A novel piezoelectret with well-defined cavities produced by threedimensional printing technology is reported. This prototyping tool allows many samples to be prepared in a single printing step and provides the possibility to design voided structures with control of the cavity geometric parameters such as height, diameter and shape. Acrylonitrile butadiene styrene piezoelectrets were fabricated by this method and measurements regarding their electrical response against time, temperature and pressure are presented. The samples show an average piezoelectric coefficient d 33 of around 100 pC/N and 70% of this piezoelectricity remains after they were exposed to temperatures up to 85°C.
This work focuses on acoustic analysis as a way of discriminating mineral oil, providing a robust technique, immune to electromagnetic noise, and in some cases, depending on the applied sensor, a low-cost technique. Thus, we propose a new method for the diagnosis of the quality of mineral oil used in electrical transformers, integrating a ferroelectric-based hydrophone and an acoustic transducer. Our classification solution is based on a supervised machine learning technique applied to the signals generated by an in-home built hydrophone. A total of three statistical datasets entries were collected during the acoustic experiments on four types of oils. The first, the second, and third datasets contain 180, 240, and 420 entries, respectively. Eighty-four features were considered from each dataset to apply to two classification approaches. The first classification approach is able to distinguish the oils from the four possible classes with a classification error less than 2%, while the second approach is able to successfully classify the oils without errors (e.g., with a score of 100%).
New environmental laws have restricted the use of hardwood trees in overhead power lines structures, such as, poles and cross-arms, leading companies to seek alternative materials. Reforested wood coated with polymeric resin has been proposed as an environmental friendly solution, with improved electrical properties and protection against external agents, e.g. moisture, ultra violet radiation and fungi. However, the single thin layer of resin, normally applied on such structures reveal to be inefficient, due to be easily damage during handling. In this paper, we present a composite coating, based on geotextile fibers and polyurethane resin that is suitable for wooden structures. Results obtained from two different tree species (from managed and reforested areas) coated with the composite reveal that the additional layer not only provided a stronger adhesion between wood and ccoating layer but also a further improvement in the electrical properties and better protection against abrasion and moisture.
Every year, different areas of knowledge are becoming more interested in 3D-printing technology. Recently, this technology was also proved to be feasible for creating sensitive materials such as piezoelectrets. This Letter extends the concept of a 3D printed piezoelectret to produce a pressure sensitive film that can be employed as an ultrasonic transducer for underwater applications, such as hydrophones. In order to achieve this, a two-layer polypropylene film was printed using a filament-based 3D printer. Afterwards, adhesive electrodes were attached on both sides of the film and electrical charging was applied. Later, the 3D printed film was mounted in a metal housing specially designed to keep the film in direct contact with the water and to isolate the electronic amplification. The validation was performed using a piezoelectric ceramic made of lead zirconate titanate (PZT), immersed in a water tank, to produce ultrasonic sweeps to be sensed by the 3D printed transducer. These tests revealed sensor sensitivities up to 600 mV and promote a precise detection of the acoustic resonance frequency of the PZT at 43.7 kHz.
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