Alan Kardek Rêgo Segundo

Bio: Alan Kardek Rêgo Segundo is an academic researcher from Universidade Federal de Ouro Preto. The author has contributed to research in topics: Capacitive sensing & Water content. The author has an hindex of 6, co-authored 33 publications receiving 84 citations.

A Novel Low-Cost Instrumentation System for Measuring the Water Content and Apparent Electrical Conductivity of Soils

Abstract: The scarcity of drinking water affects various regions of the planet. Although climate change is responsible for the water availability, humanity plays an important role in preserving this precious natural resource. In case of negligence, the likely trend is to increase the demand and the depletion of water resources due to the increasing world population. This paper addresses the development, design and construction of a low cost system for measuring soil volumetric water content (θ), electrical conductivity (σ) and temperature (T), in order to optimize the use of water, energy and fertilizer in food production. Different from the existing measurement instruments commonly deployed in these applications, the proposed system uses an auto-balancing bridge circuit as measurement method. The proposed models to estimate θ and σ and correct them in function of T are compared to the ones reported in literature. The final prototype corresponds to a simple circuit connected to a pair of electrode probes, and presents high accuracy, high signal to noise ratio, fast response, and immunity to stray capacitance. The instrument calibration is based on salt solutions with known dielectric constant and electrical conductivity as reference. Experiments measuring clay and sandy soils demonstrate the satisfactory performance of the instrument.

Development and Characterization of Titanium Dioxide Ceramic Substrates with High Dielectric Permittivities

Abstract: Titanium dioxide substrates have been synthesized by means of solid-state reactions with sintering temperatures varying from 1150 °C up to 1350 °C. X-ray diffraction and scanning electron microscopy (SEM) where employed to investigate the crystal structure, grain size and porosity of the resulting samples. The obtained ceramics are tetragonal (rutile phase) with average grain sizes varying from 2.94 µm up to 5.81 µm. The average grain size of samples increases with increasing temperature, while the porosity decreases. The effect of microstructure on the dielectric properties has been also studied. The reduction of porosity of samples significantly improves the dielectric parameters (relative dielectric permittivity and loss tangent) in comparison to those of commercial substrates, indicating that the obtained ceramic substrates could be useful in the miniaturization of telecommunication devices.

Portable non-invasive capacitive transducer for measuring fuel level

Abstract: The use of combustion engines in portable applications has several applications, such as: high-pressure washers, motogenerators, crushers and pumping. However, the autonomy of such equipment does not always follow its advancement in efficiency and robustness. Therefore, the monitoring of the fuel level of these machines is necessary to know about their autonomy. This article refers to the development of a portable capacitive transducer for fuel level measurement, consisting of a plug-in device, easy to install and compact. From its construction and configuration, the device produces a frequency signal inversely proportional to the capacitance variation of the sensor element. The transducer technique is non-invasive and it takes advantage of the tank shell characteristic construction for coupling of the device.

Development of an educational tool for control engineering

Abstract: On this work, a device was made in order to help the visualization by the student of a PID temperature control and thus fix the concepts learned in the classroom. This device was built primarily with a PIC18F4550 microcontroller, a mini cooler from a PC, a heat resistor, LM35 temperature sensors, liquid crystal display, USB connector, transistors, LEDs, potentiometers, resistors and capacitors. The USB connection is responsible for recording the microcontroller firmware (bootloader mode), for interfacing with a supervisory software, and to supply the system. The heat resistor provides heat to the system. On the other hand, the cooler has the function of removing heat from the system. The liquid crystal display helps the student to check the temperature, the constants of the controller (K p , K i and K d ) and the set point temperature or the cooler voltage. The potentiometers provide the option to run the system in open loop, that is, they serve to make the control of the heat supplied by the heat resistor and the cooler voltage manually. Both the heat resistor and the cooler are controlled via transistors switched by PWMs (Pulse Wide Modulation). A computer program was developed in C Sharp language to display the temperature over time measured by the sensors. The program also is used to adjust the constants K p , K i and K d of the controller and the temperature set point. The microcontroller firmware allows the system to operate in both open and closed loop modes. This work allows the student to learn in practice the control actions when the controller parameters are changed, contributing to improve the acknowledgment of Control Engineering.

Capacitive Impedance Measurement: Dual-frequency Approach.

Abstract: The most widely used technique for measuring capacitive impedances (or complex electrical permittivity) is to apply a frequency signal to the sensor and measure the amplitude and phase of the output signal. The technique, although efficient, involves high-speed circuits for phase measurement, especially when the medium under test has high conductivity. This paper presents a sensor to measure complex electrical permittivity based on an alternative approach to amplitude and phase measurement: The application of two distinct frequencies using a current-to-voltage converter circuit based in a transimpedance amplifier, and an 8-bit microcontroller. Since there is no need for phase measurement and the applied frequency is lower compared to the standard method, the circuit presents less complexity and cost than the traditional technique. The main advance presented in this work is the use of mathematical modeling of the frequency response of the circuit to make it possible for measuring the dielectric constant using a lower frequency than the higher cut-off frequency of the system, even when the medium under test has high conductivity (tested up to 1220 μS/cm). The proposed system caused a maximum error of 0.6% for the measurement of electrical conductivity and 2% for the relative dielectric constant, considering measurement ranges from 0 to 1220 μS/cm and from 1 to 80, respectively.

Design and Calibration of a Low-Cost SDI-12 Soil Moisture Sensor

Abstract: Water is the main limiting factor in agricultural production as well as a scarce resource that needs to be optimized. The measurement of soil water with sensors is an efficient way for optimal irrigation management. However, commercial sensors are still too expensive for most farmers. This paper presents the design, development and calibration of a new capacitive low-cost soil moisture sensor that incorporates SDI-12 communication, allowing one to select the calibration equation for different soils. The sensor was calibrated in three different soils and its variability and accuracy were evaluated. Lower but cost-compensated accuracy was observed in comparing it with commercial sensors. Field tests have demonstrated the temperature influence on the sensor and its capability to efficiently detect irrigation and rainfall events.

Review of soil salinity assessment for agriculture across multiple scales using proximal and/or remote sensors

Abstract: Mapping and monitoring soil spatial variability is particularly problematic for temporally and spatially dynamic properties such as soil salinity. The tools necessary to address this classic problem only reached maturity within the past 2 decades to enable field- to regional-scale salinity assessment of the root zone, including GPS, GIS, geophysical techniques involving proximal and remote sensors, and a greater understanding of apparent soil electrical conductivity (ECa) and multi- and hyper-spectral imagery. The concurrent development and application of these tools have made it possible to map soil salinity across multiple scales, which back in the 1980s was prohibitively expensive and impractical even at field scale. The combination of ECa-directed soil sampling and remote imagery has played a key role in mapping and monitoring soil salinity at large spatial extents with accuracy sufficient for applications ranging from field-scale site-specific management to statewide water allocation management to control salinity within irrigation districts. The objective of this paper is: (i) to present a review of the geophysical and remote imagery techniques used to assess soil salinity variability within the root zone from field to regional scales; (ii) to elucidate gaps in our knowledge and understanding of mapping soil salinity; and (iii) to synthesize existing knowledge to give new insight into the direction soil salinity mapping is heading to benefit policy makers, land resource managers, producers, agriculture consultants, extension specialists, and resource conservation field staff. The review covers the need and justification for mapping and monitoring salinity, basic concepts of soil salinity and its measurement, past geophysical and remote imagery research critical to salinity assessment, current approaches for mapping salinity at different scales, milestones in multi-scale salinity assessment, and future direction of field- to regional-scale salinity assessment.

A portable triboelectric spirometer for wireless pulmonary function monitoring.

Abstract: Coronavirus disease 2019 (COVID-19) as a severe acute respiratory syndrome infection has spread rapidly across the world since its emergence in 2019 and drastically altered our way of life. Patients who have recovered from COVID-19 may still face persisting respiratory damage from the virus, necessitating long-term supervision after discharge to closely assess pulmonary function during rehabilitation. Therefore, developing portable spirometers for pulmonary function tests is of great significance for convenient home-based monitoring during recovery. Here, we propose a wireless, portable pulmonary function monitor for rehabilitation care after COVID-19. It is composed of a breath-to-electrical (BTE) sensor, a signal processing circuit, and a Bluetooth communication unit. The BTE sensor, with a compact size and light weight of 2.5 cm3 and 1.8 g respectively, is capable of converting respiratory biomechanical motions into considerable electrical signals. The output signal stability is greater than 93% under 35%-81% humidity, which allows for ideal expiration airflow sensing. Through a wireless communication circuit system, the signals can be received by a mobile terminal and processed into important physiological parameters, such as forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC). The FEV1/FVC ratio is then calculated to further evaluate pulmonary function of testers. Through these measurement methods, the acquired pulmonary function parameters are shown to exhibit high accuracy (>97%) in comparison to a commercial spirometer. The practical design of the self-powered flow spirometer presents a low-cost and convenient method for pulmonary function monitoring during rehabilitation from COVID-19.

A review on polyvinylidene fluoride polymer based nanocomposites for energy storage applications

Abstract: Dielectric polymer nanocomposite materials with great energy density and efficiency look promising for a variety applications. This review presents the research on Poly (vinylidene fluoride) (PVDF) polymer and copolymer nanocomposites that are used in energy storage applications such as capacitors, supercapacitors, pulse power energy storage, electric vehicles, energy harvesting, etc. It mainly focuses on the electrical characteristics of the composite film materials with various types of filler. The electrical properties of the composite films have been explored including dielectric permittivity, dielectric loss, dielectric breakdown strength, energy density, and efficiency, as well as finite element analysis. Nanomaterials with surface modification can improve the electrical properties of the composites. Recently, compared to two-phase nanocomposites and three-phase nanocomposites, the multilayer nanocomposites with either combination of fillers and polymers aid to enhance electrical characteristics even more. The various materials used in supercapacitors are studied. It is observed that the usage of PVDF-based polymer composites in energy storage devices is very prospective, and future research into innovative polymer composites and ways to enhance their properties might be considerable.