Fish use their lateral line system to detect minute water motions. The lateral line consists of superficial neuromasts and canal neuromasts. The response properties of canal neuromasts differ from those of superficial ones. Here, we report the design, fabrication, and characterization of an artificial lateral line canal system. The characterization was done under various fluid conditions, including dipolar excitation and turbulent flow. The experimental results with dipole excitation match well with a mathematical model. Canal sensors also demonstrate significantly better noise immunity compared with superficial ones. Canal-type artificial lateral lines may become important for underwater flow sensing

Bleckmann, Horst

Klein, Adrian

Liu, Chang

Yang, Yingchen

English

Scholarworks@UTRGV Univ. of Texas RioGrande Valley

University of Texas Rio Grande Valley ScholarWorks @ UTRGV Mechanical Engineering Faculty Publications and Presentations College of Engineering and Computer Science 7-14-2011 Artificial lateral line canal for hydrodynamic detection Yingchen Yang Adrian Klein Horst Bleckmann Chang Liu Follow this and additional works at: https://scholarworks.utrgv.edu/me_fac  Part of the Mechanical Engineering Commons Appl. Phys. Lett. 99, 023701 (2011); https://doi.org/10.1063/1.3610470 99, 023701© 2011 American Institute of Physics.Artificial lateral line canal for hydrodynamicdetectionCite as: Appl. Phys. Lett. 99, 023701 (2011); https://doi.org/10.1063/1.3610470Submitted: 14 September 2010 • Accepted: 22 June 2011 • Published Online: 14 July 2011Yingchen Yang, Adrian Klein, Horst Bleckmann, et al.ARTICLES YOU MAY BE INTERESTED IN Fish-inspired self-powered microelectromechanical flow sensor with biomimetic hydrogelcupulaAPL Materials 5, 104902 (2017); https://doi.org/10.1063/1.5009128Engineering biomimetic hair bundle sensors for underwater sensing applicationsAIP Conference Proceedings 1965, 160003 (2018); https://doi.org/10.1063/1.5038533A MEMS SOI-based piezoresistive fluid flow sensorReview of Scientific Instruments 89, 025001 (2018); https://doi.org/10.1063/1.5022279Artificial lateral line canal for hydrodynamic detectionYingchen Yang,1,2 Adrian Klein,3 Horst Bleckmann,3 and Chang Liu1,a)1Department of Mechanical Engineering, Northwestern University, Evanston, IIllinois 60208, USA2Department of Engineering, University of Texas at Brownsville, Brownsville, Texas 78520, USA3Institut für Zoologie, Universität Bonn, Poppelsdorfer Schloss, D-53115 Bonn, Germany(Received 14 September 2010; accepted 22 June 2011; published online 14 July 2011)Fish use their lateral line system to detect minute water motions. The lateral line consists ofsuperficial neuromasts and canal neuromasts. The response properties of canal neuromasts differfrom those of superficial ones. Here, we report the design, fabrication, and characterization of anartificial lateral line canal system. The characterization was done under various fluid conditions,including dipolar excitation and turbulent flow. The experimental results with dipole excitationmatch well with a mathematical model. Canal sensors also demonstrate significantly better noiseimmunity compared with superficial ones. Canal-type artificial lateral lines may become importantfor underwater flow sensing. VC 2011 American Institute of Physics. [doi:10.1063/1.3610470]Fish use the mechanosensory lateral line to detectnearby weak water motions and pressure gradients. Lateralline information enables fish to avoid predators, track prey,swim in schools, maintain position in turbulent environ-ments, and circumnavigate underwater objects.1–4 The basicunit of the lateral line is the neuromast, a mechanosensitivestructure that consists of hair cells whose ciliary bundles pro-ject into a gelatinous cupula.5 Up to several thousand, neuro-masts, distributed across the head, body, and tail fin of fish,constitute the lateral line system. Lateral line neuromasts fallinto two categories: superficial neuromasts that are locatedon the skin and canal neuromasts that are situated in subepi-dermal fluid-filled canals.5,6 Canal neuromasts respond to theoutside flow through a series of pores opening to the environ-ment. Local pressure gradients outside the fish induce fluidmovement inside lateral line canals that in turn displace thecupulae of canal neuromasts and elicit a neuronal responsein the afferent nerve fibers that innervate the neuromast.7Canal neuromasts have some unique response propertiesnot observed in superficial neuromasts.8–11 One is a band-pass filtering feature. Canal neuromasts are insensitive to theDC-component of bulk water flow velocity and to high-fre-quency (>100 Hz for the ruffe)8 flow velocity fluctuations.The selective sensing of mid-frequencies may be crucial forthe survival of fish: Hydrodynamic disturbances caused byother animals are mainly in the frequency range of 0.5 toabout 100 Hz.10 The second characteristic is the noise rejec-tion. The lateral line canal system rejects most of the back-ground noise caused by bulk water flow.11 This leads to anincrease in the signal-to-noise ratio and thus eases the detec-tion of prey-borne stimuli.8 Further, lateral line canals pro-vide a physical protection to the canal neuromasts.12A man-made artificial lateral line system may be impor-tant for many engineering applications, especially for under-water robots and vehicles. In our earlier research, artificiallateral lines based on superficial neuromasts have been dem-onstrated.13,14 In the present work, we developed an artificiallateral line canal (ALLC) and characterized its responseproperties. Both band-pass filtering and noise-rejection func-tions were examined.Biomimetic neuromasts (BNs, Fig. 1(a)) developed in ourearlier work15 were employed to constitute the ALLC. The BNcharacterization in water flow shows a standard deviation ofless than 5% of the mean flow velocity employed.15 In ALLCfabrication, the BN array was flush-mounted in a milled sloton a printed circuit board (PCB), with the sensing directions ofindividual BNs all along the array (Fig. 1(b)). The canal struc-ture was fabricated using stereolithography technique. It wasthen assembled to the BN array and held down by glue. TheBNs were wire-bonded to the PCB to achieve electrical con-nection to the outside circuit. After encapsulating the wire-bonds with epoxy glue, the yielded ALLC structure was pla-narized using polydimethylsiloxane (PDMS) to form a smoothfront surface (Fig. 1(c)). The canal (diameter 4 mm) had asemicylindrical shape. The pores (diameter 0.8 mm) wereevenly distributed with a spacing of 6 mm, i.e., with a spacingthat matched the BN spacing.A physical-mathematical model was developed to char-acterize the ALLC before testing. The model was adaptedfrom an analytical study on arthropod filiform hairs byFIG. 1. (a) (Color online) Scanning electron micrograph of a BN. (b) Dia-gram illustrating the structural detail of the ALLC. (c) Picture of theassembled ALLC.a)Author to whom correspondence should be addressed. Electronic mail:changliu@northwestern.edu.0003-6951/2011/99(2)/023701/3/$30.00 VC 2011 American Institute of Physics99, 023701-1APPLIED PHYSICS LETTERS 99, 023701 (2011)Humphrey et al.,16 with notable variations being incorpo-rated. Our BNs more closely resembled the morphologicalstructure of filiform hairs rather than the structure of fishneuromasts that have a nearly hemispherical shape.9 This isattributed to the current microfabrication process.The BN’s hair (550 lm tall, 80 lm in diameter) is mod-eled as a rigid body with no deformation under load, but thesilicon cantilever beam where the hair sits is much more de-formable. Thus, the flow-induced free-end angular deflectionof the beam is the same as the rigid hair’s angular displace-ment. Under periodic oscillating boundary layer conditions,the governing equation of the BN hair’s angular displace-ment h is the conservation of angular momentumðI þ Iq þ IlÞ€hþ Rl _hþ Sh¼ 4plGðH0VFydyþpqd24 plG2fg ðH0_VFydy; (1)where q, l, f, d, H, I, Iq, Il, Rl, S, G, and g are parameter asdefined in Humphrey et al.16 VF is the velocity profile insidethe canal caused by the oscillatory pressure gradient betweenthe two adjacent pores. In the modeling, the semicircularcross-section of the canal in the ALLC was approximated as acircular cross-section with the same hydraulic diameter,which is 2.4 mm. Then inside the canal of radius R¼ 1.2 mm,at a distance r from the canal axis, the velocity of an oscillat-ing flow driven by pressure gradient can be described asVFðr; f ; tÞ ¼ A0ei2pfti2pf1J0ffiffiffiffiffiffiffiffi2iprd J0ffiffiffiffiffiffiffiffi2ipRd " #; (2)where J0, d, and A0 are defined in van Netten.8Using a numerical approach, the velocity profile VF andits time derivative _VF can be calculated from Eq. (2), and thetwo integrals over the height H of the hair in Eq. (1) can beobtained. Based on that, numerically solving Eq. (1) givesthe angular displacement h of the hair under specified condi-tions. Using this physical-mathematical model, the steady-state angular displacement of the hair in response to the fre-quency variation of the oscillatory canal flow under a fixedacceleration amplitude of the external water flow was gener-ated and plotted in Fig. 2. For convenience purpose, theacceleration amplitude was chosen to be 1 m/s2 that corre-sponded to a pressure gradient amplitude along the canal of1 KPa/m. For the ALLC with dimensions and geometricapproximation specified in the foregoing, the numericalresults suggest a band-pass characteristic with a peak at 0.4Hz. Below the peak frequency, BN response decreasesmildly with decreasing frequency. Yet, remarkable drop canstill be observed when the frequency is approaching zero.Above the peak frequency, it drops at a much steeper slopewith increasing frequency. This frequency response trend ofthe ALLC resembles that of a canal neuromast in fish, asillustrated in Fig. 7 by van Netten.8 Depending on the fishspecies, the peak frequencies of canal neuromasts may varyfrom below 1 Hz to a few hundred Hertz.8 In comparison,the demonstrated ALLC emulates a lower end case of its bio-logical counterpart, representing a big fish.The ALLC’s modeling results were also verified experi-mentally in a dipolar flow field. A sphere (radius a¼ 6.4mm), attached to a minishaker, was vertically vibrated inwater to serve as a dipole source. The ALLC was placed inwater horizontally with all the pores facing up. The dipolesource was right above one pore (namely P1), and the dis-tance from the center of the dipole source to the top surfaceof the ALLC is l¼ 11.4 mm. Using a dipole analyticalmodel,17 the pressure gradient between the pore P1 and theadjacent pore P2, with a spacing of Dx¼ 6 mm, can beexpressed asdpdx¼ 1l2 lðl2 þ ðDxÞ2Þ3=2 !qa32DxAssinð2pftÞ; (3)where As is the acceleration amplitude of the sphere. Duringthe experiments, the dipole frequency f was swept from 0.4Hz up to 95 Hz. For comparison with modeling results, thepressure gradient was maintained constant at dp=dx ¼ 1KPa/m. This was achieved by monitoring the dipole acceler-ation using an accelerometer attached to the minishaker. Thepressure gradient amplitude was then calculated using Eq.(3) based on the reading from the accelerometer.The experimental results are also plotted in Fig. 2 interms of BN output versus sphere vibration frequency. Notethat for our BN with the structure as illustrated in Fig. 1(a), itsoutput is linearly proportional to the hair’s angular displace-ment.15 Therefore, after normalization with maxima, the ex-perimental results are directly comparable with the modelingresults. Overall, the results from the two approaches matchreasonably well—they both show a mild climbing followedby a quick drop. The peak frequency from experiments is 0.6Hz, which is a little higher than the 0.4 Hz obtained from mod-eling. The small discrepancy is mainly due to the geometricalapproximation of the canal from a semicircular cross-sectionin experiments to a circular cross-section in the modeling,both having the same hydraulic diameter. It should be notedthat after the peak, the experimental data fall off faster thanthe modeling data. Before the peak, the experimental data forvery low frequencies were not obtained due to the limitedcapability of the shaker employed.Having the band-pass filter function of the ALLC beendemonstrated (with near-zero-Hertz response not experimen-tally examined), the noise-rejection capability was thenexamined experimentally in the follows. The noise herein isFIG. 2. Frequency responses of the BN in terms of the hair’s angular dis-placement from modeling and the sensor output from experiments, normal-ized with their maxima.023701-2 Yang et al. Appl. Phys. Lett. 99, 023701 (2011)defined as any random and irregular hydrodynamic signa-tures that demonstrate broadband spectra with no dominantfrequencies. In the present approach, the noise was generatedby turbulent flows. Both a canal BN (from the ALLC) and asuperficial BN were employed for comparative experimentsin a water channel (Fig. 3). A dipole field was superimposedon the channel flow; it was generated by a sphere vibratingat 20 Hz. Note that, this frequency is somewhat away fromthe ALLC’s peak frequency (below 1 Hz). This frequencywas chosen in order to obtain a reasonably strong dipolar ve-locity field, which would otherwise not be able to achievedue to the limited capability of the shaker employed. Duringthe experiments, the two types of BNs were placed close toeach other as shown in Fig. 3(b). The turbulent boundarylayer flow that developed along the top surface of the plateinduced strong hydrodynamic noise to the superficial BNs,and the noise level increased with increasing inflow velocity.Four inflow velocities in the presence of the dipole fieldwere examined: no-flow, low-speed (0.04 m/s), medium-speed (0.08 m/s), and high-speed (0.12 m/s).Fig. 3(c) shows the spectra of the output signals of thetwo BNs. Each spectrum was directly derived from a single-set raw data without filtering. In still water with a dipole fieldonly, both the superficial BN and canal BN clearly showpeaks at the dipole frequency. The signal from the superficialBN is much stronger than that from the canal BN for twomain reasons: (i) the superficial BN was closer to the dipolesource than the canal BN (Fig. 3(b)), and (ii) the in-canalflow oscillation at the dipole frequency of 20 Hz was attenu-ated (Fig. 2). As the inflow velocity increases, the signalfrom the superficial BN becomes increasingly noisy, espe-cially in the low frequency regime. On the other hand, thecanal BN is barely affected by the background turbulentnoise in the entire observed frequency range. Eventually, thesuperficial BN becomes overwhelmed by the low frequencynoise and renders incapable of detecting the 20 Hz stimuluswhile the canal BN performs just as well.The noise-rejection capability of the ALLC is in linewith that of a fish canal neuromast.11 Yet, no matter whetherin a fish lateral line canal or in our ALLC, it seems that thenoise-rejection capability that filters out background noise inthe entire observed frequency range contradicts with theband-pass filter function. While an in-depth understanding ofthis seemingly contradiction deserves systematic research,we propose a preliminary explanation. The flow outside acanal influences the flow inside the canal via pores, or morespecifically, via the pressure difference between the pores.For an oscillatory flow (with the frequency in the range forband-pass) to be fully developed inside the canal, the pressuredifference to drive the flow needs to periodically repeat for atleast a few cycles. The excited flow is weak in the first cycleand then gradually strengthens and reaches steady oscillatorystate in the following cycles. A well-developed and well-organized external flow, e.g., a dipolar flow, can fully excitean oscillatory flow inside the canal in this fashion. In contrast,the turbulent background noise reflects the chaotic nature ofthe external driving flow that varies quickly and randomly.Consequently, using an external turbulent flow to drive thefluid inside the canal with no successive excitation cycles fornearly any frequency components, it would be hard for anyinternal flow to fully develop and instantly follow. As aresult, the canal possesses a noise-rejection feature.This work was supported by the DARPA BioSenSE pro-gram (Contract No. FA9550-05-1-0459).1J. H. S. Blaxter and L. A. Fuiman, in The Mechanosensory Lateral Line:Neurobiology and Evolution, edited by S. Coombs, P. Görner, and H.Münz (Springer, New York, 1989), pp. 481–499.2D. Hoekstra and J. Janssen, Environ. Biol. Fishes 12, 111 (2006).3B. L. Partridge and T. J. Pitcher, J. Comp. Physiol., A 135, 315 (1980).4E. S. Hassan, in The Mechanosensory Lateral Line: Neurobiology andEvolution, edited by S. Coombs, P. Görner, and H. Münz (Springer, NewYork, 1989), pp. 217–228.5S. Coombs, J. Janssen, and J. F. Webb, in Sensory Biology of Aquatic Ani-mals, edited by J. Atema, R. R. Fay, A. N. Popper, and W. N. Tavolga(Springer, New York, 1988), pp. 553–593.6A. Schmitz, H. Bleckmann, and J. Mogdans, J. Morphol. 269, 751 (2008).7A. J. Hudspeth, Y. Choe, A. D. Mehta, and P. Martin, Proc. Natl. Acad.Sci. U.S.A. 97, 11765 (2000).8S. M. van Netten, Biol. Cybern. 94, 67 (2006).9J. Engelmann, W. Hanke, and H. Bleckmann, Nature 408, 51 (2000).10H. Bleckmann, Reception of Hydrodynamic Stimuli in Aquatic and Semia-quatic Animals (Springer, New York, 1994).11J. Engelmann, W. Hanke, and H. Bleckmann, J. Comp. Physiol., A 188,513 (2002).12S. Dijkgraaf, Biol. Rev. 38, 51 (1962).13Y. Yang, J. Chen, J. Engel, S. Pandya, N. Chen, C. Tucker, S. Coombs, D.L. Jones, and C. Liu, Proc. Natl. Acad. Sci. U.S.A. 103, 18891 (2006).14Y. Yang, N. Nguyen, N. Chen, M. Lockwood, C. Tucker, H. Hu, H. Bleck-mann, C. Liu, and D. L. Jones, Bioinspiration Biomimetics 5, 9 (2010).15N. Chen, C. Tucker, J. Engel, Y. Yang, S. Pandya, and C. Liu, J. Micro-electromech. Syst. 16, 999 (2007).16J. Humphrey, R. Devarakonda, I. Iglesias, and F. G. Barth, Philos. Trans.R. Soc. London, Ser. B 340, 423 (1993).17A. J. Kalmijn, in Sensory Biology of Aquatic Animals, edited by J. Atema,R. R. Fay, A. N. Popper, and W. N. Tavolga (Springer, New York, 1988),pp. 83–130.FIG. 3. (Color online) (a) Side view of the experimental setup. The waterflow is from right to left, and the sphere shakes up and down. (b) Picture show-ing the arrangement of the superficial BN, ALLC, and the vibrating sphere.(c) Spectra of the two types of BNs at various inflow velocities. The blue onesare from the superficial BN, and the red ones are from the canal BN.023701-3 Yang et al. Appl. Phys. Lett. 99, 023701 (2011)

Artificial lateral line canal for hydrodynamic detection

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