Active High-Throughput Micromixer Using Injected Magnetic Mixture Underneath Microfluidic Channel

Microfluidics has a lot of applications in fields ranging from pharmaceutical to energy, and one of the major applications is micromixers. A challenge faced by most micromixers is the difficulty in mixing within micro-size fluidic channels because of the domination of laminar flow in a small channel. Hence, magnetic field generated by permanent magnets and electromagnets have been widely used to mix ferrofluids with other sample fluids on a micro level. However, permanent magnets are bulky, and electromagnets produce harmful heat to biological samples; both properties are detrimental to a microfluidic chip’s performance. Taking these into consideration, this study proposes rapid mixing of ferrofluid using a two-layer microfluidic device with microfabricated magnet. Two microfluidic chips that consist of microchannels and micromagnets respectively are fabricated using a simple and low-cost soft lithography method. The custom-designed microscale magnet consists of an array of stripes and is bonded below the plane of the microchannel. The combination of the planar location and angle of the array of magnets allow the migration of ferrofluids, hence mixing it with buffer flow. Parametric studies are performed to ensure comprehensive understanding, including the angle of micro-scale magnets with respect to the fluidic channels, total flow rate and density of the array of magnets. The result from this study can be applied in chemical synthesis and pre-processing, sample dilution, or inducing reactions between samples and reagent.

Longitudinal Motion Based Lightweight Vehicle Payload Parameter Real-Time Estimations

This paper proposes a longitudinal motion based payload parameter estimator (PPE) design for four-wheel-independently driven lightweight vehicles (LWVs), whose dynamics and control are substantially affected by their payload variations due to the LWVs' significantly reduced sizes and weights. Accurate and real-time estimation of payload parameters, including payload mass and its onboard planar location, will be helpful for LWV control (particularly under challenging driving conditions) and load monitoring. The proposed estimation method consists of three steps in sequential: tire effective radius identification for undriven wheels at constant speed driving; payload mass estimation during acceleration–deceleration period; and payload planar location estimation (PPLE). The PPLE is divided into two parts: a tire nominal normal force estimator (NNFE) based on a recursive least squares algorithm using signals generated by the redundant inputs, and a parameter calculator combining these estimated nominal normal forces. The prototype LWV is a lightweight electric ground vehicle (EGV) with separable torque control of the four wheels enabled by four in-wheel motors, which allow redundant input injections in the designed maneuvers. Experimental results obtained on an EGV road test show that the proposed PPE is capable of accurately estimating payload parameters, and it is independent of other unknown parameters such as tire-road friction coefficient.