A Microfluidic Rotational Motor Driven by Circular Vibrations

Abstract

Constructing micro-sized machines always involves the problem of how to bring the energy (electric, magnetic, light, electro wetting, vibrational, etc.) source to the device to produce mechanical movements. The paper presents a rotational micro-sized motor (the diameter of the rotor is 350 µm) driven by low frequency (200–700 Hz) circular vibrations, made by two piezoelectric actuators, through the medium of a water droplet with diameter of 1 mm (volume 3.6 µL). The theoretical model presents how to produce the circular streaming (rotation) of the liquid around an infinitely long pillar with micro-sized diameter. The practical application has been focused to make a time-stable circular stream of the medium around the finite long vibrated pillar with diameter of 80 µm in the presence of disturbances produced by the vibrated plate where the pillar is placed. Only the time-stable circular stream in the water droplet around the pillar produces enough energy to rotate the micro-sized rotor. The rotational speed of the rotor is controlled in both directions from −20 rad/s to +26 rad/s. 3D printed mechanical amplifiers of vibrations, driven by piezoelectric actuators, amplify the amplitude of the piezoelectric actuator up to 20 µm in the frequency region of 200 to 700 Hz.

Soft Robotic Grippers

“…b) Operation of a capillary gripper picking up a micro‐object. Reproduced under the terms of the CC BY license . Copyright 2017, The Authors, published by MDPI.…”

“…Capillary adhesion has been used specifically for manipulation of micro‐objects . Grippers using this adhesion technology exploit capillary lifting force of a liquid (generally water) bridging the gripper and the object.…”

“…Grippers in this category are suitable for micromanipulation, since the capillary force is dominant at the micro‐nanoscale. Figure d shows the operation of a capillary gripper picking up a micro‐object made of polystyrene . The object, which has diameter of 30 µm, is lifted using the thin water layer formed on the gripper due to ambient humidity.…”

A Pot-Like Vibrational Microfluidic Rotational Motor

“…Of course, the motors worked well if the rotational speeds of the loaded rotors were also lower than the maximal rotational speeds of the unloaded rotors. In this case, the maximal torque was higher than those estimated by Equations (17) and (18), but with lower dynamics. The rotor rotational speed measurements were done with the use of a highspeed camera attached to the microscope.…”

“…The same method as in the previous cited reference was used in the research of Uran et al [ 17 ], where whirling of the liquid around the pillar in a droplet of water was used to rotate a disc (diameter 350 µm) centered with the pillar. They reported the maximum rotation speed around 26 rad/s, controllable in both directions and with maximal torque of 0.2 pNm.…”