Frieder Lucklum

Realization of Complex 3-D Phononic Crystals With Wide Complete Acoustic Band Gaps

Phononic crystals (PnCs) offer unique band structures for acoustic wave propagation. Fabricating intricate three-dimensional (3-D) PnCs allows a new class of devices with complex phononic band structures beyond capabilities of two-dimensional (2-D) designs. We have successfully fabricated novel 3-D PnCs with 1-mm lattice constant and minimum feature sizes as low as 100 μm using high-resolution stereolithography printing. Here, we report the first theoretical calculations and experimental results demonstrating wide complete 3-D phononic band gaps not attainable by corresponding 2-D structures with the same lattice geometry. Longitudinal and shear-wave propagation is suppressed by more than -60 dB in frequency bands as wide as 400 kHz to 1 MHz.

3D Printing Solutions for Microfluidic Chip-To-World Connections

The connection of microfluidic devices to the outer world by tubes and wires is an underestimated issue. We present methods based on 3D printing to realize microfluidic chip holders with reliable fluidic and electric connections. The chip holders are constructed by microstereolithography, an additive manufacturing technique with sub-millimeter resolution. The fluidic sealing between the chip and holder is achieved by placing O-rings, partly integrated into the 3D-printed structure. The electric connection of bonding pads located on microfluidic chips is realized by spring-probes fitted within the printed holder. Because there is no gluing or wire bonding necessary, it is easy to change the chip in the measurement setup. The spring probes and O-rings are aligned automatically because of their fixed position within the holder. In the case of bioanalysis applications such as cells, a limitation of 3D-printed objects is the leakage of cytotoxic residues from the printing material, cured resin. This was solved by coating the 3D-printed structures with parylene-C. The combination of silicon/glass microfluidic chips fabricated with highly-reliable clean-room technology and 3D-printed chip holders for the chip-to-world connection is a promising solution for applications where biocompatibility, optical transparency and accurate sample handling must be assured. 3D printing technology for such applications will eventually arise, enabling the fabrication of complete microfluidic devices.

Band gap characterization of complex unit cell geometries for 3D phononic crystals

We report on experimental characterization of acoustic band gaps for complex three-dimensional phononic crystals. Utilizing 3D unit cell geometries arranged in a cubic lattice, we can achieve uniquely wider band gaps with stronger suppression of acoustic waves than possible with two-dimensional realizations. Beyond our previously established simple cubic arrangement of three cylindrical holes derived from the classic 2D square array of holes, we investigate unit cells comprising a spherical cavity, a rectangular scaffold, and a spherical ball connected by cylindrical beams. All samples have been additively manufactured using microstereolithography printing in the same geometric arrangement with a lattice constant of 1 mm and variations of the characteristic dimensions to achieve different volumetric filling factors. Maximum band gap widths over 1 MHz at gap center frequencies around 750 - 850 kHz have been measured.

3D printed pressure sensor with screen-printed resistive read-out

By combining different additive manufacturing techniques, we can merge various functionalities in single, custom designed printed components. In this work we coupled a 3D printed pressure chamber with a screen-printed resistive strain gauge to form a robust, fully printed pressure sensor. This demonstrator illustrates the suitability of using printed, polymer-based materials not only for rapid prototyping but also for rapid manufacturing of application specific sensor devices. Evaluating the change in resistance of a half-bridge layout, we characterized the circular cylindrical measurement chamber with integrated fluidic connectors for different membrane thicknesses in a pressure range of 0 to 1000 mbar.

Experimental and numerical analysis of complete acoustic band gaps in three-dimensional phononic crystals

In this contribution, we focus on the analysis of complete omnidirectional acoustic band gaps in additively manufactured three-dimensional (3D) phononic crystals. We present a numerical analysis of band structure and phononic band gaps of different cubic unit cell geometries. For validation, we report experimental results for transmission of acoustic waves in different characteristic spatial directions through various phononic crystal samples. These results are supplemented by numerical transmission analysis. The elements form the building blocks of wideband, high-resolution phononic-fluidic systems for measuring physical properties such as fluid density, speed of sound, and concentration.

Creation of hydrophilic microfluidic devices for biomedical application through stereolithography

We present a method to graft a layer of poly-ethylene-glycol (PEG) to the surface of stereo-lithography fabricated or 3D-printed microfluidic devices rendering it hydrophilic and repellent to the adhesion of proteins. The PEG forms a rigid bond with the surface that is more stable than many coatings or surface treatments. This makes stereolithography much more attractive as a prototyping platform for microfluidics. The method has been proven with two different resins by different manufacturers, showing the universality of said treatment.

3D phononic-fluidic cavity sensor for resonance measurements of volumetric fluid properties

Additively manufactured 3D phononic crystals have demonstrated wide acoustic band gaps and strong acoustic mode suppression not attainable by corresponding 2D designs. In this work we present the combination of these air-filled 3D structures with an enclosed fluidic cavity resonator in a single printed sensor element for the first time. This combination drastically improves the sensitivity of the cavity resonance signal. An analytical 1D calculation demonstrates this phononic-fluidic sensor concept and is used to approximate suitable geometric designs, which are subsequently fabricated using microstereolithography printing. Our experimental results show clearly separated resonance frequencies for different liquids introduced into the cavity, with frequency shifts correlating to differences in density and speed of sound.