Mechanical low-frequency filter via modes separation in 3D periodic structures

This work presents a strategy to design three-dimensional elastic periodic structures endowed with complete bandgaps, the first of which is ultra-wide, where the top limits of the first two bandgaps are overstepped in terms of wave transmission in the finite structure. Thus, subsequent bandgaps are merged, approaching the behaviour of a three-dimensional low-pass mechanical filter. This result relies on a proper organization of the modal characteristics, and it is validated by performing numerical and analytical calculations over the unit cell. A prototype of the analysed layout, made of Nylon by means of additive manufacturing, is experimentally tested to assess the transmission spectrum of the finite structure, obtaining good agreement with numerical predictions. The presented strategy paves the way for the development of a class of periodic structures to be used in robust and reliable wave attenuation over a wide frequency band

Magnetohydrodynamic pumping in nuclear magnetic resonance environments

We present a DC magnetohydrodynamic (MHD) pump as component of a nuclear magnetic resonance (NMR) microfluidic chip. This is the first time that MHD pumping in an NMR environment was observed and demonstrated. This chip generates a maximum flow rate of 1.5 μL min−1 (2.8 mm s−1 in the microchannel) for an applied voltage of 19 V with only 38 mW of power consumption in a 7 T superconductive magnet. We developed a simple method of flow rate measurement inside the bulky NMR magnet by monitoring the displacement of a liquid–liquid interface of two immiscible liquids in an off-chip capillary. We compared and validated this flow measurement technique with another established technique for microfluidics based on the displacement of microbeads. This allowed us to characterize and compare the flow rate generated by the micropump on top of a permanent magnet (B1 = 0.33 T) with the superconductive magnet (B0 = 7.05 T). We observed a 21-fold increase in flow rate corresponding to the ratio of the magnetic field intensities (B0/B1 = 21) in accordance with the theoretical flow dependence on the magnetic field intensity. The final aim is to integrate MHD pumps together with planar coils in a microfluidic system for NMR analysis. The high performance of MHD pumps at relatively low flow rates is seen as an asset for NMR and MRI applications

Rapid Prototyping of 3D Phononic Crystals using High-resolution Stereolithography Fabrication

AbstractWe present proof-of-concept devices to validate the suitability of high-resolution stereolithography fabrication, polymer material properties, and increased design freedom for realizing 3D phononic crystals. The maskless, single-step technology enables the fabrication of freeform 3D microstructures with high accuracy, which allows rapid prototyping of novel designs and leads to fast optimization cycles. Experimental results for devices with feature sizes down to 100 μm successfully indicate phononic band gap behavior, which is required for applications as sensor and microsystem structures

Magnetic direct generation of acoustic resonances in silicon membranes

High-Q silicon membranes have been fabricated as resonator elements for excitation by magnetic direct generation of acoustic waves. Operating in the thickness shear mode, these inexpensive sensor elements are remotely excited by a planar spiral coil, driven by a radio frequency current and a strong static magnetic field. Modelling and FEM simulation have been done to improve the understanding of the sensor principle. Strong resonances with Q-factors up to 105 could be excited and detected successfully. Mass loading of these resonators shows Sauerbrey-like frequency shifts similar to quartz crystal microbalance sensors. © 2006 IOP Publishing Ltd

Miniature 3D Gas Chromatography Columns with Integrated Fluidic Connectors Using High-resolution Stereolithography Fabrication

AbstractIn this manuscript we report on design, fabrication, and characterization of miniature gas chromatography columns with arbitrary 3D geometry and integrated connectors as separation elements for a mobile ethylene sensor system. In contrast to planar microfabrication, these columns have been realized in a single step additive manufacturing process using high-resolution stereolithography printing. This maskless technology enables the combination of freeform 3D microstructures with packaging aspects in one bulk element. For applications in food monitoring, the columns were packed with Carbosieve®-SII particles as adsorbents. With the printed columns a minimal gas concentration of 35 ppb (3σ) ethylene can be detected. Retention times of 400 s for ethylene and 1035 s for water and no signal peak overlap show an improved separation capability

3-D-printed smart screw: functionalization during additive fabrication

Integrating sensors into machine parts is a necessary step for the development of smart or intelligent components. Sensors integrated into materials such as concrete, fiber compounds, or metals are already used to measure strain, temperature, or corrosion. The integration is mostly done during fabrication, where the sensor is recast in the material during processing. However, approaches to integrate sensors into parts fabricated by additive manufacturing are still rarely found. Especially in the case of rapid prototyping, additive techniques are already substituting the machining of parts using classical technologies like cutting, drilling and milling. To characterize such 3-D-printed machine parts the direct integration of sensing elements is the next logical step. This can be done in multi-material printing by using insulating, magnetic, and conductive materials. In the case of single material printing, our idea is to integrate a sensing element during the printing process itself. As proof-of-concept, we present the functionalization of 3-D-printed screws. Strain gauges screen-printed on a 6 µm thick foil are interposed into the 3-D part during microstereolithography printing. We measure the torsional strain in the screw head to calculate the prestressing force in screws made from different plastic materials. We also analyze the defect effect by comparing it to screws without integrated elements