Micro-force Sensor Research Articles

Generative Force of Self-Oscillating Gel

We succeeded in measuring the generative force of a self-oscillating polymer gel in an aqueous solution comprising the three substrates of the Belousov-Zhabotinsky (BZ) reaction (malonic acid, sodium bromate, and nitric acid) under constant temperature. In this study, we developed an apparatus with a microforce sensor for measuring the generative force of small-sized gels (1 mm(3)). The self-oscillating polymer gel directly converts the chemical energy of the BZ reaction into mechanical work. It was determined that the generative force of the self-oscillating gel was 972 Pa, and the period of self-oscillation was 480 s at 18 °C. We demonstrated that the generative force of the gel was about a hundredth the generative force of a muscle in the body. We analyzed the time dependence of the color change in the self-oscillating polymer gel. The color of the gel changed periodically owing to the cyclic change in the redox state of the Ru moiety, induced by the BZ reaction. The peaks of the waveforms of the generative force and color change were almost identical. This result showed that the generative force was synchronized with the periodical change in the oxidation number of the Ru catalytic moiety in the gel. To understand a theoretical basis for the generative force of a self-oscillating gel, we considered a general theory that is based on the volume phase transition of gel and the two-parameter Oregonator model of the BZ reaction.

A miniature reflective micro-force sensor based on a microfiber coupler

A compact highly sensitive microfiber coupler based reflective micro-force sensor is presented. The device is fabricated by fusing two twisted optical fibers and then connecting two of the pigtails to form a Sagnac loop. The sensor has a high force sensitivity of ~3754 nm/N which is three orders of magnitude larger than traditional optical fiber force sensors, and a low detection limit of ~1.6 µN. The good repeatability is also shown in this paper.

MEMS based low cost piezoresistive microcantilever force sensor and sensor module

In the present work, we report fabrication and characterization of a low-cost MEMS based piezoresistive micro-force sensor with SU-8 tip using laboratory made silicon-on-insulator (SOI) substrate. To prepare SOI wafer, silicon film (0.8µm thick) was deposited on an oxidized silicon wafer using RF magnetron sputtering technique. The films were deposited in argon (Ar) ambient without external substrate heating. The material characteristics of the sputtered deposited silicon film and silicon film annealed at different temperatures (400–1050°C) were studied using atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The residual stress of the films was measured as a function of annealing temperature. The stress of the as-deposited films was observed to be compressive and annealing the film above 1050°C resulted in a tensile stress. The stress of the film decreased gradually with increase in annealing temperature. The fabricated cantilevers were 130μm in length, 40μm wide and 1.0μm thick. A series of force–displacement curves were obtained using fabricated microcantilever with commercial AFM setup and the data were analyzed to get the spring constant and the sensitivity of the fabricated microcantilever. The measured spring constant and sensitivity of the sensor was 0.1488N/m and 2.7mV/N. The microcantilever force sensor was integrated with an electronic module that detects the change in resistance of the sensor with respect to the applied force and displays it on the computer screen.

Microdevice arrays of high aspect ratio poly(dimethylsiloxane) pillars for the investigation of multicellular tumour spheroid mechanical properties.

We report the design, fabrication and evaluation of an array of microdevices composed of high aspect ratio PDMS pillars, dedicated to the study of tumour spheroid mechanical properties. The principle of the microdevice is to confine a spheroid within a circle of micropillars acting as peripheral flexible force sensors. We present a technological process for fabricating high aspect ratio micropillars (300 μm high) with tunable feature dimensions (diameter and spacing) enabling production of flexible PDMS pillars with a height comparable to spheroid sizes. This represents an upscale of 10 along the vertical direction in comparison to more conventional PDMS pillar force sensors devoted to single cell studies, while maintaining their force sensitivity in the same order of magnitude. We present a method for keeping these very high aspect ratio PDMS pillars stable and straight in liquid solution. We demonstrate that microfabricated devices are biocompatible and adapted to long-term spheroid growth. Finally, we show that the spheroid interaction with the micropillars' surface is dependent on PDMS cellular adhesiveness. Time-lapse recordings of growth-induced micropillars' bending coupled with a software program to automatically detect and analyse micropillar displacements are presented. The use of these microdevices as force microsensors opens new prospects in the fields of tissue mechanics and pharmacological drug screening.

A Micro-Force Sensor with Slotted-Quad-Beam Structure for Measuring the Friction in MEMS Bearings

Presented here is a slotted-quad-beam structure sensor for the measurement of friction in micro bearings. Stress concentration slots are incorporated into a conventional quad-beam structure to improve the sensitivity of force measurements. The performance comparison between the quad-beam structure sensor and the slotted-quad-beam structure sensor are performed by theoretical modeling and finite element (FE) analysis. A hollow stainless steel probe is attached to the mesa of the sensor chip by a tailor-made organic glass fixture. Concerning the overload protection of the fragile beams, a glass wafer is bonded onto the bottom of sensor chip to limit the displacement of the mesa. The calibration of the packaged device is experimentally performed by a tri-dimensional positioning stage, a precision piezoelectric ceramic and an electronic analytical balance, which indicates its favorable sensitivity and overload protection. To verify the potential of the proposed sensor being applied in micro friction measurement, a measurement platform is established. The output of the sensor reflects the friction of bearing resulting from dry friction and solid lubrication. The results accord with the theoretical modeling and demonstrate that the sensor has the potential application in measuring the micro friction force under stable stage in MEMS machines.

In situ SEM electromechanical characterization of nanowire using an electrostatic tensile device

This paper presents a method for simultaneously performing mechanical tensile test and electrical test on nanowire in SEM. For this purpose, an electrostatic tensile device is designed, fabricated and tested. In order to simplified the testing system, microforce sensor beam is used to measure the tensile force applied to the nanowire instead of traditional capacitive force sensor. Special care is taken on the design and fabrication process to improve the resolution of mechanical measurement by SEM imaging. Mechanical properties such as Young's modulus, elastic limit and fracture strength, and electrical resistance of nanowire can be obtained in the process of tensile testing using this device. Cu nanowire and SiC nanowire are tested as examples in this paper. Smaller Young's modulus is found in both nanowires due to the imperfection in crystallization. On the other hand, electrical properties under different tensile stress are characterized for both nanowires. Nonlinear and identical I–V curves are revealed for Cu nanowire, and linear I–V curves and the piezoresistive effect are revealed for SiC nanowire. The gauge factor of SiC nanowire is calculated and turns out to be compatible with the values of bulk SiC published in the literature.

Structural Design of 2D Piezoresistive Micro-Force Sensor

In order to detect the tool-substrate contact force and the tool-target interaction force during nano-manipulation process, a novel MEMS based 2D piezoresistive micro-force sensor structure was proposed. This structure can realize the 3D hardware decoupling for the X，Y and Z axis. Thus, the force detection in the vertical direction (Z axis) and parallel direction reference to base (X axis) can be done simultaneously. Theoretical analysis shows that this structure has a good structural sensitivity. The rationality and feasibility of the structure were confirmed by simulation results.

Robotic cell injection force control based on static PVDF sensor and Fuzzy-PID control method

Cell injection procedure is very essential in the field of molecular biology, and the injection force affects the success rates very much. However, conventional methods of manipulating individual biological cell failed to make use of the injection force information. This article is intended to design a static micro-force sensor with a simple structure which employs the piezoelectric material PVDF (polyvinylidene fluoride) film as its sensing element to detect the micro-force during cells injection and to develop a close-loop control method to regulate the whole fore-tracking system. A Fuzzy-PID and an ordinary PD feedback control method are employed separately in this article to regulate the micro-force tracking system which is used to carry out automatic living-cell injection tests. Experimental results with different control methods are achieved. And the Fuzzy-PID and PVDF sensor based force control method is validated.

THE MEASUREMENT OF MICROFORCE-SENSOR THERMAL DRIFT MEASURED BY BALANCE IN CMS

The micro-force sensors were widely used in the areas of micro-assembly, micro-factories, micro-robotics, MEMS characterization, Nano-manipulation, Biological and biomedical research, Material properties, etc. It was also used as a transfer standard in micro-force machine or instrument. The capacitance-type force sensor was used to sense forces with micro-Newton (sub-milligram) resolution. And it was used as a transducer for the micro-force instrument in CMS. In this paper, we will report the preliminary results of thermal drift properties in capacitance-type force sensor.

A thin film micro-force sensor using double concentric circle optical fibre

For the purpose of measuring µN- and mN-level micro-force, the optical reflection characteristics of a circular thin film are utilized to develop a micro-force sensor and double concentric circle fibres are used to measure the micro-force. This paper focuses on the relation between the output parameters of the system, namely the voltage ratio of the two receiving fibres, and the micro-force, the diameter, the thickness and the materials of the thin film, as well as the displacement between the fibre probe and the film. A measurement platform has been set-up and a large number of experiments have been conducted to determine the relationship between the voltage ratio and the micro-force, the diameter and the thickness of the thin film by using a least square exponential fitting algorithm. Furthermore, the errors between the calculating values from the fitting equation and the experimental values are obtained and analysed, which supports the conclusion that when the micro-force is in the range of 0–10 mN, the equation can be used to measure the micro-force with the resolution of 10 µN in the error range of −1.5%–+2.5%, and an automatic measurement process is realized.

E-Cadherin-Dependent Stimulation of Traction Force at Focal Adhesions via the Src and PI3K Signaling Pathways

The interplay between cadherin- and integrin-dependent signals controls cell behavior, but the precise mechanisms that regulate the strength of adhesion to the extracellular matrix remains poorly understood. We deposited cells expressing a defined repertoire of cadherins and integrins on fibronectin (FN)-coated polyacrylamide gels (FN-PAG) and on FN-coated pillars used as a micro-force sensor array (μFSA), and analyzed the functional relationship between these adhesion receptors to determine how it regulates cell traction force. We found that cadherin-mediated adhesion stimulated cell spreading on FN-PAG, and this was modulated by the substrate stiffness. We compared S180 cells with cells stably expressing different cadherins on μFSA and found that traction forces were stronger in cells expressing cadherins than in parental cells. E-cadherin-mediated contact and mechanical coupling between cells are required for this increase in cell-FN traction force, which was not observed in isolated cells, and required Src and PI3K activities. Traction forces were stronger in cells expressing type I cadherins than in cells expressing type II cadherins, which correlates with our previous observation of a higher intercellular adhesion strength developed by type I compared with type II cadherins. Our results reveal one of the mechanisms whereby molecular cross talk between cadherins and integrins upregulates traction forces at cell-FN adhesion sites, and thus provide additional insight into the molecular control of cell behavior.

A Novel Integrated Multifunction Micro-Sensor for Three-Dimensional Micro-Force Measurements

An integrated multifunction micro-sensor for three-dimensional micro-force precision measurement under different pressure and temperature conditions is introduced in this paper. The integrated sensor consists of three kinds of sensors: a three-dimensional micro-force sensor, an absolute pressure sensor and a temperature sensor. The integrated multifunction micro-sensor is fabricated on silicon wafers by micromachining technology. Different doping doses of boron ion, placement and structure of resistors are tested for the force sensor, pressure sensor and temperature sensor to minimize the cross interference and optimize the properties. A glass optical fiber, with a ladder structure and sharp tip etched by buffer oxide etch solution, is glued on the micro-force sensor chip as the tactile probe. Experimental results show that the minimum force that can be detected by the force sensor is 300 nN; the lateral sensitivity of the force sensor is 0.4582 mV/μN; the probe length is linearly proportional to sensitivity of the micro-force sensor in lateral; the sensitivity of the pressure sensor is 0.11 mv/KPa; the sensitivity of the temperature sensor is 5.836 × 10−3 KΩ/°C. Thus it is a cost-effective method to fabricate integrated multifunction micro-sensors with different measurement ranges that could be used in many fields.

A Microvalve Driven by a Ferrofluid-Based Actuator

A novel ferrofluid-based microvalve adopting an electromagnetic actuation is presented. In the device, ferrofluid controlled by magnetic force is used as a microactuator. The deflection of the diaphragm caused by the ferrofluid-based actuator opens or closes the fluid flow in the microchannel. A detailed description of the design and working principle of the microvalve is presented. The driving force generated by the ferrofluid under applied magnetic field has been measured by a microforce sensor. And the deflection of the diaphragm has been simulated by ANSYS software.

A Micro-Force-Tracking System Based on PVDF Static Micro-Force Sensor and Fuzzy-PID Control Method

This article is intended to design a static micro-force sensor with a simple structure employing the polymer material PVDF (polyvinylidene fluoride) film as its sensing element, and will carry out some micro-force tracking tests. During the tracking tests, this paper employs a Fuzzy-PID control method and an ordinary PD control method to control the system, and will also analyze the results of them.

Study on a Micro-Force Generated Mechanism for Sensor Calibration

The current method of micro-force generated for sensor calibration is scarcity and complexity. In the paper we propose a mechanism based on flexible hinges for micro-force, illustrate its working principle and establish the mechanical model. By theoretical analysis the analytical expression of the force reduction multiplier is derived. After initializing some parameters, the result shows that this mechanism can produce the large range and high resolution force of µN. The force can be applied in calibration of micro-force sensor.

The Role of Exploratory Conditions in Bio-Inspired Tactile Sensing of Single Topogical Features

We investigate the mechanism of tactile transduction during active exploration of finely textured surfaces using a tactile sensor mimicking the human fingertip. We focus in particular on the role of exploratory conditions in shaping the subcutaneous mechanical signals. The sensor has been designed by integrating a linear array of MEMS micro-force sensors in an elastomer layer. We measure the response of the sensors to the passage of elementary topographical features at constant velocity and normal load, such as a small hole on a flat substrate. Each sensor’s response is found to strongly depend on its relative location with respect to the substrate/skin contact zone, a result which can be quantitatively understood within the scope of a linear model of tactile transduction. The modification of the response induced by varying other parameters, such as the thickness of the elastic layer and the confining load, are also correctly captured by this model. We further demonstrate that the knowledge of these characteristic responses allows one to dynamically evaluate the position of a small hole within the contact zone, based on the micro-force sensors signals, with a spatial resolution an order of magnitude better than the intrinsic resolution of individual sensors. Consequences of these observations on robotic tactile sensing are briefly discussed.

Precision friction measurement between ultrathin wire and microprobe

In this study, using an experimental technique based on small-span bending, the friction behaviors of ultrathin Pt wires with the tungsten microprobes have been reported. In the technique, friction force for sliding of a simply supported wire under bending load applied by closely positioned two opposite probes is measured by a microforce sensor. The force sensor is a capacitive detection type double-beam passive cantilever. Specificity of the microforce sensor provides the technological advantage for precise measurement of friction and normal contact forces sequentially under the observation by a high-resolution digital microscope. Static and kinetic frictions due to externally applied force, internal adhesive force and relative motion are successfully determined. Furthermore, the measured friction in wire-probe contact is used in the determination of the mechanical properties of the wire material.

Quantifying growth mechanics of living, growing plant cells in situ using microrobotics

Plant cell growth is a fundamental process during plant development and the developmental biology society has studied cell growth from various aspects using physiological, biochemical, genetic, mathematical and modelling approaches. Recent advances in the field of biology demonstrate a need for investigation and quantification of the mechanics of growth at individual cellular levels. Here, we describe a microrobotic system capable of performing automated mechanical characterisation of living plant cells in situ as these cells proliferate and grow. The microrobotic measurement system employs a single-axis capacitive MEMS microforce sensor, a multi-axis positioning system with position feedback, a high-resolution optical microscope and a custom–user interface for the guiding of the automated measurement process. The system has been applied to measure mechanical properties of Lilium pollen tubes approximately 20 µm wide. The measurements were performed in growth medium, and the observed growth rate of the pollen tubes is about 20 µm per minute. For the mechanical characterisation of pollen tubes, nano-Newton level loads and nanometric indentations are applied. The force-deformation data obtained show a difference in stiffness from the tip to the apex demonstrating that the developed measurement system is a promising tool for better understanding the mechanics of plant cell growth.

Analysis of a passive microforce sensor based on magnetic springs and upthrust buoyancy

Abstract This paper is focused on the design and modeling of a new micro and nano force sensor using magnetic springs. The force sensitive part is a macroscopic horizontal rigid platform used as a floating seismic mass. This platform presents a naturally stable equilibrium state for its six degrees of freedom (dof) thanks to the combination of upthrust buoyancy and magnetic forces. This force sensor allows the measurement of the external horizontal force and the vertical torque applied to the platform. Thanks to the magnetic springs configuration used, the seismic mass presents a 0.02 N/m horizontal mechanical stiffness (similar to the stiffness of a thin AFM micro-cantilever). The measurement range typically varies between ±50 μN. The resolution depends on the displacement sensors used to measure the seismic mass displacement and on the environmental conditions (ground, liquid and air vibrations). In steady state, this displacement is proportional to the applied force. Resolution of less than 10 nN can be reached with the use of an anti-vibration table.

Investigation of loading and force sensing properties of a probe-type microforce sensor with force-distance curves

In this paper, the force-distance curves have been employed to investigate the force sensing properties of the probe-type microforce sensors. In the preliminary studies, two kinds of probe-type microforce sensors have been used to load the objects with dry and wetted surfaces. One is a developed piezoresistive cantilever force sensor with sensitivity of 35 μN/V and the other an atomic force microscope (AFM) cantilever beam probe with sensitivity of 10.4 nN/V. The force outputs corresponding to the regimes of approaching, indenting, and loading are obtained, and the properties of the stability in the approaching regime of the sensors, local mechanical behavior of the tested objects in the indenting regime, and the force sensing of the global samples are analyzed. Experimental results of this analysis are also presented.