Charge Amplifier Circuit Research Articles

Triboelectric gait sensing analysis system for self‐powered IoT‐based human motion monitoring

AbstractQuantitative analysis of gait parameters, such as stride frequency and step speed, is essential for optimizing physical exercise for the human body. However, the current electronic sensors used in human motion monitoring remain constrained by factors such as battery life and accuracy. This study developed a self‐powered gait analysis system (SGAS) based on a triboelectric nanogenerator (TENG) fabricated electrospun composite nanofibers for motion monitoring and gait analysis for regulating exercise programs. The SGAS consists of a sensing module, a charging module, a data acquisition and processing module, and an Internet of Things (IoT) platform. Within the sensing module, two specialized sensing units, TENG‐S1 and TENG‐S2, are positioned at the forefoot and heel to generate synchronized signals in tandem with the user's footsteps. These signals are instrumental for real‐time step count and step speed monitoring. The output of the two TENG units is significantly improved by systematically investigating and optimizing the electrospun composite nanofibers' composition, strength, and wear resistance. Additionally, a charge amplifier circuit is implemented to process the raw voltage signal, consequently bolstering the reliability of the sensing signal. This refined data is then ready for further reading and calculation by the micro‐controller unit (MCU) during the signal transmission process. Finally, the well‐conditioned signals are wirelessly transmitted to the IoT platform for data analysis, storage, and visualization, enhancing human motion monitoring.image

Design and integrated stroke sensing of a high-response piezoelectric direct-drive valve enhanced by push-pull compliant mechanisms.

Enhancing the dynamic bandwidth of flow control valves based on piezoelectric actuators has attracted much attention in the field of precision fluid control. This paper reports a high-speed piezoelectric direct-drive flow control valve with an enhanced flow rate by introducing a new push-pull complementary compliant mechanism. An improved semi-rhombus compliant amplifying mechanism is designed to amplify the microstroke of piezo-stacks with an enhanced resonance frequency. To facilitate the design, the dynamic stiffness model of the compliant amplifying mechanism is derived and the structural parameters are optimized using the Pareto multi-objective optimization strategy. In addition, a polyvinylidene fluoride (PVDF) based high-response displacement sensor with an improved differential charge amplifier circuit is developed and integrated into the valve to measure the spool displacement in real time. A proof-of-concept prototype is fabricated, and the flow characteristics are experimentally tested in a closed-loop control with the PVDF sensor. The flow rate and dynamic bandwidth of the presented piezo-valve are evidently enhanced, reaching the dynamic bandwidth in excess of 920 Hz (-3 dB) and the flow rate of ±6 l/min (corresponding stroke is 0.2 mm) under the supply pressure of 70 bars.

Digital Ultrasonic Sensing Device with Programmable Frequency: Development and Analysis

Ultrasonic wave is widely used in Structure Health Monitoring (SHM) systems. A piezoelectric transducer (PZT) is one of the most widely used sensors to acquire the structure's ultrasonic wave. As today's world is digital, it is necessary to digitize the traditional analog PZT sensing system. This paper describes the development and analysis of a digital ultrasonic sensing device (DUSD) for PZT sensors. We removed the complexities of the analog circuit by interfacing the microcontroller directly with the charge amplifier circuit. The microcontroller used in this research is a 32-bit ARM Cortex-M4 with in-built FPU (Floating Point Unit) and DSP (Digital signal processing) instructions. These features make it possible to compute complex signal processing algorithms and methods in the controller itself. The developed sensing device can communicate with the user and other devices using Universal Asynchronous Receiver/Transmitter (UART). The user can select cut-off frequencies of both high pass filters (HPF) and low pass filters (LPF) as well as types of data (ultrasonic waves, damage index) that the user wishes to collect from the device. To illustrate the proficiencies of the device, the ultrasonic wave was collected and evaluated to detect the damage in the test specimen.

Design of a low cost, double triangle, piezoelectric sensor for respiratory monitoring applications

In this paper, a novel piezoelectric sensor is presented for patient's breath monitoring applications. Breath rate monitoring is important especially for the new coronavirus patients. In this work, a piezoelectric sensor is designed in the form of a vertex-attached triangular beam made of Polyvinylidene fluoride (PVDF) and Polydimethylsiloxane (PDMS). It exploits chest displacement to distinguish breathing vibrations. The device shape and dimensions have been designed for low frequency operation. The output respiration signal is amplified using a low power charge amplifier circuit. The sensor can be placed in a vest and fastened as a belt, or be attached to the chest by a tape. A low pass filter is used to eliminate the noise from the environment and body movement. Among the most important features are high accuracy, low resonance frequency to distinguish chest movement, low weight, low cost, portability, and reliability. Simulation of the designed sensor using COMSOL shows output voltage of 1 V at breathing frequency of 0.2 Hz.

The Design and Verification of an Active SAMSR Ultrasonic Guided Wave Monitoring System with Ultra-Low Crosstalk.

Due to long propagation distance and high sensitivity to a variety of damages, ultrasonic guided wave technologies have been widely applied in the damage detection or health monitoring of pipe networks and large plate-like structures. However, there are two important problems to be solved when applying this technology; namely, the large scanning time required for monitoring large-scaled structures and the serious crosstalk between the actuation and receiving signals, especially when monitoring hot-spot regions. Therefore, this study mainly designed key parts, such as the matrix switcher and attenuation circuit. The single-actuation and multiple-simultaneous-reception (SAMSR) mechanism based on an analog switching matrix and a low noise charge amplifier circuit was designed and integrated with the SPI control bus to shorten the scanning time. Moreover, a two-stage attenuation circuit with an interlocking isolation structure is presented to effectively isolate the receiving signals from the actuation signals to obtain ultra-low crosstalk even under a high voltage actuation source. In this study, the designed matrix switcher and other components were integrated into the developed ultrasonic guided wave monitoring system. Several experiments were conducted on a stiffened composite structure to illustrate the effectivity of the developed SAMSR ultrasonic guided wave system by comparing the signals collected with those from a commercial ultrasonic guided wave system.

MEMS directional acoustic sensor with charge amplifier based electronic readout

MEMS acoustic sensors based on the operating principle of the Ormia ochracea fly provide a unique way to determine the direction of sound. A typical sensor consists of two wings coupled by a bridge and the entire mechanical structure attached to a substrate using two torsional legs. The sensor mechanical structure has two different vibration modes which can be coupled by placing their resonant frequencies close to each other. The acoustic wave impinging on the sensor induces displacements which are detected using comb finger capacitors at the edges of the wings. Previously, this has been accomplished using the universal capacitive readout MS3110, which is prone to static variations of the comb finger capacitors. In this work, a charge amplifier circuit was developed to independently measure the displacements of the wings under sound excitation. The ability to simultaneously read these displacements is needed to determine the bearing of sound using a single MEMS sensor, in contrast to previously reported works that needed either a calibrated microphone or a second MEMS sensor to determine the incident sound pressure level. Measurements showed that both the phase difference and amplitude difference of oscillating wings were strongly dependent on the incident angle of sound.

A Paper-Based Piezoelectric Accelerometer.

This paper presents the design and testing of a one-axis piezoelectric accelerometer made from cellulose paper and piezoelectric zinc oxide nanowires (ZnO NWs) hydrothermally grown on paper. The accelerometer adopts a cantilever-based configuration with two parallel cantilever beams attached with a paper proof mass. A piece of U-shaped, ZnO-NW-coated paper is attached on top of the parallel beams, serving as the strain sensing element for acceleration measurement. The electric charges produced from the ZnO-NW-coated paper are converted into a voltage output using a custom-made charge amplifier circuit. The device fabrication only involves cutting of paper and hydrothermal growth of ZnO NWs, and does not require the access to expensive and sophisticated equipment. The performance of the devices with different weight growth percentages of the ZnO NWs was characterized.

Epitaxial PMnN-PZT/Si MEMS ultrasonic rangefinder with 2 m range at 1 V drive

In this study, we successfully developed a high signal-to-noise ratio (SNR) rangefinder based on a piezoelectric micromachined ultrasonic transducer (pMUT). A c-axis-oriented Pb(Mn1/3,Nb2/3)O3-Pb(Zr,Ti)O3 (PMnN-PZT) epitaxial thin film was employed as a piezoelectric transducer considering its outstanding figures-of-merit for SNR, due to the high piezoelectric coefficient and small relative permittivity (typical values: e31,f=−14C/m2, εr=200–300). The pMUTs was based on an epitaxial PMnN-PZT/Si diaphragm structure and prototyped from a SOI substrate; its rangefinding ability was evaluated with a pair of devices, specifically, transmitter and receiver, respectively. As a result, the maximum range was estimated to be over 2m at a low actuating voltage of 1Vp-p, when 12dB was set as the threshold SNR. The energy consumption of the transmitter was as small as ∼5nJ for the generation of a 50-cycle ultrasonic burst. The noise analysis of the receiver’s charge amplifier circuit indicated that this system could be improved by the optimization of bandwidth and by eliminating external noise. We believe that this high performance pMUT rangefinder will be utilized in various applications of consumer electronics or as an alternative to the bulk piezoelectric ceramic rangefinder in the near future.

Equivalent magnetic noise reduction at high frequency range due to polarized direction optimization in Terfenol-D/Pb(Mg1/3Nb2/3)O3-PbTiO3 magnetoelectric laminate sensors

In this paper, we investigate the responsivities and output voltage noise power spectral densities of magnetoelectric (ME) laminate sensors, consisting of length magnetized Terfenol-D alloys and transverse/width poled Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNT) crystals (i.e. L-T mode and L-W mode respectively), which are directly integrated with custom-build low noise charge amplifier circuits. Both the theoretical analyses and experimental results prove that the L-W mode sensor with the optimized polarized direction of the PMNT plate possesses lower magnetic detection limit at the interested high frequency range of 10kHz≤f≤50kHz. The equivalent magnetic noise (EMN) of the L-W mode sensor is 0.78pT/Hz1/2 at 30kHz, which is about 1.7 times lower than the 1.35pT/Hz1/2 for conventional L-T mode sensor. Furthermore, an effective method of using operational amplifiers with low equivalent input noise voltage and employing ME laminate composites with high voltage coefficient to reduce the EMNs of the ME laminate sensors at high frequency range has been established.

A miniaturized wireless accelerometer with micromachined piezoelectric sensing element

A miniaturized wireless accelerometer using a piezoelectric micro sensing element is designed, theoretically analyzed, and demonstrated for remote mechanical vibration monitoring. The micro sensing element comprises a micromachined monolithic silicon seismic mass and multiple silicon beams coated with in-plane polarized (Pb, La)(Zr, Ti)O3 (PLZT) ferroelectric thin film. A low profile compact package is obtained for accommodating all the micro sensing element, charge amplifier and signal processing circuits, radio frequency module, and battery. The electrical output linearly proportional to the vibration acceleration is amplified, digitalized and transmitted to a remote base unit through radio frequency communication. The effects of the device package on the dynamic response of the wireless piezoelectric accelerometer including shielding of ambient interference are investigated.

Paper-based piezoelectric touch pads with hydrothermally grown zinc oxide nanowires.

This paper describes a new type of paper-based piezoelectric touch pad integrating zinc oxide nanowires (ZnO NWs), which can serve as user interfaces in paper-based electronics. The sensing functionality of these touch pads is enabled by the piezoelectric property of ZnO NWs grown on paper using a simple, cost-efficient hydrothermal method. A piece of ZnO-NW paper with two screen-printed silver electrodes forms a touch button, and touch-induced electric charges from the button are converted into a voltage output using a charge amplifier circuit. A touch pad consisting of an array of buttons can be readily integrated into paper-based electronic devices, allowing user input of information for various purposes such as programming, identification checking, and gaming. This novel design features ease of fabrication, low cost, ultrathin structure, and good compatibility with techniques in printed electronics, and further enriches the available technologies of paper-based electronics.

Design and Implementation of Digital Piezoelectric Constant Testing System

Digital piezoelectric constant testing system was designed in this paper, which was based on hydrostatic test method. The system is composed of hydrostatic device, charge amplifier circuit, peak holding circuit, A/D calibration circuit, data processing by DSP. Pressure-release value is obtained by digital pressure transmitter on the hydrostatic device. Combining with mean filtering and A/D calibration, DSP can sample accurate voltage signal. Considering the difference between the equivalent circuit of charge amplifier and its practical circuit, the calculated hydrostatic piezoelectric constant is in better agreement with the theoretical value. The experiment results show that the accuracy of testing system is less than 4%.

Modified Charge Amplifier for Stray Immune Capacitance Measurements

It is shown theoretically and by experimentation that the ac stray immune capacitance meter based on the charge amplifier circuit can be modified to reduce the effects of the parasitic capacitance across the feedback capacitor. This is achieved by simply introducing a unity gain buffer amplifier within the circuit loop.

New ways of measuring the pull-in voltage and transient behavior of parallel-plate capacitive MEMS transducers

In this paper we introduce two new ways of measuring the pull-in voltage and the transient behavior of parallel-plate capacitive microelectromechanical systems (MEMS) transducers. The advantages in the measurement speed and resolution of the so-called fast MEMS test will be discussed. Also an enhanced method, the time-resolved dynamic measurement, will be shown. With the second method, we can visualize the integral displacement of a membrane while measuring the voltage drop of a high-frequency signal over a shunt resistor/capacitor. With a more advanced charge amplifier circuit, also a force-free resonance measurement of the membrane and electrode is possible in one step. All this offers a robust and cheap option for tracing moving structures without the need of an optical line of sight.

Precision tracking of a piezo-driven stage by charge feedback control

Abstract This paper presents a novel approach for precisely controlling the motion of a piezo actuator embedded in a mechanical stage without using a displacement sensor. A piezo actuator has a high displacement resolution, but the positioning performance is degraded by hysteresis between the applied voltage and resultant displacement. However, an electromechanical model of a piezo actuator suggests that the charge flowing in the actuator is directly related to the dynamic response of the piezo displacement. Therefore, this study directly measured the charge stored in a piezo actuator, and achieved dynamic reference tracking of the actuator's displacement by regulating the charge flowing through the actuator to follow a predefined trajectory. This novel approach requires neither specially designed charge amplifier circuits nor implementation of an inverse hysteresis model. The complete model identification and the digital controller design procedure for a piezo-driven mechanical stage are presented. The charge feedback controller is designed according to the dynamic characteristics of both the actuator and the stage, so that instability is minimized relative to using a charge amplifier. The experimental results confirm satisfactory tracking performance, and reveal the influence of model uncertainties on the system performance.

ZnO Thin Film Sensor Design of the Charge Amplifier

The ZnO film as the material, the charge amplifier and the accelerometer in one set, to record and display the measurement data directly, simplifying the testing system to improve the test accuracy and reliability. Charge amplifier circuit is designed to be simple, easy to debug, high integration, low cost, favorable ZnO thin films driven by the widespread use of the accelerometer.

Design of Hydrostatic Piezoelectric Constant Testing System

A new testing method for hydrostatic piezoelectric constant, dh , was studied in this paper. This testing system consists of five parts, which are hydrostatic simulator, signal acquisition and processing circuits, data acquisition, serial communication interact circuit, data processing and display. Researched the method of signal acquisition for hydrostatic piezoelectric charge, designed the charge amplifier circuit, signal processing circuit as well as the data acquisition and serial communication interact circuit with microcomputer, programmed for the date acquisition and processing system software. The hydrostatic piezoelectric constant, dh , of piezoelectric ceramic samples were tested. The experimental results showed that this new testing method is available. The new testing system is characteristic of manipulation simply and low cost.

A high-performance MEMS capacitive strain sensing system

This paper describes the design of a functional strain sensing module with large dynamic range (80 dB), DC to 10 kHz response, high resolution, and mini size for industrial applications, such as the rolling-element bearings research. The design of the MEMS capacitive strain sensor employs mechanical amplifications of package design and buckle beams as well as the linear differential comb capacitor. The sensor is interfaced with a low noise charge amplifier, mixer, and filter circuits to provide an analog output that demonstrated a resolution of 0.09 microstrains with a maximum range of ±1000 microstrains. The sensor and the electronic circuits, including a temperature sensor, can be integrated on a chip, and packaged as a small functional unit. Additional electronics were integrated with the interface circuit on the chip that provide A/D conversion, radio frequency power supply, and digital signal telemetry to a near-by control unit. Preliminary test results are compared with the design simulation.

Monolithic integration of Si-PIN diodes and n-channel double-gate JFET's for room temperature X-ray spectroscopy

We report on Junction Field Effect Transistors and PIN diodes monolithically integrated on high-resistivity silicon by adopting a non-standard technology recently developed at IRST. In particular, a test structure, consisting of a small PIN diode DC-coupled to an integrated n-channel JFET in the double-gate configuration was fully characterised and spectroscopic measurements were carried out by adopting a novel double-feedback charge amplifier circuit. An ENC of about 60 electrons r.m.s. has been obtained at room temperature and at 10 μs shaping time; such a resolution is shown to be determined by the relatively high total capacitance present in this preliminary set-up, associated with the 1/ f series noise of the transistor.

Compensating sensor device for a charge amplifier circuit used in piezoelectric hydrophones

To compensate for the effect of external parameters on piezoelectric sensors connected to a charge amplifier, a small portion of this sensor is used to form the feedback capacitor of the amplifier. These parameters then have the same effect on the sensor and on the capacitor, thus making it possible to provide compensation to hydrophones made of piezoelectric polymer material.