Magnetic field exposure and behavioral monitoring system

To maximize the availability and usefulness of a small magnetic field expos ure laboratory, we designed a magnetic field exposure system that has been used to test human subjects, caged or confined animals, and cell cultures. The magnetic field exposure system consists of three orthogonal pairs of co ils 2 m square x 1 m separation, 1.751 m x 0.875 m separation, and 1.5 m x 0.75 m separation. Each coil consisted of ten turns of insulated 8 gauge st randed copper conductor. Each of the pairs were driven by a constant-curren t amplifier via digital to analog (D/A) converter. A 9 pole zero-gain activ e Bessel low-pass filter (1 kHz corner frequency) before the amplifier inpu t attenuated the expected high frequencies generated by the D/A conversion. The magnetic field was monitored with a 3D fluxgate magnetometer (0-3 kHz, +/- mT) through an analog to digital converter. Behavioral monitoring util ized two monochrome video cameras (viewing the coil center vertically and h orizontally), both of which could be video recorded and real-time digitally Moving Picture Experts Group (MPEG) encoded to CD-ROM. Human postural sway (standing balance) was monitored with a 3D forceplate mounted on the floor , connected to an analog to digital converter. Lighting was provided by 12 offset overhead dimmable fluorescent track lights and monitored using a dig itally connected spectroradiometer. The do resistance, inductance of each c oil pair connected in series were 1.5 m coil (0.27 Omega, 1.2 mH), 1.75 m c oil (0.32 Omega, 1.4 mH), and 2 m coil (0.38 Omega, 1.6 mH). The frequency response of the 1.5 m coil set was 500 Hz at +/- 463 muT, 1 kHz at +/- 232 muT, 150 us rise time from -200 uT(pk) to +200 muT(pk) (square wave) and is limited by the maximum voltage (+/- 146 V) of the amplifier (Bessel filter bypassed). Bioelectromagnetics 22:401-407, 2001. (C) 2001 Wiley-Liss. Inc.