Sensing tactile microvibrations with the BioTac — Comparison with human sensitivity

The human fingertip is exquisitely sensitive to vibrations that are essential to detect slip and discriminate textures. Achieving similar functions with prosthetic and robotic hands will require tactile sensors with similar sensitivity. Many technologies have been developed to sense such vibrations, yet none have achieved the requisite sensitivity in a package that is robust enough to meet practical applications. The BioTac®, developed by the authors, uses an incompressible liquid as an acoustic conductor to convey vibrations from the skin to a wide bandwidth pressure transducer located deep in the rigid core of the mechatronic finger, where it is protected from damage. Signal conditioning electronics were designed to achieve sensitivity down to the theoretical noise floor of the transducer, making the device very sensitive to the smallest of vibrations, even sound. We demonstrate here that this device exceeds human performance in detecting sustained vibrations (capable of sensing vibrations as small as a few nanometers at ~330Hz) as well as very small transient events that arise when small particles are dropped on the finger. This overcomes the supposition that such sensitivity requires fragile sensory elements to reside near the vulnerable contact surfaces.