This article presents an adaptive group-based sparse representation scheme for image reconstruction in electrical capacitance tomography. Compared to conventional sparsity-based methods, the proposed ...method can accurately recover the shape and location of abnormities by exploiting local self-similarity and the sparsity of the image in the form of group, consisting of a central block and neighboring local blocks. Each group can be represented by sparse coefficients and representation matrices obtained via adaptive self-learning from the current reconstructed image, leading to more sparsity and less computation. This scheme can be efficiently solved by the split Bregman iteration method, which can achieve accurate reconstruction within a few iterations. It has advantages in efficiently exploring the global sparsity and neighboring self-similarity in the reconstructed image simultaneously for enhanced image quality. Numerical simulations and phantom experiments were carried out to validate the proposed method. Results show that the proposed method can reconstruct more accurate images of abnormities of complex shapes than typical sparsity-based methods by consuming less computational resources. This is of great potential in fulfilling the high requirements on both the temporal and spatial resolutions in the imaging of dynamic processes, such as multiphase flows.
Planar electrical capacitance tomography (ECT) has broad application prospects in the defect detection of composite materials. The image reconstruction of planar ECT is a nonlinear and ill-posed ...inverse problem, which limits the accuracy of image reconstruction. An image reconstruction method based on the density-based spatial clustering of applications with noise cluster (DBSCAN) and self-adaptive alternating direction method of multipliers (SADMM) algorithms is proposed in this paper. Firstly, the characteristic capacitance values are extracted from the independent measurement capacitance values through the DBSCAN algorithm. Then, the original inverse problem is transformed into a set of local optimization sub-problems, and the SADMM algorithm with an adaptive penalty parameter is used to solve these subproblems to reconstruct the image. The experimental results show that the average relative error of the reconstructed images obtained by this algorithm is 0.086, which is significantly lower than other algorithms, the presented algorithm has higher anti-noise performance and can provide more accurate reconstructed images.
A complete smart capacitive sensor solution based on a microcontroller was developed. This approach includes the development of both the hardware and software. The hardware part comprises an 8-bit ...microcontroller equipped with two timers/counters and a three-gate stable RC relaxation oscillator. The software part handles system configuration, measurement control, communication control, and data processing. Hence, the microcontroller acts as a frequency meter with an adaptive measuring time, and the relaxation oscillator generates a square wave with a frequency depending on the value of the capacitance of the sensor. The paper also proposes a calibration method that reduces the measurement range to 1 pF. The experimentally proven relative measurement errors of sensor capacitance are less than 0.012% for values smaller than 12 pF, and less than 0.0084% for values from 12 pF to 300 pF.
Electrical capacitance tomography (ECT) and electrical resistance tomography (ERT) are promising techniques for multiphase flow imaging due to high-speed, low-cost, noninvasive, and visualization ...features. At present, ECT/ERT dual-mode imaging is generally accomplished by the combination of ECT and ERT sensors implemented through different electrode arrays, and with separate systems to collect the projection data, due to their different sensing principles. To expand different sensing ranges of ECT and ERT, a dual-mode tomography over a wide electrical sensing frequency band based on dual-frequency response is proposed in this article. A dual-frequency excitation/probing scheme is used to measure the capacitance and conductance of the fluid through one set of electrode arrays, to visualize the permittivity and conductivity distribution in the same pipe cross section. The frequency responses of different combinations of conductive, weakly conductive, and nonconductive substances were tested. Static and dynamic experimental tests were carried out. The experimental results in ECT and ERT are satisfactory, demonstrating the feasibility of the proposed ECT/ERT dual-mode technique.
This paper experimentally investigates the performance of three-phase voltage source pulsewidth modulation (PWM) converter, with the grid interfaced photovoltaic energy conversion system being the ...main application. In such applications the ground leakage current common mode current (CMC) should be much less than an ampere and this is difficult to obtain in transformerless (direct) connected systems. With the target being the reduction of the common mode voltage (CMV) and CMC, the converter performance is investigated thoroughly. Conventional PWM methods space vector PWM (SVPWM) and discontinuous PWM (DPWM) and recently developed reduced common mode voltage PWM (RCMV-PWM) methods active zero state PWM (AZSPWM) and near state PWM (NSPWM) are considered. The performance of a 1-kW rated PWM rectifier with additional common-mode capacitor emulating a PV system has been experimentally investigated. It is shown that the CMV and CMC of the tested RCMV-PWM methods is significantly less than conventional methods. In particular, NSPWM yields the best overall performance including low ground leakage current, low inverter output (phase current) and input (dc-link current) ripple, and low switching losses. Accounting for the parasitic capacitance effect, the resonant frequency of the common-mode circuit is identified and it is used in the converter design for the purpose of avoiding resonances involving large CMV-CMC. This paper aims help the design engineer select the appropriate PWM method for grid-connected applications and provides some design rules of thumb.
This paper presents a catheter-based capacitive force sensor interface for cardiovascular diagnosis. The force sensor is implemented on a flexible printed circuit board (FPCB) substrate with a ...force-sensitive polydimethylsiloxane (PDMS), and a force-induced change in a capacitance of the sensor is measured by a precision capacitive sensor interface. To recover the performance degradation caused by the large parasitic capacitance C P of a long catheter, we present a parasitic insensitive analog front-end (AFE) with active C P cancellation, which employs a charge amplifier and a negative capacitor at the virtual ground of the charge amplifier. The prototype sensor was measured with a force loader in whole blood. The proposed AFE successfully cancels C P of 348 pF in a 0.9-m-long sensor and measurement results show the SNR of 53.8 dB and the capacitance resolution of 16 aF, a 19.6 dB improvement by canceling nonideal effect of C P . This corresponds to a force resolution of 2.22 gf, which is 9.29× reduction compared to the work without the C P cancellation. The proposed sensor interface is insensitive to C P from hundreds to 1-nF level, and the force-dependent stiffness of two different tissues has been successfully distinguished with an ex-vivo experiment. The proposed sensor interface enables the integration of capacitive force sensors in a smart catheter.
A conventional electrical capacitance tomography (ECT) sensor consists of multiple rectangular electrodes in a single plane. To generate 3-D images, some researchers use an ECT sensor with multiplane ...rectangular electrodes and in-line arrangement of different electrode planes and measure the capacitance between the electrode pairs not only within the same plane but also between different planes. Because those electrode pairs in different planes are far away from each other, the measured capacitance signals between them are weak and, hence, are easily affected by noise, resulting in the obvious disturbance on the measured signals and, hence, low image quality. To address those problems, the 3-D ECT sensors with different arrangements and different shapes of electrodes are studied to investigate the effect of different arrangements and different shapes of electrodes on the measured capacitance signals and the image quality. Four 3-D ECT sensors are made with different arrangements or shapes of electrodes: rectangular electrodes are in line arrangement, whereas diamond, circular, and hexagon electrodes are staggered arrangement. The performance of the four 3-D ECT sensors is compared. The results show that 3-D ECT sensors with staggered electrodes can decrease the disturbance on the measured signals and improve the image quality of static models compared with that with conventional rectangular electrodes. Among the three 3-D ECT sensors with staggered electrodes, the 3-D ECT sensor with hexagonal electrodes has superior performance to the other two 3-D ECT sensors with diamond and circular electrodes. It was used to measure moving objects and a fluidized bed.
Fabrication of unconventional energy storage devices with high stretchability and performance is challenging, but critical to practical operations of fully power-independent stretchable electronics. ...While supercapacitors represent a promising candidate for unconventional energy-storage devices, existing stretchable supercapacitors are limited by their low stretchability, complicated fabrication process, and high cost. Here, we report a simple and low-cost method to fabricate extremely stretchable and high-performance electrodes for supercapacitors based on new crumpled-graphene papers. Electrolyte-mediated-graphene paper bonded on a compliant substrate can be crumpled into self-organized patterns by harnessing mechanical instabilities in the graphene paper. As the substrate is stretched, the crumpled patterns unfold, maintaining high reliability of the graphene paper under multiple cycles of large deformation. Supercapacitor electrodes based on the crumpled graphene papers exhibit a unique combination of high stretchability (e.g., linear strain ~300%, areal strain ~800%), high electrochemical performance (e.g., specific capacitance ~196 F g(-1)), and high reliability (e.g., over 1000 stretch/relax cycles). An all-solid-state supercapacitor capable of large deformation is further fabricated to demonstrate practical applications of the crumpled-graphene-paper electrodes. Our method and design open a wide range of opportunities for manufacturing future energy-storage devices with desired deformability together with high performance.
To reduce the power consumption in scaled CMOS integrated circuits, transistors operating at low supply voltage with steep subthreshold swing (SS) are highly desirable. The negative capacitance (NC) ...effect in ferroelectric materials has emerged as a possible solution for achieving steep SS in transistors. In order to effectively leverage this effect in device applications, a proper understanding of its time-dependent nature is crucial. Here, we demonstrate that the NC effect occurs within a time window which is bounded by the switching time of ferroelectric domains at the faster time limit and screening charge compensation time of polarization at the slower time limit. We study this temporal dynamics of NC effect both by performing the transient measurements of metal-ferroelectric hafnium zirconium oxide-insulator-semiconductor capacitor connected in series with a load resistor and by characterizing NC field-effect transistors (NCFETs) at different time scales. Our experimental results provide deeper insight into the understanding of NC effect, reveal the time dependent switching nature of NCFETs, and pave way for the advancement of steep-slope transistors technology.
In this work, the time-delay effect on device operation caused by capacitance is studied in terms of phase-change memory (PCM) integrated with an ovonic threshold switch (OTS) selector. The ...capacitance studied in this work is the intrinsic capacitance associated with capacitive reactance of the PCM itself. The capacitance of the PCM in the amorphous state was measured, and it presents an exponential dependence on voltage bias. Through the simulation model of an OTS-PCM integrated device that considering the measured capacitance behavior, the time-delay characteristics of the integrated device for the SET process with various pulses were investigated. Results indicate that the onset of the threshold switching (TS) is delayed in the PCM but occurs early in the OTS with capacitance in the integrated device. In addition, it is found that the variable capacitance behavior can not only minimize the delay effect, but also accelerate the SET operation under certain conditions in the integrated device. Our results can provide practical guidance for the design of fast operating devices.
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