Solid State Communications 149 (2009) 667–669 Contents lists available at ScienceDirect Solid State Communications journal homepage: www.elsevier.com/locate/ssc Experimental investigation of negative refraction and imaging of 8-fold-symmetry phononic quasicrystals Shasha Peng, Xuefei Mei, Pei Pang, Manzhu Ke ∗ , Zhengyou Liu Key Lab of Acoustic and Photonic Materials and Devices of Ministry of Education and Department of Physics, Wuhan University, Wuhan 430072, China article info Article history: Received 18 February 2009 Accepted 23 February 2009 by A.H. MacDonald Available online 28 February 2009 PACS: 43.20.+g 43.35.+d 63.20.e Keywords: A. Phononic quasicrystal D. Acoustic wave D. Negative refraction abstract The focus behaviors of acoustic wave through 8-fold-symmetry phononic quasicrystals have been observed experimentally in this paper. By measuring the field distributions in the image plane, we obtain an elongated image of a point source which has a similar result with phononic crystals. The negative refraction index was measured in two different ways which are very consistent with each other. These properties make the phononic quasicrystals (PQCs) promising for application in a range of phononic devices. © 2009 Elsevier Ltd. All rights reserved. Recently, negative refraction and left-hand materials (LHMs) have attracted a great deal of attention from both the theoretical and the experimental sides for their huge potential applications. The negative refraction behavior and imaging effect in photonic crystals have been experimentally demonstrated [1–7]. The phenomena of negative refraction were also found to exist in some periodic phononic crystals (PC) [8–11]. The physical principle for negative refraction effect in the PCs stems from the dispersion characteristic of wave propagation in such a periodic medium, which can be described by the equivalent frequency surface of the band structure [1,12–14]. It is interesting that the phenomena of negative refraction were also found to exist in some quasiperiodic photonic quasicrys- tals. Very recently, Feng et al. [15] showed the negative refrac- tion in some photonic quasicrystal structures theoretically and experimentally. The interest in photonic quasicrystals motivates the research for analogous phenomena in phononic quasicrystals, which are the elastic and acoustic analogs of photonic quasicrys- tals. Zhang et al. [16] investigated the focus features of the acoustic wave through high-symmetry phononic quasicrystal (QC) by using numerical simulation methods. But as far as we known, the focus imaging and negative refractive index of phononic quasicrystals lacks experimental confirmation. Strictly speaking, the properties ∗ Corresponding author. Tel.: +86 27 68754613; fax: +86 27 68752569. E-mail address: mzke@whu.edu.cn (M. Ke). of wave transport in the quasiperiodic phononic crystals cannot be described by analyzing the equifrequency surface of the band structures. Although recent experiments [17] showed that analo- gous concepts of Bloch-like functions and Bloch-like states in the periodic structures could be applied approximately to some qua- sicrystals, the similar theory of the equifrequency surface was not stated. Through experiment the negative refraction and imaging effect for the phononic quasicrystal could be observed dramatically and directly. In this work, we focus on the experimental veri- fication of negative refraction for two-dimensional (2D) 8-fold- symmetry phononic quasicrystal. The phononic quasicrystal sample investigated in our exper- iment is composed of 8-fold-symmetry quasicrystal array steel cylinders (with diameter d = 1 mm) immersed in water. The near- est neighbor distance of two steel cylinders is a = 1.8 mm. And sample thickness is 12.5 mm (about 7a), and width is 74 mm (about 41a). Our experimental setup is based on the well-known ultra- sonic transmission technique [18]. Fig. 1 gives a schematic diagram of the experimental setup, showing the position of the phononic quasicrystal with respect to the generating ultrasonic transducer and the detecting pinducer. The entire assembly was immersed in water. A pulser/receiver generator (Panametrics model 5800PR) produces a short duration pulse. We used a focus immersion trans- ducer as the generating transducer which has a center frequency of 0.5 MHz. The focus transducer serves as a point source in the experiment which has a focus spot of about 3 mm in diameter, and placed at 8 mm (about 4.5a) from the front surface of the sample. The pulses transmitted through the sample were detected 0038-1098/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2009.02.022