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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.
- Submarine cables as precursors of persistent systems for large scale oceans monitoring and autonomous underwater vehicles operationPublication . Tieppo, Marcos; Pereira, Eduardo; Garcia, Laura Gonzalez; Rolim, Margarida; Castanho, Emanuel; Matos, Anibal; Silva, António; Ferreira, Bruno; Pascoal, Maria; Almeida, Eduardo; Costa, Filipe; Zabel, Fred; Faria, Joao; Azevedo, Jose; Alves, Jose; Moutinho, Jose; Goncalves, Luis; Martins, Marcos; Cruz, Nuno; Abreu, Nuno; Silva, Pedro; Viegas, Rúben; Jesus, Sergio; Chen, Tania; Miranda, Tiago; Papalia, Alan; Hart, Douglas; Leonard, John; Haji, Maha; de Weck, Olivier; Godart, Peter; Lermusiaux, PierreLong-term and reliable marine ecosystems monitoring is essential to address current environmental issues, including climate change and biodiversity threats. The existing oceans monitoring systems show clear data gaps, particularly when considering characteristics such as depth coverage or measured variables in deep and open seas. Over the last decades, the number of fixed and mobile platforms for in situ ocean data acquisition has increased significantly, covering all oceans' regions. However, these are largely dependent on satellite communications for data transmission, as well as on research cruises or opportunistic ship surveys, generally presenting a lag between data acquisition and availability. In this context, the creation of a widely distributed network of SMART cables (Science Monitoring And Reliable Telecommunications) - sensors attached to submarine telecommunication cables - appears as a promising solution to fill in the current ocean data gaps and ensure unprecedented oceans health continuous monitoring. The K2D (Knowledge and Data from the Deep to Space) project proposes the development of a persistent oceans monitoring network based on the use of telecommunications cables and Autonomous Underwater Vehicles (AUVs). The approach proposed includes several modules for navigation, communication and energy management, that enable the cost-effective gathering of extensive oceans data. These include physical, chemical, and biological variables, both registered with bottom fixed stations and AUVs operating in the water column. The data that can be gathered have multiple potential applications, including oceans health continuous monitoring and the enhancement of existing ocean models. The latter, in combination with geoinformatics and Artificial Intelligence, can create a continuum from the deep sea to near space, by integrating underwater remote sensing and satellite information to describe Earth systems in a holistic manner.
- In-Lab demonstration of an underwater acoustic spiral sourcePublication . Viegas, Rúben; Zabel, Friedrich; Silva, AntónioUnderwater acoustic spiral sources can generate spiral acoustic fields where the phase depends on the bearing angle. This allows estimating the bearing angle of a single hydrophone relative to a single source and implementing localization equipment, e.g., for target detection or unmanned underwater vehicle navigation, without requiring an array of hydrophones and/or projectors. A spiral acoustic source prototype made out of a single standard piezoceramic cylinder, which is able to generate both spiral and circular fields, is presented. This paper reports the prototyping process and the multi-frequency acoustic tests performed in a water tank where the spiral source was characterized in terms of the transmitting voltage response, phase, and horizontal and vertical directivity patterns. A receiving calibration method for the spiral source is proposed and showed a maximum angle error of 3° when the calibration and the operation were carried out in the same conditions and a mean angle error of up to 6° for frequencies above 25 kHz when the same conditions were not fulfilled.
- 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.
- Spiral beacon calibration and experiments for underwater localizationPublication . Viegas, Rúben; Zabel, Friedrich; Gomes, João; Silva, AntónioUnderwater localization and navigation are still challenging tasks due to the underwater acoustic channel characteristics. Spiral sources are underwater transducers that create structured acoustic fields from which the angle to the source can be readily obtained. The angle estimation is obtained from the phase difference between transmitted circular and spiral fields, but for reliable operation the transducers must be properly calibrated. This paper presents a spiral source calibration procedure with the integration of a stepper motor to measure phase and amplitude features of the transmitted circular and spiral fields, at multiple bearing angles. The calibration was performed for two developed prototypes, which in turn determined the most appropriate operating frequency range. For one of the prototypes, its linearity was confirmed at all the tested frequency ranges through homogeneity and additivity tests. In addition to calibration, acoustic localization experiments were carried out with the transmission of circular and spiral fields, with a comparative analysis against footage captured from the top of the test pool. The phase difference of the mobile hydrophone was subtracted to the phase difference of the reference hydrophone to compute the angle between the spiral beacon and the mobile hydrophone. The localization results revealed noteworthy angular errors, hypothesized to be associated with the Doppler effect induced by the movement of the mobile hydrophone. These calibration and localization experiments suggest that spiral sources could be an important enabling technology for safe and reliable localization of underwater vehicles.