Wednesday, 16 April 2014

Simple NMR Part 1

This post will outline the absolutely most basic NMR that will be built.

Field

The earths magnetic field will be used. Alignment with the field will be done with a compass.

Transmit/Receive Coil (T/R coil)

60m of 30-gauge copper wire will be used. Purchased from The Source. The wire will simply be left on the spool and used as is. The receive coil will be tuned with a capacitor.

Polarizing Coil

A polarization pulse will be generated to enhance the signal strength. 12m of 22-guage copper wire will be used. The polarization coil will be wound atop the T/R coil spool.

Control Electronics

All of the electronics will be powered by an ATX power supply from an old computer. The polarization coil will be turned on and off through a relay. The T/R coil will be switched between transmit and receive mode by way of a another relay. Both relays will be controlled by a MSP 430 microcontroller and a some switching transistors. The MSP430 will be controlled by a PC through a serial connection.

Transmit/Receive Electronics

In the earths magnetic field, the Larmor frequency is expected to be ~2kHz. This makes a PC's sound card the perfect device to record data.

The transmit signal will leave the sound card of the PC and go to a LF411 operational amplifier. The output of the amplifier will go to the relay and then to to the T/R coil.

The received signal will leave the T/R coil and go through the relay, then to the LF1115 operational amplifier where the signal will be amplified tens of thousands of times. The output of this amplifier will go to a PC's sound card.

Software

GNU Radio will be used as a function/pulse generator and for interpreting the receive signal. The relays will be controlled by a C++ program on the PC side. On the MSP 430 side of life, I will write a C program that runs on the MSP430 using the open toolchain.

Shielding

The coil of the experiment will be shielded by a large pot that is usually used for cooking corn. The relays should probably be kept away from the amplifiers and the amplifiers should also be shielded.

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