Digital control system for automatic magnetic field profiling

H. SEGNORILE; L. REVELLO; P. NOVISARDI; D. REGUERA; E. ANOARDO

Aachen, Alemania

Congreso; CMMR6, The 6th Colloquium on Mobile Magnetic Resonance, Specialized Colloque Ampere; 2006

NMR experiments often require particular profiling of the magnetic field, like timeindependent(schimming) or time-dependent gradient compensation (thermal drift in fieldcycling applications), generation of magnetic field gradients with a particular spatial dependence (ex-situ, field-matching). With the aim of having a universal system able to deal with all such possibilities in a simple way, we developed a digital system that uses the NMR signal itself as a main sensor, with the possibility of including additional information from supplementary sensing devices. The hardware platform is developed around a 30F3013 DsPIC [1]. In its current version, the system is armed with two analog inputs and two UART (Universal Asynchronous Receiver-Transmitter) ports allowing handshaking mode of data transmission-reception. The design includes on-board programming of the unit. The system can be syncronized with the NMR unit to trigger the acquisition of the FID signal and any additional information from other sensing devices. The information is processed within the loaded programm in order to decide actions that are exported through one UART port. The profiling of the magnetic field is performed through adequate coils placed in strategic positions according to the particular case. Then the cycle is restarted until its convergence.Each coil is driven by an individual current source. The set is controlled from one UART through an adequate interface. As a test case the system was prepared for authomatic shimming. The programm uses the SSC (Statistical Signal Characterization) method in order to get a fast convergence [2].1. P. Novisardi, L. Revello and H. Segnorile, Undergraduate Tesis, Universidad Tecnológica Nacional FRC, 2006.2. H. L. Hirsch, Statistical Signal Characterization, Artech House (1992).