Immediately within the bore of the magnet are the shim coils for homogenizing the B o field. Within the shim coils is the probe. The probe contains the RF coils for producing the B 1 magnetic field necessary to rotate the spins by 90 o or 180 o . The RF coil also detects the signal from the spins within the sample. The sample is positioned within the RF coil of the probe.
Some probes also contain a set of gradient coils.
These coils produce a gradient in B o along the X, Y, or Z axis. The heart of the spectrometer is the computer. It controls all of the components of the spectrometer. The RF components under control of the computer are the RF frequency source and pulse programmer. The source produces a sine wave of the desired frequency.