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This research aimed to preserve the chitinase catalytic activity using alginate and zinc oxide nanoparticles (ZnO-NPs), to evaluate its thermal stability at 37 ºC, 50 ºC, and 70 ºC and its ability to detect Rhizopus stolonifer , Colletotrichum fragariae , and Alternaria alternata in a capacitive transducer-based biosensor. The ZnO-NPs measured less than 100 nm. The phosphate buffer-citric acid was a better solvent than water. Al+ZnONPs Ch showed the highest thermal stability at 37 ºC and 50 ºC (2 IU) for 45 d. Conversely, the free enzyme lost its activity from day 1–28 at 37 ºC (3.3 IU-2.8 IU), and alginate-encapsulated chitinase (AlCh) had the lowest activity at 50 ºC during 45 d (1.3 IU). Chitinase, alginate, and the ZnO-NPs were confirmed for FTIR spectra. The Al+ZnONPs Ch had the best response in the biosensor, observing a decrease in electrical frequency when the concentration of the tested fungi increased (106 spores mL−1 =100–250 kHz and 104 spores mL−1 = 400 kHz). In conclusion, at 37 ºC and 50 ºC, the chitinase had a stable catalytic activity compared to the remaining treatments, and it could be used to detect fungi in a biosensor at concentrations from 103 to 106 spores mL−1. [Display omitted] • The chitinase activity was preserved for 45d by encapsulating in alginate and ZnO. • Chitinase was thermally stable at 37 ºC and 50 ºC when encapsulated in alginate. • Encapsulated chitinase had a higher response to fungi detection than free chitinase. • In the biosensor, the electrical frequency decreases as fungi concentration increases. • The biosensor could detect the fungi concentration but not the fungi genre. [ABSTRACT FROM AUTHOR]

A three-axis seismic accelerometer was developed and created, containing three uniaxial mutually perpendicular sensors, the sensitivity axis of each sensor is located at an angle of 54.736° to the local gravitational vertical. For the first time, additional magnetic rigidity has been introduced into each device, allowing the device to be finely tuned to the conditions of a particular planet. However, the accumulated experience in conducting ground-based tests has shown the need to improve the uniaxial seismic accelerometer, which can significantly improve the characteristics of the device. First, we use a single material—beryllium bronze BrB-2—for the manufacture of massive test mass suspension elements with a thickness of 1.5 mm and an elastic element made of a thin strip 10–20 microns thick, which reduces the likelihood of instability. Secondly, we reduce the gap in the capacitors of capacitive converters from 0.25 to 0.1–0.15 mm to significantly increase the conversion slope of the capacitive sensor. Thirdly, we change the technology of setting up the device, for which we combine all the elements of the sensitive part of a uniaxial seismogravimeter using special vertical inserts. This allows us to place the device as a whole in a system for its configuration, eliminating the possibility of failure of individual elements, thereby increasing the reliability of the device. [ABSTRACT FROM AUTHOR]

A new, improved approach in the design of broadband seismometers is presented. The design results in the implementation of a high performance, low cost, and simple-to-operate instrument. The proposed seismometer is based on a modified accelerometer followed by a continuous time integrator for providing velocity voltage output. It has a broadband response, flat in velocity from 120 s to 75 Hz, high sensitivity 1200 V/(m/s), and 40 Vpp differential output range. The acceleration integration method provides high performance at low frequencies, with self-noise well below the New Low Noise Model at the range 80 s–16 Hz. The mechanical system provides a perfectly linear response of its displacement sensing system. Evaluation, classification, and noise determination of the presented instrument are performed in terms of direct experimental measurements, simulations, and calculations based on raw data from the proposed sensor and from a commercial product with approximately equivalent performance. Its technical features and performance specifications guarantee accurate sensing of local events, with maximum power at the frequency range of 5 to 10 Hz, but also make it ideal for the recording of distant tectonic activity, where extremely weak motions at long periods are expected. The whole design is robust, lightweight, and weatherproof, comprising in this way a useful tool to geoscientists. [ABSTRACT FROM AUTHOR]

The challenges of providing national metrological organizations with category 1 working standards are considered with regard to the current needs in the field of reference ultrasonic measurement in solids. An upgraded reference installation is presented for performing precise measurements of the propagation velocities of longitudinal and shear ultrasonic waves, as well as the damping coefficient of longitudinal ultrasonic waves in solids. Measurements of the acoustic parameters of solids are performed by pulse-echo and resonance methods using contactless broadband capacitance methods of excitation and registration of ultrasonic waves. This installation is used as a category 1 working standard in accordance with the State verification schedule for the instruments designed to measure the propagation velocities and damping coefficient of ultrasonic waves in solids. The technical instruments included in the installation (mechanical and electronic parts) have been upgraded, analog measuring devices have been replaced with digital ones, methods for measuring the acoustic parameters of solids based on the use of digital measuring instruments have been developed, and the thickness range of installed ultrasonic standards has been expanded. The composition and main components of the reference installation along with the used measurement methods and principles of operation of the installation under various operating conditions are described. The technical and metrological characteristics of the installation are provided. The sources of measurement error (uncertainty) have been analyzed. The field of application of the results includes high-precision measurements of the acoustic characteristics of solid media, as well as metrological support of ultrasonic nondestructive testing and diagnostics. [ABSTRACT FROM AUTHOR]

The measurements of wafers' surface profile are crucial for safeguarding the fabrication quality of integrated circuits and MEMS devices. The current techniques measure the profile mainly by moving a capacitive or optical spacing sensing probe along multiple lines, which is high-cost and inefficient. This paper presents the calculation, simulation and experiment of a method for measuring the surface profile with arrayed capacitive spacing transducers. The calculation agreed well with the simulation and experiment. Finally, the proposed method was utilized for measuring the profile of a silicon wafer. The result is consistent with that measured by a commercial instrument. As a movement system is not required, the proposed method is promising for industry applications with superior cost and efficiency to the existing technology. [ABSTRACT FROM AUTHOR]

Capacitive transducers are the core of electrostatic space accelerometers and have been applied in several space science missions. However, the noise of the front-end circuit in a capacitive transducer is a major limitation to capacitance resolution. The current theoretical models cannot accurately and comprehensively describe the performance of the front-end circuit in an ultra-high precision capacitive transducer. In this study, we modified the sensitivity and noise models of the front-end circuit and verified them by precision experiments. Under the guidance of the corrected models, we optimized the total stray capacitance by thickening the insulating layer between the shield and signal from 123 pF to 38 pF, thereby reducing the noise to 0.08 aF/Hz $^{\text {1/2}}$. We believe that this work will support the development of an ultrasensitive electrostatic accelerometer for application in space science missions. [ABSTRACT FROM AUTHOR]

Suppression of spurious vibrations and accurate control of mechanical damping is critical in MEMS devices to ensure optimal performance, sensitivity and reliability. Conventional control schemes such as feedback-based mechanical vibration absorbers or viscous dampers are either complex to implement at the micro scale or result in a higher sensor noise floor due to thermomechanical processes. In this paper, we present a tunable electrical autoparametric vibration control scheme that is applied to a capacitive MEMS resonator. In the proposed method, energy is transferred from the primary mechanical resonating element to a secondary electrical resonator via parametric mode coupling, thereby enabling dramatic reduction in the amplitude of mechanical vibration without introducing significant linear damping. As the threshold for parametric coupling is determined by electrical resistance, the system can be tuned easily to adjust the magnitude, rate and bandwidth of vibration suppression in the mechanical structure. A 1D lumped parameter model is developed to numerically analyse the behavior of the autoparametric vibration control system followed by experiments performed using a micromachined resonator array to validate the proposed model. The proposed circuit-based scheme provides an easily integratable and tunable solution to control damping in MEMS sensors and actuators. [2021-0095] [ABSTRACT FROM AUTHOR]

The measurements of wafers’ surface profile are crucial for safeguarding the fabrication quality of integrated circuits and MEMS devices. The current techniques measure the profile mainly by moving a capacitive or optical spacing sensing probe along multiple lines, which is high-cost and inefficient. This paper presents the calculation, simulation and experiment of a method for measuring the surface profile with arrayed capacitive spacing transducers. The calculation agreed well with the simulation and experiment. Finally, the proposed method was utilized for measuring the profile of a silicon wafer. The result is consistent with that measured by a commercial instrument. As a movement system is not required, the proposed method is promising for industry applications with superior cost and efficiency to the existing technology.

We document a feedback controller design for a nonlinear electrostatic transducer that exhibits a strong unloaded resonance. Challenging features of this type of transducer include the presence of multiple fixed points (some of which are unstable), nonlinear force-to-deflection transfer, effective spring-constant softening due to electrostatic loading and associated resonance frequency shift. Furthermore, due to the utilization of lowpass filters in the electronic readout circuitry, a significant amount of transport delay is introduced in the feedback loop. To stabilize this electro-mechanical system, we employ an active disturbance-rejecting controller with nonlinear force mapping and delay synchronization. As demonstrated by numerical simulations, the combination of these three control techniques stabilizes the system over a wide range of electrode deflections. The proposed controller shows good setpoint tracking and disturbance rejection, and improved settling time, compared to the sensor alone. [ABSTRACT FROM AUTHOR]

A shear-stress or skin-friction sensor for hypersonic flow measurements is presented. The sensor measures the displacement of a spring-mounted rectangular plate using a differential capacitance-based detection scheme. The 1.8-mm $\times $ 1.8-mm sensor is fabricated using a silicon-on-insulator wafer with a 20- $\mu \text{m}$ -thick epitaxial layer and packaged into a cylindrical form-factor with a 1/4-in diameter. Wall-shear-stress measurements are performed at a Mach-2.3 supersonic wind-tunnel facility at The University of Arizona. The sensors observe several features anticipated from hypersonic/supersonic flow physics, including the passing of normal shocks and the reversal of measured shear polarity when flow separation is deliberately induced via the use of a compression ramp. Furthermore, the measured value for dc wall-shear stress agrees with the model predictions for fully developed turbulent boundary layers. [2018-0191] [ABSTRACT FROM AUTHOR]

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We document a feedback controller design for a nonlinear electrostatic transducer that exhibits a strong unloaded resonance. Challenging features of this type of transducer include the presence of multiple fixed points (some of which are unstable), nonlinear force-to-deflection transfer, effective spring-constant softening due to electrostatic loading and associated resonance frequency shift. Furthermore, due to the utilization of lowpass filters in the electronic readout circuitry, a significant amount of transport delay is introduced in the feedback loop. To stabilize this electro-mechanical system, we employ an active disturbance-rejecting controller with nonlinear force mapping and delay synchronization. As demonstrated by numerical simulations, the combination of these three control techniques stabilizes the system over a wide range of electrode deflections. The proposed controller shows good setpoint tracking and disturbance rejection, and improved settling time, compared to the sensor alone.

Ultra-sensitive inertial sensors are one of the key components in satellite Earth’s gravity field recovery missions and space gravitational wave detection missions. Low-noise capacitive position transducers are crucial to these missions to achieve the scientific goal. However, in actual engineering applications, the sensor head and electronics unit usually place separately in the satellite platform where a connecting cable is needed. In this paper, we focus on the stray-capacitance influences of coaxial cables which are used to connect the mechanical core and the electronics. Specially, for the capacitive transducer with a differential transformer bridge structure usually used in high-precision space inertial sensors, a connecting method of a coaxial cable between the transformer’s secondary winding and front-end circuit’s preamplifier is proposed to transmit the AC modulated analog voltage signal. The measurement and noise models including the stray-capacitance of the coaxial cable under this configuration is analyzed. A prototype system is set up to investigate the influences of the cables experimentally. Three different types and lengths of coaxial cables are chosen in our experiments to compare their performances. The analysis shows that the stray-capacitance will alter the circuit’s resonant frequency which could be adjusted by additional tuning capacitance, then under the optimal resonant condition, the output voltage noises of the preamplifier are measured and the sensitivity coefficients are also calibrated. Meanwhile, the stray-capacitance of the cables is estimated. Finally, the experimental results show that the noise level of this circuit with the selected cables could all achieve 1–2 × 10−7 pF/Hz1/2 at 0.1 Hz.

Capacitive transducers are widely used in fundamental physics experiments, seismology, Earth or planetary observations, and space scientific and technical applications because of their high precision, simple structure, and compatibility with various measurements. However, in real applications, there is a trade-off between their resolution and dynamic range. Therefore, this paper is aimed at enlarging the dynamic range while ensuring high resolution. In this paper, a noise analysis of a capacitive transducer is presented, which shows that the amplitude noise of the carrier wave is the main limiting factor. Hence, a new method of generating a carrier wave with lower-amplitude noise is proposed in the paper. Based on the experimental verification, it is found that the carrier wave produced through the new method performed significantly better than the typical digital carrier wave when they were compared in the same sensing circuit. With the carrier wave produced through the new method, the dynamic range of the capacitive transducer can reach 120.7 dB, which is 18.3 dB greater than for the typical direct digital synthesis (DDS) method. In addition, the resolution of the carrier wave is mainly limited by the voltage reference components.

Capacitive MEMS accelerometers with area-variable periodic-electrode displacement transducers found wide applications in disaster monitoring, resource exploration and inertial navigation. The bonding-induced warpage, due to the difference in the coefficients of thermal expansion of the bonded slices, has a negative influence on the precise control of the interelectrode spacing that is essential to the sensitivity of accelerometers. In this work, we propose the theory, simulation and experiment of a method that can alleviate both the stress and the warpage by applying different bonding temperature on the bonded slices. A quasi-zero warpage is achieved experimentally, proving the feasibility of the method. As a benefit of the flat surface, the spacing of the capacitive displacement transducer can be precisely controlled, improving the self-noise of the accelerometer to 6 ng/√Hz @0.07 Hz, which is about two times lower than that of the accelerometer using a uniform-temperature bonding process.

A class of actively calibrated line mounted capacitive voltage transducers are introduced as a viable line mountable instrumentation option for deploying large numbers of voltage transducers onto the medium and high voltage systems. Active calibration is shown to reduce the error of line mounted voltage measurements by an order of magnitude from previously published techniques. The instrument physics and sensing method is presented and the performance is evaluated in a laboratory setting. Finally, a roadmap to a fully deployable prototype is shown. [ABSTRACT FROM AUTHOR]

Abstract—: A family of seismometers has been developed with capacitive transducers that convert the relative displacement between the inertial mass and the base of the instrument into an electric signal. These high-sensitivity seismometers have a unified electronic circuit; they can be rather easily manufactured, installed, and calibrated, which makes mass production of these instruments look promising. To assess the possibility of using these seismometers as substitutes for imported counterparts, a comparative analysis was carried out to study the performance of a portable short-period SM-3E broadband digital seismometer and imported seismometers of the same type. Seismic recordings of these instruments were statistically analyzed in the time and frequency domains. [ABSTRACT FROM AUTHOR]

Capacitive micromachined ultrasonic transducers (CMUTs) represent an effective alternative to piezoelectric transducers for medical ultrasound imaging applications. They are microelectromechanical devices fabricated using silicon micromachining techniques, developed in the last two decades in many laboratories. The interest for this novel transducer technology relies on its full compatibility with standard integrated circuit technology that makes it possible to integrate on the same chip the transducers and the electronics, thus enabling the realization of extremely low-cost and high-performance devices, including both 1-D or 2-D arrays. Being capacitive transducers, CMUTs require a high bias voltage to be properly operated in pulse-echo imaging applications. The typical bias supply residual ripple of high-quality high-voltage (HV) generators is in the millivolt range, which is comparable with the amplitude of the received echo signals, and it is particularly difficult to minimize. The aim of this paper is to analyze the classical CMUT biasing circuits, highlighting the features of each one, and to propose two novel HV generator architectures optimized for CMUT biasing applications. The first circuit proposed is an ultralow-residual ripple (<5 \mu \textV ) HV generator that uses an extremely stable sinusoidal power oscillator topology. The second circuit employs a commercially available integrated step-up converter characterized by a particularly efficient switching topology. The circuit is used to bias the CMUT by charging a buffer capacitor synchronously with the pulsing sequence, thus reducing the impact of the switching noise on the received echo signals. The small area of the circuit (about 1.5 cm2) makes it possible to generate the bias voltage inside the probe, very close to the CMUT, making the proposed solution attractive for portable applications. Measurements and experiments are shown to demonstrate the effectiveness of the new approaches presented. [ABSTRACT FROM PUBLISHER]

Pull-in effect is a common phenomenon during anodic bonding, a key step in thefabrication processes of capacitive sensors and actuators. To assist the designs and fabrications ofthese transducers, this paper presents an analytical method for modelling the pull-in effect duringanodic bonding. The pull-in effect model was verified by finite element analysis and a verificationexperiment respectively. The verification results indicate that the analytical method for modellingthe pull-in effect during anodic bonding is capable for predicting pull-in voltages of anodicallybonded capacitive sensors and actuators in a universal and practical manner without any additionalfabrication process.

This work focuses on a polymer based capacitive harvester which can be fabricated with help of roll-to-roll and low cost printing methods. In contrast to electrostatic MEMS based parallel plate transducers or dielectric elastomer systems here, the capacitance is varied as function of the mechanical load by changing of the top electrode area with help of an electrically conducting composite elastomer. In case of a composite elastomer electrode the maximum capacitance in compressed state does not only depend on the thickness and permitivity of the dielectric but first of all on the quality of the interface and the micro structure of the conducting phase in the composite electrode at the interface which was investigated by FEM Maxwell simulation. An equivalent circuit model is used to study the influence of the leakage current inside the dielectric and the bulk resistivity of the elastomer electrode. First experiments with state of the art polymer, thin film and novel printed dielectrics in contact with elastomer electrodes have been performed to prove the harvesting principle at low frequencies. Charges between 25 and 70 nAs per cm2 have been transferred per cycle at 100 V/200 V while the maximum capacity was between 0.4 and 0.8 nF/cm2. [ABSTRACT FROM AUTHOR]

A family of seismometers has been developed with capacitive transducers that convert the relative displacement between the inertial mass and the base of the device into an electric signal. The seismometers have high sensitivity and a unified electronic circuit, and they can be rather easily manufactured, installed, and calibrated. Mass production of these instruments looks promising. To assess the possibility of using these seismometers as substitutes for imported counterparts, a comparative analysis was carried out to study the performance of an SM-3E broadband sensor with a capacitive transducer and imported STS-2 and CMG-6T seismometers. Seismic recordings of these three instruments mounted on the same pedestal were statically analyzed in the time and frequency domains. [ABSTRACT FROM AUTHOR]

Vegetables are important food products, therefore practical methods of control for concentrations of useful and harmful elements in vegetables make actual issue for the research. Vegetable juice is object of the research. Subject of the audit is defined by dependence of electrical properties of juice, containing sodium and cuprum ions on concentrations of these substances in the juice. Aim of the research is to develop a quick method to determine concentration of useful minerals and harmful substances in the vegetable juice according electrical parameters. The method of control for quality parameters of vegetable juice, proposed by the author, is based on immittance method. Main units of measuring tools for immittance control of quality parameters of vegetable juice are a capacitive transducer, RLC-meter and block of results processing and control (PC). Principle of measuring tools operation expects: under laboratory conditions the model fluids are created, i. e. carrot juices of known characteristics, which are placed in a capacitive transducer with square graphite electrodes which are completely immersed in the liquid; RLC-meter in asynchronous mode transfers a test signal to the capacitive transducer; in response the model liquid characteristics come to the RLC-meter (active and reactive components of the electric conductivity of juice). Studies of the model fluids have resulted in determination of dependency of active and reactive component of the conductivity on chemical nature and concentration of useful minerals and harmful substances. The measured values are compared to the set values for comparison. Results of the comparison help to make conclusions about content of harmful substances. Measuring is done in few seconds and can be used in real production conditions for quick quality control of vegetables. [ABSTRACT FROM AUTHOR]

This paper presents the design, fabrication, and experimental results of an in-plane MEMS capacitive flow sensor that uses the displacement of a micro-fabricated paddle caused by dynamic gas pressure for measuring the velocity of the flow of surrounding gas. The fabrication process is simple; the prototype is fabricated on 100-μm device Silicon-On-Insulator wafers using only three photo-lithographic mask layers. The device area is 5.5 mm by 5.5 mm. A comb-drive capacitance is used as the transducer for the flow sensor. Measurements show that the output capacitance C is a quadratic function of the gas velocity v , C = k 1 v 2 + k 2 v + C p , where k 1 = −8.5 fF/(m/s) 2 , k 2 = 73.6 fF/(m/s) and C p = 16 pF. The advantage of using a capacitive sensing mechanism is that it is virtually insensitive to changes in ambient temperature. Experimental results show that the output capacitance changed only slightly, about 0.21–0.34%, when the temperature changed from 23 °C to 43 °C. Simplicity of fabrication, combined with insensitivity to variations in ambient temperature makes this sensor ideal for widespread deployment to monitor the flow in natural gas pipelines. [ABSTRACT FROM AUTHOR]

We consider methods for the separate determination of the parameters of capacitive transducers according to instantaneous values of transient processes in a measuring circuit, which ensures an increase in the accuracy of the measurements as a result of the use of a multiple-element replacement for the transducer. [ABSTRACT FROM AUTHOR]