To determine the characteristics of flow sensors, a suitable source for flow generation is required. We discuss three different sources for oscillating air flow, by considering their acoustic impedance, frequency range, velocity and ability to distinguish between flow and pressure. We discuss the impact of these sources on characterization of our biomimetic hair flow sensors, which operate at flow velocities from 1–100 mm/s within a frequency range from 10–1000 Hz

Dagamseh, A.M.K.

Droogendijk, H.

Krijnen, G.J.M.

Sanders, R.G.P.

Yntema, D.R.

English

Yntema, Doekle Reinder

Sanders, Remco G.P.

Krijnen, Gijsbertus J.M.

University of Twente Research Information

On the use of various oscillatory air flow fields forcharacterization of biomimetic hair flow sensorsH. Droogendijk, A.M.K. Dagamseh, D.R. Yntema, R.G.P. Sanders and G.J.M. KrijnenMESA+ Research Institute, University of Twente, Enschede, THE NETHERLANDSE-mail: h.droogendijk@utwente.nlTo determine the characteristics of flow sensors, asuitable source for flow generation is required. Wediscuss three different sources for oscillating air flow,by considering their acoustic impedance, frequencyrange, velocity and ability to distinguish betweenflow and pressure. We discuss the impact of thesesources on characterization of our biomimetic hairflow sensors (Fig. 1), which operate at flow velocitiesfrom 1–100 mm/s within a frequency range from10–1000 Hz [1, 2].First, a loudspeaker was used as source. Itsfrequency range is in the order of 10–1000 Hz,capable of generating high flow velocities (up to 1m/s) The distance of the loudspeaker to the sensoris of importance, since the typically small acousticimpedance (the ratio of flow to pressure) decreaseswith distance to the loudspeaker [3]. Using thiswell modeled and characterized source (Fig. 2),we determined the sensor’s mechanical transfer(both magnitude and phase), all using laser dopplervibrometry (LDV). Also, a clear directivity profilewas observed, indicating that the sensor is mainlyresponsive towards flow.Another used source is a vibrating sphere, whichbehaves more like a monopole than a dipole sourcein the near field compared to a loudspeaker. Thevibrating sphere is typically used for frequenciesin the range of 10–100 Hz. A property of thesphere’s near field is that for measuring right belowit (Fig. 3) the acoustical impedance is theoreticallyzero, meaning no pressure fluctuations and thus onlyflow [4]. We used this source for realizing a nearlyincompressible flow field for lateral line experiments.Measurements with a reference flow sensor and ourflow sensors showed both a flow profile in closeresemblance with the theoretical predictions fordipole source flows (Fig. 4).The third type of source used is a standingwave tube (Fig. 5). Inside, well-defined patterns ofstanding waves occur at frequencies depending onthe tube geometry [5]. Advantages are the rangeof frequencies (10–4000 Hz) together with highflow velocities (up to 1 m/s). An advantage is theability to distinguish between pressure and particlevelocity (i.e. flow), since for standing waves thereis a 90 degrees phase difference between pressureand particle velocity. Exploiting this property, welearned that our flow sensor has finite pressuresensitivity. However, directivity measurements usinga loudspeaker showed almost exclusively sensitivityto flow (Fig. 6). This is explained by the acousticimpedance at the sensor’s position, which was muchsmaller in case of the loudspeaker. Therefore, theacoustic impedance matters for measurement qualityon our flow sensors.In conclusion, depending on the design andapplication of flow sensors, a suitable source isrequired to determine the sensor properties. Forour sensors, the combination of three different flowsources gave good insights in the behavior of ourflow sensory system.Word count: 439REFERENCES[1] M. A. Dijkstra, J. J. J. van Baar, R. J. Wiegerink, T. S. J.Lammerink, J. H. de Boer and G. J. M. Krijnen, “Artificialsensory hairs based on the flow sensitive receptor hairs ofcrickets”, J. Micromech. Eng., Vol. 15, pp. S132–S138, 2005.[2] C. M. Bruinink, R. K. Jaganatharaja, M. J. de Boer, J.W. Berenschot, M. L. Kolster, T. S. J. Lammerink, R. J.Wiegerink and G. J. M. Krijnen, “Advancements in tech-nology and design of biomimetic flow-sensor arrays”, Proc.,MEMS 2009 Conference, Sorrento, Italy, Jan. 25–29, 2009,pp. 152–155.[3] K. Beissner, “On the plane-wave approximation of acousticintensity”, J. Acoust. Soc. Am., Vol. 71 pp. 1406-1411, 1982.[4] H. Lamb, “Hydrodynamics”, Cambridge University Press,Cambridge, 6th edition, 1932.[5] D. R. Yntema, W. F. Druyvesteyn, and M. C. Elwenspoek,“A four particle velocity sensor device”, J. Acoust. Soc. Am.,Vol. 119, pp. 943-951, 2006.Fig. 1. MEMS hair flow sensors.11010010 100 1000Transfer(mm/s/V)Frequency (Hz)Loudspeaker characterizationMeasuredModelFig. 2. Comparing model and LDV measurements of theloudspeaker.xyDFig. 3. Schematic of a vibrating sphere.-1.2-0.8-0.400.40.81.2-0.18 -0.12 -0.06 0 0.06 0.12 0.18NormalizedoutputPosition (m)Characterization by vibrating sphereMeas. u//(x)Model u//(x)Meas. u⊥(x)Model u⊥(x)Fig. 4. Comparing model and measurements of the vibratingsphere.u0LoudspeakerLprefPressure sensorDevice Under Test (DUT)u(x)xFig. 5. Schematic of a standing wave tube.0.010.1110 100 1000NormalizedacousticpropertyFrequency (Hz)Standing wave tube – Distinguish abilityPressureParticle velocityMeasurementsFig. 6. Determining flow and pressure sensitivity using thestanding wave tube.

On the Use of Various Oscillatory Air Flow Fields for Characterization of Biomimetic Hair Flow Sensors

NARCIS 

To determine the characteristics of flow sensors, a suitable source for flow generation is required. We discuss three different sources for oscillating air flow, by considering their acoustic impedance, frequency range, velocity and ability to distinguish between flow and pressure. We discuss the impact of these sources on characterization of our biomimetic hair flow sensors, which operate at flow velocities from 1-100 mm/s within a frequency range from 10-1000 Hz

On the use of various oscillatory air flow fields for characterization of biomimetic hair flow sensors

 P28   On the use of various oscillatory air flow fields for characterization of biomimetic hair flow sensors  H. Droogendijk, A.M.K. Dagamseh, D.R. Yntema, R.G.P. Sanders, G.J.M. Krijnen Transducers Science and Technology group (TST group), MESA+ Research Institute, University of Twente, Enschede, The Netherlands To determine the characteristics of flow sensors, a suitable source for flow generation is required. We discuss three different sources for oscillating air flow, by considering their acoustic impedance, frequency range, velocity and ability to distinguish between flow and pressure. We discuss the impact of these sources on characterization of our biomimetic hair flow sensors, which operate at flow velocities from 1-100 mm/s within a frequency range from 10-1000 Hz. First, a loudspeaker was used as source. Its frequency range is in the order of 10-1000 Hz, capable of generating high flow velocities (up to 1 m/s) The distance of the loudspeaker to the sensor is of importance, since the typically small acoustic impedance (the ratio of flow to pressure) decreases with distance to the loudspeaker. Using this source, we determined the sensor's mechanical transfer (both magnitude and phase) using laser vibrometry. Also, a clear directivity profile was observed, indicating that the sensor is mainly responsive towards flow. Another used source is a vibrating sphere, which behaves more like a monopole than a dipole source in the near field compared to a loudspeaker. The vibrating sphere is typically used for frequencies in the range of 10-100 Hz. A property of the vibrating sphere's near field is that for measuring right below the sphere its acoustical impedance is theoretically zero, meaning no pressure fluctuations and thus only flow. We used this source for realizing a nearly incompressible flow field for lateral line experiments. Measurements with a reference flow sensor and our flow sensors showed both a flow profile in close resemblance with the theoretical predictions for dipole source flows. The third type of source used is a standing wave tube. Inside, well-defined patterns of standing waves occur at frequencies depending on the tube geometry. Advantages are the range of frequencies (10-4000 Hz) together with high flow velocities (up to 1 m/s). The acoustic impedance varies with frequency and depends on the position in the tube. Another advantage is the ability to distinguish between pressure and particle velocity (i.e. flow), since for standing waves there is a 90 degrees phase difference between pressure and particle velocity. Exploiting this property, we learned that our flow sensor has finite pressure sensitivity. However, directivity measurements using a loudspeaker showed almost exclusively sensitivity to flow. This is explained by the acoustic impedance at the sensor's position, which was much smaller in case of the loudspeaker. Therefore, the acoustic impedance matters for measurement quality on our flow sensors. In conclusion, depending on the design and application of flow sensors, a suitable source is required to determine the sensor properties. For our sensors, the combination of three different flow sources gave good insights in the behavior of our flow sensory system.         

A four particle velocity sensor device”,

Advancements in technology and design of biomimetic ﬂow-sensor arrays”,

Artiﬁcial sensory hairs based on the ﬂow sensitive receptor hairs of crickets”,

Hydrodynamics”,

On the plane-wave approximation of acoustic intensity”,

On the Use of Various Oscillatory Air Flow Fields for Characterization of Biomimetic Hair Flow Sensors

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