Smart Mechanical Dipole: a device for the measurement of sphere motion in behavioral and neurophysiological experiments.

Fluid motion and pressure fields induced by vibrating spheres are frequently used to investigate the function of biological mechanosensory systems and artificial sensors. The calibration of the sphere motion amplitude (displacement, velocity, acceleration), time course and vibration direction often demands expensive equipment. To mitigate this requirement, we have developed a high-quality, low-cost device that we term a 'Smart Mechanical Dipole'. It provides real-time measurement of sphere acceleration along three axes and can be used to obtain an accurate stimulation trace. We applied digital filtering to equalize the frequency response of the vibrating sphere, which also reduced unwanted amplitude and frequency changes in the hydrodynamic signal. In addition, we show that the angular orientation of the rod to which the sphere was attached, i.e. axial versus transverse, but not the immersion depth of the sphere affected sphere vibration behavior.