Recently, researchers started to engineer not only the outer shape of objects, but also their internal microstructure. Such objects, typically based on 3D cell grids, are also known as metamaterials. Metamaterials have been used, for example, to create materials with soft and hard regions.

Vibration motors are often used to generate tactile feedback to enhance human-machine interactions and provide information about the environment. We are interested in using these motors to enhance user feedback when wearing below-knee prostheses by providing informational cues via vibrations on the thigh. Our initial designs to hold the motors against the thigh resulted in a weak perception of vibration. We took an engineering approach to improve sensation by modeling the system and designing a new device that maximized skin displacement. Our results show the new suspended design increased skin displacement for both types of vibrational motors.

Vibration motors are often used to generate tactile effects by exciting a mass at a given frequency and amplitude. The characteristic impedance of this vibrotactile device is not always in harmony with the impedance of the human skin. This impedance mismatch can result in poor energy transfer, necessitating larger motors and greater power consumption than otherwise required. Herein, we investigate the feasibility of improving the energy transfer by placing a medium between the skin and the motor, which we dub an impedance adapter. We simulate the effects of this impedance adapter using a mathematical model, and evaluate its effect on skin displacement and a parameter we call skin stimulus. Skin stimulus is introduced as a measure of the perceptive effects of a haptic system, and is used to compare results between systems with an impedance adapter and those without. Our findings suggest a factor of four improvement in skin displacement and a two-fold increase in skin stimulus are possible by introducing an optimized impedance adapter.

Vibrotactile devices suffer from poor energy efficiency, arising from a mismatch between the device and the impedance of the human skin. This results in over-sized actuators and excessive power consumption, and prevents development of more sophisticated, miniaturized and low-power mobile tactile devices. In this paper, we present the experimental evaluation of a vibrotactile system designed to match the impedance of the skin to the impedance of the actuator. This system is able to quadruple the motion of the skin without increasing power consumption, and produce sensations equivalent to a standard system while consuming 1/2 of the power. By greatly reducing the size and power constraints of vibrotactile actuators, this technology offers a means to realize more sophisticated, smaller haptic devices for the user interface community.