Abstract
Oceans all over the world are an important way of sustainability in the lives of many people and have a high impact on the economy of most of the coastal countries. With the growth of underwater activity provided by the development of autonomous and remotely controlled vehicles and with the appearance of new underwater sensors, there is also a need to develop and design more robust underwater wireless networks to provide better and faster communications among the devices connected to the network. Nowadays several technologies provide wireless underwater communications. In this work, we address acoustic technology and the implementation of an acoustic communication system which applies a version of frequency modulation. The main goal of this work is to study the 4-FSK modulation technique and verify the efficiency of the communication system according to variables such as communication distance and baud rate. This implementation uses FPGA systems and Xilinx Vitis Model Composer software and MATLAB Simulink software for simulation. The developed communication system was tested in a controlled environment at two stages: aquarium and pool. The tests were carried out transmitting at 3 different baud rates (40, 100 and 200 kbps) in a distance of 100 cm in the aquarium and 5 meters in the pool.

Abstract
Implementing Artificial Reefs (AR) is seen as a worldwide strategy to overcome the problematic environmental impacts due to climate change, overfishing and other activities that damage natural habitats and ecosystems. The production and deployment of ARs involve a series of technical challenges and this work explores a possible alternative solution to overcome some of these challenges. This work addresses a new system for building underwater modular structures integrating monitoring sensors, exploring the potential that Flat Knitted textiles have when specifically designed and used as Knitted Textile Preforms (KTPs) for concrete filling. The casting of AR modules directly in their final position, underwater, brings new paradigms to the design and production of ARs clusters with more complex geometries and geometrical continuity between modules. This manuscript is dedicated to the analysis of variables such as injection pressure and its variations during filling and curing, respectively, as well as the textile structure and geometrical design. It also addresses the possibilities of the technology to embed environmental sensors, which will add functions to the AR structure.

Abstract
The oceans are abundant in natural diversity, minerals and energy resources, and there is an urgent need for a better understanding of its ecosystems and dynamics. The Synchronous Oceanic and Atmospheric Data Acquisition (SONDA) Project intends to contribute to better atmospheric and oceanic modelling and monitoring by launching High-Altitude Balloons (HAB) equipped with atmospheric and deep-sea probes to be released in oceanic areas of interest. This work reports the development and validation of three different probes: 1) atmospheric monitoring with APRS communications to be launched by HAB; 2) oceanographic monitoring; and 3) deep-sea monitoring with satellite communications. All probes were preliminarily tested in a semi-controlled fluvial environment, and posteriorly in real field conditions in the Azores Islands, Portugal. During the campaign, the Atmospheric probe was launched by HAB and its communications were tested with fixed and mobile ground stations, the oceanographic probe was deployed for three days to monitor the effect of a geothermal spring in the sea and the deep-sea probe was released into the Atlantic Ocean.

Abstract
Advancement and opportunity in the Internet of Things (IoT) and circular economy are pushing the technologies required to develop eco-friendly memory devices, computing devices, advanced sensors, and actuators. In this manuscript, a thermally cycled lithium niobate pyroelectric crystal is used to store the surface charges in different dielectric samples (Kapton, Parafilm, and Teflon). Charge storing parameters, such as the effect of temperature ramp, the gap between the dielectric-to-pyroelectric, and the effect of charging cycles, were studied to understand the surface charge formation on dielectric samples. Pyroelectrically charged dielectrics showed a surface potential of up to 400 V, with a linear dependence on the thermal gradient of the pyroelectric crystal. The charged surface showed good charge storage uniformity and stability at high temperatures (90 degrees C) and relative humidity (>85%). Using the pyroelectrically charged dielectrics, wearable motion sensors offering output signals in the range of tens of millivolts and a digital flexible invisible memory encoding with polarity switched (positive and negative charges) electrostatic bits are demonstrated.

Abstract
A versatile, miniaturized, cost-effective, low-power wave profile and tide monitoring system, capable of long-term and scalable deployment, was developed to integrate pressure and temperature sensors in an RS485 network, for standalone operation with organized memory or real-time shared data monitoring. The pressure and temperature sensors are controlled by low-power microcontrollers, that communicate the data periodically to a datalogger, that depending on the application, store it in a removable SD card or send it to a server via Wi-Fi. The data is then analyzed to compensate for the loss in amplitude sensitivity according to the sensor's depth. The wave profile can be sampled at a maximum rate of 100 Hz, with a 1 cm resolution. The system was tested successfully in real-life conditions, in rivers Douro and Cavado, and off the coast of Viana do Castelo.

Abstract
Composites of poly(vinyl alcohol) (PVA) in the shape of braids, in combination with crystals of hydroxyapatite (HAp), were analyzed to perceive the influence of this bioceramic on both the quasi-static and viscoelastic behavior under tensile loading. Analyses involving energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) allowed us to conclude that the production of a homogeneous layer of HAp on the braiding surface and the calcium/phosphate atomic ratio were comparable to those of natural bone. The maximum degradation temperature established by thermogravimetric analysis (TGA) showed a modest decrease with the addition of HAp. By adding HAp to PVA braids, an increase in the glass transition temperature (Tg) is noticed, as demonstrated by dynamic mechanical analysis (DMA) and differential thermal analysis (DTA). The PVA/HAp composite braids' peaks were validated by Fourier transform infrared (FTIR) spectroscopy to be in good agreement with common PVA and HAp patterns. PVA/HAp braids, a solution often used in the textile industry, showed superior overall mechanical characteristics in monotonic tensile tests. Creep and relaxation testing showed that adding HAp to the eight and six-braided yarn architectures was beneficial. By exhibiting good mechanical performance and most likely increased biological qualities that accompany conventional care for bone applications in the fracture healing field, particularly multifragmentary ones, these arrangements can be applied as a fibrous fixation system.