Sensor Circuit Research Articles

Self-Powered Food Assessment System Using LSTM Network and 915 MHz RF Energy Harvesting

This study proposes a self-powered food monitoring system that benefits from far-field RF Energy harvesting and deep learning techniques. Recent smart IoT systems for food quality management mainly focused on the appearance of Total Volatile Organic Compounds (TVOCs) during food preservation, which has the limitations of large power consumption, complex configuration, and low accuracy. Different from these methods, we aim to measure the gradual increase in air pressure inside food packages caused by gas emissions during food quality deterioration. With this new approach, the designed sensor circuit's energy consumption is reduced significantly than in conventional systems. The sensor module's operation power is supplied by an RF energy harvester capable of converting electromagnetic waves in space into electrical energy. We adopted a Yagi three elements as a receiver antenna in the RF energy scavenging module to enhance the harvested power and transmission distance. The designed antenna has a high gain of 6.54dBi in the direction of maximum radiation and voltage standing wave ratio (VSWR) better than 1.3 in approximately 60 MHz band (890-950 MHz). To demonstrate the feasibility of the proposed system, a set of experiments were conducted with different sorts of food such as pork, chicken, and fish. Raw data of food storage temperature, air pressure, and storage time obtained from the battery-less sensor module were analyzed and utilized to assess food quality changes. Several classification models, including LSTM, 1D-CNN, MLP, and SVM were developed and trained on the pork, chicken, and fish datasets to predict different food quality states. Experimental results show that the LSTM classifier, which can extract temporal characteristics from the dataset, achieves the best accuracy of above 99% on all three datasets. The food classification performance is investigated based on training accuracy and confusion matrix.

Developing a smart walking cane with remote electrocardiogram and fall detection

This study developed a smart cane with remote electrocardiogram (ECG) and fall detection. The cane comprises a self-developed ECG detection circuit, fall detection module composed of a three-axis gyroscope and three-axis accelerator, and two wireless transmission modules. The data reception end features a human–machine interface with self-developed ECG analysis and fall detection programs, providing reference data for identifying an abnormal situation. The hardware of the proposed system is divided into two parts. First, ECG detection is achieved using a copper column-shaped detector in place of conventional ECG electrodes. The self-developed sensor circuit amplifies the collected signals and filters unwanted noise to generate complete ECG signals. An Arduino MEGA microcontroller board and the two wireless transmission modules then transmit the signals to the human–machine interface. Second, fall detection is achieved using the aforementioned fall detection module to collect numerical data, which are then transmitted to the human–machine interface through the Arduino MEGA and wireless transmission modules. The proposed system can be applied to real-time monitoring and provide reference data for health care professionals and nursing personnel.

Driver Circuit Improvement of Eddy Current Sensor in Displacement Measurement of High-Speed Rotor

Displacement sensor is the key component of the magnetic levitation system. Reducing complexity and improving reliability of the sensor circuits are very important to mass production of magnetic levitation devices. In this article, an improved driver circuit of eddy current sensor is proposed. In order to generate a stable oscillating source with high stability and good precision of frequency, a crystal oscillator circuit with power boost is used to replace the traditional Colpitts oscillator circuit. The improved modulation circuit is composed of passive components with a simple structure for improving reliability. The parameters design method of the modulation circuit is analyzed in detail, which greatly affects the sensitivity and linearity of the sensor. The experimental results show that the designed eddy current sensor has good linearity (1.12%) and sensitivity (2.14 V/mm), and it can ensure the stable operation of the magnetic levitated turbomolecular pump at the rated speed.

Direct Ink Writing Method for Manufacturing Electronic Circuits Using Multiwalled Carbon Nanotubes and Polyvinyl Alcohol Composites

Abstract Usage of conductive materials for manufacturing electronic circuits using 3D printing methods plays a prominent role in sensing applications and has achieved significant growth in recent years. This growth has led to the development of stretchable, flexible electronics and wearable electronics that are useful as sensing applications in the fields of real-time health monitoring systems. In this paper, a multiwalled carbon nanotube (MWCNT)-based electronic circuit was developed using the 3D printing technique called direct ink writing (DIW). Polyvinyl alcohol (PVA) was used as the binder material to make the MWCNT ink for printing. Different concentrations of MWCNT ink were prepared using 5, 10, and 15 wt. % PVA solutions. The viscosity of MWCNT inks was measured using a rheometer (cone and plate type). The ink exhibited shear thinning behavior, which is suitable for DIW. Finally, the printing of a designed electronic circuit was carried out using a pneumatic extrusion–based 3D printer. The strain sensor circuit—measuring 20 mm long, 9.2 mm wide, and 0.8 mm thick—is manufactured by the 3D printer. Electrical resistivity of strain sensor circuit is evaluated by adopting a two-probe method; the observed resistivity value was 1.7 × 10−2 Ωm for MWCNT ink made with 10 wt. % PVA solution and 1.97 × 10−2 Ωm for MWCNT ink made with 15 wt. % PVA solution.

Graphene/PSMA composite for gas sensing application

This paper presents the fabrication of conducting polymer sensor which comprise of graphene-poly styrene-co-maleic acid (PSMA) composite that responds to volatile organic compound (VOC) via a change in the electrical resistance of the sensors. Five sensors composed of different material ratio were fabricated to find out the most prominent weight percentage ratio (wt %) for optimum sensor response. Those materials were deposited onto silver electrode using drop-casting method. NI Card PCIE-6323 measures the voltage obtained from the sensor circuit and the resistance of the gas sensor monitored using LabVIEW instrument. It was observed from the experiments that combination of 60% graphene and 40% PSMA gives the highest sensor response.

Method to Reduce Quantization Error in Direct Interface Circuits for Resistive Sensors

Reading resistive sensors and converting their information to digital values is a matter of great interest in practical applications. Direct Interface Circuits (DICs) perform this task efficiently through a resistance-to-time-to-digital conversion. The main benefit of this type of circuit is the simplicity of its design and the accuracy of the results. However, one of its drawbacks is that quantization errors in the measurements seriously compromise accuracy if the information is not converted using a high-frequency clock or with high capacitor values. To avoid this situation, this article presents a new type of DIC with the same passive elements as a classic DIC, but which uses a high value resistor in the final instant of the resistance-to-time conversion. The circuit has been implemented using a commercial FPGA with the capture module operating at different clock frequencies. The results show that relative errors in measuring resistors of up to $33~\Omega $ decrease to 1.56% when operating with a 12.5 MHz timer.

Guest Editorial Special Issue on Advanced Interface Circuits for Autonomous Smart Sensors

The quote by Lord Kelvin, “if you can’t measure it, you can’t improve it,” best captures the invaluable role of sensors in any system. It also implies that to improve the performance of a system one needs to employ advanced sensor solutions. The performance requirements vary from one application to another, but are always associated with accuracy, repeatability, reproducibility, range, power consumption, ease of installation, and maintenance. In the modern era of data science, machine learning, and artificial intelligence, there is an ever-increasing need for low-cost, high-performing sensors in high volumes.

Performance Verification of a Digital Interface Suitable for a Broad Class of Resistive Sensors

An improved digital interface circuit for resistive sensors is proposed in this paper. The circuit offers many positive features, such as (1) use of single-reference voltage in its architecture, (2) facility to tune/preset the sensor-excitation current, even for different values of resistive sensors, (3) minimal dependence on many circuit non-ideal parameters. The working of the circuit is mathematically described in this paper, followed by its extensive error evaluation. Detailed simulation and experimental studies are performed to verify the feasibility of the interface for three different types of sensors. These studies show that the circuit can efficiently be used in temperature-monitors, magnetometers, and displacement-sensing. The maximum experimental nonlinearity observed from all of these sensor configurations does not exceed 0.06 %. Then, the extensive studies are carried out by simulation as well as experimentation to show the effect of environmental temperature changes on the proposed circuit. Finally, the proposed circuit is compared with some of the recent resistive digital interfaces.

The Design of the Electromyography Sensor with the Modifying Circuit

The project is about using the Electromyography (EMG) sensor to display the muscle movement and use connecting circuit to modify the signal from the EMG sensor. The modifying circuit connected to the EMG sensor include the amplifier circuit to amplify the signal, the filter to remove the DC offset and the high frequency noise, the rectifier for the positive swing of the signal and the envelope detector to smooth the signal. The circuit is designed according to the signal amplitude and the frequency spectrum and is simulated on the Multisim and have the output. The actual circuit is built as in the simulation and the signal is from the electrode. The output is in audiovisual and performance of the EMG sensor circuit is demonstrated by experiment. The design of the EMG in the project uses the simple component in electronic circuit with the desired output. The display of the EMG sensor in the project is audiovisual which provides the user with output format both in visual and in audio that allows hearing disability and visual disability users to use the EMG sensor.

A microcontroller-based interface circuit for non-linear resistive sensors

This article proposes a circuit based on a microcontroller unit (MCU) for the direct measurement and linearization of non-linear resistive sensors, such as thermistors. The measurement relies on an embedded digital timer and does not require (either embedded or external) operational amplifiers or an analog-to-digital converter, thus resulting in a low-cost, low-power design solution. The circuit includes a known resistor with a twofold function: it is a reference for circuit auto-calibration purposes, and it is in parallel with the non-linear resistive sensor for linearization purposes. A prototype is implemented with an 8-bit MCU (ATtiny 2313) applied to a commercial thermistor, and the results show a non-linearity error smaller than 1% full-scale span.

On-screen fingerprint sensor with optically and electrically tailored transparent electrode patterns for use on high-resolution mobile displays

In this study, a mutual capacitive-type on-screen fingerprint sensor, which can recognize fingerprints on a display screen to provide smartphones with full-screen displays with a minimal bezel area, is fabricated. On-screen fingerprint sensors are fabricated using an indium tin oxide transparent conductor with a sheet resistance of ~10 Ω/sq. and a transmittance of ~94% (~86% with the substrate effect) in the visible wavelength range, and assembled onto a display panel. Even at this high transmittance, the electrodes can degrade the display quality when they are placed on the display. The interference between periodic display pixel arrays and sensor patterns can lead to the Moiré phenomenon. It is necessary to find an appropriate sensor pattern that minimizes the Moiré pattern, while maintaining the signal sensitivity. To search for appropriate patterns, a numerical calculation is carried out over wide ranges of pitches and rotation angles. The range is narrowed for an experimental evaluation, which is used to finally determine the sensor design. As the selected sensor pitches are too small to detect capacitance variations, three unit patterns are electrically connected to obtain a unit block generating a larger signal. By applying the selected sensor pattern and circuit driving by block, fingerprint sensing on a display is demonstrated with a prototype built on a commercial smartphone.

전자기유도 방식 에너지 하베스팅 메커니즘을 이용한 축산용 IoT 센서의 설계 및 구현에 관한 연구

To determine diseases and estrus periods, the biometric information of cows is important, which can directly affect the profits of livestock farmers. As such, real-time management incorporating IoT technology is desired. Since history information of individual objects is essential for determining diseases and estrus periods using IoT sensors, lifetime for more than 10 years and power supply of sensors are very important. Therefore, this study proposes a design technology that can extend the life of IoT sensors to more than 10 years by power supply based on the energy harvesting mechanism of the electromagnetic induction method and by low-power sensor circuit design. In this study, an electromagnetic induction method by cow"s kinetic energy is presented, and a prototype is constructed and tested to verify the applicability. Further, this study presents an algorithm for estimating the amount of internal power generation by using the acceleration data inside the sensor.

Image Decomposition Sensor Based on Conditional Adversarial Model

In this paper, we propose an Image Decomposition Sensor based on Conditional Adversarial Model (CAM). The presented device decomposes intrinsic image into reflectance layer and shadow layer and the Conditional Adversarial Model (CAM) trains the intrinsic image decomposition to obtain high quality reflectance image and shadow image. By enhancing the shadow image, we can get a larger range of contrast images. Besides, we adopt reduced lookup table based pipeline architecture to greatly reduce the overall computing time. The image decomposition device solves the problems such as limited contrast and color distortion and is used for application of image contrast enhancement. The sensor circuit provide excellent auxiliary effects for system that need to rely on high-speed image processing.

A 0.39–3.56-μW Wide-Dynamic-Range Universal Multi-Sensor Interface Circuit

This paper presents an ultra-low-power, widedynamic-range interface circuit for capacitive and resistive sensors. The circuit is implemented as a switched-capacitor circuit using programmable capacitors to achieve high configurability. The circuit was fabricated using a CMOS 0.18 μm process. Different types of capacitive and resistive sensors were measured using the interface to demonstrate its support for multi-sensor systems with an ultra-low-power budget. Experimental results show that the circuit is able to interface various sensors within the overall capacitance range of 0.6-550 pF and resistance range of 3.7-5100 kΩ, while consuming only 0.39-3.56 μW from a 1.2 V supply. A proximity, gesture, and touch-sensing system is also developed consisting of the designed interface circuit and a sensor element that is able to detect the displacement of an object up to 15 cm from the sensing electrodes consuming only 0.83 μW from a 1.2 V supply.

A high performance integrated readout circuit for wavefront sensors

This work presents an integrated pixel topology that promises to offer superior performance in a Hartmann–Shack Wavefront Sensor (WFS) with an orthogonal array of Quad Cells serving as Position-Sensitive Detectors. The readout integrated circuit for each photodiode is fully compliant to any standard CMOS microelectronics technology and is advantageously tolerant to high background illumination levels whereas maintaining both high linearity and high sensitivity. To assess the operation of this pixel on the focal-plane array of the WFS, we developed a computational platform encompassing a full detection chain comprising wavefront sampling, photodetection, electronic circuitry and wavefront reconstruction. It couples an algorithm written in C to SPICE (Simulated Program with Integrated Circuits Emphasis). The platform is technology agnostic and flexible, enabling easy modification to represent different detection or reconstruction methods. The results obtained with the proposed pixel have been compared to those obtained with a conventional pixel in CMOS image sensor.

Cost-Effective DC Current Suppression for Single-Phase Grid-Connected PV Inverter

Due to the disparity of power modules, asymmetry of driving pulses and measurement errors of sensors, dc currents may be injected to grid-connected photovoltaic (PV) inverters. The dc current injection may cause magnetic saturation of the power transformers. To solve this issue, this article thus proposes an effective current control strategy and compensation method, which does not require any extra sensor and hardware circuit. First, the root-cause of dc current injection is comprehensively analyzed. Subsequently, a proportional-integral-resonant (PIR) controller is proposed to eliminate the dc component caused by disparity of power modules, asymmetry of driving pulses and measurement errors of grid voltage. The injected dc current caused by grid current measurement error is estimated from the line-frequency ripple of the dc-link voltage, and then it is suppressed by a feedback compensation controller. In addition, the dc current rejection capability is evaluated, and the proposed method is benchmarked with the virtual capacitor-based method. Finally, experimental tests are performed on a 1.2-kW single-phase PV inverter to verify the effectiveness of the proposal.

An efficient macro model for CMOS-MEMS thermal wind speed sensor

In this paper, we propose a thermal wind speed sensor Verilog-A model with thermal-fluid-electric hybrid characteristics. Because the structure of the thermal wind sensor and the interface circuit chip are designed separately, which cannot effectively carry out MEMS-IC (integrated circuit) co-simulation, the overall performance of the sensor and interface circuit chip is prone to large deviation. At the same time, the separation of MEMS structure and IC design process leads to long product development cycle and high cost. This paper proposes an improved simulation model by analyzing the behavior characteristics of the thermal wind speed sensor. The simulation model consists of 11 thermistors, 3 capacitors, a voltage-controlled voltage source, and a voltage-controlled current source. The Taylor series expansion of the differential equation of heat conduction is carried out, and then the thermistor and capacitor networks are established according to the corresponding relationship between the thermal parameters and the electrical parameters, including the thermal conduction unit, the convection unit and the heat capacity in the chip. The model fully considers the effects of various physical effects and parasitic effects, and is implemented using the hardware description language Verilog-A. The sensor and interface circuit can be simulated simultaneously to optimize the circuit design. It is beneficial to the integration of sensors and interface circuit, reducing the number of tape-outs, increasing the success rate, and reducing costs. The consistency between the simulation results and the experimental curves verified the correctness of the macro model. The behavior characteristics of constant power (CP) and constant temperature heating were described. In CP mode, the output voltage error is less than ± 6.5%, the chip temperature error is less than 4.0%. The presented modeling approach can be the basis for the development of complete MEMS-IC design technology library of thermal wind speed sensor, aiming at optimum designs of integrated thermal wind speed sensor.

Design and Implementation of Dynamic FPAA Based Interface Circuit for Thin Film Lead-Free Piezoelectric Sensors

Design and Implementation of Dynamic FPAA Based Interface Circuit for Thin Film Lead-Free Piezoelectric Sensors

Low-power in-pixel buffer circuit for smart image sensor

Purpose The smart image sensor (SIS) which integrated with both sensor and smart processor has been widely applied in vision-based intelligent perception. In these applications, the linearity of the image sensor is crucial for better processing performance. However, the simple source-follower based readout circuit in the conventional SIS introduces significant nonlinearity. This paper aims to design a low-power in-pixel buffer circuit applied in the high-linearity SIS for the smart perception applications. Design/methodology/approach The linearity of the SIS is improved by eliminating the non-ideal effects of transistors and cancelling dynamic threshold voltage that changes with the process variation, voltage and temperature. A low parasitic capacitance low leakage switch is proposed to further improve the linearity of the buffer. Moreover, an area-efficient SIS architecture with a sharing mechanism is presented to further reduce the number of in-pixel transistors. Findings A low parasitic capacitance low leakage switch and a gate-source voltage pre-storage method are proposed to further improve the linearity of the buffer. Nonlinear effects introduced by parasitic capacitance switching leakage, etc., have been investigated and solved by proposing low-parasitic and low-leakage switches. The linearity is improved without a power-hungry operational amplifier-based calibration circuit and a noticeable power consumption increment. Originality/value The proposed design is implemented using a standard 0.18-µm CMOS process with the active area of 102 µm2. At the power consumption of 5.6 µW, the measured linearity is −63 dB, which is nearly 27 dB better than conventional active pixel sensor (APS) implementation. The proposed low-power buffer circuit increase not only the performance of the SIS but also the lifetime of the smart perception system.

Recent developments in graphene based field effect transistors.

This paper presents a comprehensive survey on the recent developments in Graphene Field Effect Transistor (G-FET), considering various aspects such as fabrication, modelling and simulation tools and applications especially in sensors, highlighting the future directions. Complying with the Moore’s law, to increase the transistor density of an Integrated Circuit, new alternate materials for fabrication have been tried, instead of silicon due to its limitations in reducing transistor dimensions. Graphene, one such material, proves to be a suitable alternate for silicon due to the factors like superior carrier mobility and very high trans-conductance gain, etc and G-FET is becoming the most suitable choice for high-speed analog VLSI, RF, and bio- sensor circuits.