EM Field Head Tracking System specifications

Schematic of the Sphere Head Tracking System

Introduction

The EM Field Head Tracking System is used for recording head movements of the subject during a trial. The system consists of the following parts:

Three oscillators at roughly 45, 55 and 65 kHz or 50, 60, 70 kHz for X, Y and Z direction.
Three signal amplifiers that amplify the oscillator signals.
six field coils that make a cube of roughly 3x3x3 meters.
A small pick-up coil mounted on a glasses frame that is worn by the subject during the experiment.
Three lock-in amplifiers that split the signal from the pick-up coil in the 3 frequency components and measures their envelope. They output analog signals between -10V and +10V.
An acquisition device converts the analog output signals from the lock-in amplifiers to digital.
A RZ6 multi I/O processor that records the acquired data.
Software that converts the recorded data to head orientations using calibration data.

The following table contains the channel convention with respect of the three directions:

Channel	Frequency	Orientation	Color	Polarity
Channel 1	45 kHz	Frontal	Red	Front = positive; Back = negative
Channel 2	55 kHz	Vertical	Blue	Right = positive; Left = negative
Channel 3	65 kHz	Horizontal	Yellow	Up = positive; Down = negative