1063-7710/00/4604- $20.00 © 2000 MAIK “Nauka/Interperiodica” 0439 Acoustical Physics, Vol. 46, No. 4, 2000, pp. 439–444. Translated from Akusticheskiœ Zhurnal, Vol. 46, No. 4, 2000, pp. 509–514. Original Russian Text Copyright © 2000 by Karabutov, Kozhushko, Pelivanov, Podymova. Studies of the structure and condition of composite materials and items made of them is of great scientific and practical interest. One of the basic methods of non- destructive testing of composites is the ultrasonic tech- nique. The majority of composite materials have peri- odic structures, and, therefore the study of acoustic properties of periodic structures is quite topical. It is easy to calculate the elastic moduli and the attenuation coefficient for ultrasound in transversely isotropic and orthotropic composite materials in the long-wave approximation. These studies were reviewed in our pre- vious papers [1, 2]. In the general case, the spectrum of the ultrasound transmission through a periodic struc- ture consists of alternating pass and stop bands. Such stop bands were observed experimentally in glass-rein- forced plastic composites [3]. Experimental studies of ultrasonic propagation in periodic structures are few in number. Basically, such investigations are restricted to considering one-dimen- sional periodic structures. This is connected with the fact that multidimensional periodic systems have dif- ferent characteristic periods of their structure in differ- ent directions, and sources of wide-band acoustic sig- nals are necessary for their investigation. Conventional piezoelectric radiators are of little use for this purpose. Scott and Gordon [4] studied both theoretically and experimentally the ultrasonic propagation in a periodic structure consisting of six periodically arranged glass and water layers of thickness 1.22 and 1 mm, respec- tively. For this structure, the presence of stop and pass bands for ultrasound in the range 1–8 MHz was demon- strated. Existence of pass and stop bands in the transmission spectrum of a periodic structure was also demonstrated theoretically and experimentally by James et al. [5]. It was found that the presence of defects in a periodic structure gives rise to a local transmission maximum in the stop band of the transmission spectrum. Thus, James et al. [5] demonstrated an opportunity for the diagnostics of a periodic structure with defects. Kushwacha [6], Young-Sang Joo et al. [7], and Maidanic and Becker [8] theoretically analyzed the band structure of ultrasonic transmission spectra for a system consisting of metal cylindrical rods positioned in parallel in the air or in a liquid. A theoretical study of ultrasonic propagation in two- and three-dimensional periodic structures was conducted by Kushwacha et al. [9, 10]. The corresponding problem is solved using the Bloch theorem and the Fourier transform, and the solu- tion is reduced to the determination of the eigenvalues of the wave vectors of acoustic waves propagating in periodic structures. Papers devoted to the investigation of the ultrasonic wave propagation in composite struc- tures in the case of the acoustic wavelength being close to the structure period were reviewed by Nayfeh [11], who analyzed various theoretical models of one- and three-dimensional ordered composite structures. The frequency spectrum of ultrasonic transmission through a two-dimensional structure in the form of a system of 36 metal rods of diameter 2.34 cm positioned in the nodes of a square grid with the period 3.7 cm was studied by Robertson and Rudi [12]. The existence of stop bands for the ultrasonic transmission in the fre- quency range up to 10 kHz was proved experimentally. Photoacoustic Study of the Transmission of Wide-Band Ultrasonic Signals through Periodic One-Dimensional Structures A. A. Karabutov, V. V. Kozhushko, I. M. Pelivanov, and N. B. Podymova International Laser Center, Moscow State University, Vorob’evy gory, Moscow, 119899 Russia e-mail: ivan@gpwpl.phys.msu.su Received June 8, 1999 Abstract—The propagation of wide-band acoustic pulses in one-dimensional periodic structures consisting of alternating plexiglas and water layers is studied theoretically and experimentally. The experiment is carried out with the use of the wide-band photoacoustic spectroscopy based on the laser excitation of ultrasound and a wide-band signal detection. The fact that the transmission spectrum of a periodic structure has alternating pass and stop bands is confirmed experimentally. The width and localization of the stop bands strongly depend on the thickness of the layers and on the phase velocity of ultrasound in them. It is demonstrated that defects of the structure periodicity give rise to one or several local transmission maxima in the stop band and to a mod- ification of the pass band. The amplitude and position of a local maximum in the stop band strongly depend on the position of the defective layer. The experimental data agree well with the results of numerical simulation. © 2000 MAIK “Nauka/Interperiodica”.