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Journal ArticleDOI

Capacitive Impedance Measurement: Dual-frequency Approach.

04 Jun 2019-Sensors (Multidisciplinary Digital Publishing Institute)-Vol. 19, Iss: 11, pp 2539
TL;DR: 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.
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.

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Citations
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Journal ArticleDOI
06 Dec 2020
TL;DR: It is obvious that fully printed sensor elements based on cheap and environmentally friendly carbon layers printed on the wood substrate can compete with conventionally made sensors based on copper.
Abstract: Digitization of industrial processes using new technologies (IoT—Internet of Things, IoE—Internet of Everything), including the agriculture industry, are globally gaining growing interest. The precise management of production inputs is essential for many agricultural companies because limited or expensive sources of water and nutrients could make sustainable production difficult. For these reasons, precise data from fields, plants, and greenhouses have become more important for decision making and for the proper dosage of water and nutrients. On the market are a variety of sensors for monitoring environmental parameters within a precise agricultural area. However, the high price, data storage/transfer functionality are limiting so cost-effective products capable to transfer data directly to farmers via wireless IoT networks are required. Within a given scope, low-price sensor elements with an appropriate level of sensor response are required. In the presented paper, we have developed fully printed sensor elements and a dedicated measuring/communicating unit for IoT monitoring of soil moisture. Various fabrication printing techniques and a variety of materials were used. From the performed study, it is obvious that fully printed sensor elements based on cheap and environmentally friendly carbon layers printed on the wood substrate can compete with conventionally made sensors based on copper.

12 citations

Journal ArticleDOI
TL;DR: The reduction of porosity of samples significantly improves the dielectric parameters (relative dielectrics 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.
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.

11 citations


Cites background from "Capacitive Impedance Measurement: D..."

  • ...The impedance meter imposes an electromagnetic wave, at a given frequency, and analyzes the reflected wave to obtain the dielectric parameters [27,28]....

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Journal ArticleDOI
TL;DR: In this paper, a new time-domain measurement method for determining the capacitance and resistance values of lossy relative humidity capacitive sensors is presented based on a direct sensor-to-microcontroller interface for microcontrollers with internal analog comparators and timers.

11 citations

Journal ArticleDOI
TL;DR: In this article , the effect of Baculovirus infection on one of its host cells (Sf9 cells) through many electrical features such as capacitance, impedance, permittivity, and conductivity was characterized.
Abstract: Traditional biosensors are costly, cumbersome, and take a long time to report results, which limit their use in resource-constrained areas. Due to its high integration, customized architecture, and ease of mass processing, biosensors have been widely used in biomedical applications in recent years. In this paper, a biosensor is implemented using flexible printed circuit board technology for monitoring and identifying the effect of Baculovirus infection on one of its host cells (Sf9 cells) through many electrical features such as capacitance, impedance, permittivity, and conductivity. Furthermore, the effect of viral infection with different particle concentrations at different times was characterized. The results proved that the virus has a rapid effect on the cell by losing its electrical properties, which were clear from the decrease in electrical properties (e.g., capacitance, impedance, permittivity, and conductivity). Moreover, we introduced an equivalent model to represent the normal cells and infected cells based on the experimental results obtained for capacitance values. The proposed model simulation results are matched with the results obtained experimentally, which leads to the use of the model for predicting baculovirus infection.

5 citations

Journal ArticleDOI
TL;DR: In this article, the capacitive method was used to determine the dielectric constant of the iron ore located between the sensor electrodes and, consequently, the moisture in a conveyor belt.
Abstract: Water content or moisture of materials is a parameter widely used in the industry. In mining, it is an important variable to control in iron ore production. High moistures may cause instability of iron ore piles and may make transport by ship unfeasible. Therefore, this paper presents the development of a system for measuring iron ore moisture on a conveyor belt (laboratory-scale). The structure that supports the sensor has two degrees of freedom, which allow perpendicular and parallel movements. The parallel movement makes the relative velocity between the measurement cell and the ore almost zero. The vertical movement allows the sensor to be placed at different depths in the ore. These sets enable real-time and in situ measurements. The system uses the capacitive method to determine the dielectric constant of the iron ore located between the sensor electrodes and, consequently, the moisture. This system has a measuring range of 0 to 14% on a dry basis and presents an uncertainty up to 0.07 percentage points for a 2-standard-deviation confidence level. In the validation process, the absolute error was less than 0.34 percentage point in the mining interest range of 6 to 14%. The founded results achieve a significant advance in the development of real-time equipment for measuring ore moisture since there is no device capable of doing it with the necessary level of accuracy and precision. For mining, this kind of system represents a big step to take corrective and preventive decisions around iron ore moisture control.

3 citations

References
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Journal ArticleDOI
TL;DR: An automated irrigation system developed to optimize water use for agricultural crops has the potential to be useful in water limited geographically isolated areas.
Abstract: An automated irrigation system was developed to optimize water use for agricultural crops. The system has a distributed wireless network of soil-moisture and temperature sensors placed in the root zone of the plants. In addition, a gateway unit handles sensor information, triggers actuators, and transmits data to a web application. An algorithm was developed with threshold values of temperature and soil moisture that was programmed into a microcontroller-based gateway to control water quantity. The system was powered by photovoltaic panels and had a duplex communication link based on a cellular-Internet interface that allowed for data inspection and irrigation scheduling to be programmed through a web page. The automated system was tested in a sage crop field for 136 days and water savings of up to 90% compared with traditional irrigation practices of the agricultural zone were achieved. Three replicas of the automated system have been used successfully in other places for 18 months. Because of its energy autonomy and low cost, the system has the potential to be useful in water limited geographically isolated areas.

591 citations

Journal ArticleDOI
TL;DR: In this article, a low-cost soil water content sensor (ECH2O probe model EC-5, Decagon Devices Inc., Pullman, WA) using laboratory as well as field experiments was evaluated.

336 citations

Journal ArticleDOI
TL;DR: In this article, a simplified impedance measuring system is used to determine soil water content, which can be used in field data loggers to calculate the soil water volumetric fraction.

296 citations

Journal ArticleDOI
TL;DR: In this article, a series of laboratory experiments were performed in order to systematically explore the dielectric response of soils to a frequency range of 1 to 50 MHz, and the authors found that the real and imaginary components of soil dielectrics vary with the amount of moisture in the soil.
Abstract: A series of laboratory experiments were performed in order to systematically explore the dielectric response of soils to a frequency range of 1 to 50 MHz. A network analyzer and a coaxial-transmission-line type of dielectric probe were used to measure the complex (both real and imaginary) dielectric response of moist soils. The dielectric probe was placed in a modified Tempe cell in which the moisture content of the soil under investigation could be varied. Both the real and imaginary components of the dielectric permittivity of the moist soils investigated are greatest at 1 MHz and monotonically decrease with frequency. The variation in the dielectric constant among these soils is also greatest at 1 MHz and decreases with increasing frequency. The soils that have a large imaginary dielectric constant also have the largest real dielectric constant dispersion. The loss tangent for a given soil is relatively independent of moisture content over a wide range of soil moisture conditions. At low water contents, both the real and imaginary dielectric values begin to drop rapidly with decreasing water content. There is a significant temperature dependence present in the dielectric response of moist soils, which changes markedly with frequency. Ionic conductivity is the predominant mechanism causing the imaginary dielectric response and can account for many features of the observed dielectric response. A Looyenga-type mixing model incorporating ionic conductivity can account for the frequency dependence of the dielectric constant of soils

295 citations

Journal ArticleDOI
01 Jan 1999
TL;DR: In this article, the authors presented a highly sensitive AC-based capacitance measuring circuit, which has been specially designed for this purpose, and a PC-based ECT system with this circuit.
Abstract: Electrical capacitance tomography (ECT) is a new technology that is used to visualise the internal behaviour of industrial processes comprising dielectric components. A particular difficulty with capacitance measurement for tomography is that the stray capacitance to earth of an ECT sensor is large (/spl sim/150 pF) compared with the interelectrode capacitance to be measured (usually <0.5 pF), and the measurement range is wide (0.01-2 pF). The authors present a highly sensitive AC-based capacitance measuring circuit, which has been specially designed for this purpose, and a PC-based ECT system with this circuit. Experimental results show that this ECT system can measure as small as 0.01 pF capacitance with 0.0002 pF error, and could collect tomographic image data at more than 100 frames per second.

270 citations