No abstract

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%).

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.

Electrically charged porous electret films, reported as ferroelectrets or piezoelectrets, have drawn the attention of researchers due to their high piezoelectric activity, low density, and flexibility. This paper introduces a ferroelectret design for the development of piezoelectric-magnetic responses. Samples are prepared with an additional magnetic layer placed above open tubular channels made from fused electret films, and the piezoelectric direct effect of electrically charged samples is monitored. The results of the measurements show approximately 900 pC N−1 piezoelectric coefficients d33. The piezoelectric-magnetic effect is an electrical response from a mechanical deformation caused by an external magnetic force. The magnetic field pulls the magnetic layer, mechanically deforming the electrically charged tubular structure, which creates a charge compensation to be measured as a charge density variation. A setup especially assembled for measuring the piezoelectric-magnetic response is described together with piezoelectric-magnetic values ranging from 94 up to 275 pC T−1.