Spectral Biomimetic Technique for Wood Classification Inspired by Human Echolocation

Palatal clicks are most interesting for human echolocation. Moreover, these sounds are suitable for other acoustic applications due to their regular mathematical properties and reproducibility. Simple and nondestructive techniques, bioinspired by synthetized pulses whose form reproduces the best features of palatal clicks, can be developed. The use of synthetic palatal pulses also allows detailed studies of the real possibilities of acoustic human echolocation without the problems associated with subjective individual differences. These techniques are being applied to the study of wood. As an example, a comparison of the performance of both natural and synthetic human echolocation to identify three different species of wood is presented. The results show that human echolocation has a vast potential. 1. Introduction Acoustic techniques have been shown to be an invaluable tool for the study of many types of materials. Wood is an excellent material to test the limitations and potential of noninvasive acoustic methods due to its complexity and availability [1]. However, most currently used methods work in the ultrasonic range, [2, 3]. Studies of biological tissues in the audible range are scarce [4–6]. Measurement of acoustic properties of porous materials with impedance tubes is a powerful common procedure. Top quality comercial systems are available and several international standards are published [7]. Acoustic pulse reflectometry is a more recent technique for reconstructing the profile of ducts and other waveguides using pulse reflections from unknown duct geometries [8]. Other techniques have been developed for determining the properties of porous materials, mainly laser vibrometry and acoustic excitation based methods [9]. However, the use of impedance tubes is not suitable for real time monitoring of wood properties in harsh environments like sawmills or for inspecting large wood structures noninvasively. Wood species classification using impedance tubes, acoustic pulse reflectometry in the audible range or laser vibrometry is not reported in the literature, as far as we know. As an alternative technique to echolocation pulses, stress wave analysis using acoustic impact has been successfully used by our group to classify some wood species [10]. However, scanning pulse-echo methods are more suitable to study large sections of wood, like pillars and beams. Human echolocation enables the perception of objects through reflected echoes. Certain sounds are more appropriate for human echolocation as they produce clearer echoes. Previous studies have shown