Experimental evidence of bandgap structures in the lower jaw of the bottlenose dolphin (tursiops truncatus)

Previous studies using the TLM numerical modelling technique have demonstrated the potential existence of bandgap structures within the lower jawbone of the Atlantic Bottlenose dolphin (Tursiops truncatus). The study presented here shows experimental evidence of the existence of these bandgaps within a 2-D structure that mimics the prinnciple dimensions of the lower teeth and jawbone of the Bottlenose dolphin. The bandgap present is due to the tooth structure in the lower jaw forming a periodic array of scattering elements, which results in the formation of an acoustic stop band that is angular dependent

Measurement of a biomimetic antenna in the shape of a bat's ear

This paper presents a series of measurements of a novel antenna that physically resembles the ear of a bat. The antenna consists of a circular ground plane with a central monopole element. An equilateral triangular conducting plate is curved around the ground so that the base of the triangle is electrically connected to the perimeter of the circle and is of the same length. The input characteristic is reminiscent of a simple monopole above a circular ground, providing there are a sufficient number of modes in the triangular plate at the frequency of interest. In contrast to the plain monopole, certain frequencies yield a high gain and a radiation pattern with low side lobes. Measurements presented in this paper suggest that the antenna performance is broadly comparable with its acoustic analogue, although there are differences between the acoustic and electromagnetic implementation which have yet to be resolved

Temporal and spectral characteristics of a marine piling operation in shallow water

Analysis of the underwater radiate acoustic characteristics for marine piling operations for two pile diameters, 2m and 4.74m, in a relatively shallow water site are presented. Measurements of the entire piling sequence for several piles were conducted at ranges from 10m to 22km for piles in 10-20 m water depth. Variations in the temporal and spectral characteristics of radiated energy are analysed in context of pile size, range from source, hammer energy used and pile penetration depth. Analysis of hammer energy used shows a strong interdependence between mechanical strike ‘hammer’ energy and underwater radiated acoustic energy. This process appears ‘coarsely’ linear for individual piling operations although considerable variation in overall gradient were observed between operations. For individual hammer energy step increases often the largest increases in radiated energy were observed at the initial hammer energy increase, with subsequent strikes at the same hammer energy resulting in a gradual reduction in radiated energy to a level 1-2 dB lower. These effects are potentially due to sediment compacting / relaxation effects relating to the time and number of strikes and penetration. Temporal and spectral variations in radiated energy due to pile penetration are also examined for fixed hammer energy and range. Simultaneous recordings of radiated energy made at increasing distances from the pile showed evidence of temporal and spectral dispersion effects consistent with relatively shallow water propagation. Correlation of received levels at various ranges in differing seabed topographies were made suggesting complex shallow water modal propagation dependant on both the source and environment characteristics including seabed topography, sediment type and water column acoustic properties

Wind turbines and bat mortality: interactions of bat echolocation pulses with moving turbine rotor blades.

Wind power is a rapidly growing energy technology, popular for being a clean, reliable and cost-efficient renewable energy source. However, recently concern has been growing over the impact of wind turbines on flying wildlife, with both birds and bats found dead around turbine bases and observed collisions with moving turbine rotors. This phenomenon is widespread and has received enough attention to warrant investigation into how and why these collisions occur. In this paper we investigate the acoustic interaction of bats with wind turbines, in particular the interpretation of reflected sound pulses (echolocation) used by bats to navigate. This paper focuses on the effects of moving turbine rotor blades on reflected acoustic pulses, analogous to what might be presented to an echolocating bat approaching an operational turbine at rotor height. High frequency, simulated FM bat pulses were used to assess reflected echo properties from microturbines (experimentally and in simulation) in order to investigate what interaction rotor movements had with incoming pulses and the potential consequences for an echolocating bat near a moving wind turbine

A methodology for the measurement of radiated noise from marine piling

This paper describes a methodology that has been developed for measuring marine piling noise, which is designed to record the temporal, spatial and spectral characteristics of the radiated sound field. Results are presented for measurements of two pile diameters, 2m and 4.74m, in a shallow water site off the east coast of the UK. Measurements of the entire piling sequence for several piles were conducted at ranges from 10 m to 22 km for piles in 10-20 m water depth. To assess variations in the temporal, spatial and spectral characteristics, a number of recording systems were simultaneously deployed at various ranges and depths, allowing the full piling sequence to be measured. This allowed assessment of source level variation at fixed locations, and the effect of propagation within the water column