Micromachines2014, 5(3), 711-721; doi:10.3390/mi5030711 - published 12 September 2014 Show/Hide Abstract
Abstract: This paper presents the progress of monolithic technology for microwaveapplication, focusing on gallium nitride technology advances in the realization of integratedpower amplifiers. Three design examples, developed for microwave backhaul radios, areshown. The first design is a 7 GHz Doherty developed with a research foundry, while thesecond and the third are a 7 GHz Doherty and a 7–15 GHz dual-band combined poweramplifiers, both based on a commercial foundry process. The employed architectures, themain design steps and the pros and cons of using gallium nitride technology are highlighted.The measured performance demonstrates the potentialities of the employed technology, andthe progress in the accuracy, reliability and performance of the process.
Micromachines2014, 5(3), 697-710; doi:10.3390/mi5030697 - published 11 September 2014 Show/Hide Abstract
Abstract: Flexures are components of micro-mechanisms efficiently replacing classical multi-part joints found at the macroscale. So far, flexures have been limited to two-dimensional planar designs due to the lack of a suitable three-dimensional micromanufacturing process. Here we demonstrate and characterize a high-strength transparent monolithic three-dimensional flexural component fabricated out of fused silica using non-ablative femtosecond laser processing combined with chemical etching. As an illustration of the potential use of this flexure, we propose a design of a Hoecken linkage entirely made with three-dimensional cross-spring pivot hinges.
Micromachines2014, 5(3), 681-696; doi:10.3390/mi5030681 - published 10 September 2014 Show/Hide Abstract
Abstract: We propose a single cell extraction chip with an open structure, which utilizes vibration-induced whirling flow and a single cell catcher. By applying a circular vibration to a micropillar array spiral pattern, a whirling flow is induced around the micropillars, and target cells are transported towards the single cell catcher placed at the center of the spiral. The single cell catcher is composed of a single-cell-sized hole pattern of thermo-responsive gel. The gel swells at low temperatures (≲32 ◦C) and shrinks at high temperatures (≳32 ◦C), therefore, its volume expansion can be controlled by an integrated microheater. When the microheater is turned on, a single cell is trapped by the hole pattern of the single cell catcher. Then, when the microheater is turned off, the single cell catcher is cooled by the ambient temperature. The gel swells at this temperature, and the hole closes to catch the single cell. The caught cell can then be released into culture wells on a microtiter plate by heating the gel again. We conducted single cell extraction with the proposed chip and achieved a 60% success rate, of which 61% cells yielded live cells.
Micromachines2014, 5(3), 667-680; doi:10.3390/mi5030667 - published 10 September 2014 Show/Hide Abstract
Abstract: Stop-flow lithography (SFL) is a microfluidic-based particle synthesis method, in which photolithography with a two dimensional (2D) photomask is performed in situ within a microfluidic environment to fabricate multifunctional microstructures. Here, we modified the SFL technique by utilizing an adjustable electrostatic-force-modulated 3D (EFM-3D) mask to continuously fabricate microlens structures for high-throughput production. The adjustable EFM-3D mask contains a layer filled with a UV-absorbing liquid and transparent elastomer structures in the shape of microlenses between two conductive glass substrates. An acrylate oligomer stream is photopolymerized via the microscope projection photolithography, where the EFM-3D mask was set at the field-stop plane of the microscope, thus forming the microlens structures. The produced microlens structures flow downstream without adhesion to the polydimethysiloxane (PDMS) microchannel surfaces due to the existence of an oxygen-aided inhibition layer. Microlens structures with variations in curvature and aperture can be produced by changing objective magnifications, controlling the morphology of the EFM-3D mask through electrostatic force, and varying the concentration of UV-light absorption dyes. We have successfully demonstrated to produce microlens structures with an aperture ranging from 50 μm to 2 mm and the smallest focus spot size of 0.59 μm. Our proposed method allows one to fabricate microlens structures in a fast, simple and high-throughput mode for application in micro-optical systems.
Micromachines2014, 5(3), 654-666; doi:10.3390/mi5030654 - published 1 September 2014 Show/Hide Abstract
Abstract: This paper reports the numerical and experimental analysis of the acoustic streaming effect in a fluidic domain. The actuation of a piezoelectric transducer generates acoustic waves that propagate to the fluids, generating pressure gradients that induce the flow. The number and positioning of the transducers affect the pressure gradients and, consequently, the resultant flow profile. Two actuation conditions were considered: (1) acoustic streaming generated by a 28 μm thick β-poly(vinylidene fluoride) (β-PVDF) piezoelectric transducer placed asymmetrically relative to the fluidic domain and (2) acoustic streaming generated by two 28 μm thick β-PVDF piezoelectric transducers placed perpendicularly to each other. The transducers were fixed to the lower left corner of a poly(methyl methacrylate) (PMMA)cuvette and were actuated with a 24 Vpp and 34.2 MHz sinusoidal voltage. The results show that the number of transducers and their positioning affects the shape and number of recirculation areas in the acoustic streaming flows. The obtained global flows show great potential for mixing and pumping, being an alternative to the previous geometries studied by the authors, namely, a single transducer placed symmetrically under a fluidic domain.
Micromachines2014, 5(3), 622-653; doi:10.3390/mi5030622 - published 29 August 2014 Show/Hide Abstract
Abstract: The development and application of magnetic technologies employing microfabricated magnetic structures for the production of switching components has generated enormous interest in the scientific and industrial communities over the last decade. Magnetic actuation offers many benefits when compared to other schemes for microelectromechanical systems (MEMS), including the generation of forces that have higher magnitude and longer range. Magnetic actuation can be achieved using different excitation sources, which create challenges related to the integration with other technologies, such as CMOS (Complementary Metal Oxide Semiconductor), and the requirement to reduce power consumption. Novel designs and technologies are therefore sought to enable the use of magnetic switching architectures in integrated MEMS devices, without incurring excessive energy consumption. This article reviews the status of magnetic MEMS technology and presents devices recently developed by various research groups, with key focuses on integrability and effective power management, in addition to the ability to integrate the technology with other microelectronic fabrication processes.