Search Results (52)

A novel piezoresistive cantilever microprobe (PCM) with an integrated electrothermal or piezoelectric actuator has been designed to replace current commercial PCMs, which require external actuators to perform contact-resonance imaging (CRI) of workpieces and avoid unwanted “forest of peaks” observed at large travel speed in the millimeter-per-second range. Initially, a PCM with integrated resistors for electrothermal actuation (ETA) was designed, built, and tested. Here, the ETA can be performed with a piezoresistive Wheatstone bridge, which converts mechanical strain into electrical signals by boron diffusion in order to simplify the production process. Moreover, a new substrate contact has been added in the new design for an AC voltage supply for the Wheatstone bridge to reduce parasitic signal influence via the EAM (Electromechanical Amplitude Modulation) in our homemade CRI system. Measurements on a bulk Al sample show the expected force dependence of the CR frequency. Meanwhile, fitting of the measured contact-resonance spectra was applied based on a Fano-type line shape to reveal the material-specific signature of a single harmonic resonator. However, noise is greatly increased with the bending mode and contact force increasing on viscoelastic samples. Then, to avoid unspecific peaks remaining in the spectra of soft samples, cantilevers with integrated piezoelectric actuators (PEAs) were designed. The numbers and positions of the actuators were optimized for specific CR vibration modes using analytical modeling of the cantilever bending based on the transfer-matrix method and Hertzian contact mechanics. To confirm the design of the PCM with a PEA, finite element analysis (FEA) of CR probing of a sample with a Young’s modulus of 10 GPa was performed. Close agreement was achieved by Fano-type line shape fitting of amplitude and phase of the first four vertical bending modes of the cantilever. As an important structure of the PCM with a PEA, the piezoresistive Wheatstone bridge had to have suitable doping parameters adapted to the boundary conditions of the manufacturing process of the newly designed PCM. Full article

MEMS acoustic sensors are a type of physical quantity sensor based on MEMS manufacturing technology for detecting sound waves. They utilize various sensitive structures such as thin films, cantilever beams, or cilia to collect acoustic energy, and use certain transduction principles to read out the generated strain, thereby obtaining the targeted acoustic signal’s information, such as its intensity, direction, and distribution. Due to their advantages in miniaturization, low power consumption, high precision, high consistency, high repeatability, high reliability, and ease of integration, MEMS acoustic sensors are widely applied in many areas, such as consumer electronics, industrial perception, military equipment, and health monitoring. Through different sensing mechanisms, they can be used to detect sound energy density, acoustic pressure distribution, and sound wave direction. This article focuses on piezoelectric, piezoresistive, capacitive, and optical MEMS acoustic sensors, showcasing their development in recent years, as well as innovations in their structure, process, and design methods. Then, this review compares the performance of devices with similar working principles. MEMS acoustic sensors have been increasingly widely applied in various fields, including traditional advantage areas such as microphones, stethoscopes, hydrophones, and ultrasound imaging, and cutting-edge fields such as biomedical wearable and implantable devices. Full article

In this paper, the impact of Lorentz forces and temperature on the natural frequencies of a piezoresistive sensor composed of two microcantilevers with integrated U-shaped thin-film aluminum heaters are investigated. Two types of experiments were performed. In the first, the sensor was placed in a magnetic field so that the current flowing in the heater, in addition to raising the temperature, produced Lorentz forces, inducing normal stresses in the plane of one of the microcantilevers. In the second, which were conducted without magnetic fields, only the temperature variation of the natural frequency was left. In processing of the results, the thermal variations were subtracted from the variations due to both Lorentz forces and temperature in the natural frequency, resulting in the influence of the Lorentz forces only. Theoretical relations for the Lorentz frequency offsets were derived. An indirect method of estimating the natural frequency of one of the cantilevers, through a particular cusp point in the amplitude–frequency response of the sensor, was used in the investigations. The findings show that for thin microcantilevers with silicon masses on the order of 4 × 10⁻⁷ g and currents of 25 µA, thermal eigenfrequency variations are dominant. The results may have applications in the design of similar microsensors with vibrational action. Full article

Electrothermal piezoresistive resonant cantilever sensors have been fabricated with embedded actuating (heating resistor) and sensing (piezo resistors) parts, with the latter configured in a Wheatstone bridge circuit. Due to the close spacing between these two elements, a direct thermal parasitic effect on the resonant sensor during the actuating-sensing process leads to asymmetric amplitude and reversing phase spectral responses. Such a condition affects the precise determination of the cantilever’s resonant frequency, f₀. Moreover, in the context of phase-locked loop-based (PLL) resonance tracking, a reversing phase spectral response hinders the resonance locking due to its ambiguity. In this work, a replica of the baseline spectral was applied to remove the thermal parasitic effect on the resonance spectra of the cantilever sensor, and its capability was simulated through mathematical analysis. This replica spectral was subtracted from the parasitized spectral using a particular calculation, resulting in optimized spectral responses. An assessment using cigarette smoke particles performed a desired spectral shifting into symmetrical amplitude shapes and monotonic phase transitions, subsequently allowing for real-time PLL-based frequency tracking. Full article

MXenes are a new family of two-dimensional (2D) nanomaterials. They are inorganic compounds of metal carbides/nitrides/carbonitrides. Titanium carbide MXene (Ti${}_3$C${}_2$-MXene) was the first 2D nanomaterial reported in the MXene family in 2011. Owing to the good physical properties of Ti${}_3$C${}_2$-MXenes (e.g., conductivity, hydrophilicity, film-forming ability, elasticity) various applications in wearable sensors, energy harvesters, supercapacitors, electronic devices, etc., have been demonstrated. This paper presents the development of a piezoresistive Ti${}_3$C${}_2$-MXene sensor followed by experimental investigations of its dynamic response behavior when subjected to structural impacts. For the experimental investigations, an inclined ball impact test setup is constructed. Stainless steel balls of different masses and radii are used to apply repeatable impacts on a vertical cantilever plate. The Ti${}_3$C${}_2$-MXene sensor is attached to this cantilever plate along with a commercial piezoceramic sensor, and their responses for the structural impacts are compared. It is observed from the experiments that the average response times of the Ti${}_3$C${}_2$-MXene sensor and piezoceramic sensor are $1.28\pm 0.24$$\mathsf{\mu }$s and $31.19\pm 24.61$$\mathsf{\mu }$s, respectively. The fast response time of the Ti${}_3$C${}_2$-MXene sensor makes it a promising candidate for monitoring structural impacts. Full article

To meet the measurement needs of multidimensional high-g acceleration in fields such as weapon penetration, aerospace, and explosive shock, a biaxial piezoresistive accelerometer incorporating tension–compression is meticulously designed. This study begins by thoroughly examining the tension–compression measurement mechanism and designing the sensor’s sensitive structure. A signal test circuit is developed to effectively mitigate cross-interference, taking into account the stress variation characteristics of the cantilever beam. Subsequently, the signal test circuit of anti-cross-interference is designed according to the stress variation characteristics of the cantilever beam. Next, the finite element method is applied to analyze the structure and obtain the performance indices of the range, vibration modes, and sensitivity of the sensor. Finally, the process flow and packaging scheme of the chip are analyzed. The results show that the sensor has a full range of 200,000 g, a sensitivity of 1.39 µV/g in the X direction and 1.42 µV/g in the Y direction, and natural frequencies of 509.8 kHz and 510.2 kHz in the X and Y directions, respectively. Full article

In this study, an electrostatic force-driven on-chip tester consisting of a mass with four guided cantilever beams was employed to extract the process-related bending stiffness and piezoresistive coefficient in-situ for the first time. The tester was manufactured using the standard bulk silicon piezoresistance process of Peking University, and was tested on-chip without additional handling. In order to reduce the deviation from process effects, the process-related bending stiffness was first extracted as an intermediate value, namely, 3590.74 N/m, which is 1.66% lower than the theoretical value. Then, the value was used to extract the piezoresistive coefficient using a finite element method (FEM) simulation. The extracted piezoresistive coefficient was 9.851 × 10⁻¹⁰ Pa⁻¹, which essentially matched the average piezoresistive coefficient of the computational model based on the doping profile we first proposed. Compared with traditional extraction methods, such as the four-point bending method, this test method is on-chip, achieving automatic loading and precise control of the driving force, so it has high reliability and repeatability. Because the tester is manufactured together with the MEMS device, it has the potential to be used for process quality evaluation and monitoring on MEMS sensor production lines. Full article

It is expected that human iPS cell-derived cardiomyocytes (hiPSC-CMs) can be used to treat serious heart diseases. However, the properties and functions of human adult cardiomyocytes and hiPSC-CMs, including cell maturation, differ. In this study, we focused on the temperature dependence of hiPSC-CMs by integrating the temperature regulation system into our sensor platform, which can directly and quantitatively measure their mechanical motion. We measured the beating frequency of hiPSC-CMs at different environmental temperatures and found that the beating frequency increased as the temperature increased. Although the rate at which the beating frequency increased with temperature varied, the temperature at which the beating stopped was relatively stable at approximately 20 °C. The stopping of beating at this temperature was stable, even in immature hiPSC-CMs, and was considered to be a primitive property of cardiomyocytes. Full article

A flexible piezoresistive sensor was developed as an accelerometer based on Graphene/PVDF nanocomposite to detect low-frequency and low amplitude vibration of industrial machines, which may be caused due to misalignment, looseness of fasteners, or eccentric rotation. The sensor was structured as a cantilever beam with the proof mass at the free end. The vibration caused the proof mass to accelerate up and down, which was converted into an electrical signal. The output was recorded as the change in resistance (response percentage) with respect to the acceleration. It was found that this accelerometer has a capability of detecting acceleration up to 8 g_pk-pk in the frequency range of 20 Hz to 80 Hz. The developed accelerometer has the potential to represent an alternative to the existing accelerometers due to its compactness, simplicity, and higher sensitivity for low frequency and low amplitude applications. Full article

We addressed the coating 5 mm-long cantilever microprobes with a viscoelastic material, which was intended to considerably extend the range of the traverse speed during the measurements of the 3D surface topography by damping contact-induced oscillations. The damping material was composed of epoxy glue, isopropyl alcohol, and glycerol, and its deposition onto the cantilever is described, as well as the tests of the completed cantilevers under free-oscillating conditions and in contact during scanning on a rough surface. The amplitude and phase of the cantilever’s fundamental out-of-plane oscillation mode was investigated vs. the damping layer thickness, which was set via repeated coating steps. The resonance frequency and quality factor decreased with the increasing thickness of the damping layer for both the free-oscillating and in-contact scanning operation mode, as expected from viscoelastic theory. A very low storage modulus of $E^{\prime }\approx 100\mathrm{kPa}$, a loss modulus of $E^{″}\approx 434\mathrm{kPa}$, and a density of $\rho \approx 1.2\mathrm{g}{\mathrm{cm}}^{-3}$ were yielded for the damping composite. Almost critical damping was observed with an approximately 130 µm-thick damping layer in the free-oscillating case, which was effective at suppressing the ringing behavior during the high-speed in-contact probing of the rough surface topography. Full article

In this study, thin films of zinc oxide doped with fluorine ZnO: F were deposited via ultrasonic spray pyrolysis (USP) with an atomic ratio of [F/Zn] in a starting solution of 15 at.% on borosilicate glass coverslips and SiO₂/Si substrates. The structure, electrical resistivity, and thickness were obtained via X-ray diffraction, the four-point technique, and profilometry, respectively. A ZnO: F piezoresistor was modeled at the fixed end of the cantilever through lithography and chemical etching. A SiO₂/Si cantilever structure was used to evaluate the piezoresistivity of a ZnO: F thin film, and temperature coefficient of resistance (TCR) measurements were performed in an electric furnace. The strain on the ZnO: F piezoresistor caused by the application of masses at the free end of the cantilever was determined using a theoretical equation, in addition to a simulation in the COMSOL Multiphysics 5.3a FEM (finite element method) software considering the dimensions and materials of the manufactured device. The ZnO: F thin films were hexagonal wurtzite (phase 002), with thicknesses in the range from 234 nm to 295 nm and with resistivities of the order of 10⁻² Ω.cm. The ZnO: F thin-film piezoresistor showed a gauge factor (GF) of 12.7 and a TCR of −3.78 × 10⁻³ %/K up to 525 K, which are suitable properties for sensor development. Full article

Magnetic Force Microscopy (MFM) is among the best techniques for examining and assessing local magnetic characteristics in surface structures at scales and sizes. It may be viewed as a unique way to operate atomic force microscopy with a ferromagnetic tip. The enhancement of magnetic signal resolution, the utilization of external fields during measurement, and quantitative data analysis are now the main areas of MFM development. We describe a new structure of MFM design based on a cryogen-free superconducting magnet. The piezoelectric tube (PZT) was implemented with a tip-sample coarse approach called SpiderDrive. The technique uses a magnetic tip on the free end of a piezo-resistive cantilever which oscillates at its resonant frequency. We obtained a high-quality image structure of the magnetic domain of commercial videotape under extreme conditions at 5 K, and a high magnetic field up to 11 T. When such a magnetic field was gradually increased, the domain structure of the videotape did not change much, allowing us to maintain the images in the specific regions to exhibit the performance. In addition, it enabled us to locate the sample region in the order of several hundred nanometers. This system has an extensive range of applications in the exploration of anisotropic magnetic phenomena in topological materials and superconductors. Full article

Wearable sensor devices with minimal discomfort to the wearer have been widely developed to realize continuous measurements of vital signs (body temperature, blood pressure, respiration rate, and pulse wave) in many applications across various fields, such as healthcare and sports. Among them, microelectromechanical systems (MEMS)-based differential pressure sensors have garnered attention as a tool for measuring pulse waves with weak skin tightening. Using a MEMS-based piezoresistive cantilever with an air chamber as the pressure change sensor enables highly sensitive pulse-wave measurements to be achieved. Furthermore, the initial static pressure when attaching the sensor to the skin is physically excluded because of air leakage around the cantilever, which serves as a high-pass filter. However, if the frequency characteristics of this mechanical high-pass filter are not appropriately designed, then the essential information of the pulse-wave measurement may not be reflected. In this study, the frequency characteristics of a sensor structure is derived theoretically based on the air leakage rate and chamber size. Subsequently, a pulse wave sensor with a MEMS piezoresistive cantilever element, two air chambers, and a skin-contacted membrane is designed and fabricated. The developed sensor is 30 mm in diameter and 8 mm in thickness and realizes high-pass filter characteristics of 0.7 Hz. Finally, pulse wave measurement at the neck of a participant is demonstrated using the developed sensor. It is confirmed that the measured pulse wave contains signals in the designed frequency band. Full article

This paper reports on a mask-type sensor for simultaneous pulse wave and respiration measurements and eye blink detection that uses only one sensing element. In the proposed sensor, a flexible air bag-shaped chamber whose inner pressure change can be measured by a microelectromechanical system-based piezoresistive cantilever was used as the sensing element. The air bag-shaped chamber is fabricated by wrapping a sponge pad with plastic film and polyimide tape. The polyimide tape has a hole to which the substrate with the piezoresistive cantilever adheres. By attaching the sensor device to a mask where it contacts the nose of the subject, the sensor can detect the pulses and eye blinks of the subject by detecting the vibration and displacement of the nose skin caused by these physiological parameters. Moreover, the respiration of the subject causes pressure changes in the space between the mask and the face of the subject as well as slight vibrations of the mask. Therefore, information about the respiration of the subject can be extracted from the sensor signal using either the low-frequency component (<1 Hz) or the high-frequency component (>100 Hz). This paper describes the sensor fabrication and provides demonstrations of the pulse wave and respiration measurements as well as eye blink detection using the fabricated sensor. Full article

An electrothermal piezoresistive cantilever (EPC) sensor is a low-cost MEMS resonance sensor that provides self-actuating and self-sensing capabilities. In the platform, which is of MEMS-cantilever shape, the EPC sensor offers several advantages in terms of physical, chemical, and biological sensing, e.g., high sensitivity, low cost, simple procedure, and quick response. However, a crosstalk effect is generated by the coupling of parasitic elements from the actuation part to the sensing part. This study presents a parasitic feedthrough subtraction (PFS) method to mitigate a crosstalk effect in an electrothermal piezoresistive cantilever (EPC) resonance sensor. The PFS method is employed to identify a resonance phase that is, furthermore, deployed to a phase-locked loop (PLL)-based system to track and lock the resonance frequency of the EPC sensor under cigarette smoke exposure. The performance of the EPC sensor is further evaluated and compared to an AFM-microcantilever sensor and a commercial particle counter (DC1100-PRO). The particle mass–concentration measurement result generated from cigarette-smoke puffs shows a good agreement between these three detectors. Full article