);
É RF pulses are characterised by their duration, amplitude, and phase;
É NMR signals are demodulated to audio frequencies (kHz) before digitisation;
É Quadrature detection allows distinction of positive and negative frequency offsets.
CHEM-6154 Lecture 2: Instrumentation | Recapitulation
16 | Recapitulation
Take-home messages from today:É NMR magnets are based on low-Tc superconductors, and require cooling with liquid He;
É The quality of the NMR probe is crucial for sensitivity and resolution;
É Coaxial cables are conduits for electromagnetic radiation. They are characterised by theirwave impedance Z (typically 50 Ω);
É RF pulses are characterised by their duration, amplitude, and phase;
É NMR signals are demodulated to audio frequencies (kHz) before digitisation;
É Quadrature detection allows distinction of positive and negative frequency offsets.
CHEM-6154 Lecture 2: Instrumentation | Recapitulation
16 | Recapitulation
Take-home messages from today:É NMR magnets are based on low-Tc superconductors, and require cooling with liquid He;
É The quality of the NMR probe is crucial for sensitivity and resolution;
É Coaxial cables are conduits for electromagnetic radiation. They are characterised by theirwave impedance Z (typically 50 Ω);
É RF pulses are characterised by their duration, amplitude, and phase;
É NMR signals are demodulated to audio frequencies (kHz) before digitisation;
É Quadrature detection allows distinction of positive and negative frequency offsets.
CHEM-6154 Lecture 2: Instrumentation | Recapitulation
16 | Recapitulation
Take-home messages from today:É NMR magnets are based on low-Tc superconductors, and require cooling with liquid He;
É The quality of the NMR probe is crucial for sensitivity and resolution;
É Coaxial cables are conduits for electromagnetic radiation. They are characterised by theirwave impedance Z (typically 50 Ω);
É RF pulses are characterised by their duration, amplitude, and phase;
É NMR signals are demodulated to audio frequencies (kHz) before digitisation;
É Quadrature detection allows distinction of positive and negative frequency offsets.
CHEM-6154 Lecture 2: Instrumentation | Recapitulation
16 | Recapitulation
Take-home messages from today:É NMR magnets are based on low-Tc superconductors, and require cooling with liquid He;
É The quality of the NMR probe is crucial for sensitivity and resolution;
É Coaxial cables are conduits for electromagnetic radiation. They are characterised by theirwave impedance Z (typically 50 Ω);
É RF pulses are characterised by their duration, amplitude, and phase;
É NMR signals are demodulated to audio frequencies (kHz) before digitisation;
É Quadrature detection allows distinction of positive and negative frequency offsets.
CHEM-6154 Lecture 2: Instrumentation | Recapitulation
16 | Recapitulation
Take-home messages from today:É NMR magnets are based on low-Tc superconductors, and require cooling with liquid He;
É The quality of the NMR probe is crucial for sensitivity and resolution;
É Coaxial cables are conduits for electromagnetic radiation. They are characterised by theirwave impedance Z (typically 50 Ω);
É RF pulses are characterised by their duration, amplitude, and phase;
É NMR signals are demodulated to audio frequencies (kHz) before digitisation;
É Quadrature detection allows distinction of positive and negative frequency offsets.
CHEM-6154 Lecture 2: Instrumentation | Recapitulation
16 | Recapitulation
Take-home messages from today:É NMR magnets are based on low-Tc superconductors, and require cooling with liquid He;
É The quality of the NMR probe is crucial for sensitivity and resolution;
É Coaxial cables are conduits for electromagnetic radiation. They are characterised by theirwave impedance Z (typically 50 Ω);
É RF pulses are characterised by their duration, amplitude, and phase;
É NMR signals are demodulated to audio frequencies (kHz) before digitisation;
É Quadrature detection allows distinction of positive and negative frequency offsets.