A micro whisker transducer with sensorless mechanical impedance detection capability for fluid and tactile sensing in space-limited applications

• Micro whisker transducer for fluid and tactile sensing in space-limited applications like minimally invasive surgery.
• Sensorless detection — reduces size and cost, simplifies instrumentation and eliminates loading effect.
• New initial contact detection algorithm — avoids advanced microscope system to monitor insertion and detection.
• Supervised learning-based transduction matrix identification — addresses difficulties due to miniaturization of the μWT.
• Mechanical impedance — can be further processed to extract fluid viscosity/density or stiffness of biological tissue/cell.

A micro whisker transducer (μWT) is developed featuring sensorless capability of detecting force, motion and mechanical impedance simply from the voltage, current and electrical impedance of the actuator itself. This unique sensorless detection capability is achieved by a single transduction matrix [T] characterizing both the forward actuation function and the backward sensing function of the electro-mechanical transducer. With this new detection technique, the traditional complex mechanical impedance detection requiring three transducers is simplified to using only one. And the loading effect due to additional sensors is eliminated. The problem of identifying the transduction matrix of the μWT due to its miniaturization is addressed by introducing a new identification process of supervised learning from a training sample set of fluid loads. In addition, an initial contact detection algorithm is proposed based on a confidence interval of the measured electrical impedance which simplifies the detection process by eliminating the need of the advanced microscope system. The μWT is validated and tested through detecting the mechanical impedances of various fluid loads in experimental studies. The accuracy of mechanical impedance detection is confirmed with deviation less than 2.6% for a wide range of loads. All these capabilities and features make the μWT well suited for fluid and tactile sensing in space-limited applications like minimally invasive surgery (MIS) to detect mechanical properties of body fluids and tissues.