Hindawi Publishing Corporation Journal of Engineering Volume 2013, Article ID 549865, 10 pages http://dx.doi.org/10.1155/2013/549865 Research Article Modal Analysis of 27 mm Piezo Electric Plate for Small-Scale Underwater Sonar-Based Navigation M. O. Afolayan, D. S. Yawas, C. O. Folayan, and S. Y. Aku Mechanical Engineering Department, Ahmadu Bello University, Samaru Zaria 810006, Nigeria Correspondence should be addressed to M. O. Afolayan; tunde afolayan@yahoo.com Received 14 September 2012; Revised 15 January 2013; Accepted 12 February 2013 Academic Editor: Jie Zhou Copyright © 2013 M. O. Afolayan et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tis work presents progress towards the development of a small-scale, purely sonar-based navigation device for a robotic fsh (∼394 mm long). Aperture overloading of small (5 mm diameter) ultrasonic transmitters does not allow them to be used efectively inside water. A test on a 27mm diameter buzzer piezo plate shows promising performance under water at frequencies from 4.5 kHz to 80 kHz. ANSYS-based simulation was therefore used to fnd modal frequencies at higher frequencies so as to optimize this encouraging result. Te simulation process also discovered several antiresonant frequencies such as 38.5 kHz, 54 kHz, and 57.5 kHz. All frequencies above the 8th harmonic (10,589.02 Hz) are out of phase with the input load except a resonance frequency of 42.5 kHz and an antiresonance frequency of 56.5 kHz. Also, the frst harmonic (1,648.73 Hz) is the only frequency that gave a nodal deformation. 1. Introduction Many marine organisms such as dolphin navigate using ultrasonic means. Artifcial systems such as autonomous underwater vehicles (AUV) and remotely operated system (ROV) commonly use acoustic means in their navigation, object detections, and avoidance, control, and communica- tion. Underwater modems such as those used by Eustice et al. [1] are ofen based on acoustic links that transmit at a very low frequency to extremely high frequencies while bearing data in the kilobit. (kb) range as exemplifed by Kumagai et al. [2] work. According to Eustice et al. [1], “few techniques exist for reliable three-dimensional position sensing for underwater vehicles. Depth, altitude, heading, and roll/pitch attitude can all be instrumented with high-bandwidth internal sen- sors.” Many AUV are equipped with multiple numbers of dead-reckoning sensors, such as Doppler velocity logs and inertial measurement systems, or magnetic compasses to estimate vehicle position. In contrast, the exact coordinate of the robots remains difcult to instrument and is normally measured acoustically in oceanographic and commercial applications and even in submarines [1, 3, 4]. Other methods used on the surface such as inertia navigation and accumulate error that is further aggravated by water waves and currents [5]. Sonar systems have been very attractive for underwater imagery—being capable of longer range and in a variety of water conditions such as poor visibility and lighting [6–8]. Te lower frequencies are even more efective for longer ranges as depicted in Table 1; they decay extremely slowly in water [5]. In robotics, sonar systems are ofen used for ranging due to their low cost and small size. Te signal is sent out continuously or pulsed. Te pulsed mode is used for eliminating frequent misreading caused by crosstalk or external sources operating nearby [9]. Safety and reliability are factors universally desired in any system design. Navigation based on acoustic has its own inherent problems also. High-power ultrasonic systems have been known to negatively afect underwater ecosystem [14]. Also very powerful low-frequency and activated sonars (and midfrequency sonar) have been claimed to also afect marine life [15]. Another problem is that acoustic degrades in cluttered environments such as reefs or close to the seafoor and subsea structures [8]. In the presence of air bubbles, the signature of object to be detected is adversely afected [16] although algorithms exist for overcoming such limitation.