Effect of curvature on sound propagation in the ear canal.

In this paper, we investigate the effect of the curvature and torsion of the ear canal on its resonance through a comparison between several ear canal models. Utilizing Stinson's ear canal geometries as a reference, we build and analyze several ear canal models using both transmission matrix and numerical methods for the purpose of comparative assessment. A conical transmission unit, which considers visco-thermal effects, is employed for the modeling of the human ear canal. While the transfer matrix and numerical method agree well for a straight axis model, this simplification results in up to 20% deviation from a curved canal. We propose the curve twist ratio as a metric to quantify the influence of curvature on the ear canal and find that our proposed metric can effectively express the error introduced by the simplified straight axis model. Upon this metric, an empirical equation is proposed for incorporating the curvature effect in the transmission matrix method, enabling it to generate comparable results to those of the numerical method, which considers the effect of the curvature and torsion, thus dramatically accelerating computation.

Complete phononic band gaps in the 3D Yablonovite structure with spheres.

In this work we present the theoretical and experimental verification of complete phononic band gaps in the Yablonovite structure with additional spheres in a face-centered cubic arrangement. The Finite Difference Time Domain method was used in the calculations of band structure and transmission spectrum. Different spatial directions and different polarizations of the incident acoustic field were investigated numerically and experimentally. Phononic band gaps in the acoustic band structure and in the transmission spectrum were calculated for all the examined cases of spatial directions and polarizations. The complete band gaps of the theoretical findings were confirmed by experimental measurements of 3D-printed prototype samples. All results are in very good agreement and validate complete phononic band gaps in these structures.

Miniature 3D-Printed Centrifugal Pump with Non-Contact Electromagnetic Actuation.

We present a miniature 3D-printed dynamic pump using the centrifugal operating principle. Dynamic pumps typically yield higher flow rates than displacement pumps at reasonable output pressure. Realizing smaller devices suitable for millifluidic and microfluidic applications brings challenges in terms of design, fabrication and actuation. By using microstereolithography printing we have reduced the overall size to an effective pumping volume of 2.58 mL. The free-moving rotor consists of an impeller and permanent magnets embedded during the printing process, which allow for non-contact electromagnetic actuation. The pump is driven by periodically switching the current through stator coils, controlled by a custom built circuit using a Hall effect sensor. It achieves a maximum flow rate of 124 mL/min and a hydrostatic pressure of up to 2400 Pa.

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.

Realization of Complex 3D Phononic Crystals with Wide Complete Acoustic Band Gaps.

Phononic crystals offer unique band structures for acoustic wave propagation. Fabricating intricate threedimensional phononic crystals allows a new class of devices with complex phononic band structures beyond capabilities of two-dimensional designs. We have successfully fabricated novel 3D phononic crystals with 1 mm lattice constant and minimum feature sizes as low as 100 micron using high-resolution stereolithography printing. Here we report the first theoretical calculations and experimental results demonstrating wide complete 3D phononic band gaps not attainable by corresponding 2D 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.

Electromagnetic-acoustic high-Q silicon resonators for liquid phase sensing.

Piezoelectric and electrostatic excitation are the standard transduction methods of ultrasonic sensors. However, electromagnetic-acoustic transduction has been demonstrated as a suitable alternative with unique advantages of noncontact excitation and multi-mode vibration in inexpensive materials, such as thin metal plates. We have also demonstrated the use of high-Q silicon membranes as resonator elements. Here, we report on the utilization of these devices as liquid phase sensors for density and viscosity measurements.

Miniaturized sensors for the viscosity and density of liquids--performance and issues.

This paper reviews our recent work on vibrating sensors for the physical properties of fluids, particularly viscosity and density. Several device designs and the associated properties, specifically with respect to the sensed rheological domain and the onset of non-Newtonian behavior, are discussed.