Hageman Kristin N, Chow Margaret R, Roberts Dale C, Della Santina Charles C
Dept. of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205 USA.
Dept. of Neurology, Johns Hopkins School of Medicine, Baltimore, MD 21205 USA.
IEEE Trans Instrum Meas. 2021;70:1-9. doi: 10.1109/tim.2020.3020682. Epub 2020 Aug 31.
Vestibular and oculomotor research often requires measurement of 3-dimensional (3D) eye orientation and movement with high spatial and temporal precision and accuracy. We describe the design, implementation, validation and use of a new magnetic coil system optimized for recording 3D eye movements using small scleral coils in animals.
Like older systems, the system design uses off-the-shelf components to drive three mutually orthogonal alternating magnetic fields at different frequencies. The scleral coil voltage induced by those fields is decomposed into 3 signals, each related to the coil's orientation relative to the axis of one field component. Unlike older systems based on analog demodulation and filtering, this system uses a field-programmable gate array (FPGA) to oversample each induced scleral coil voltage (at 25 Msamples/s), demodulate in the digital domain, and average over 25 ksamples per data point to generate 1 ksamples/s output in real time.
Noise floor is <0.036° peak-to-peak and linearity error is < 0.1° during 345° rotations in all three dimensions.
This FPGA-based design, which is both reprogrammable and freely available upon request, delivers sufficient performance to record eye movements at high spatial and temporal precision and accuracy using coils small enough for use with small animals.
前庭和动眼神经研究通常需要以高空间和时间精度及准确性测量三维（3D）眼位方向和运动。我们描述了一种新的磁线圈系统的设计、实施、验证及应用，该系统经过优化，可使用小动物的小型巩膜线圈记录3D眼动。
与旧系统一样，该系统设计使用现成组件来驱动三个相互正交、频率不同的交变磁场。由这些磁场感应产生的巩膜线圈电压被分解为3个信号，每个信号都与线圈相对于一个场分量轴的方向有关。与基于模拟解调与滤波的旧系统不同，该系统使用现场可编程门阵列（FPGA）对每个感应到的巩膜线圈电压进行过采样（采样率为25 Msamples/s），在数字域进行解调，并对每个数据点的25 k个样本求平均值，以实时生成1 k个样本/秒的输出。
在所有三个维度上进行345°旋转时，本底噪声峰峰值<0.036°，线性误差<0.1°。
这种基于FPGA的设计既可以重新编程，又可应要求免费提供，具有足够的性能，能够使用小到足以用于小动物的线圈，以高空间和时间精度及准确性记录眼动。
