Capacitive Detection Research Articles

Design of analog front-end integrated circuit of tactile sensor for human-machine interface

—In this paper, a highly integrated analog front-end chip for sensor data acquisition and readout is designed, which is applied to a pressure-to-capacitance-conversion 16 × 16 tactile sensor array. In this design, a 16-channel capacitance-to-digital converter using a combination of op-amp-based Capacitance-Voltage Converter (CVC) and column-parallel Single-Slope Analog-to-Digital Converter (SS ADC) converters has been implemented, increasing the readout speed of the sensor array and saving the chip area. In addition, a sequence of scanning circuit suitable for the 16 × 16 array is proposed, so that the CVC and column-parallel SS ADCs are in a pipelined working mode, which further improves the speed of data conversion and readout. The integrated circuit (IC) is designed and taped out in a 0.18-μm CMOS process technology. The measurement results show that the chip can reach the capacitance detection range from 1 pF to 9.1 pF, and it achieves a detection accuracy of 9 fF under 10-bit ADC quantization. Under the clock frequency of 64 MHz, the refresh rate of the entire array is 3906 fps, and the overall power consumption of the front-end IC is 7.5 mW.

Design of a fast and low-noise front-end electronics developed for the measurements of low- and medium-energy charged particles in space plasma environments.

A fast and low-noise front-end electronics for amplifying and filtering the signal generated by a silicon detector has been designed, simulated, developed, and characterized as the main part of the detection chain for an instrument devoted to the measurements of low- and medium-energy charged particles in space plasma environments. The targeted low energy threshold is 10keV with a 10% resolution. The simulated performances of the developed electronics reach a gain bandwidth of up to 16.1GHz, a noise level at the input of 0.96 nV/Hz-1/2, and an equivalent noise charge of 4.62keV. The experimental measurements with injection testing show resolution below 5keV and a low threshold of 31.46keV. Radioactive testing shows a resolution of 30.9keV because the detector capacitance is larger than expected (21 vs 10 pF). A good agreement between simulation with a 21 pF detector capacitance and experimental measurement is achieved within 18%.

Study on driving noise of quartz flexible accelerometer torquer

The distributed capacitance inside the quartz flexible accelerometer (QFA) coupled the high frequency voltage excitation signal in the differential capacitance detection circuit to the torquer coil, and superimposes the torquer driving current to form the driving noise. In this study, the values of the distributed capacitance inside the QFA were simulated. According to the formation mechanism of the QFA driving noise, the equivalent circuit model of the driving noise is established, and the driving noise characteristics of the detection circuit with single excitation and double excitation source are analyzed. The theoretical and experimental results show that the electric field coupled driving noise transmission system is a first-order system with high-pass characteristics. The driving noise of the single excitation detection circuit is larger than that of the dual excitation detection circuit (DEDC), and the DEDC can reduce the driving noise by 39.77% when the QFA shell is grounded. The equivalent acceleration of the electric field coupled driving noise is between tens of μg to hundreds of mg, which is one of the important noise sources that affect the measurement accuracy of the QFA. A measure was proposed to suppress the high-frequency driving noise by adding a low-pass filter after the sampling output of the driving current, which can reduce the driving noise to 1.85 μg and effectively reduce the influence of the driving noise on the measurement accuracy of the QFA.

Design and Experiment of Capacitive Rice Online Moisture Detection Device.

To solve the problems of poor stability and low monitoring precision in the online detection of rice moisture in the drying tower, we designed an online detection device for rice moisture at the outlet of the drying tower. The structure of a tri-plate capacitor was adopted, and the electrostatic field of the tri-plate capacitor was simulated using COMSOL software. A central composite design of three factors and five levels was carried out with the thickness, spacing, and area of the plates as the influencing factors and the capacitance-specific sensitivity as the test index. This device was composed of a dynamic acquisition device and a detection system. The dynamic sampling device was found to achieve dynamic continuous sampling and static intermittent measurements of rice using a ten-shaped leaf plate structure. The hardware circuit of the inspection system with STM32F407ZGT6 as the main control chip was designed to realize stable communication between the master and slave computers. Additionally, an optimized BP neural network prediction model based on the genetic algorithm was established using the MATLAB software. Indoor static and dynamic verification tests were also carried out. The results showed that the optimal plate structure parameter combination includes a plate thickness of 1 mm, plate spacing of 100 mm, and relative area of 18,000.069 mm2 while satisfying the mechanical design and practical application needs of the device. The structure of the BP neural network was 2-90-1, the length of individual code in the genetic algorithm was 361, and the prediction model was trained 765 times to obtain a minimum MSE value of 1.9683 × 10-5, which was lower than that of the unoptimized BP neural network with an MSE of 7.1215 × 10-4. The mean relative error of the device was 1.44% under the static test and 2.103% under the dynamic test, which met the accuracy requirements for the design of the device.

In silico selection of an aptamer for the design of aptamer-modified magnetic beads bearing ferrocene co-immobilized label for capacitive detection of acetamiprid.

In silico evaluation of aptamer/target interactions can facilitate the development of efficient biosensor with high specificity and affinity. In this work, we present in silico, i.e. structural similarity, molecular docking and molecular dynamics selection of the aptamer with sufficient binding properties for acetamiprid (ACE), a nicotine-like pesticide, and its use to design aptamer-modified magnetic beads bearing ferrocene co-immobilized label for capacitive detection of ACE. Taking advantages of the aptamer higher stability and binding affinity, the specific properties of magnetic beads and the redox properties of ferrocene moiety, the developed aptasensor showed promising analytical performances for ACE detection, using electrochemical capacitance spectroscopy, with a linear response ranging from 1fM to 100 pM and a limit of detection of 0.94fM(S/N=3). Furthermore, it was successfully applied to detect ACE in fortified tomatoes samples, proving a promising approach for routine detection of pesticide in real agricultural samples.

CMOS Capacitive Sensor for DNA Detection in Undiluted Ionic Solution

Capacitive detection of affinity-bound biomolecules enables rapid and label-free bioassays suitable for point-of-care diagnostic applications. However, direct detection at high ionic strengths is severely limited by the Debye charge-screening effect of the electric double layer on the sensor surface, leading most studies to be performed at diluted ionic strengths. In this study, probe-target deoxyribonucleic acid (DNA) hybridization was successfully measured by modulating the electric field of the interdigitated sensing electrodes to reduce charge screening. The developed 8 × 8 complementary metal oxide semiconductor (CMOS) capacitive sensor array exhibited a sensitivity of 150 fF/log10[DNA] measured at 15 MHz from 10 aM to 100 pM with a response time of approximately 400 seconds. The array also exhibited a pH sensitivity of 354 fF/pH.

A High-Performance Dual-Channel MEMS Microwave Power Sensor With Cantilever Beam

In order to optimize the sensitivity and overload power of microwave power sensor, a dual-channel MEMS microwave power sensor with cantilever beam is proposed in this paper. GaAs MMIC process and MEMS technology are used for design and manufacturing. The theoretical model of MEMS dual-channel microwave power sensor with cantilever beam is established. The influence of the size of the cantilever beam on the microwave performance, overload power and sensitivity of the sensor is studied. The microwave performance and sensitivity of three sensors with different cantilever beam sizes were tested. At 8-12 GHz, the return loss of three sensors are -10.6 dB~-57.2 dB@ 200 μm beam length, -10.6 dB~-62.4 dB@300 μm beam length, and -12.0 dB~-62.3 dB@400 μm beam length, respectively. They all show good microwave performance. At 10 GHz, the sensitivities of capacitive detection channel of three sensors are 16.3 fF/W, 65.6 fF/W and 144.4 fF/W respectively. And the sensitivities of thermoelectric detection channel are 142.3 mV/W, 109.5 mV/W and 82.9 mV/W respectively. The sensitivities of dual-channel MEMS microwave power sensors with cantilever beam are improved compared with the traditional microwave power sensor, which has certain reference value for the design of MEMS microwave power sensors.

Weak Capacitance Detection Circuit of Micro-Hemispherical Gyroscope Based on Common-Mode Feedback Fusion Modulation and Demodulation.

As an effective capacitance signal produced by a micro-hemisphere gyro is usually below the pF level, and the capacitance reading process is susceptible to parasitic capacitance and environmental noise, it is highly difficult to acquire an effective capacitance signal. Reducing and suppressing noise in the gyro capacitance detection circuit is a key means to improve the performance of detecting the weak capacitance generated by MEMS gyros. In this paper, we propose a novel capacitance detection circuit, where three different means are utilized to achieve noise reduction. Firstly, the input common-mode feedback is applied to the circuit to solve the input common-mode voltage drift caused by both parasitic capacitance and gain capacitance. Secondly, a low-noise, high-gain amplifier is used to reduce the equivalent input noise. Thirdly, the modulator-demodulator and filter are introduced to the proposed circuit to effectively mitigate the side effects of noise; thus, the accuracy of capacitance detection can be further improved. The experimental results show that with the input voltage of 6 V, the newly designed circuit produces an output dynamic range of 102 dB and the output voltage noise of 5.69 nV/√Hz, achieving a sensitivity of 12.53 V/pF.

CMOS readout FEE based TV-BLR module for CdZnTe pixel detectors in high count rate applications

In this study, a time-variant baseline restorer (TV-BLR) circuit was designed and implemented to address the poor frequency selectivity issue in the shaping units of most state-of-the-art readout electronics for CdZnTe/CdTe detectors used in biomedical imaging applications. The proposed circuit improves image quality by canceling the artifacts that result from poor temporal and energy resolution in PET imaging. The proposed circuit consists of a Charge Sensitive Preamplifier (CSP) followed by a classical pole-zero compensation circuit. Two stages of integrators are added and a frequency rectifier module named the TV-BLR circuit has been built. The open-loop amplifier for the CSP is a single-ended input stage amplifier, designed for low-power applications with a maximum power consumption of 43 µW from a 1.2 V supply voltage, verified through post-layout Monte Carlo simulations. The TV-BLR increases the selectivity of the shaping filter, lowers the equivalent noise charge (ENC), and restores the baseline of the circuit to only 143 µV dc-offset. It also extends the counting rate behavior of the system by handling the time-over-threshold (ToT), which depends on the tail current (Itail) of the comparator stage. The circuit was designed, simulated, and validated for an input dynamic of 2–12.5fC, providing an energy range of 55.1–354.3 keV. The design has a charge-to-voltage conversion factor of 56.7 mV/fC with a 4% non-linearity error for an input detector capacitance of 200 fF, while achieving an optimal ENC of 57.4 e − RMS ± 0.1 e−/fC with 13.27 ns peaking time. Process Voltage Temperature (PVT) analysis was performed to validate the simulation results and performance metrics of the design. The proposed design improves energy resolution and avoids energy losses due to the readout system.

Oxidating liquid metal interface integrated capacitive pressure detection

Oxidating liquid metal interface integrated capacitive pressure detection

A Novel Dual-Mode Sensor for the Detection of Interface Flaw in “Insulator-Conductor” Composite Structures

“Insulator-conductor” composite structures have been extensively used in a vast number of fields in recent years. However, due to different factors including but not limited to environmental and adverse working conditions, the interface between the insulator and conductor is prone to flaws. Therefore, non-destructive testing (NDT) techniques are needed to inspect the functionality and integrity of such composite structures. A dual-mode sensor that combines principles of eddy current and capacitive sensing is proposed to detect the interfacial flaws in “insulator-conductor” composite structures. The proposed sensor uses phase switching excitation to switch between inductive and capacitive detection modes, and the feasibility of the method was analyzed by equivalent circuit analysis and Finite Element (FE) simulations. The dual-mode sensor was fabricated on a single Printed Circuit Board (PCB) and used for experimental investigation on specimens of “Perspex-aluminum” composite structures. The experimental results verified the results of equivalent circuit analysis and FE simulation, and showed that the proposed sensor is able to detect corrosion under insulation, surface cracking on the conductor and interface debonding. Results also show that the detected information of the two modes complement each other, proving that the detection method has the ability to evaluate flaws in complex situations at the interface.

A study of the signal rising edge produced by a charge sensitive preamplifier connected to a 4H-SiC detector

In a general semiconductor detector system, the output amplitude of the charge-sensitive preamplifier (CSA) is proportional to the total charge induced by incident particles. The rising edge of the output signal provides information on the input current. The shape of the rising edge is not only affected by the carrier drifting but the discharge process of the equivalent capacitance (the detector capacitance and the capacitance caused by the detector package and the connecting cable, namely the stray capacitance) and the input resistance of the CSA. The equivalent capacitance and the input resistance often has a time constant of tens nanoseconds, which significantly affects the rising edge, particularly for fast detectors such as silicon carbide or diamond. This paper describes an α-particle testing system based on a Schottky 4H-SiC detector. The junction capacitance of the detector can be adjusted by changing the bias voltage, and the derivative waveforms of the CSA output are analyzed using an equivalent circuit. The results show that the falling edge of the derivative waveform corresponds to the discharge process of the equivalent capacitance and the input resistance in the circuit. The parameters of the detector capacitance, the stray capacitance and the input resistance can be obtained through fitting the decay time. The duration of the induced current of the detector can be measured from the rising edge of the derivative waveform. By comparing the theoretical and the measured value, the carrier mobility at different bias voltages can be derived.

Analysis of Noise-Detection Characteristics of Electric Field Coupling in Quartz Flexible Accelerometer

The internal electric field coupling noise of a quartz flexible accelerometer (QFA) restricts the improvement of the measurement accuracy of the accelerometer. In this paper, the internal electric field coupling mechanism of a QFA is studied, an electric field coupling detection noise model of the accelerometer is established, the distributed capacitance among the components of the QFA is simulated, the structure of the detection noise transfer system of different carrier modulation differential capacitance detection circuits is analyzed, and the influence of each transfer chain on the detection noise is discussed. The simulation results of electric field coupling detection noise show that the average value of detection noise can reach 41.7 μg, which is close to the effective resolution of the QFA, 50 μg. This confirms that electric field coupling detection noise is a non-negligible factor affecting the measurement accuracy of the accelerometer. A method of adding a high-pass filter to the front of the phase-shifting circuit is presented to suppress the noise of electric field coupling detection. This method attenuates the average value of the detected noise by about 78 dB, and reduces the average value of the detected noise to less than 0.1 μg, which provides a new approach and direction for effectively breaking through the performance of the QFA.

SECALROC2: A Low-Noise, High-Speed, and Full Digital Outputs Front-End ASIC for STCF Electromagnetic Calorimeter With APD Detectors

In this work, a low-noise and high-rate front-end readout application-specific integrated circuit (ASIC) named SECALROC2 for the electromagnetic calorimeter (ECAL) in the super tau-charm factory (STCF) is presented. The chip is designed to process signals generated from avalanche photodiode detectors (APDs) for both energy and time measurement. The large detector capacitance and leakage current of the APD pose a great challenge to the noise and speed performance of the front-end readout circuit (ROC). A low-noise preamplifier and a fifth-order high-linearity shaper with adjustable peaking times are proposed to decrease noise induced by the 270-pF detector capacitance. A peak detect-and-hold circuit and a high-linearity differential analog buffer are adopted to convert each peak voltage of the shaper to differential voltages with sufficient driving capability. A fast shaper and a discriminator are implemented to produce trigger signals for the time of arrival (TOA) measurement. To reduce the complexity and power consumption of the ECAL system, a 12-bit 10-MS/s pipelined analog-to-digital converter (ADC) and a 16-bit three-stage time-to-digital converter (TDC) with 42-ps bin size TDC are integrated on-chip for full-digitalized outputs. This ASIC was designed and fabricated in a standard commercial 1P6M 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> mixed-signal CMOS process and the chip area occupancy is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.4\times1.6$ </tex-math></inline-formula> mm2. The experimental results show that the input charge of the ASIC ranges from 3.2 to 400 fC. The measured nonlinear error of the system is less than 2.5% with an event rate up to 400 kcps. The equivalent noise charge (ENC) is 1367 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{e}^{-}$ </tex-math></inline-formula> + 4.93 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{e}^{-}$ </tex-math></inline-formula> /pF at 800-ns peaking time. The timing resolution is better than 540 ps at an input charge of 160 fC. The measured ENC can achieve 3820 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{e}^{-}$ </tex-math></inline-formula> when the ASIC is connected to an APD detector. The effective number of bits (ENOB) of the ADC is 10.8-bit when operated at 10 MS/s.

A High-Linearity Closed-Loop Capacitive Micro-Accelerometer Based on Ring-Diode Capacitance Detection.

This paper presents an implementation scheme and experimental evaluation of a high-linearity closed-loop capacitive accelerometer based on ring-diode capacitance detection. By deducing the capacitance detection model of the ring-diode considering the influence of the diode, the existing theoretical model error of the ring-diode is corrected and a closed-loop scheme of reusing the detection electrode and the control electrode of the MEMS die is designed to apply this detection scheme to the parallel-plate accelerometer, which only has three independent electrodes. After analyzing the non-linear problems in the existing closed-loop control schemes, a theoretically absolute linear closed-loop control scheme is proposed, and an integrated closed-loop accelerometer is realized by combining the closed-loop diode detection. The experimental results of the ring-diode detection model are in agreement with the theoretical formula. The non-linearity of the accelerometer within ±1 g after the closed-loop is 130 ppm, compared with 1500 ppm when the open-loop is used.

Dynamic Detection Based on Planar Array Capacitance for Adhesive Defects of Thermal Protection Structure

The defect detection of thermal protective structures is of great significance in ensuring the safe flight of aircraft. In this paper, a dynamic measurement method based on the planar capacitance sensing principle is proposed to solve the problem of detecting defects in the adhesive layer of large-area thermal protection structures. This paper analyses the principle of capacitive sensing and establishes a planar array capacitive dynamic detection system. The dielectric distribution of the structural components to be measured is obtained at different locations by moving the array of electrode sensors regularly. To obtain the dielectric distribution information of the complete structure, the dielectric distribution at adjacent locations is spliced and fused. To achieve the precise location of the overlapping areas in the image to be fused, an image alignment method based on coordinates is adopted. The experimental results show that our proposed method can detect defects in the adhesive layer of large-area thermal protection structures and achieve complete visualization of the adhesive layer.

Highly Integrated μGC Based on a Multisensing Progressive Cellular Architecture with a Valveless Sample Inlet

Microscale gas chromatographs (μGCs) promise in-field analysis of volatile organic compounds (VOCs) in environmental and industrial monitoring, healthcare, and homeland security applications. As a step toward addressing challenges with performance and manufacturability, this study reports a highly integrated monolithic chip implementing a multisensing progressive cellular architecture. This architecture incorporates three μGC cells that are customized for different ranges of analyte volatility; each cell includes a preconcentrator and separation column, two complementary capacitive detectors, and a photoionization detector (PID). An on-chip carrier gas filter scrubs ambient air for the analysis. The monolithic chip, with all 16 components, is 40.3 × 55.7 mm2 in footprint. To accommodate surface adsorptive and low-volatility analytes, the architecture eliminates the commonly used inlet valve, eliminating the need for chemically inactive surfaces in the valves and pumps, allowing the use of standard parts. Representative analysis is demonstrated from a nonpolar 14-analyte mixture, a polar 12-analyte mixture, and a 3-phosphonate ester mixture, covering a wide vapor pressure range (0.005-68.5 kPa) and dielectric constant range (1.8-23.2). The three types of detectors show highly complementary responses. Quantitative analysis is shown in the tens to hundreds ppb range. With 200 mL samples, the projected detection limits reach 0.12-4.7 ppb. Limited tests performed at 80% humidity showed that the analytes with vapor pressures <12 kPa were unaffected. A typical full run takes 28 min and consumes 2.3 kJ energy for the fluidic elements (excluding electronics). By eliminating chip-to-chip fluidic interconnections and requiring just one custom-fabricated element, this work presents a path toward high-performance and highly manufacturable μGCs.

Capacitive NO2 Detection Using CVD Graphene-Based Device.

A graphene-based capacitive NO2 sensing device was developed by utilizing the quantum capacitance effect. We have used a graphene field-effect transistor (G-FET) device whose geometrical capacitance is enhanced by incorporating an aluminum back-gate electrode with a naturally oxidized aluminum surface as an insulating layer. When the graphene, the top-side of the device, is exposed to NO2, the quantum capacitance of graphene and, thus, the measured capacitance of the device, changed in accordance with NO2 concentrations ranging from 1-100 parts per million (ppm). The operational principle of the proposed system is also explained with the changes in gate voltage-dependent capacitance of the G-FET exposed to various concentrations of NO2. Further analyses regarding carrier density changes and potential variances under various concentrations of NO2 are also presented to strengthen the argument. The results demonstrate the feasibility of capacitive NO2 sensing using graphene and the operational principle of capacitive NO2 sensing.

Polyoxometalate-based metal–organic supramolecular architectures derived from two new pyrimidine-amide ligands as supercapacitors and multifunctional electrochemical sensors

Two polyoxometalate (POM)-based metal–organic supramolecular architectures based on two new pyrimidine-amide ligands were prepared. Both of them possess high specific capacitance, good sensitivity and low detection limit for Cr(vi) and Fe(iii) ions.

A Soft, Fast and Versatile Electrohydraulic Gripper with Capacitive Object Size Detection (Adv. Funct. Mater. 3/2023)

A Soft, Fast and Versatile Electrohydraulic Gripper with Capacitive Object Size Detection (Adv. Funct. Mater. 3/2023)