Bandwidth enhancement : correcting magnitude and phase distortion in wideband piezoelectric transducer systems

Acoustic ultrasonic measurements are widespread and commonly use transducers exhibiting resonant behaviour due to the piezoelectric nature of their active elements, being designed to give maximum sensitivity in the bandwidth of interest. We present a characterisation of such transducers that provides both magnitude and phase information describing the way in which the receiver responds to a surface displacement over its frequency range. Consequently, these devices work efficiently and linearly over only a very narrow band of their overall frequency range. In turn, this causes phase and magnitude distortion of linear signals. To correct for this distortion, we introduce a software technique, which considers only the input and the final output signals of the whole systemwhich is therefore generally applicable to any acoustic system. By correcting for the distortion of the magnitude and phase responses, we have ensured the signal seen at the receiver replicates the desired signal. We demonstrate a bandwidth extension on the received signal from 60-130 kHz at -6dB to 40-200 kHz at -1dB in a test system. The linear chirp signal we used to demonstrate this method showed the received signal to be almost identical to the desired linear chirp. Such systemcharacterisation will improve ultrasonic techniques when investigating material properties by maximising the accuracy of magnitude and phase estimations

A Novel Algorithm to Estimate Closely Spaced Source DOA

In order to improve resolution and direction of arrival (DOA) estimation of two closely spaced sources, in context of array processing, a new algorithm is presented. However, the proposed algorithm combines both spatial sampling technic to widen the resolution and a high resolution method which is the Multiple Signal Classification (MUSIC) to estimate the DOA of two closely spaced sources impinging on the far-field of Uniform Linear Array (ULA). Simulations examples are discussed to demonstrate the performance and the effectiveness of the proposed approach (referred as Spatial sampling MUSIC SS-MUSIC) compared to the classical MUSIC method when it’s used alone in this context

A novel bio-inspired acoustic ranging approach for a better resolution achievement

Bat and dolphin use sound to survive and have greatly superior capabilities to current technology with regard to resolution, object identification and material characterisation. Some bats can resolve some acoustic pulses thousands of times more efficiently than current technology (Thomas & Moss, 2004 ). Dolphins are capable of discriminating different materials based on acoustic energy, again significantly out-performing current detection systems. Not only are these animals supreme in their detection and discrimination capabilities, they also demonstrate excellent acoustic focusing characteristics - both in transmission and reception. If it could approach the efficiencies of bat and cetacean systems, the enormous potential for acoustic engineering, has been widely recognised. Whilst some elements of animal systems have been applied successfully in engineered systems, the latter have come nowhere near the capabilities of the natural world. Recognizing that engineered acoustic systems that emulate bat and cetacean systems have enormous potential, we present in this chapter a breakthrough in high-resolution acoustic imaging and physical characterization based on bio-inspired time delay estimation approach

Short pulse multi-frequency phase-based time delay estimation

An approach for time delay estimation, based on phase difference detection, is presented. A multiple-frequency short continuous wave pulse is used to solve the well-known phase ambiguity problem when the maximum distance exceeds a full wavelength. Within an unambiguous range defined with the lowest frequency difference between components, the corresponding phase difference is unique and any distance within this range can be determined. Phase differences between higher frequency components are used to achieve a finer resolution. The concept will be presented and the effectiveness of the approach will be investigated through theoretical and practical examples. The method will be validated using underwater acoustic measurements, simulating noisy environments, demonstrating resolutions better than a 50th of a wavelength, even in the presence of high levels (−5 dB) of additive Gaussian noise. Furthermore, the algorithm is simple to use and can be easily implemented, being based on phase detection using the discrete Fourier transform

Bat-inspired distance measurement using phase information

A new approach to time delay estimation, based on the inclusion of phase di®erence information between components of the received sig- nal is presented. A multi-component signal has been developed to solve the phase ambiguity problem. We present the concept and investigate its effectiveness through theoretical and practical examples, including underwater acoustic measurements, taking noisy environments into ac- count. We demonstrate resolutions better than a ¯ftieth of a wave- length, even in the presence of high levels (-5dB) of additive gaussian noise