Flexible tactile sensors capable of detecting the magnitude and direction of the applied force together are of great interest for application in human-interactive robots, prosthetics, and bionic arms/feet. Human skin contains excellent tactile sensing elements, mechanoreceptors, which detect their assigned tactile stimuli and transduce them into electrical signals. The transduced signals are transmitted through separated nerve fibers to the central nerve system without complicated signal processing. Inspired by the function and organization of human skin, we present a piezoresistive type tactile sensor capable of discriminating the direction and magnitude of stimulations without further signal processing. Our tactile sensor is based on a flexible core and four sidewall structures of elastomer, where highly sensitive interlocking piezoresistive type sensing elements are embedded. We demonstrate the discriminating normal pressure and shear force simultaneously without interference between the applied forces. The developed sensor can detect down to 128 Pa in normal pressure and 0.08 N in shear force, respectively. The developed sensor can be applied in the prosthetic arms requiring the restoration of tactile sensation to discriminate the feeling of normal and shear force like human skin.

In this research, we have developed a multi-channel piezoelectric acoustic sensor (McPAS) that mimics the function of the natural basilar membrane capable of separating incoming acoustic signals mechanically by their frequency and generating corresponding electrical signals. The McPAS operates without an external energy source and signal processing unit with a vibrating piezoelectric thin film membrane. The shape of the vibrating membrane was chosen to be trapezoidal such that different locations of membrane have different local resonance frequencies. The length of the membrane is 28 mm and the width of the membrane varies from 1 mm to 8 mm. Multiphysics finite element analysis (FEA) was carried out to predict and design the mechanical behaviors and piezoelectric response of the McPAS model. The designed McPAS was fabricated with a MEMS fabrication process based on the simulated results. The fabricated device was tested with a mouth simulator to measure its mechanical and piezoelectrical frequency response with a laser Doppler vibrometer and acoustic signal analyzer. The experimental results show that the as fabricated McPAS can successfully separate incoming acoustic signals within the 2.5 kHz–13.5 kHz range and the maximum electrical signal output upon acoustic signal input of 94 dBSPL was 6.33 mVpp. The performance of the fabricated McPAS coincided well with the designed parameters.

High sensitive flexible and wearable devices which can detect delicate touches have attracted considerable attentions from researchers for various promising applications. This research was aimed at enhancing the sensitivity of a MWCNT/PDMS piezoresistive tactile sensor through modification of its surface texture in the form of micropillars on MWCNT/PDMS film and subsequent low energy Ar⁺ ion beam treatment of the micropillars. The introduction of straight micropillars on the MWCNT/PDMS surface increased the sensitivity under gentle touch. Low energy ion beam treatment was performed to induce a stiff layer on the exposed surface of the micropillar structured MWCNT/PDMS film. The low energy ion bombardment stabilized the electrical properties of the MWCNT/PDMS surface and tuned the curvature of micropillars according to the treatment conditions. The straight micropillars which were treated by Ar⁺ ion with an incident angle of 0° demonstrated the enhanced sensitivity under normal pressure and the curved micropillars which were treated with Ar⁺ ion with an incident angle of 60° differentiated the direction of an applied shear pressure. The ion beam treatment on micropillar structured MWCNT/PDMS tactile sensors can thus be applied to reliable sensing under gentle touch with directional discrimination.

Integrating tactile sensors into robotic applications is still a challenge because of sensor interconnection and various form factors. Newly developed magnetic synapse sensors have high sensitivity and remote sensing capability, but integration with a robotic finger is an issue because of the air-transmitting tubes that need to be connected from the sensor to the remotely located base unit. This study proposes an integrated design of a multi-joint robotic finger with magnetic synapse sensors inspired by the human's joint mechanism and synapse system. The rolling contact joint inspired by human's finger joints can easily have hollow channels and insert air-transmitting tubes through a rotating joint compared to the traditional pin joint. The rolling contact joint also minimizes the length variation of the tube when the joint rotates because the center of rotation changes. Modularized sensor units capable of changing the sensor sensitivity and sensing range have been developed and applied to the remote tactile sensing system. A three-finger gripper with three joints per finger with an integrated three-tactile sensor array was prototyped to explore the feasibility of the units. The sensor sensitivity was 0.016 mV/kPa, and the sensing range was 350 kPa. The robotic fingers integrated with a high-sensitivity sensor array can grasp objects with various shapes and compliance (i.e., artificial flowers, paper cups, and wine glasses) without damaging the objects using tactile feedback.

This paper presents the development of a piezoelectric artificial cochlea (PAC) device capable of analyzing vibratory signal inputs and converting them into electrical signal outputs without an external power source by mimicking the function of human cochlea within an audible frequency range. The PAC consists of an artificial basilar membrane (ABM) part and an implantable packaged part. The packaged part provides a liquid environment through which incoming vibrations are transmitted to the membrane part. The membrane part responds to the transmitted signal, and the local area of the ABM part vibrates differently depending on its local resonant frequency. The membrane was designed to have a logarithmically varying width from 0.97 mm to 8.0 mm along the 28 mm length. By incorporating a micro-actuator in an experimental platform for the package part that mimics the function of a stapes bone in the middle ear, we created a similar experimental environment to cochlea where the human basilar membrane vibrates. The mechanical and electrical responses of fabricated PAC were measured with a laser Doppler vibrometer and a data acquisition system, and were compared with simulation results. Finally, the fabricated PAC in a biocompatible package was developed and its mechanical and electrical characteristics were measured. The experimental results shows successful frequency separation of incoming mechanical signal from micro-actuator into frequency bandwidth within the 0.4 kHz–5 kHz range.

This paper presents the development of piezoelectric artificial cochlear (P-AC) capable of analyzing incoming acoustic or mechanical signals without external power source. The P-AC consists of membrane part and package part. The package part provides liquid environment through which the incoming signal is transmitted to membrane part. The membrane part responds to the transmitted signal and local area of the membrane part vibrates differently depending on its local resonant frequency. Previously in our group, we have demonstrated the feasibility of the P-AC with trapezoidal membrane part as sound analyzer by using mouth simulator as a sound input. In this research, we modified the P-AC to have the membrane part of logarithmically varying width. Also by incorporating mico-actuator into the package part that mimic the function of stapes bone in middle ear, we created similar environment to cochlear where human basilar membrane vibrates. The fabricated P-AC successfully demonstrates frequency separation of incoming mechanical signal from micro-actuator into several frequency bands within human hearing range.