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Laser textured GFRP superhydrophobic surface as an underwater acoustic absorption metasurface
Applied Surface Science 463 (2019) 741–746
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Laser textured GFRP superhydrophobic surface as an underwater acoustic absorption metasurface Guang Fenga,1, Fengping Lia,1, Wei Xuea, Ke Suna, Huan Yanga,b, Qiaofei Pana, Yu Caoa,
T
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a
Zhejiang Key Laboratory of Laser Processing Robot, College of Mechanical & Electrical Engineering, Wenzhou University, Wenzhou 325035, China International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology of Ministry of Education, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Metasurface Laser texturing Superhydrophobic Absorption coefficient
Underwater acoustic absorption metasurfaces (UAAMs), featured with artificial periodic unit cells as acoustic micro-absorbers, are crucial for the enhancement of the underwater stealth, energy transition, sonar detection, etc. How to implement the acoustic metasurfaces for practical engineering applications requires the support of efficient manufacturing techniques. Here we present a simple way of laser texturing for fabrication of the patterned superhydrophobic surface on glass fiber reinforced plastic (GFRP). Unlike the traditional acoustic absorbing material whose thickness should match the corresponding wavelength, the laser textured superhydrophobic micro-grooves have thickness less than the absorption sound wavelength by 2–3 orders of magnitude but promisingly demonstrate over 88% of the underwater incident acoustic power absorption from 50 kHz to 250 kHz. The physical mechanism of the UAAM ascribes to the multiple interface scattering effect induced by the air layer between water and superhydrophobic micro-nano structures.
1. Introduction Efficient control of the generation, propagation, reception, and processing of sound waves is the basic problem and long pursuit of the acoustics. Modern complex sound field processing problems such as aircraft [1], submarine noise isolation [2], underwater sonar detection [3], and music hall’s acoustic design [4] are increasingly related to the manipulation of selective acoustic absorption/transmission. Acoustic metasurfaces are artificial composite structures built by repetitive unit cells whose dimensions are much smaller than the acoustic wavelength and have many special acoustic properties which greatly expand the connotation of natural acoustic materials with applications such as oneway transportation [5], cloaking [6], super absorption [7], etc. Acoustic metasurfaces have been a research hotspot as a candidate smart module in intelligent acoustic design for years. Pioneering works on acoustic metasurfaces have inspired extensive studies. Extraordinary acoustic wave transmission was predicted by Zhang [8], followed by Lu et al. [9] who first reported the extraordinary acoustic wave transmission of grating structure. Recently, several groups measured the transmission properties of sound through plates with slits and holes [10–12] and proposed three types of the acoustic extraordinary transmission: periodic-lattice resonances [13], Fabry-Perot–type resonances
[12], and elastic Lamb-mode resonances [14]. J. Mei. et al. [7] achieved very high acoustic absorption at resonant frequencies through the concentration of curvature energy at the perimeters of asymmetrically shaped platelets and G. Ma. et al. [15] investigated the acoustic metasurfaces with hybrid resonances. In the field of underwater acoustic absorption, one of the most efficient technological solutions is the use of decoupling coatings and anechoic coatings [16], but the problem is the size of the coating is on the same order of wavelength, which restrains the use of the coating. Li. et al. [17] investigated the asymmetric underwater acoustic transmission by a plate with quasi-periodic surface ridges. Owing to the huge ratio of 3600 in the acoustic impedances from water to air, only 0.1% of the acoustic energy is naturally transmitted at such a boundary. Eun Bok. et al. [18] investigated the metasurface for water-to-air sound transmission, allowing about 30% of the incident acoustic power from water to be transmitted into the air. In this study, a simple way of laser texturing is proposed for the fabrication of the patterned superhydrophobic surface on glass fiber reinforced plastic (GFRP), which demonstrates selectively high absorption of a sound wave as a promising underwater acoustic absorption metasurface (UAAM).
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Corresponding author. E-mail address: [email protected] (Y. Cao). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.apsusc.2018.09.005 Received 4 May 2018; Received in revised form 16 August 2018; Accepted 1 September 2018 Available online 01 September 2018 0169-4332/ © 2018 Elsevier B.V. All rights reserved.
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Fig. 1. Setup of the laser micro-machining system and the cross grid patterns on GFRP specimen.
Fig. 2. The experimental setup for ultrasonic transmission coefficient test.
2. Experimental
optimized dimensions by multiple pre-tests to achieve high contact angle and low slip angle as a low-adhesion superhydrophobic (LASH) surface, specifically 25 μm of depth, 20 μm of width and the spacing between the crossed micro-grooves is 40 μm. (Heptadecafluoro-1,1,2,2tetradecyl) trimethoxysilane (PSD-J20P, Shenzhen Passedat Chemical co. Ltd.) is spin-coated and heat-treated by thermostat at 170 °C for 30 min as the chemical modifier that lower the solid surface energy and make the laser textured surface superhydrophobic. The micro-morphologies of the prepared superhydrophobic GFRP surfaces are investigated by Laser Scanning Confocal Microscopy (OSL 4100, OLYMPUS) and the Scanning Electron Microscope (SEM) (QUANTA 200F, FEI). Static contact angles (SCAs) [inserted in Fig. 6(c) and (d)] are measured five times at different tested area using a video optic CA instrument (OCA15EC, Dataphysics) equipped with a goniometer. The images of a 3 μL distilled water droplet placed on the specimen’s surface are analyzed by a Low-Band Axisymmetric Drop Shape Analysis (LBADSA) software. The temperature and relative humidity in the SCAs tests are 25 °C and 65% RH, respectively. An ultrasonic transmissivity measurement system is built to measure the underwater acoustic absorption properties, as shown in Fig. 2. The overall system is immersed in a muffler pool for measurement of underwater sonar transmission coefficient, which includes a signal generation (AFG 3021B, Tektronix), transducer (DYW-50/200-NA) as
Glass fiber reinforced plastic (GFRP) is the most common type of fiber-reinforced plastic using glass fiber which is cheaper and more flexible than carbon fiber. GFRPs are stronger than many metals by weight, and can be molded into complex shapes, which have wide applications in aircraft, boats, pipes, bath tubs and sonar dome, etc. Therefore, GFRP (Shenzhen Shengjili co. Ltd.) plates with the dimensions of 200 × 200 × 1 mm3 are used as the substrates. The GFRP plates are ultrasonically cleaned in anhydrous ethanol solution for 10 min and then blow dried before and after the laser texturing. A laser micro-machining system is used for precision ablating grid groove patterns on GFRP surfaces, as shown in Fig. 1(a). The UV laser (Awave355, Apto-Wave co. Ltd.) outputs pulsed Gaussian laser beam at an average power of 3 Watts, wavelength of 355 nm, the pulse width of 20 ns, and the focused laser spot diameter of 15 μm. At an operational pulse repetition rate of 90 kHz and X-Y galvo-scanning speed of 200 mm/s, the designed grid patterns are laser textured on the GFRP specimen surfaces by 6 times repetitive scanning, as shown in Fig. 1(b) and (c). Thus, the used laser pulse fluence for the texturing of GFRP surface is 4.72 J/cm2, which is near four time of threshold fluence (1.2 J/cm2, obtained by experimental) to get the designed microgroove structures. The fabricated crossed micro-grooves pattern has the 742
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an ultrasonic source, hydrophone (CS-3) as an ultrasonic detector and oscilloscope (Tektronix TDS 2012B). The signal generator is used to generate short-duration pulse, which would be converted into short duration acoustic pulses by the transducer. The water temperature is set to 20 °C. The GFRP specimen with superhydrophobic (SH) surface is placed between the transducer and the hydrophone receiver. The distance D1 from the source to GFRP specimen is 5 cm, and the distance D2 from GFRP specimen to the detector is 10 cm. The hydrophone received signals are linked to the oscilloscope for real-time display. 3. Results and discussion Transmission coefficient is defined as the ratio of the transmitted sound flux to the incident sound flux through a layer of the medium at a given frequency and condition [19]. For the scenario of underwater sound wave transmission through a GFRP plate, the transmission coefficient T can be calculated by the Eqs. (1) and (2):
T=
|pta |2 /2ρ1 C1 |pIa |2 /2ρ1 C1
k = w / c = 2π / λ
=
4 4cos2 kD + (R12 + R21)2sin2 kD
Fig. 3. Comparison of underwater transmission coefficients of theoretical, untreated, single-side and double-side laser textured GFRP, single-side and double-side laser textured GFRP after immersed in water for 2 h.
(1) (2)
where D is the thickness of the GFRP specimen, R12 is the ratio of the acoustic impedance value of the acoustic wave in the GFRP to the acoustic impedance value of the acoustic wave in the water, R21 is the acoustic impedance value of the acoustic wave in the water and the acoustic wave in the GFRP impedance ratio, k is the wave number. The transmission coefficient Eqs. (1) and (2) indicate that when the thickness is below ¼ of the incident wavelength, a thinner material is naturally better than a thicker one for sound wave transmission. Once the thickness of the specimen reaches an odd multiple of the ¼ wavelength, the reflected signal from back interface would destructively interfere with the incident signal causing the transmission coefficient to reach its minimum value. Nevertheless, when the thickness of the specimen reaches an integral multiple of half wavelength, the reflected wave would have interfered constructively with the incident wave, which results in maximum transmission. In order to investigate the effect of surface wettability on acoustic performance, laser texturing was used for fabrication of GFRP superhydrophobic surface. There are lots of papers that reported controlling the surface wettability by direct laser texturing, such as A. He et al. [20] fabricated copper superhydrophobic surface with adjustable adhesion by nanosecond laser ablation; Anne-MarieKietzig et al. [21] investigated the Cassie-Baxter to Wenzel wetting transitions on the laser patterned metallic superhydrophobic surfaces; and the effect of pulsed ultraviolet laser modification on the surface wettability of polycarbonate was studied by S. Wang et al. [22]; while here we demonstrate the control of underwater acoustic absorption property by laser textured superhydrophobic hierarchical micro-nano structures. The frequency range for the measurement of underwater acoustic absorption is chosen between 50 kHz and 250 kHz, which is contained in the normal working frequency of sonar. The transmission coefficient curves of normal incident ultrasonic waves to untreated, single-side and double-side laser textured GFRP, single-side and double-side laser textured GFRP after immersed in water for 2 h are shown in Fig. 3. As the acoustic frequency increases from 50 kHz to 250 kHz (corresponding to the wavelength range of 2.97 cm–0.59 cm in water), the transmission coefficient of untreated GFRP decreases from 0.95 to 0.57, which basically corresponded with a theoretical evaluation obtained according to the Eqs. (1) and (2). However, the transmission coefficients of singleside and double-side ablated SH surface retain very low value between 0.15 and 0.05 through the overall frequency range. Comparing with a transmission coefficient of untreated GFRP, the transmission coefficient of ablated GFRP is lower much, the maximum reduction of 86% (50 kHz) and minimization reduction of 52% (250 kHz). The air layer and periodic groove structure plays a significant role in the reduction of
transmission coefficient. After GFRP SH specimen immersed in water for 2 h, the transmission coefficients of both single-side and double-side ablated SH surface are obviously improved, the former decreases from 0.71 to 0.32, the latter decreases from 0.53 to 0.21, respectively. The reason is that comparing with the specimen of single-side ablated, the double-side ablated specimen will dissipate the sound waves on both side. Meanwhile, with the immersion time increase, the transmission coefficients of single-side and double-side ablated SH surface will increase due to the disappearance of the air layer. Reflection coefficients are also tested by placing the transducer and hydrophone on the same side with the specimen. The transducer emits a sound source perpendicular to the specimen, and the hydrophone receives the reflected sound wave at 45° from the vertical. The comparison of reflection coefficient curves of untreated GFRP, laser textured GFRPs with single-side and double-side SH surfaces is shown in Fig. 4. With the increase of the frequency from 50 kHz to 250 kHz, the reflection coefficients of an untreated, single-side and double-side laser textured GFRP, single-side and double-side laser textured GFRP after immersed in water for 2 h decrease with a similar trend. Laser textured microstructures increase the surface reflectivity of acoustic waves, especially in the low-frequency range that has a maximum increase of
Fig. 4. Comparison of underwater reflection coefficients of untreated, singleside, double-side laser textured GFRP, and the single-side and double-side laser textured GFRP after immersed in water for 2 h. 743
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microstructure of ablated. The insert in Fig. 6(c) is the image of static contact angles (SCAs) for the prepared GFRP SH specimen, which is 155.7° and static contact angles (SCAs) for untreated GFRP specimen is 76.3°, respectively. And the sliding angle of GFRP SH specimen is 5°. The Fig. 7 schematically shows the microscopic contact state of the laser textured SH surface underwater. The water is suspended on the top of the papillae and the space among papillae formed an air layer shown in Fig. 7(a), which makes a water/air/papillae interface [23]. Note that this illustration is different from the theory of solid/liquid interface in liquid, where no obvious air layer existed. Conversely, the “air layer effect” on SH surface underwater is rather close to a drop on it (predicated by Cassie-Baxter theory). With the immersion time increase, the air layer trapped in the hierarchical micro-nano structures (laser induced micro-grooves with sub-micron humps and pores) will detach or diffuse into the surrounding water, which leads to the wetting transition from Cassie-Baxter state [Fig. 7(a)] to Wenzel state [Fig. 7(b)]. P. Lv et al. [24] investigated the metastable states and wetting transition of submerged superhydrophobic structures, which demonstrated that the water would gradually immerse the pores with the increase of pressure. In our research, the change of wetting transition affects the acoustic performance. After GFRP SH specimen immersed in water for 2 h as shown in Fig. 7(b), the transmission coefficients of single-side and double-side ablated SH surface is obviously improved. The reflection coefficients of single-side and double-side ablated SH surface decreased a little. The absorption coefficients of single-side and double-side ablated SH surface decreased obviously. When the SH surfaces are immersed in the water, the air layer has a significant effect on the transmission coefficient. Owing to the existence of air layer, the impedance from water to GFRP will increase a lot that proved by the transmission coefficient of SH surface GFRP in Fig. 5. Therefore, the air layer should be a key factor to the effect on transmission coefficient of ablated GFRP. On the other hand, the micromorphology of laser textured GFRP has deep grooves, which is an effective sound absorption structure. When the sound wave entry the deep grooves, its energy would be absorbed by the deep grooves [25–27]. More specifically, these micro-grooves are interconnected and open outward rather than closed, making the sound wave easy to enter the grooves, while in comparison of the closed grooves cannot play the role of sound absorption. Moreover, GFRP matches the acoustic characteristic impedance of water, enabling the sound energy to enter the sound absorbing material without reflection, and the bulk of the incoming acoustic energy is absorbed. The acoustic coupling between adjacent grooves has an effect on acoustic attenuation. The upper sides of the ridges, as well as the bottoms of the grooves, are assumed to be sound absorbing, according to De Bruin’s theory [26], which separate the sound field into two parts. One is in the upper half-space above the ridges, named region I; the other is the field inside the grooves, named region II. In region I, the sound field is considered as a superposition of incident plane wave and reflected plane waves. In region II, the sound field is considered as a superposition of waveguide modes. Considering the effect of the region I and II, the sound absorption coefficient ∝θ, φ can be deduced as the Eq. (4):
6% (at 60 kHz) when compared with untreated reflectivity. After GFRP SH specimen immersed in water for 2 h, the reflection coefficients of both single-side and double-side ablated SH surfaces are slightly decreased, the former decreases about 3% from 50 kHz to 250 kHz, while the latter decreases about 7% from 50 kHz to 250 kHz. As the Cassie-Baxter wetting theory predicted [as shown in Fig. 7(a)], a large number of tiny air layer will be trapped in the bottom of the laser ablated micro-grooves when the superhydrophobic surface initially immersed underwater, which forms the array of liquid/air/ solid interfaces along the grooves. The shape of interface of liquid/air is similar to the laser ablated groove structure that behaves as a good sound absorption structure. Furthermore, the uneven interface is easy to cause the scattering of sound waves. Therefore, there is practically no difference between these two surfaces in reflection coefficient. Meanwhile, with the immersion time increase, the reduction of reflection coefficient of single-side and double-side ablated SH surface is the disappearance of the air layer increases the transmission energy of sound waves. Based on the test results of the transmission coefficient (T) and reflection coefficient (R), the absorption coefficient (A) defined as Eq. (3) [7] is shown in Fig. 5.
A = 1−R2−T 2
(3)
The absorption coefficients of GFRP specimens with single-side and double-side laser textured SH surfaces are higher than 0.88, and both have a distinctive enhancement than untreated GFRP’s on a wide frequency range from 50 kHz to 250 kHz. The absorption rate of the laser textured microstructures maximally increased by 85% (50 kHz) compared to the untreated, which indicates the use of laser textured SH surfaces makes GFRP an extremely fine acoustic absorber and a promising Underwater Acoustic Absorption Metasurface (UAAM). After GFRP SH specimen immersed in water for 2 h, the absorption coefficients of both single-side and double-side ablated SH surfaces decrease obviously. Because of the double-side absorptive micro-nano structures, the absorption coefficient of double-side ablated SH surface is higher than the single-side ablated SH surface. The action mechanism of laser-textured SH surface as a UAAM could be attributed to the unique surface morphology and wettability of the water-solid interface. The SEM images of the laser textured GFRP surface in (Fig. 6) shows a periodic papillary morphology, with multi microparticles. The average size of these micro-protruding structures is about 20 μm, with an average depth of 25 μm. The structure of a micrograph in Fig. 6(b) and (d) are under a higher magnification. The surfaces mainly consist of the micro-pillars. In the Fig. 6(c) the 3D
∝θ, φ = 1−
∑ Re|βr |
|Rr |2
βr β0
(4)
A detailed derivation for Eq. (4) can be found in De Bruin’s theory [26]. The acoustic scattered field above the structure is expanded in a spectrum of plane waves and the field in the groove in a superposition of standing waveguide modes, which can cause an acoustic attenuation. Meanwhile, the dimensions, groove depth and width, and the period of the structure have an influence on acoustic absorption. The other reason is that the medium of the acoustic wave is water, which differs from the sound wave in air. There is an air layer between water and superhydrophobic structure, which contributes to the achievement of
Fig. 5. Comparison of underwater absorption coefficients of untreated, singleside and double-side laser textured GFRP, single-side and double-side laser textured GFRP after immersed in water for 2 h. 744
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Fig. 6. SEM and laser confocal microscopy images of laser textured GFRP SH surface, the inserts in (c) is the images of static contact angles (SCAs).
Fig. 7. schematic of the microscopic contact state of (a) superhydrophobic surface underwater (Cassie-Baxter state) and (b) superhydrophobic surface after immersed in water for 2 h (Wenzel state).
4. Conclusion
an attenuation characteristic. There are studies about how the surface pattern (ridges or grooves) profile affect the acoustic performance. H. X. Sun et al. investigated the asymmetric underwater acoustic transmission by a plate with quasiperiodic surface ridges [14] and a tunable acoustic diode made by a metal plate with single-sided periodical grating structure immersed in water [27]. J. Wang et al. [28] studied the prediction of sound absorption of a periodic groove structure with rectangular profile whose dimension is less than the test sound wavelength by 0–1 orders of magnitude. In this work, the fabricated crossed micro-grooves are set to the optimized dimensions of 25 μm in depth, 20 μm in width and the spacing of 40 μm, which is less than the absorption sound wavelength by 2–3 orders of magnitude. Future study will focus on the effect of groove depth and spacing in order to manipulate the acoustic response of the UAAM.
Laser-ablated the patterned structure, and then it was modified by (Heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane to obtain superhydrophobic surface on GFRP. The SCAs of superhydrophobic surface GFRP is 155.7°. Then the transmission coefficient, reflection coefficient and absorption coefficient of untreated, single-sided ablated and double-sided ablated GFRP were measured underwater. The transmission coefficient of ablated GFRP is obviously lower than the transmission coefficient of untreated GFRP. However, the reflection coefficient has little change. The absorption coefficient of ablated GFRP is obviously higher than the transmission coefficient of untreated GFRP, in particular, it achieves about over absorption coefficient of 88% from 50 kHz to 250 kHz. The physical mechanism of the UAAM ascribes to the multiple interface scattering effect induced by the air layer between water and superhydrophobic micro structures, which causes the 745
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attenuation of acoustic waves. After GFRP SH specimen immersed in water for 2 h, the transmission coefficients of single-side and doubleside ablated SH surface is obviously improved. The reflection coefficients of single-side and double-side ablated SH surface decreased a little. The absorption coefficients of single-side and double-side ablated SH surface decreased obviously. The reason is wetting transition of superhydrophobic surface GFRP effect the underwater sound propagation. However, 2 h duration time are too short to use the UAAM for practical underwater application. There were some reported works related to the durability/renewability of bionic super-hydrophobic surface [20,29]. The future work might be the novel design of near-surface multi-layer micro-pore structures and active bubble production mechanisms, which can also be prepared using lasers as a tool, to improve the durability of superhydrophobic surfaces that effectively increase the duration time of the UAAM. The process simplicity of the laser texturing of UAAM gives promising applications for underwater acoustic absorption scenarios, such as anechoic tile.
[9]
[10]
[11]
[12]
[13] [14] [15] [16]
[17]
Acknowledgment This work is financially supported by the National Natural Science Foundation of China (Grant Nos.U1609209, 51375348) and Zhejiang Provincial Natural Science Funds for Distinguished Young Scholar (Grant No. LR15E050003).
[18]
References
[21]
[19] [20]
[1] R.W. Paterson, P.G. Vogt, W.M. Foley, Design and development of the united aircraft research laboratories acoustic research tunnel, J. Aircraft 10 (2012) 427–433. [2] Y. Qu, J. Su, H. Hua, G. Meng, Structural vibration and acoustic radiation of coupled propeller-shafting and submarine hull system due to propeller forces, J. Sound Vib. 401 (2017) 76–93. [3] B. Allotta, A. Ridolfi, M. Bianchi, F. Fanelli, J. Gelli, N. Monni, D. Nocciolini, M. Pagliai, L. Paolucci, T. Pecorella, Employment of an autonomous underwater vehicle as mobile bridge among heterogeneous acoustic nodes, IFAC-PapersOnLine 50 (2017) 12380–12385. [4] M. Galiana, C. Llinares, Á. Page, Subjective evaluation of music hall acoustics: response of expert and non-expert users, Build. Environ. 58 (2012) 1–13. [5] B. Liang, B. Yuan, J.C. Cheng, Acoustic diode: rectification of acoustic energy flux in one-dimensional systems, Phys. Rev. Lett. 103 (2009) 104301. [6] B.I. Popa, L. Zigoneanu, S.A. Cummer, Experimental acoustic ground cloak in air, Phys. Rev. Lett. 106 (2011) 253901. [7] J. Mei, G. Ma, M. Yang, Z. Yang, W. Wen, P. Sheng, Dark acoustic metamaterials as super absorbers for low-frequency sound, Nat. Commun. 3 (2012) 756. [8] X. Zhang, Acoustic resonant transmission through acoustic gratings with very
[22]
[23] [24] [25] [26] [27] [28] [29]
746
narrow slits: multiple-scattering numerical simulations, Phys. Rev. B 71 (2005) 241102. M.H. Lu, X.K. Liu, L. Feng, J. Li, C.P. Huang, Y.F. Chen, Y.Y. Zhu, S.N. Zhu, N.B. Ming, Extraordinary acoustic transmission through a 1D grating with very narrow apertures, Phys. Rev. Lett. 99 (2007) 174301. J. Christensen, A.I. Fernandezdominguez, F.D. Leonperez, L. Martinmoreno, F.J. Garciavidal, Collimation of sound assisted by acoustic surface waves, Nat. Phys. 3 (2007) 851–852. J. Christensen, L. Martinmoreno, F.J. Garciavidal, Theory of resonant acoustic transmission through subwavelength apertures, Phys. Rev. Lett. 101 (2008) 014301. B. Hou, J. Mei, M. Ke, W. Wen, Z. Liu, J. Shi, P. Sheng, Tuning Fabry-Perot resonances via diffraction evanescent waves, Phys. Rev. B: Condens. Matter 76 (2007) 293–300. Z. Liu, X. Zhang, Y. Mao, Y.Y. Zhu, Z. Yang, C.T. Chan, P. Sheng, Locally resonant sonic materials, Science 289 (2000) 1734–1736. Y. Shiraishi, Asymmetric acoustic transmission in multiple frequency bands, Appl. Phys. Lett. 107 (2015) 104301. G. Ma, M. Yang, S. Xiao, Z. Yang, P. Sheng, Acoustic metasurface with hybrid resonances, Nat. Mater. 13 (2014) 873–878. C. Audoly, Acoustic Characterisation of Anechoic or Decoupling Coatings Taking into Account the Supporting Hull, RINA warship conference - Naval submarines and UUV, 2011, pp. 165–169. C. Li, M. Ke, Y. Ye, S. Xu, C. Qiu, Z. Liu, Broadband asymmetric acoustic transmission by a plate with quasi-periodic surface ridges, Appl. Phys. Lett. 105 (2014) 104301. E. Bok, J.J. Park, H. Choi, C.K. Han, O.B. Wright, S.H. Lee, Metasurface for water-toair sound transmission, Phys. Rev. Lett 120 (2018) 044302. D. Gonghuan, Z. Zhemin, G. Xiufen, Acoustic Foundation, 3rd ed., Nanjing University Press, 2012, pp. 131–144 (in Chinese). A. He, W. Liu, W. Xue, H. Yang, Y. Cao, Nanosecond laser ablated copper superhydrophobic surface with tunable ultrahigh adhesion and its renewability with low temperature annealing, Appl. Surf. Sci. 434 (2018). A. MarieKietzig, M.N. Mirvakili, Saeid Kamal, Peter Englezos, S. Hatzikiriakos, Laser-patterned super-hydrophobic pure metallic substrates: cassie to wenzel wetting transitions, J. Adhesion Sci. Technol. 25 (2011) 2789–2809. S. Wang, J. Liu, L. Ming, X. Zeng, The effect of pulse ultraviolet laser modification on the surface wetting property of polycarbonate, Opto-Electronic Eng. 40 (2013) 77–82. X. Sheng, J. Zhang, Air layer on superhydrophobic surface underwater, Coll. Surf. A 377 (2011) 374–378. P. Lv, Y. Xue, Y. Shi, H. Lin, H. Duan, Metastable states and wetting transition of submerged superhydrophobic structures, Phys. Rev. Lett. 112 (2014) 196101. F. Liu, S. Peng, H. Jia, M. Ke, Z. Liu, Strongly localized acoustic surface waves propagating along a V-groove, Appl. Phys. Lett. 94 (2009) 225. A. De Bruijn, The sound absorption of an absorbing periodically uneven surface of rectangular profile, Acta Acust. United Acust. 18 (1967). H.X. Sun, S.Y. Zhang, X.J. Shui, A tunable acoustic diode made by a metal plate with periodical structure, Appl. Phys. Lett. 100 (2012) 104301. J. Wang, P. Leistner, X. Li, Prediction of sound absorption of a periodic groove structure with rectangular profile, Appl. Acoust. 73 (2012) 960–968. S.Y. Lin, Z. Xu, C. Wang, D. Zhao, Electrodeposited ultraviolet-durable biomimetic super-hydrophobic surface, Ceram. Int. 42 (2016) 16424–16430.
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Full Length Article
Laser textured GFRP superhydrophobic surface as an underwater acoustic absorption metasurface Guang Fenga,1, Fengping Lia,1, Wei Xuea, Ke Suna, Huan Yanga,b, Qiaofei Pana, Yu Caoa,
T
⁎
a
Zhejiang Key Laboratory of Laser Processing Robot, College of Mechanical & Electrical Engineering, Wenzhou University, Wenzhou 325035, China International Collaborative Laboratory of 2D Materials for Optoelectronics Science and Technology of Ministry of Education, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Metasurface Laser texturing Superhydrophobic Absorption coefficient
Underwater acoustic absorption metasurfaces (UAAMs), featured with artificial periodic unit cells as acoustic micro-absorbers, are crucial for the enhancement of the underwater stealth, energy transition, sonar detection, etc. How to implement the acoustic metasurfaces for practical engineering applications requires the support of efficient manufacturing techniques. Here we present a simple way of laser texturing for fabrication of the patterned superhydrophobic surface on glass fiber reinforced plastic (GFRP). Unlike the traditional acoustic absorbing material whose thickness should match the corresponding wavelength, the laser textured superhydrophobic micro-grooves have thickness less than the absorption sound wavelength by 2–3 orders of magnitude but promisingly demonstrate over 88% of the underwater incident acoustic power absorption from 50 kHz to 250 kHz. The physical mechanism of the UAAM ascribes to the multiple interface scattering effect induced by the air layer between water and superhydrophobic micro-nano structures.
1. Introduction Efficient control of the generation, propagation, reception, and processing of sound waves is the basic problem and long pursuit of the acoustics. Modern complex sound field processing problems such as aircraft [1], submarine noise isolation [2], underwater sonar detection [3], and music hall’s acoustic design [4] are increasingly related to the manipulation of selective acoustic absorption/transmission. Acoustic metasurfaces are artificial composite structures built by repetitive unit cells whose dimensions are much smaller than the acoustic wavelength and have many special acoustic properties which greatly expand the connotation of natural acoustic materials with applications such as oneway transportation [5], cloaking [6], super absorption [7], etc. Acoustic metasurfaces have been a research hotspot as a candidate smart module in intelligent acoustic design for years. Pioneering works on acoustic metasurfaces have inspired extensive studies. Extraordinary acoustic wave transmission was predicted by Zhang [8], followed by Lu et al. [9] who first reported the extraordinary acoustic wave transmission of grating structure. Recently, several groups measured the transmission properties of sound through plates with slits and holes [10–12] and proposed three types of the acoustic extraordinary transmission: periodic-lattice resonances [13], Fabry-Perot–type resonances
[12], and elastic Lamb-mode resonances [14]. J. Mei. et al. [7] achieved very high acoustic absorption at resonant frequencies through the concentration of curvature energy at the perimeters of asymmetrically shaped platelets and G. Ma. et al. [15] investigated the acoustic metasurfaces with hybrid resonances. In the field of underwater acoustic absorption, one of the most efficient technological solutions is the use of decoupling coatings and anechoic coatings [16], but the problem is the size of the coating is on the same order of wavelength, which restrains the use of the coating. Li. et al. [17] investigated the asymmetric underwater acoustic transmission by a plate with quasi-periodic surface ridges. Owing to the huge ratio of 3600 in the acoustic impedances from water to air, only 0.1% of the acoustic energy is naturally transmitted at such a boundary. Eun Bok. et al. [18] investigated the metasurface for water-to-air sound transmission, allowing about 30% of the incident acoustic power from water to be transmitted into the air. In this study, a simple way of laser texturing is proposed for the fabrication of the patterned superhydrophobic surface on glass fiber reinforced plastic (GFRP), which demonstrates selectively high absorption of a sound wave as a promising underwater acoustic absorption metasurface (UAAM).
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Corresponding author. E-mail address: [email protected] (Y. Cao). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.apsusc.2018.09.005 Received 4 May 2018; Received in revised form 16 August 2018; Accepted 1 September 2018 Available online 01 September 2018 0169-4332/ © 2018 Elsevier B.V. All rights reserved.
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Fig. 1. Setup of the laser micro-machining system and the cross grid patterns on GFRP specimen.
Fig. 2. The experimental setup for ultrasonic transmission coefficient test.
2. Experimental
optimized dimensions by multiple pre-tests to achieve high contact angle and low slip angle as a low-adhesion superhydrophobic (LASH) surface, specifically 25 μm of depth, 20 μm of width and the spacing between the crossed micro-grooves is 40 μm. (Heptadecafluoro-1,1,2,2tetradecyl) trimethoxysilane (PSD-J20P, Shenzhen Passedat Chemical co. Ltd.) is spin-coated and heat-treated by thermostat at 170 °C for 30 min as the chemical modifier that lower the solid surface energy and make the laser textured surface superhydrophobic. The micro-morphologies of the prepared superhydrophobic GFRP surfaces are investigated by Laser Scanning Confocal Microscopy (OSL 4100, OLYMPUS) and the Scanning Electron Microscope (SEM) (QUANTA 200F, FEI). Static contact angles (SCAs) [inserted in Fig. 6(c) and (d)] are measured five times at different tested area using a video optic CA instrument (OCA15EC, Dataphysics) equipped with a goniometer. The images of a 3 μL distilled water droplet placed on the specimen’s surface are analyzed by a Low-Band Axisymmetric Drop Shape Analysis (LBADSA) software. The temperature and relative humidity in the SCAs tests are 25 °C and 65% RH, respectively. An ultrasonic transmissivity measurement system is built to measure the underwater acoustic absorption properties, as shown in Fig. 2. The overall system is immersed in a muffler pool for measurement of underwater sonar transmission coefficient, which includes a signal generation (AFG 3021B, Tektronix), transducer (DYW-50/200-NA) as
Glass fiber reinforced plastic (GFRP) is the most common type of fiber-reinforced plastic using glass fiber which is cheaper and more flexible than carbon fiber. GFRPs are stronger than many metals by weight, and can be molded into complex shapes, which have wide applications in aircraft, boats, pipes, bath tubs and sonar dome, etc. Therefore, GFRP (Shenzhen Shengjili co. Ltd.) plates with the dimensions of 200 × 200 × 1 mm3 are used as the substrates. The GFRP plates are ultrasonically cleaned in anhydrous ethanol solution for 10 min and then blow dried before and after the laser texturing. A laser micro-machining system is used for precision ablating grid groove patterns on GFRP surfaces, as shown in Fig. 1(a). The UV laser (Awave355, Apto-Wave co. Ltd.) outputs pulsed Gaussian laser beam at an average power of 3 Watts, wavelength of 355 nm, the pulse width of 20 ns, and the focused laser spot diameter of 15 μm. At an operational pulse repetition rate of 90 kHz and X-Y galvo-scanning speed of 200 mm/s, the designed grid patterns are laser textured on the GFRP specimen surfaces by 6 times repetitive scanning, as shown in Fig. 1(b) and (c). Thus, the used laser pulse fluence for the texturing of GFRP surface is 4.72 J/cm2, which is near four time of threshold fluence (1.2 J/cm2, obtained by experimental) to get the designed microgroove structures. The fabricated crossed micro-grooves pattern has the 742
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an ultrasonic source, hydrophone (CS-3) as an ultrasonic detector and oscilloscope (Tektronix TDS 2012B). The signal generator is used to generate short-duration pulse, which would be converted into short duration acoustic pulses by the transducer. The water temperature is set to 20 °C. The GFRP specimen with superhydrophobic (SH) surface is placed between the transducer and the hydrophone receiver. The distance D1 from the source to GFRP specimen is 5 cm, and the distance D2 from GFRP specimen to the detector is 10 cm. The hydrophone received signals are linked to the oscilloscope for real-time display. 3. Results and discussion Transmission coefficient is defined as the ratio of the transmitted sound flux to the incident sound flux through a layer of the medium at a given frequency and condition [19]. For the scenario of underwater sound wave transmission through a GFRP plate, the transmission coefficient T can be calculated by the Eqs. (1) and (2):
T=
|pta |2 /2ρ1 C1 |pIa |2 /2ρ1 C1
k = w / c = 2π / λ
=
4 4cos2 kD + (R12 + R21)2sin2 kD
Fig. 3. Comparison of underwater transmission coefficients of theoretical, untreated, single-side and double-side laser textured GFRP, single-side and double-side laser textured GFRP after immersed in water for 2 h.
(1) (2)
where D is the thickness of the GFRP specimen, R12 is the ratio of the acoustic impedance value of the acoustic wave in the GFRP to the acoustic impedance value of the acoustic wave in the water, R21 is the acoustic impedance value of the acoustic wave in the water and the acoustic wave in the GFRP impedance ratio, k is the wave number. The transmission coefficient Eqs. (1) and (2) indicate that when the thickness is below ¼ of the incident wavelength, a thinner material is naturally better than a thicker one for sound wave transmission. Once the thickness of the specimen reaches an odd multiple of the ¼ wavelength, the reflected signal from back interface would destructively interfere with the incident signal causing the transmission coefficient to reach its minimum value. Nevertheless, when the thickness of the specimen reaches an integral multiple of half wavelength, the reflected wave would have interfered constructively with the incident wave, which results in maximum transmission. In order to investigate the effect of surface wettability on acoustic performance, laser texturing was used for fabrication of GFRP superhydrophobic surface. There are lots of papers that reported controlling the surface wettability by direct laser texturing, such as A. He et al. [20] fabricated copper superhydrophobic surface with adjustable adhesion by nanosecond laser ablation; Anne-MarieKietzig et al. [21] investigated the Cassie-Baxter to Wenzel wetting transitions on the laser patterned metallic superhydrophobic surfaces; and the effect of pulsed ultraviolet laser modification on the surface wettability of polycarbonate was studied by S. Wang et al. [22]; while here we demonstrate the control of underwater acoustic absorption property by laser textured superhydrophobic hierarchical micro-nano structures. The frequency range for the measurement of underwater acoustic absorption is chosen between 50 kHz and 250 kHz, which is contained in the normal working frequency of sonar. The transmission coefficient curves of normal incident ultrasonic waves to untreated, single-side and double-side laser textured GFRP, single-side and double-side laser textured GFRP after immersed in water for 2 h are shown in Fig. 3. As the acoustic frequency increases from 50 kHz to 250 kHz (corresponding to the wavelength range of 2.97 cm–0.59 cm in water), the transmission coefficient of untreated GFRP decreases from 0.95 to 0.57, which basically corresponded with a theoretical evaluation obtained according to the Eqs. (1) and (2). However, the transmission coefficients of singleside and double-side ablated SH surface retain very low value between 0.15 and 0.05 through the overall frequency range. Comparing with a transmission coefficient of untreated GFRP, the transmission coefficient of ablated GFRP is lower much, the maximum reduction of 86% (50 kHz) and minimization reduction of 52% (250 kHz). The air layer and periodic groove structure plays a significant role in the reduction of
transmission coefficient. After GFRP SH specimen immersed in water for 2 h, the transmission coefficients of both single-side and double-side ablated SH surface are obviously improved, the former decreases from 0.71 to 0.32, the latter decreases from 0.53 to 0.21, respectively. The reason is that comparing with the specimen of single-side ablated, the double-side ablated specimen will dissipate the sound waves on both side. Meanwhile, with the immersion time increase, the transmission coefficients of single-side and double-side ablated SH surface will increase due to the disappearance of the air layer. Reflection coefficients are also tested by placing the transducer and hydrophone on the same side with the specimen. The transducer emits a sound source perpendicular to the specimen, and the hydrophone receives the reflected sound wave at 45° from the vertical. The comparison of reflection coefficient curves of untreated GFRP, laser textured GFRPs with single-side and double-side SH surfaces is shown in Fig. 4. With the increase of the frequency from 50 kHz to 250 kHz, the reflection coefficients of an untreated, single-side and double-side laser textured GFRP, single-side and double-side laser textured GFRP after immersed in water for 2 h decrease with a similar trend. Laser textured microstructures increase the surface reflectivity of acoustic waves, especially in the low-frequency range that has a maximum increase of
Fig. 4. Comparison of underwater reflection coefficients of untreated, singleside, double-side laser textured GFRP, and the single-side and double-side laser textured GFRP after immersed in water for 2 h. 743
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microstructure of ablated. The insert in Fig. 6(c) is the image of static contact angles (SCAs) for the prepared GFRP SH specimen, which is 155.7° and static contact angles (SCAs) for untreated GFRP specimen is 76.3°, respectively. And the sliding angle of GFRP SH specimen is 5°. The Fig. 7 schematically shows the microscopic contact state of the laser textured SH surface underwater. The water is suspended on the top of the papillae and the space among papillae formed an air layer shown in Fig. 7(a), which makes a water/air/papillae interface [23]. Note that this illustration is different from the theory of solid/liquid interface in liquid, where no obvious air layer existed. Conversely, the “air layer effect” on SH surface underwater is rather close to a drop on it (predicated by Cassie-Baxter theory). With the immersion time increase, the air layer trapped in the hierarchical micro-nano structures (laser induced micro-grooves with sub-micron humps and pores) will detach or diffuse into the surrounding water, which leads to the wetting transition from Cassie-Baxter state [Fig. 7(a)] to Wenzel state [Fig. 7(b)]. P. Lv et al. [24] investigated the metastable states and wetting transition of submerged superhydrophobic structures, which demonstrated that the water would gradually immerse the pores with the increase of pressure. In our research, the change of wetting transition affects the acoustic performance. After GFRP SH specimen immersed in water for 2 h as shown in Fig. 7(b), the transmission coefficients of single-side and double-side ablated SH surface is obviously improved. The reflection coefficients of single-side and double-side ablated SH surface decreased a little. The absorption coefficients of single-side and double-side ablated SH surface decreased obviously. When the SH surfaces are immersed in the water, the air layer has a significant effect on the transmission coefficient. Owing to the existence of air layer, the impedance from water to GFRP will increase a lot that proved by the transmission coefficient of SH surface GFRP in Fig. 5. Therefore, the air layer should be a key factor to the effect on transmission coefficient of ablated GFRP. On the other hand, the micromorphology of laser textured GFRP has deep grooves, which is an effective sound absorption structure. When the sound wave entry the deep grooves, its energy would be absorbed by the deep grooves [25–27]. More specifically, these micro-grooves are interconnected and open outward rather than closed, making the sound wave easy to enter the grooves, while in comparison of the closed grooves cannot play the role of sound absorption. Moreover, GFRP matches the acoustic characteristic impedance of water, enabling the sound energy to enter the sound absorbing material without reflection, and the bulk of the incoming acoustic energy is absorbed. The acoustic coupling between adjacent grooves has an effect on acoustic attenuation. The upper sides of the ridges, as well as the bottoms of the grooves, are assumed to be sound absorbing, according to De Bruin’s theory [26], which separate the sound field into two parts. One is in the upper half-space above the ridges, named region I; the other is the field inside the grooves, named region II. In region I, the sound field is considered as a superposition of incident plane wave and reflected plane waves. In region II, the sound field is considered as a superposition of waveguide modes. Considering the effect of the region I and II, the sound absorption coefficient ∝θ, φ can be deduced as the Eq. (4):
6% (at 60 kHz) when compared with untreated reflectivity. After GFRP SH specimen immersed in water for 2 h, the reflection coefficients of both single-side and double-side ablated SH surfaces are slightly decreased, the former decreases about 3% from 50 kHz to 250 kHz, while the latter decreases about 7% from 50 kHz to 250 kHz. As the Cassie-Baxter wetting theory predicted [as shown in Fig. 7(a)], a large number of tiny air layer will be trapped in the bottom of the laser ablated micro-grooves when the superhydrophobic surface initially immersed underwater, which forms the array of liquid/air/ solid interfaces along the grooves. The shape of interface of liquid/air is similar to the laser ablated groove structure that behaves as a good sound absorption structure. Furthermore, the uneven interface is easy to cause the scattering of sound waves. Therefore, there is practically no difference between these two surfaces in reflection coefficient. Meanwhile, with the immersion time increase, the reduction of reflection coefficient of single-side and double-side ablated SH surface is the disappearance of the air layer increases the transmission energy of sound waves. Based on the test results of the transmission coefficient (T) and reflection coefficient (R), the absorption coefficient (A) defined as Eq. (3) [7] is shown in Fig. 5.
A = 1−R2−T 2
(3)
The absorption coefficients of GFRP specimens with single-side and double-side laser textured SH surfaces are higher than 0.88, and both have a distinctive enhancement than untreated GFRP’s on a wide frequency range from 50 kHz to 250 kHz. The absorption rate of the laser textured microstructures maximally increased by 85% (50 kHz) compared to the untreated, which indicates the use of laser textured SH surfaces makes GFRP an extremely fine acoustic absorber and a promising Underwater Acoustic Absorption Metasurface (UAAM). After GFRP SH specimen immersed in water for 2 h, the absorption coefficients of both single-side and double-side ablated SH surfaces decrease obviously. Because of the double-side absorptive micro-nano structures, the absorption coefficient of double-side ablated SH surface is higher than the single-side ablated SH surface. The action mechanism of laser-textured SH surface as a UAAM could be attributed to the unique surface morphology and wettability of the water-solid interface. The SEM images of the laser textured GFRP surface in (Fig. 6) shows a periodic papillary morphology, with multi microparticles. The average size of these micro-protruding structures is about 20 μm, with an average depth of 25 μm. The structure of a micrograph in Fig. 6(b) and (d) are under a higher magnification. The surfaces mainly consist of the micro-pillars. In the Fig. 6(c) the 3D
∝θ, φ = 1−
∑ Re|βr |
|Rr |2
βr β0
(4)
A detailed derivation for Eq. (4) can be found in De Bruin’s theory [26]. The acoustic scattered field above the structure is expanded in a spectrum of plane waves and the field in the groove in a superposition of standing waveguide modes, which can cause an acoustic attenuation. Meanwhile, the dimensions, groove depth and width, and the period of the structure have an influence on acoustic absorption. The other reason is that the medium of the acoustic wave is water, which differs from the sound wave in air. There is an air layer between water and superhydrophobic structure, which contributes to the achievement of
Fig. 5. Comparison of underwater absorption coefficients of untreated, singleside and double-side laser textured GFRP, single-side and double-side laser textured GFRP after immersed in water for 2 h. 744
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Fig. 6. SEM and laser confocal microscopy images of laser textured GFRP SH surface, the inserts in (c) is the images of static contact angles (SCAs).
Fig. 7. schematic of the microscopic contact state of (a) superhydrophobic surface underwater (Cassie-Baxter state) and (b) superhydrophobic surface after immersed in water for 2 h (Wenzel state).
4. Conclusion
an attenuation characteristic. There are studies about how the surface pattern (ridges or grooves) profile affect the acoustic performance. H. X. Sun et al. investigated the asymmetric underwater acoustic transmission by a plate with quasiperiodic surface ridges [14] and a tunable acoustic diode made by a metal plate with single-sided periodical grating structure immersed in water [27]. J. Wang et al. [28] studied the prediction of sound absorption of a periodic groove structure with rectangular profile whose dimension is less than the test sound wavelength by 0–1 orders of magnitude. In this work, the fabricated crossed micro-grooves are set to the optimized dimensions of 25 μm in depth, 20 μm in width and the spacing of 40 μm, which is less than the absorption sound wavelength by 2–3 orders of magnitude. Future study will focus on the effect of groove depth and spacing in order to manipulate the acoustic response of the UAAM.
Laser-ablated the patterned structure, and then it was modified by (Heptadecafluoro-1,1,2,2-tetradecyl) trimethoxysilane to obtain superhydrophobic surface on GFRP. The SCAs of superhydrophobic surface GFRP is 155.7°. Then the transmission coefficient, reflection coefficient and absorption coefficient of untreated, single-sided ablated and double-sided ablated GFRP were measured underwater. The transmission coefficient of ablated GFRP is obviously lower than the transmission coefficient of untreated GFRP. However, the reflection coefficient has little change. The absorption coefficient of ablated GFRP is obviously higher than the transmission coefficient of untreated GFRP, in particular, it achieves about over absorption coefficient of 88% from 50 kHz to 250 kHz. The physical mechanism of the UAAM ascribes to the multiple interface scattering effect induced by the air layer between water and superhydrophobic micro structures, which causes the 745
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attenuation of acoustic waves. After GFRP SH specimen immersed in water for 2 h, the transmission coefficients of single-side and doubleside ablated SH surface is obviously improved. The reflection coefficients of single-side and double-side ablated SH surface decreased a little. The absorption coefficients of single-side and double-side ablated SH surface decreased obviously. The reason is wetting transition of superhydrophobic surface GFRP effect the underwater sound propagation. However, 2 h duration time are too short to use the UAAM for practical underwater application. There were some reported works related to the durability/renewability of bionic super-hydrophobic surface [20,29]. The future work might be the novel design of near-surface multi-layer micro-pore structures and active bubble production mechanisms, which can also be prepared using lasers as a tool, to improve the durability of superhydrophobic surfaces that effectively increase the duration time of the UAAM. The process simplicity of the laser texturing of UAAM gives promising applications for underwater acoustic absorption scenarios, such as anechoic tile.
[9]
[10]
[11]
[12]
[13] [14] [15] [16]
[17]
Acknowledgment This work is financially supported by the National Natural Science Foundation of China (Grant Nos.U1609209, 51375348) and Zhejiang Provincial Natural Science Funds for Distinguished Young Scholar (Grant No. LR15E050003).
[18]
References
[21]
[19] [20]
[1] R.W. Paterson, P.G. Vogt, W.M. Foley, Design and development of the united aircraft research laboratories acoustic research tunnel, J. Aircraft 10 (2012) 427–433. [2] Y. Qu, J. Su, H. Hua, G. Meng, Structural vibration and acoustic radiation of coupled propeller-shafting and submarine hull system due to propeller forces, J. Sound Vib. 401 (2017) 76–93. [3] B. Allotta, A. Ridolfi, M. Bianchi, F. Fanelli, J. Gelli, N. Monni, D. Nocciolini, M. Pagliai, L. Paolucci, T. Pecorella, Employment of an autonomous underwater vehicle as mobile bridge among heterogeneous acoustic nodes, IFAC-PapersOnLine 50 (2017) 12380–12385. [4] M. Galiana, C. Llinares, Á. Page, Subjective evaluation of music hall acoustics: response of expert and non-expert users, Build. Environ. 58 (2012) 1–13. [5] B. Liang, B. Yuan, J.C. Cheng, Acoustic diode: rectification of acoustic energy flux in one-dimensional systems, Phys. Rev. Lett. 103 (2009) 104301. [6] B.I. Popa, L. Zigoneanu, S.A. Cummer, Experimental acoustic ground cloak in air, Phys. Rev. Lett. 106 (2011) 253901. [7] J. Mei, G. Ma, M. Yang, Z. Yang, W. Wen, P. Sheng, Dark acoustic metamaterials as super absorbers for low-frequency sound, Nat. Commun. 3 (2012) 756. [8] X. Zhang, Acoustic resonant transmission through acoustic gratings with very
[22]
[23] [24] [25] [26] [27] [28] [29]
746
narrow slits: multiple-scattering numerical simulations, Phys. Rev. B 71 (2005) 241102. M.H. Lu, X.K. Liu, L. Feng, J. Li, C.P. Huang, Y.F. Chen, Y.Y. Zhu, S.N. Zhu, N.B. Ming, Extraordinary acoustic transmission through a 1D grating with very narrow apertures, Phys. Rev. Lett. 99 (2007) 174301. J. Christensen, A.I. Fernandezdominguez, F.D. Leonperez, L. Martinmoreno, F.J. Garciavidal, Collimation of sound assisted by acoustic surface waves, Nat. Phys. 3 (2007) 851–852. J. Christensen, L. Martinmoreno, F.J. Garciavidal, Theory of resonant acoustic transmission through subwavelength apertures, Phys. Rev. Lett. 101 (2008) 014301. B. Hou, J. Mei, M. Ke, W. Wen, Z. Liu, J. Shi, P. Sheng, Tuning Fabry-Perot resonances via diffraction evanescent waves, Phys. Rev. B: Condens. Matter 76 (2007) 293–300. Z. Liu, X. Zhang, Y. Mao, Y.Y. Zhu, Z. Yang, C.T. Chan, P. Sheng, Locally resonant sonic materials, Science 289 (2000) 1734–1736. Y. Shiraishi, Asymmetric acoustic transmission in multiple frequency bands, Appl. Phys. Lett. 107 (2015) 104301. G. Ma, M. Yang, S. Xiao, Z. Yang, P. Sheng, Acoustic metasurface with hybrid resonances, Nat. Mater. 13 (2014) 873–878. C. Audoly, Acoustic Characterisation of Anechoic or Decoupling Coatings Taking into Account the Supporting Hull, RINA warship conference - Naval submarines and UUV, 2011, pp. 165–169. C. Li, M. Ke, Y. Ye, S. Xu, C. Qiu, Z. Liu, Broadband asymmetric acoustic transmission by a plate with quasi-periodic surface ridges, Appl. Phys. Lett. 105 (2014) 104301. E. Bok, J.J. Park, H. Choi, C.K. Han, O.B. Wright, S.H. Lee, Metasurface for water-toair sound transmission, Phys. Rev. Lett 120 (2018) 044302. D. Gonghuan, Z. Zhemin, G. Xiufen, Acoustic Foundation, 3rd ed., Nanjing University Press, 2012, pp. 131–144 (in Chinese). A. He, W. Liu, W. Xue, H. Yang, Y. Cao, Nanosecond laser ablated copper superhydrophobic surface with tunable ultrahigh adhesion and its renewability with low temperature annealing, Appl. Surf. Sci. 434 (2018). A. MarieKietzig, M.N. Mirvakili, Saeid Kamal, Peter Englezos, S. Hatzikiriakos, Laser-patterned super-hydrophobic pure metallic substrates: cassie to wenzel wetting transitions, J. Adhesion Sci. Technol. 25 (2011) 2789–2809. S. Wang, J. Liu, L. Ming, X. Zeng, The effect of pulse ultraviolet laser modification on the surface wetting property of polycarbonate, Opto-Electronic Eng. 40 (2013) 77–82. X. Sheng, J. Zhang, Air layer on superhydrophobic surface underwater, Coll. Surf. A 377 (2011) 374–378. P. Lv, Y. Xue, Y. Shi, H. Lin, H. Duan, Metastable states and wetting transition of submerged superhydrophobic structures, Phys. Rev. Lett. 112 (2014) 196101. F. Liu, S. Peng, H. Jia, M. Ke, Z. Liu, Strongly localized acoustic surface waves propagating along a V-groove, Appl. Phys. Lett. 94 (2009) 225. A. De Bruijn, The sound absorption of an absorbing periodically uneven surface of rectangular profile, Acta Acust. United Acust. 18 (1967). H.X. Sun, S.Y. Zhang, X.J. Shui, A tunable acoustic diode made by a metal plate with periodical structure, Appl. Phys. Lett. 100 (2012) 104301. J. Wang, P. Leistner, X. Li, Prediction of sound absorption of a periodic groove structure with rectangular profile, Appl. Acoust. 73 (2012) 960–968. S.Y. Lin, Z. Xu, C. Wang, D. Zhao, Electrodeposited ultraviolet-durable biomimetic super-hydrophobic surface, Ceram. Int. 42 (2016) 16424–16430.