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- Development of a high-power multilayer PVDF acoustic projector for 40 to 80 kHz bandPublication . Silva, António; Hughes, Ashley; Pozzatti, Daniel; Zabel, Friedrich; Viegas, Rúben; Martins, MarcosA piston type projector using the PVDF piezoelectric polymer was developed for operating in underwater environment, below 100 kHz. For those frequencies PZT piezoelectric ceramic is usually a preferable choice and PVDF is only considered for frequencies above a few hundreds of kHz. This paper will show that efficient underwater acoustic projectors for frequencies below 100 kHz can be implemented regarding an appropriate impedance adapter is being used. The developed project presents a calibrated transmitting voltage response (TVR) of approximately 166, 160 and 175 dB at 40, 50 and 75 kHz, respectively. The PVDF TVR values are compatible with the PZT projectors available on market with the advantage of having a larger bandwidth than most PZT projectors. To the authors knowledge this is the first time that a PVDF projector attain such characteristics. Although theoretically the PVDF projector bandwidth is larger than 40 to 80 kHz, in practice it was observed that only between those frequencies the project presents a stable operation for the transmission of long-term signals.
- Integrated approach for modeling acoustic propagation and projectors/hydrophones electronicsPublication . Viegas, Rúben; Pozzatti, Daniel; Zabel, Friedrich; Silva, AntónioUnderwater acoustic propagation models (APM) are useful tools to predict acoustic propagation, making it possible to implement and test equalization algorithms for Underwater Acoustic Communication (UWAC) systems. To our knowledge, none of the APMs developed so far consider the distortion induced by the associated electronic circuits, impedance adaptors and acoustic transducers on signal propagation, which are important mainly in broadband applications. This paper describes the functioning of a new model capable of predicting the aforementioned distortions on the projector and hydrophone. The electro-Acoustic Propagation Model (eAPM) calculates the frequency response of the circuits with frequency-dependent characteristic components (transducers and impedance adaptors) using SPICE simulations and simulates the acoustic propagation using an Time-Variable APM (TV-APM), all embedded in a single model. SPICE simulations require the insertion of electrical impedance measurements from the transducers and impedance adaptors. eAPM also uses the projector's Transmitting Voltage Response (TVR) and the hydrophone's Open Circuit Voltage Response (OCVR), that can be obtained through equipment calibration. The model output signals have a good agreement with the signal experimentally recorded, showing that the eAPM allows for in-lab prediction of the distortion induced by the transducers and electronics and its impact on an application in a realistic acoustic propagation environment. The developed model can be used to predict distortions on broadband UWAC systems and also to support the development of new transducers, especially those with a wide bandwidth response.