Flow Measurement and Instrumentation 16 (2005) 7–12 www.elsevier.com/locate/flowmeasinst Microfluidic oscillator for gas flow control and measurement Eliphas Wagner Simões a,b,∗ , Rogerio Furlan c,a , Roberto Eduardo Bruzetti Leminski a , Mário Ricardo Gongora-Rubio a,b , Marcos Tadeu Pereira b , Nilton Itiro Morimoto a , Jorge J. Santiago Avilés d a Laboratório de Sistemas Integráveis, Universidade de São Paulo, SP, Brazil b Instituto de Pesquisas Tecnológicas, São Paulo, SP, Brazil c University of Puerto Rico, Department of Physics and Electronics, Humacao, Puerto Rico d University of Pennsylvania, Department of Electrical and Systems Engineering, Philadelphia, PA, United States Received 23 September 2004; received in revised form 24 November 2004; accepted 26 November 2004 Abstract Microfluidic oscillators were obtained from wall attachment microfluidic amplifiers using a feedback loop from the outputs to the control inputs. These devices can be used as flow meters when the oscillation frequency is proportional to the volumetric flow rate in subsonic and moderately compressible conditions. They can also be used as actuators, for applications involving flow control and/or mixing. The devices, presenting critical dimensions of the order of 280 μm, were fabricated using SU-8 based epoxy photoresist and conventional photolithography. The article shows the results obtained in the experimental device tests with gases (nitrogen, argon, and carbon dioxide). The typical variation of the frequency with volumetric flow presents a range close to thousands of hertz. The oscillation frequencies were obtained using hot wire filament anemometers (in this case with a diameter of 12 μm). The experimental results indicate that the operation of the microfluidic oscillator was a direct function of the length of the feedback loops and of the velocity inside of the interaction region. © 2004 Elsevier Ltd. All rights reserved. Keywords: Fluidic; Flow control; Flow meter; Microfabrication; Fluidic oscillator 1. Introduction Fluidic technology based in natural oscillation phenom- ena is a relevant topic in several strategic areas such as aerospace; automotive; military; drug research, drug dis- pensing, and dialysis in medicine; analytical chemical in- strumentation; automatic control in industries; electronics chip cooling; and others [1–7]. In these cases, the oscil- latory flowmeters use specially designed geometric con- figurations, identified by the absence of moving parts, to ∗ Corresponding author at: Laboratório de Sistemas Integráveis, Universidade de São Paulo, SP, Brazil. Tel.: +55 11 3091 5314; fax: +55 11 3091 5665. E-mail addresses: eliphas@lsi.usp.br (E.W. Simões), rfurlan@www.uprh.edu (R. Furlan), rleminski@ig.com.br (R.E. Bruzetti Leminski), gongoram@ipt.br (M.R. Gongora-Rubio), marcostp@ipt.br (M.T. Pereira), morimoto@lsi.usp.br (N.I. Morimoto), santiago@ee.upenn.edu (J.J. Santiago Avilés). 0955-5986/$ - see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.flowmeasinst.2004.11.001 create an environment where self-induced, sustained oscil- lations will occur [6,8]. Oscillating fluid flowmeters are inherently logic (digital) devices, and the basic measure- ment performed to monitor its operation is a frequency. In a properly executed flowmeter, the oscillation frequency is proportional to the volumetric flow rate, and using these devices in millimeter/micrometer scale, the operating speeds are increased over those of their macroscopic counterparts due to the reduced inertia. Furthermore, several categories and subgroups of oscillatory flowmeters exist, each with a unique shape and particular approach. This paper in partic- ular analyzes a “feedback fluidic oscillator”[6–8] obtained from a wall attachment microfluidic amplifier, as discussed below. The technology of using the flow characteristics of liquids or gases to operate a control system is fairly old; it was in the decade of the 1960s that researchers started the use of