Optical feedback interferometry (OFI) is a compact sensing technique with recent implementation for flow measurements in microchannels. We propose implementing OFI for the analysis at the microscale of multiphase flows starting with the case of parallel flows of two immiscible fluids. The velocity profiles in each phase were measured and the interface location estimated for several operating conditions. To the authors knowledge, this sensing technique is applied here for the first time to multiphase flows. Theoretical profiles issued from a model based on the Couette viscous flow approximation reproduce fairly well the experimental results. The sensing system and the analysis presented here provide a new tool for studying more complex interactions between immiscible fluids (such as liquid droplets flowing in a microchannel).
Acoustic flat lensing is achieved here by tuning a phononic array to have indefinite medium behaviour in a narrow frequency spectral region along the acoustic branch. This is confirmed by the occurrence of a flat band along an unusual path in the Brillouin zone and by interpreting the intersection point of isofrequency contours on the corresponding isofrequency surface; coherent directive beams are formed whose reflection from the array surfaces create lensing. Theoretical predictions are corroborated by time-domain experiments, airborne acoustic waves generated by a source with a frequency centered about 10.6 kHz, placed at three different distances from one side of a finite phononic crystal slab, constructed from polymeric spheres, yield distinctive focal spots on the other side. These experiments evaluate the pressure field using optical feedback interferometry and demonstrate precise control of the three-dimensional wave trajectory through a sonic crystal.The band spectra of photonic [1, 2] and phononic [3] crystals can be interpreted to predict a rich array of interesting physical effects, for instance anomalous refraction [1,4] and all-angle-negative refraction [5] amongst many others; understanding these spectra underpins advances in electronic properties, wave transport in photonics and acoustics, as well as in interference phenomena throughout many fields of physical and engineering sciences.In this Letter we report experimental results where an image of a volumetric source through a three-dimensional phononic crystal (PC) forms according to the physics of indefinite media [6], see Fig. 1. The image is not created by tilting the crystal as in acoustic superlenses [7], or at low frequencies using effective media [8] nor by negative refraction acoustic flat lenses using metamaterials [9,10]. Instead we identify critical points on the isofrequency surfaces, for a simple cubic array of rigid spheres, where beam-like trajectories are formed and use these beams, and their reflections, to create lensing; this is using the properties of indefinite media [6].The first experimental demonstration of a threedimensional flat acoustic lens in 2004 [7] used 0.8-mm tungsten carbide beads surrounded by water, with the beads closely packed in a face-centered cubic crystal structure along the body diagonal (ΓR crystal direction); the lensing function was above the phononic band gap of the PC and at 1.57 MHz with the pressure waves focused into a tight spot (about 5 mm). We give an alternative design to this well-known phononic lens, based upon a different physical mechanism, also exhibiting focusing reminiscent of the Veselago-Pendry convergent flat lens [11,12], see Fig. 1. Negative refraction and superlensing of underwater pressure waves has been theorized with an anisotropic acoustic metamaterial formed by layers of perforated rigid plates [13], that is analogous to a hyperbolic medium in electromagnetism [14].As in [7] we use an array of sound-hard spheres, although now in air, take a primitive cubic array, and take ad...
Using the optical feedback interferometry (OFI) technique, we demonstrated a miniaturized and compact sensor system based on a dedicated optical source for flowmetry at the micro-scale. In the system, polymer microlenses were integrated directly on a VCSEL (vertical-cavity surface-emitting laser) chip and the microfluidic channel chip surface using polymer-based micro-fabrication technologies. In particular, at a post-process stage, we integrated a collimation lens on a VCSEL chip of small dimensions (200 µm × 200 µm × 150 µm). This process was enabled by the soft-printing of dry thick resist films and through direct laser writing technology. We performed flow rate measurements using this new compact system, with a conventional bulk glass lens configuration for system performance evaluation. A maximum 33 dB signal-to-noise ratio was achieved from this novel ultra-compact system. To our knowledge, this is the highest signal level achieved by existing OFI based flowmetry sensors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.