|Our economically-priced magnetic
resonance system can be used to demonstrate free-induction decays, spin
echos and CPMG sequences in a lecture, or to perform experiments in advanced
lab courses. The system can be extended to also perform NQR measurements.
|The system consists of a control box (left) and a magnet box (right).
The control box contains the pulse transmitter, receiver, and a microcontroller
for easy manual operation. It can also be operated by a personal
computer. The magnet box contains a 0.4T magnet and the resonant
receiver and transmitter coil. The coil can be tuned by a variable
capacitor, allowing for measuring hydrogen and fluorine samples. Conventional
5-mm NMR tubes can be used.
The receiver and transmitter frequencies can be selected separately,
allowing for an intermediate-frequency display of the MR response of the
sample. The amplitudes of the first (pi/2) and second (pi) pulse
can be varied independently. The pulse lengths and the duration between
first and second pulse can be varied between 10 microseconds and 10 milliseconds.
A trigger pulse is generated a presettable time after the first pulse.
To improve the signal-to-noise ratio, a tunable low-pass filter is
integrated. The pulse repetition time can be selected between 60ms
The MR signal can be displayed on a digital or an analog oscillsocope.
|The NMR signal can be read and processed also
by a personal computer. Here is a CPMG sequence from a mineral oil sample.
|In addition to the intermediate frequency detector,
an envelope detector is available for easier characterization of more complex
signals (e.g., CPMG sequences).
|The system can be extended for NQR measurements (FID and
Spin Echo). Here is the time trace of a chlorine NQR FID.