Microelectromechanical Systems Force Sensors Research Articles

Towards a MEMS Force Sensor via the Electromagnetic Principle.

Force measurement is a science discipline that experiences significant progress with the introduction of new materials and evaluation methods. Many different sensor types, working on different principles, have been developed and reviewed and have found use in medicine as well as many other industries. New trends and demands require a size reduction and simple applicability, with the use of, for example, micro electromechanical systems (MEMS). For purposes of this study, the initial MEMS body is supplemented by its scaled version. Force measurement in this study works on the force to time-delay conversion principle. A compact compliant mechanical body (CCMB) with an embedded parallel resonant circuit (PRC) acting as a transducer realizes the conversion. Depending on the resonant frequency of the transducer (CCMB or MEMS), we have measured the applied force based on the reverse influence of the transducer on the surrounding EM field. The analysis shows that the transducer's resonant frequency has a detectable reverse influence on the voltage-controlled oscillator (VCO) DC supply current. The force influencing the transducer is determined by the DC supply current ripple position during the VCO frequency sweep. The study presents the method proposal and mathematical analysis, as well as its function verification by simulation and prototype measurements. The proposed principle was validated on a CCMB prototype capable of measuring forces up to ∼2.5 N at a sampling frequency of ∼23 kHz, while the measured time-delay ranges from 14.5 µs to 27.4 µs.

A High Dynamic Range Closed-Loop Stiffness-Adjustable MEMS Force Sensor

We present a microelectromechanical system (MEMS)-based closed-loop force sensor, capable of measuring bidirectional forces along one axis of motion. The device comprises an on-chip electrothermal displacement sensor and electrostatic actuators. It features a voltage-controlled stiffness-adjustment mechanism, providing the user with an additional means of tuning the sensor’s characteristics. This silicon-on-insulator device is an improvement on our previous design, offering a better dynamic range and a less complex calibration process. The sensor is fabricated based on a standard SOI MEMS process. It is then fully characterized and instrumented with a feedback controller. The closed-loop characterization reveals a ${1 {\sigma }}$ -resolution of 4.74 nN and a force sensing range of $- {211.7\, {\mu }\text {N}}$ to $\mathrm {211.5\, {\mu }N}$ , leading to a dynamic range of 92.9 dB. [2019-0248]

Design analysis of polysilicon piezoresistors PDMS (Polydimethylsiloxane) microcantilever based MEMS Force sensor

This study is aimed for the analysis of different designs for sensing low magnitude forces which lies in the micro-Newton range and suitable for biomimetic microbotics. For this, a flexible and high sensitive Micro Electro Mechanical System (MEMS) based Force sensor using piezoresistive sensing mechanism has been analyzed. Design analysis is carried out for sensitivity enhancement on microcantilever by incorporating various combinations of stress concentrated regions (SCR) and their respective arrays. The materials under consideration for sensor are polysilicon piezoresistors and Polydimethylsiloxane (PDMS) microcantilever. For design analysis, the designing and simulation work is assessed using Finite Element Analysis approach in COMSOL Multiphysics 5.3a software. The results revealed that the electrical sensitivity of 1.62 mV/[Formula: see text]N within (0–100) [Formula: see text]N operating range is achieved for microcantilever with rectangular SCR with square SCR array. This operating range has many applications in microbotic field such as sensing tactile movements. Hence, MEMS Force sensor for low magnitude forces has been designed with high sensitivity and flexibility.

MEMS piezo-resistive force sensor based on DC sputtering deposited amorphous carbon films

The rapid growing demand of micro-electromechanical system (MEMS) sensors brings an urgent need for high performance and low cost sensitive materials. In this work, amorphous carbon (a-C) film was in-situ deposited on silicon substrate as strain sensitive component using economical direct current (DC) magnetron sputtering process and the a-C sensor was systematically designed, fabricated and tested. By adjusting the negative bias voltage in the range of 0–400 V, the gauge factor (GF) of the a-C film was adjusted within the range of 3.3–6.9. What’s more, the film’s sp2 cluster size played an important role in their piezo-resistive performance and conductivity, which illustrated the thick-film resistors (TFRs) theory. Additionally, CAFM results also supported the applying of TFRs theory in this work. Benefiting from the outstanding performance of a-C film, the MEMS force sensor, consisted a Wheatstone full-bridge with four a-C piezo-resistors, had a sensitivity of 9.8 μV/V/mN and non-linearity about 2.0% FS in the testing range of 0–210 mN, while it also showed a good repeatability. These investigations provided deeper insight into the piezo-resistive behavior of a-C film and contributed to the development of high performance and more economical sensitive materials for MEMS sensors.

Piezoresistive behavior of amorphous carbon films for high performance MEMS force sensors

In this study, microelectromechanical systems (MEMS) force sensors based on H-free amorphous carbon (a-C) films with controlled piezoresistive behavior were fabricated by a facile magnetron sputtering technique. By adjusting the substrate bias voltage from 0 V (floating state) to –350 V, the gauge factor (GF) of the a-C film was modulated in the range of 1.4–12.1. Interestingly, the GF showed a strong dependence on the sp2 content and the sp2 cluster size of the film, which was consistent with the theory of thick film resistors. In addition, the sensitivity of a-C based MEMS force sensors reached 80.7 μV/V/N in the force range of 0–1.16 N, with a nonlinearity of approximately 1.3% full scale and good repeatability in over 5000 test cycles.

An adjustable-stiffness MEMS force sensor: Design, characterization, and control

This paper presents a novel one-degree-of-freedom microelectromechanical systems (MEMS) force sensor. The high-bandwidth device contains on-chip sensing and actuation mechanisms, enabling open- and closed-loop modalities. An active compliance mechanism is incorporated to render the device more conducive to characterization of soft samples. When operated in closed loop, the adjustable stiffness enables the sensor to attain a larger dynamic range and minimize the nonlinearities originating from flexures. Analytical models are employed to design and calibrate the sensor. In open loop, the sensing resolution of 23.3 nN within a bandwidth of 2.35 kHz and a full-scale range of ± 42.6 µ N are experimentally obtained. The resolution is enhanced to 9.3 nN by employing an active compliance mechanism. When operated in closed loop, a resolution of 12.9 nN is achieved within a dynamic range of 71.2 dB and a sensing bandwidth of 3.6 kHz is demonstrated. The sensor performance is tested by obtaining the stiffness of an atomic force microscope probe and measuring the force produced by a self-actuated piezoelectric microcantilever.

Feedback-Controlled MEMS Force Sensor for Characterization of Microcantilevers

This paper outlines the design and characterization of a setup used to measure the stiffness of microcantilevers and other small mechanical devices. Due to the simplicity of fabrication, microcantilevers are used as the basis for a variety of mechanical sensor designs. In a range of applications, knowledge of the stiffness of microcantilevers is essential for the accurate calibration of the sensors in which they are used. Stiffness is most commonly identified through measurement of the microcantilever's resonance frequency, which is applied to an empirically derived model. This paper uses a microelectromechanical system (MEMS)-based force sensor to measure the forces produced by a microcantilever when deformed and a piezoelectric tube-based nanopositioner to displace the microcantilever. A method of calibrating the force sensor is presented that takes advantage of the lumped nature of the mechanical system and the nonlinearity of MEMS electrostatic drives.

Stiffness of the substrate influences the phenotype of embryonic chicken cardiac myocytes

We examined the effect of substrate stiffness on the beating rate, force of contraction, and cytoskeletal structure of embryonic chicken cardiac myocytes by culturing them on laminin-coated polyacrylamide (PA) substrates. Cells cultured on PA substrates with elasticity comparable to that of the native myocardium (18 kPa) exhibited the highest beating rate during the first few days of culture. The initial beating rate of individual cells on all the substrates varied significantly but began to converge within 5 days. We also examined the focal adhesions (FAs) and cytoskeletal structure on different substrates via confocal microscopy and found a higher percentage of FAs on tissue culture (TC) plastic dishes compared with the softer PA gels. Furthermore, highly aligned sarcomeric striations were clearly visible on 18 kPa, 50 kPa, and TC dish, whereas cells on 1 kPa only showed nonaligned diffused striations. The force of contraction on these substrates was measured using a micro-electromechanical system force sensor, which showed that the force of contraction for the cells on TC dishes (F = 71.30 ± 6.38 nN) was significantly larger than those cultured on the 18-kPa PA gel (F = 30.16 ± 3.83 nN). This is most likely due to the formation of higher percentage of FAs on the TC dishes compared with fewer FAs on the softer gels. Our cumulative findings can have a significant impact on the design of 3D cardiac tissue engineered scaffolds.

A Six-Axis MEMS Force–Torque Sensor With Micro-Newton and Nano-Newtonmeter Resolution

This paper describes the design of a six-axis microelectromechanical systems (MEMS) force-torque sensor. A movable body is suspended by flexures that allow deflections and rotations along the x-, y-, and z-axes. The orientation of this movable body is sensed by seven capacitors. Transverse sensing is used for all capacitors, resulting in a high sensitivity. A batch fabrication process is described as capable of fabricating these multiaxis sensors with a high yield. The force sensor is experimentally investigated, and a multiaxis calibration method is described. Measurements show that the resolution is on the order of a micro-Newton and nano-Newtonmeter. This is the first six-axis MEMS force sensor that has been successfully developed.

Investigation of mechanical properties of soft hydrogel microcapsules in relation to protein delivery using a MEMS force sensor

This article reports the investigation of mechanical properties of alginate-chitosan microcapsules and the relation to protein delivery. For microscale compression testing, a system based on a microelectromechanical systems (MEMS) capacitive force sensor was developed. The bulk microfabricated capacitive force sensors are capable of resolving forces up to 110 microN with a resolution of 33.2 nN along two independent axes. The monolithic force sensors were directly applied to characterizing mechanical properties of soft hydrogel microparticles without assembling additional end-effectors. Protein-loaded alginate-chitosan microcapsules of approximately 20 mum in diameter were prepared by an emulsion-internal gelation-polyelectrolyte coating method. Young's modulus values of individual microcapsules with 1, 2, and 3% chitosan coating were determined through microscale compression testing in both distilled deionized (DDI) water and pH 7.4 phosphate-buffered saline (PBS). Protein release rates were also determined in DDI water and PBS. Finally, protein release rates were correlated with mechanical properties of the microcapsules.

MEMS capacitive force sensors for cellular and flight biomechanics

Microelectromechanical systems (MEMS) are playing increasingly important roles in facilitating biological studies. They are capable of providing not only qualitative but also quantitative information on the cellular, sub-cellular and organism levels, which is instrumental to understanding the fundamental elements of biological systems. MEMS force sensors with their high bandwidth and high sensitivity combined with their small size, in particular, have found a role in this domain, because of the importance of quantifying forces and their effect on the function and morphology of many biological structures. This paper describes our research in the development of MEMS capacitive force sensors that have already demonstrated their effectiveness in the areas of cell mechanics and Drosophila flight dynamics studies.