C4D Sensor Research Articles

Numerical calculation and analysis of a novel complex impedance sensing approach for in-flow droplet detection utilizing the C4D technique

This study proposed a C4D sensor structure with a novel approach utilizing the complex impedance analysis method, which includes both resistance and reactance analysis. The complex impedance analysis method provides additional information to characterize the electrical properties of solutions and strange objects moving in the fluidic channel, thus enhancing the sensitivity of conventional C4D structure. In addition, the effects of the fluidic properties, object size, excitation frequency, and sensor geometry on the performance of the proposed C4D sensor were investigated. The proposed sensor system used the finite element method analysis to investigate the performance of the proposed method. The simulation results show that the largest resistance change is approximately 27 kΩ while the largest reactance change is about 10 kΩ according to the passage of a 400 μm radius oil droplet over the sensing area in the NaCl solution channel. Furthermore, this work indirectly verifies the possibility and feasibility of the proposed impedance analysis method by utilizing the conventional C4D structure thanks to its advantages and lays a good foundation for future research work.

A Low Excitation Working Frequency Capacitively Coupled Contactless Conductivity Detection (C4D) Sensor for Microfluidic Devices.

In this work, a new capacitively coupled contactless conductivity detection (C4D) sensor for microfluidic devices is developed. By introducing an LC circuit, the working frequency of the new C4D sensor can be lowered by the adjustments of the inductor and the capacitance of the LC circuit. The limits of detection (LODs) of the new C4D sensor for conductivity/ion concentration measurement can be improved. Conductivity measurement experiments with KCl solutions were carried out in microfluidic devices (500 µm × 50 µm). The experimental results indicate that the developed C4D sensor can realize the conductivity measurement with low working frequency (less than 50 kHz). The LOD of the C4D sensor for conductivity measurement is estimated to be 2.2 µS/cm. Furthermore, to show the effectiveness of the new C4D sensor for the concentration measurement of other ions (solutions), SO42− and Li+ ion concentration measurement experiments were also carried out at a working frequency of 29.70 kHz. The experimental results show that at low concentrations, the input-output characteristics of the C4D sensor for SO42− and Li+ ion concentration measurement show good linearity with the LODs estimated to be 8.2 µM and 19.0 µM, respectively.

Investigation of the Effects of Electrode Geometry on the Performance of C4D Sensor with Radial Configuration.

Electrodes are basic components of C4D (capacitively coupled contactless conductivity detection) sensors, and different electrode structures (the configuration pattern or the electrode geometry) can lead to different measurement results. In this work, the effects of electrode geometry of radial configuration on the measurement performance of C4D sensors are investigated. Two geometrical parameters, the electrode length and the electrode angle, are considered. A FEM (finite element method) model based on the C4D method is developed. With the FEM model, corresponding simulation results of conductivity measurement with different electrode geometry are obtained. Meanwhile, practical experiments of conductivity measurement are also conducted. According to the simulation results and experimental results, the optimal electrode geometry of the C4D sensor with radial configuration is discussed and proposed. The recommended electrode length is 5–10 times of the pipe inner diameter and the recommended electrode angle is 120–160°.

New method for bubble/slug velocity measurement in small channels.

Based on the C4D technique and cross correlation velocity measurement technique, a new method for bubble/slug velocity measurement of the gas-liquid two-phase flow in small channels is proposed. A new C4D sensor, which is suitable for the parameter measurement of the gas-liquid two-phase flow in small channels, is developed by introducing the principle of capacitive reactance elimination. With two new C4D sensors, a bubble/slug velocity measurement system is developed, and the bubble/slug velocity is determined by the cross correlation velocity measurement technique. To verify the effectiveness of the proposed bubble/slug velocity measurement method, three prototypes of bubble/slug velocity measurement systems with different diameters (1.82 mm, 2.65 mm, and 2.96 mm, respectively) were established, and the bubble/slug measurement experiments were carried out. The research results show that the capacitive reactance elimination is an effective way to overcome the unfavorable influence of the coupled capacitances on measurement results. The experimental results indicate that the proposed method can successfully realize the bubble/slug velocity measurement in small channels, and the velocity measurement accuracy is satisfactory. For the three prototypes of the bubble/slug velocity measurement system, the maximum relative errors of the bubble/slug velocity measurement are all less than 5%.

Contactless conductivity sensor employing moist paper as absorbent for in-situ detection of generated carbon dioxide gas

This work presents an unconventional use of capacitively coupled contactless conductivity detector (C4D) for detection of gas absorption by moist paper with potential application for chemical analysis. To be suitable for measuring conductivity of moist paper absorbent, the C4D sensor was therefore designed in planar configuration. A layer of dry filter paper, only 20 mm × 25 mm in size, was placed on the C4D sensor and the device installed inside a specifically designed vaporization chamber. A vial (16 mm i.d., 8 mm high) containing a 150-μL solution of sodium bicarbonate was placed alongside. The filter paper was loaded with 110 μL of deionized water through an injection hole in the cover lid. A 100-μL aliquot of 2 M hydrochloric acid solution was directly dispensed into the vial through a second hole in the lid to generate CO2 gas from the bicarbonate solution. It was observed that the C4D sensor gave real-time response that corresponded to the absorption of the gas and subsequent production of H+ and HCO3− in the moist paper. The monitored signal reached a constant value at 160 s after the addition of the acid. Chemistry of the absorption process and equivalent circuit for the C4D are proposed. Direct measurement of cement powder was chosen to demonstrate the potential use of this device for quantifying the CaCO3 content of the cement. The calibration curve for 0.5–3 mg CaCO3 was linear for signals recorded at 160 s: Vdc = (0.172 ± 0.005) · (mg CaCO3) + (0.016 ± 0.009), with coefficient of determination of 0.9965. Linear calibrations were also observed when the signals were monitored at various time less than 160 s. The limit of quantitation (3 SD of intercept/slope) was 0.17 mg CaCO3. The method provided acceptable precision with %RSD of 4.6 (2 mg CaCO3, n = 10).

Measuring Method of Solid-Liquid Two-Phase Flow in Slurry Pipeline for Deep-Sea Mining

In order to reduce the influence of fluid noise on the measurement of solid-liquid two-phase flow in slurry pipeline for deep-sea mining, the technique of virtual inductance is introduced to traditional capacitively coupled contactless conductivity detection (C4D), a measuring method for solid-liquid two-phase flow based on differential C4D is proposed, and the structure of differential C4D based on three electrodes is designed. The measuring device was verified in conductive fluid channels at different salinity. The results demonstrated that the amplitude of output voltage of the measuring device decreased obviously with the increase of the salinity of the fluid, and linearly associated with the size and volume concentration of the polymetallic nodules. Virtual inductance could reduce the requirement of C4D sensor for the excitation power. The measuring device had less noise of output signal and high accuracy. When the KCl solution containing salinity is at the average salinity of seawater 3.5% and the particle size of polymetallic nodules is from 0 to 25 mm, the output voltage increased from 0 to 87 mv. The maximum relative error in two-phase flow velocity measurement is 5.2%, which showed that the measuring method for two-phase flow in the slurry pipeline based on the differential C4D is effective.

Study on the application of simulated inductor technique to the design of C4D sensor

This work focuses on the study of the application of simulated inductor technique to the design of C4D sensor. A grounded simulated inductor, which is on the basis of the classic Riordan simulated inductor, is designed. With the grounded simulated inductor, two kinds of C4D sensors based on series resonance principle are developed. One is the new C4D sensor A, which implements the conductivity measurement by the current-to-voltage conversion. The other is the new C4D sensor B, which implements the conductivity measurement by the measurement of the differential voltage. Conductivity experiments were carried out in four pipes with inner diameters of 2.2mm, 3.0mm, 4.6mm and 6.4mm. The experimental results show that the designs of the grounded simulated inductor and the two kinds of new C4D sensors are successful. The experimental results also indicate that the sensitivity and the input-output characteristic of the C4D sensor A are better than that of the C4D sensor B. Besides, compared with a practical inductor, the grounded simulated inductor has a comparable performance and has the advantage of adjustable equivalent inductance. The research results obtained in this work can provide a useful reference for the further study of C4D sensor.

A New Contactless Method for Velocity Measurement of Bubble and Slug in Millimeter-Scale Pipelines

Combining C4D technique and cross-correlation velocity measurement technique, a new measurement method, which is suitable for the bubble/slug velocity measurement in millimeter-scale pipelines, is proposed. Based on the series resonance principle and the simulated inductor technique, a new C4D sensor is developed. With two conductance signals obtained by two new C4D sensors (the upstream sensor and the downstream sensor), the bubble/slug velocity measurement is implemented by the cross-correlation velocity measurement technique. Experiments are carried out in three pipelines with different inner diameters of 4.50, 5.46, and 6.44 mm, respectively. The experimental results show that the proposed bubble/slug velocity measurement method is effective, the development of the new C4D sensor is successful, and the velocity measurement accuracy is satisfactory. The relative error of bubble velocity measurement is less than 5.41% and the relative error of slug flow velocity measurement is less than 4.90%.

New C4D Sensor with a Simulated Inductor.

A new capacitively coupled contactless conductivity detection (C4D) sensor with an improved simulated inductor is developed in this work. The improved simulated inductor is designed on the basis of the Riordan-type floating simulated inductor. With the improved simulated inductor, the negative influence of the coupling capacitances is overcome and the conductivity measurement is implemented by the series resonance principle. The conductivity measurement experiments are carried out in three pipes with different inner diameters of 3.0 mm, 4.6 mm and 6.4 mm, respectively. The experimental results show that the designs of the new C4D sensor and the improved simulated inductor are successful. The maximum relative error of the conductivity measurement is less than 5%. Compared with the C4D sensors using practical inductors, the measurement accuracy of the new C4D sensor is comparable. The research results also indicate that the adjustability of a simulated inductor can reduce the requirement for the AC source and guarantee the interchangeableness. Meanwhile, it is recommended that making the potential of one terminal of a simulated inductor stable is beneficial to the running stability. Furthermore, this work indirectly verifies the possibility and feasibility of the miniaturization of the C4D sensor by using the simulated inductor technique and lays a good foundation for future research work.

An improved capacitively coupled contactless conductivity detection sensor for industrial applications

To bring the potential power of the capacitively coupled contactless conductivity detection (C4D) technique to full play and extend the application fields of C4D, our previous work has developed a C4D sensor which is suitable for conductivity detection of electrolyte solution in industrial fields (Sensors and Actuators A 213 (2014) 1–8). With the introduction of series resonance principle, the C4D sensor can overcome the influence of coupling capacitances on conductivity measurement. By a specific design of shield configuration, the C4D sensor can overcome the influence of stray capacitances and the environment interference in industrial fields. Although the measurement performance of the C4D sensor is satisfactory and it is suitable for the conductivity detection in industrial fields, the input–output characteristic of the C4D sensor is non-monotonic, which may limit the practical applications of the C4D sensor.To overcome this drawback, an improved C4D sensor for conductivity detection in industrial fields has been developed. The basic conductivity measurement method (the series resonance principle) and the shield configuration of the improved C4D sensor are the same as those of the C4D sensor in our previous work. However, the measurement circuit of the detection path of the improved C4D sensor has been optimized. The one-inductor design has been replaced by a two-inductor design. With this optimization, the input–output characteristic of the improved C4D sensor is theoretically monotonic. Conductivity measurement experiments were carried out on four pipes with inner diameters of 1.8mm, 3.3mm, 5.0mm and 7.6mm, respectively. The experimental results indicate that the development of the improved C4D sensor is successful. In comparison with the previous C4D sensor, the measurement accuracy of the improved C4D sensor is comparable. But, the improved C4D sensor has the advantages of the monotonic input–output characteristic and the convenience for practical conductivity detection in industrial fields. Meanwhile, it is found that the input–output characteristic of the improved C4D sensor is nonlinear and the sensitivity of the improved C4D sensor decreases with the increase of conductivity.

Differential C4D sensor for conductive and non-conductive fluidic channel

This paper presents a novel design of a differential C4D (DC4D) sensor based on three electrodes for both conductive and non-conductive fluidic channel. This structure consists of two single C4D with an applied carrier sinusoidal signal to the center electrode as the excitation electrode. The electrodes are directly bonded on the PCB with built-in differential amplifier and signal processing circuit in order to reduce the parasitic component and common noise. In the non-conductive fluidic channel, the output voltage and capacitance changes 214.39 mV and 14 fF, respectively when a 3.83 μl tin particle crosses an oil channel. In conductive fluidic channel, the output voltage and admittance change up to 300 mV and 0.07 μS for the movement of a 4.88 μl plastic particle through channel. Moreover, the voltage change of this sensor is linear relation with the volume of investigated particle. This sensor also allows measuring velocity of particle inside fluidic channel and resistivity of the conductive fluidic.

Voidage measurement of gas–liquid two-phase flow based on Capacitively Coupled Contactless Conductivity Detection

Based on Capacitively Coupled Contactless Conductivity Detection (C4D) technique, a new method for the voidage measurement of conductive gas–liquid two-phase flow is proposed. 15 Conductance signals, which reflect voidage distribution of gas–liquid two-phase flow, are obtained by a six-electrode C4D sensor. With the conductance signals, the flow pattern of gas–liquid two-phase flow is identified by flow pattern classifiers and then the voidage measurement is implemented by a corresponding voidage measurement model (for each typical flow pattern, a corresponding voidage measurement model is developed). The conductance measurement of the six-electrode C4D sensor is implemented by phase sensitivity demodulation (PSD) method. The flow pattern classifiers and the voidage measurement models are developed by partial least squares (PLS) technique and least squares support vector machine (LS-SVM) technique. Static voidage measurement experiments and dynamic voidage measurement experiments show that the proposed voidage measurement method is effective, the developed six-electrode C4D sensor is successful and the measurement accuracy is satisfactory.

A new method for void fraction measurement of gas–liquid two-phase flow in millimeter-scale pipe

This work attempts to investigate the feasibility and potential of Capacitively Coupled Contactless Conductivity Detection (C4D) technique in the void fraction measurement of gas–liquid two-phase flow in millimeter-scale pipe and hence to propose a new void fraction measurement method based on C4D technique. A new C4D sensor is developed and a void fraction measurement system is constructed. As a preliminary study, the research work is focused on the void fraction measurement of two typical flow patterns (bubble flow and slug flow) in millimeter-scale horizontal pipe. The relationship between the conductance value and the void fraction is investigated. It is found that there is obvious linear relationship between the conductance value and the void fraction and flow pattern has significant influence on void fraction measurement. To overcome the influence of flow pattern, different void fraction measurement models are developed for different flow patterns. In the practical void fraction measurement process, flow pattern is firstly identified, then a corresponding void fraction measurement model is selected, and finally the void fraction measurement is implemented with the selected model and the conductance measurement obtained by the new C4D sensor. Void fraction measurement experiments are carried out (the inner diameters of the pipes are 2.8mm, 3.9mm, 5.3mm and 7.0mm, respectively). The experiment results show that the application of C4D technique to the void fraction measurement of gas–liquid two-phase flow in millimeter-scale pipe is feasible. The proposed void fraction measurement method is effective and the measurement performance is satisfactory (the maximum absolute error of void fraction measurement is less than 7%). The research results also indicate that C4D technique may have a broad application prospective and potential in the research field of two-phase flow.

Design and implementation of an industrial C4D sensor for conductivity detection

A capacitively coupled contactless conductivity detection (C4D) sensor suitable for conductivity detection of electrolyte solution in industrial fields is developed. Series resonance principle is adopted to remove the influence of coupling capacitances and hence to implement the conductivity detection in large pipelines. A special shield configuration is designed to eliminate the influence of the stray capacitance, to overcome the negative influence of the interference in industrial fields and to be suitable for the metal connection in industrial fields. Conductivity detection experiments were carried out on four different sized pipes with inner diameters of 1.8mm, 3.3mm, 5.0mm and 7.6mm, respectively. The experiment results show that the C4D sensor for industrial application is successful and the accuracy of conductivity detection is satisfactory. Discussions concerning the advantages and disadvantages of the C4D sensor are presented.

Capacitively coupled electrolyte-conductivity sensor based on high-k material of barium strontium titanate

A miniaturized capacitively coupled contactless conductivity detection (C4D) sensor based on high-k perovskite oxide of barium strontium titanate (BST) has been implemented for the first time. The BST films (∼120nm thick) of Ba0.25Sr0.75TiO3 composition were prepared on a p-Si-SiO2-Pt structure by pulsed laser deposition technique using BST targets fabricated by the self-propagating high-temperature synthesis method. The Pt electrodes were buried into the SiO2 layer to obtain a planar structure. For comparison, contact-mode electrolyte-conductivity (EC) sensors without the protective BST layer were also fabricated. To study the influence of the protective BST layer, both sensors were characterized in electrolyte solutions with various conductivities using two- and four-electrode operation modes. The impedance spectra were recorded in a frequency range from 1Hz to 1MHz. An equivalent circuit of the C4D sensor is discussed as well.Both, the EC and C4D sensor, demonstrate nearly identical sensor characteristics. The obtained results clearly show the benefits of the use of the BST-based C4D sensor in a four-electrode configuration for contactless conductivity measurements. A linear dependence between the measured conductance and the electrolyte conductivity is obtained in a wide range of electrolyte conductivity from 0.3mS/cm to 50mS/cm. Moreover, typical problems associated with contact-mode EC detection such as the effect of possible redox processes, contamination and fouling of electrodes during continuous measurements can be minimized, thus, enhancing the life-time of conductivity sensors considerably.

A New Method for Flow Rate Measurement in Millimeter-Scale Pipes

Combining the Capacitively Coupled Contactless Conductivity Detection (C4D) technique and the principle of cross correlation flow measurement, a new method for flow rate measurement in millimeter-scale pipes was proposed. The research work included two parts. First, a new five-electrode C4D sensor was developed. Second, with two conductivity signals obtained by the developed sensor, the flow rate measurement was implemented by using the principle of cross correlation flow measurement. The experimental results showed that the proposed flow rate measurement method was effective, the developed five-electrode C4D sensor was successful, and the measurement accuracy was satisfactory. In five millimeter-scale pipes with different inner diameters of 0.5, 0.8, 1.8, 3.0 and 3.9 mm respectively, the maximum relative difference of the flow rate measurement between the reference flow rate and the measured flow rate was less than 5%.

Measurement of bubble velocity using Capacitively Coupled Contactless Conductivity Detection (C4D) technique

The feasibility of applying Capacitively Coupled Contactless Conductivity Detection (C4D) technique to measurement of bubble velocity in gas–liquid two-phase flow in millimeter-scale pipe is investigated. And, a new method, which combines the C4D technique and the principle of cross-correlation velocity measurement, is proposed for the measurement of bubble velocity. This research includes two parts. First, based on the principle of C4D, a new five-electrode C4D sensor is developed. Then, with two conductivity signals obtained by the C4D sensor, the velocity measurement of bubble is implemented according to the principle of cross-correlation. The research results indicate that the C4D technique is highly effective and anticipates a broad potential in the field of two-phase flow. Experimental results show that the five-electrode C4D sensor is suitable for measuring the velocity of single bubbles with a relative error of less than 5%.

Design of capacitively coupled contactless conductivity detection sensor

As a newly developing measurement technique, capacitively coupled contactless conductivity detection (C4D) is mainly studied and used in the research field of Analytical Chemistry for ion concentration/conductivity detection in a capillary. To expand the application fields of C4D, in this work, a new C4D sensor which is suitable for conductivity detection in a millimeter scale pipe is developed. With the introductions of series resonance principle and a new shield configuration (the single-shield configuration), the negative influences of coupling capacitances and stray capacitances on the conductivity measurement are significantly reduced and the performance of the developed C4D sensor is improved. Experimental results show that the developed C4D sensor is successful and its accuracy is satisfactory. Compared with the conventional C4D sensors, the developed C4D sensor can effectively implement conductivity measurement in larger scale pipes (up to 7.8 mm i.d.) and has the advantages of wider detection range and higher detection resolution.

Application of C<sup>4</sup>D Technique to Void Fraction Measurement of Gas-Liquid Two-Phase Flow: Stratified Flow

The feasibility of applying C4D technique to void fraction measurement of gas-liquid two-phase flow is investigated in this paper. As a preliminary research, void fraction measurement under stratified flow is studied. Conductance of two-phase fluid are obtained by a new C4D sensor, and then used to measure the void fraction in 15mm i.d. pipe. An empirical correlation between void fraction and normalized conductance is developed. Thus, the void fraction can be determined by this empirical correlation with the obtained conductance. The experiment results show that applying C4D technique to the void fraction measurement of gas-liquid two-phase flow is feasible. The measurement results of void fraction are satisfactory, and the maximum absolute error of void fraction is less than 0.03.