Recent strides in micro- and nanomanufacturing technologies have sparked the development of micro-/nanorobots with enhanced power and functionality. Due to the advantages of on-demand motion control, long lifetime, and great biocompatibility, magnetic propelled micro-/nanorobots have exhibited considerable promise in the fields of drug delivery, biosensing, bioimaging, and environmental remediation. The magnetic fields which provide energy for propulsion can be categorized into rotating and oscillating magnetic fields. In this review, recent developments in oscillating magnetic propelled micro-/nanorobot fabrication techniques (such as electrodeposition, self-assembly, electron beam evaporation, and three-dimensional (3D) direct laser writing) are summarized. The motion mechanism of oscillating magnetic propelled micro-/nanorobots are also discussed, including wagging propulsion, surface walker propulsion, and scallop propulsion. With continuous innovation, micro-/nanorobots can become a promising candidate for future applications in the biomedical field. As a step toward designing and building such micro-/nanorobots, several types of common fabrication techniques are briefly introduced. Then, we focus on three propulsion mechanisms of micro-/nanorobots in oscillation magnetic fields: (1) wagging propulsion; (2) surface walker; and (3) scallop propulsion. Finally, a summary table is provided to compare the abilities of different micro-/nanorobots driven by oscillating magnetic fields.
Having a continuous mode of transportation, in the manufacturing and pharmaceutical industries, is desirable and this facilitated by the usage of dual transducer-type ultrasonic levitation-based transportation systems. It is well known that the structural and electrical parameters determine what can be transported continuously, but the relationships between these important parameters are still not clear. In this study, the vibrating plate length and the phase shift between the two transducers were investigated as both of these are key parameters for the transportation system, and affect the standing wave ratios (SWRs), the acoustic radiation forces, and consequently the way the transportation system operates. Through numerical analysis and experimental verification, it can be seen that when the sum or difference of the spatial phase difference (determined by the vibrating plate length) and the phase shift is equal to 180° × (1 + 2n) (where n is an integer), except for the spatial phase difference of 180°·m (where m is also an integer) and the SWRs approaches unity, all this implying that traveling waves (TWs) are dominantly excited on the vibrating plate. As a consequence, the TW-induced acoustic radiation force, which greatly exceeds the standing wave-induced force, causes the continuous transportation of the particle being moved in the sound field. This paper not only clarifies the requirements for generating this continuous transportation, but also provides valuable information on the practical design of such a transportation system.
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