Frequency-Controlled Wireless Passive Thermopneumatic Micromixer

This paper reports a novel wireless control of a thermopneumatic zigzag micromixer achieved by selectively activating two passive wireless heaters enabled by an external radiofrequency magnetic field. The two heaters, which are designed to have different resonant frequency (f
_r
) values of 100 and 130 MHz, are selectively activated by modulating the field frequency to their corresponding f
_r
values. Each heater is responsible for heating an air-heating chamber that is connected to a loading reservoir through a microdiffuser element, while the solutions pumped from each reservoir are mixed in a zigzag micromixing element that ends with an outlet hole. Mixing is achieved in a relatively short mixing length of a 2 mm, and was investigated over a low range of Reynold's number (Re) ≤ 10 that is suitable various biomedical applications. The numerically simulated and measured results of the proposed micromixer have shown mixing efficiencies values higher than 82% for the whole range of Re. The optimal activation switching time of the heaters is 10 s, at which the micromixer achieves a steady value of the maximum mixing efficiency after ~65 s. The micromixer provides mixing-ratio controllability with a maximum flow rate and pressure drop of ~3.4 μL/min and ~385.22 Pa, respectively.