Selective pulses having a rectangular shape are simply achieved by using low-power pulses.

The Rectangular shape is applied by default or can be alternatively defined in the SHAPE tool .

The rectangular shape is not suitable for selective excitation purposes because suffers from undesired sidelobes far from resonance

Define the shape from the XWIN-NMR shape tool:

• Select Rectangle from the Shapes menu and modify the following parameters if required:

Size of Shape: 1000
Amplitude: 100

See shape

• Store the shape from the File-->Save As ... menu.
• From the Analyze menu we can obtain the following information:

• Calculate Bandwith for Excitation [bandw2]

    Total rotation (in degree): 90
    DeltaOmega*DeltaT factor using transverse magn.: 1.116
• Calculate Bandwith for Inversion [bandw2i]

    Total rotation (in degree): 180
    DeltaOmega*DeltaT factor using -Mz: 0.392
• Calculate Bandwith for Refocusing -My [bandw2ry]

    Define Total rotation (in degree): 180
    DeltaOmega*DeltaT factor using -My: 0.748
• Calculate gammaB1max on Resonance [calcb1m]

    Length of pulse (in us): 10000
    Total rotation (in degree): 90
    Maximum gammaB1 (on resonance): 25
    Corresponding 90 degree square pulse: 10000
• Calculate gammaB1max off Resonance [calcb1mo]

    Length of pulse (in us): 10000
    Total rotation (in degree): 90
   Offset (in Hz): 3000
    Maximum gammaB1 (off resonance): 1.05e+15
    Corresponding 90 degree square pulse: 2.37e-10
• Calculate average Power Level [calcpav]

    Amplitude relative to a square pulse of 100%: 1
    Corresponding difference in dB: 0
   Power relative to a square pulse of 100%: 1
• Integrate Shape and compare to Square [integr]

    Integral ratio compared to a square pulse of 100%: 1
    Corresponding difference in dB: 0
• Integrate Shape compared to Hard Pulse [integr2]

    Length of pulse (in us): 10000
    Length of hard pulse (in us): 10
    Integral ratio compared to a square pulse of 100%: 1
    Change of power level compared to level of hard pulse in dB: 60
 
 

90 degree Rectangular Shape   (in ms)	1	5	10	20	40	60	80	100
Corresponding 180 degree Rectangular Shape   (in ms) at the same power level	2	10	20	40	80	120	160	200
Corresponding 270 degree Rectangular Shape   (in ms) at the same power level	3	15	30	60	120	180	240	300
Maximum gammaB1   (on resonance) (in Hz)	250	50	25	12.5	6.25	4.17	3.12	2.5
Change of power level   compared to level of a 10 us hard  90 degree pulse (in dB)	40	53.97	60	66.02	72.04	75.56	78.06	80

 
 
• More sophisticated excitation schemes can be derived from the Manipulate menu.

The theoretical excitation and inversion profiles of a rectangular shaped pulse can be visualized from the NMRSIM program:

A) Rectangular shaped 90 degree pulse as a excitation element:

1. Select the corresponding File-->Experiment Setup-->Load from File ... menu.
2. Choose the profile.cfg configuration file.
3. Set the shape to rect.shp in the Go-->Check Experiment parameters menu.
4. Select the Go-->Run Experiment menu.
5. The result of the simulation is displayed in the nmrsim 1 1 file into the XWIN-NMR window. Transform the data with ef (lb=1).
6. The duration of the shaped pulse can be modified by changing the P5 parameter (by default, 5 ms) in the Go-->Check Experiment parameters menu. Repeat the 4 and 5 steps to obtain the new profile.

B) Rectangular shaped 180 degree pulse as a inversion element:

1. Select the corresponding File-->Experiment Setup-->Load from File ... menu.
2. Choose the profile180.cfg configuration file.
3. Set the shape to rect.shp in the Go-->Check Experiment parameters menu.
4. Select the Go-->Run Experiment menu.
5. The result of the simulation is displayed in the nmrsim 1 1 file into the XWIN-NMR window. Transform the data with ef (lb=1).
6. The duration of the shaped pulse can be modified by changing the P5 parameter (by default, 10 ms) in the Go-->Check Experiment parameters menu. Repeat the 4 and 5 steps to obtain the new profile.

C) Rectangular shaped 180 degree pulse as a refocussing element:

1. Select the corresponding File-->Experiment Setup-->Load from File ... menu.
2. Choose the spfge.cfg configuration file.
3. Set the shape to rect.shp in the Go-->Check Experiment parameters menu.
4. Select the Go-->Run Experiment menu.
5. The result of the simulation is displayed in the nmrsim 1 1 file into the XWIN-NMR window. Transform the data with ef (lb=1).
6. The duration of the shaped pulse can be modified by changing the P5 parameter (by default, 10 ms) in the Go-->Check Experiment parameters menu. Repeat the 4 and 5 steps to obtain the new profile.