Piezoresistive Strain Sensors Research Articles

MICRO STRAIN SENSOR BASED ON DRAIN CURRENT CHANGE OF MOSFET

Many types of tactile sensor have been proposed and developed, and they are becoming miniaturized and more precise at present state. Micro tactile sensors of high performance comparable to a human being are desired for robotic application, in which skilful and dexterous motion like a human being is necessary. Micromachining is one solution to realize a practical tactile sensor. In usual researches, capacitive, piezoelectric, and piezoresistive types are employed as the measurement principle of a micromachined sensor. In this paper, the MOSFET is applied and the drain current change of it when applied strain is employed as the measurement principle of tactile sensor. A fabricated sensor based on this principle detects strain with a good linearity. The result is compared with that of a conventional piezoresistive strain sensor, which shows the sensitivity of the developed MOSFET strain sensor has a good possibility compatible to conventional type sensors.

A carbon nanotube strain sensor for structural health monitoring

A carbon nanotube polymer material was used to form a piezoresistive strain sensor forstructural health monitoring applications. The polymer improves the interfacial bondingbetween the nanotubes. Previous single walled carbon nanotube buckypaper sensorsproduced distorted strain measurements because the van der Waals attraction force allowedaxial slipping of the smooth surfaces of the nanotubes. The polymer sensor uses largermulti-walled carbon nanotubes which improve the strain transfer, repeatability andlinearity of the sensor. An electrical model of the nanotube strain sensor was derived basedon electrochemical impedance spectroscopy and strain testing. The model is useful fordesigning nanotube sensor systems. A biomimetic artificial neuron was developedby extending the length of the sensor. The neuron is a long continuous strainsensor that has a low cost, is simple to install and is lightweight. The neuron has alow bandwidth and adequate strain sensitivity. The neuron sensor is particularlyuseful for detecting large strains and cracking, and can reduce the number ofchannels of data acquisition needed for the health monitoring of large structures.

Microfabricated photoplastic cantilever with integrated photoplastic/carbon based piezoresistive strain sensor

We present an SU-8 micrometer sized cantilever strain sensor with an integrated piezoresistor made of a conductive composite of SU-8 polymer and carbon black particles. The composite has been developed using ultrasonic mixing. Cleanroom processing of the polymer composite has been investigated and it has been shown that it is possible to pattern the composite by standard UV photolithography. The composite material has been integrated into an SU-8 microcantilever and the polymer composite has been demonstrated to be piezoresistive with gauge factors around 15–20. Since SU-8 is much softer than silicon and the gauge factor of the composite material is relatively high, this polymer based strain sensor is more sensitive than a similar silicon based cantilever sensor.

Introduction to carbon nanotube and nanofiber smart materials

The potential use of carbon nanotubes and nanofibers as smart composite materials is discussed in this paper. An overview of the properties of carbon nanotube materials is presented, and then four applications under development are briefly discussed. The first application is electrochemical actuation in dry and aqueous environments. The second is a carbon nanotube polymer piezoresistive strain sensor developed for structural health monitoring. Third, nanotubes are used with an electrolyte for harvesting power from structural vibration. Fourth, a carbon nanotube bioelectronic sensor is discussed. Tying all this together, a vision is presented for using nanoscale smart materials to synthesize intelligent electronic structures with prescribed elastic and electrical properties for a wide range of new applications. Hurdles to be overcome to achieve this goal are also discussed.

화학적 성분 분석능력을 가진 원자 현미경의 제작

This paper describes a novel concept of a chemically sensitive scanning force microscope (CS-SFM). It consists of the conventional SFM and the time-of-flight mass spectrometer (TOF-MS). A switchable cantilever (SC) fabricated by the micromachining technology combines each advantage of two completely different systems, SFM and TOF-MS. The CS-SFM offers to produce both images of topography and chemical information simultaneously. First we employed a rotatable tip holder based on 4 piezotube actuators for demonstration of the possibility of the CS-SFM concept. Second the CS-SFM concept is optimized with the micromachining technology. The micromachined SC with an integrated bimorph actuator and a piezoresistive strain sensor provides a reasonable switching speed of <TEX>${\sim}10$</TEX> ms which is very attractive for the CS-SFM application. The SC is currently being integrated in an ultra-high-vacuum system to perform various experiments.

Amicromachined active tactile sensor for hardness detection

We developed a new type of micromachined tactile sensor that detects both the contact force and hardness of an object. It consists of a diaphragm with a mesa structure, a piezo-resistive strain sensor on the diaphragm, and a chamber for pneumatic actuation. We designed the device specifications to detect humanfinger touch. We developed the fabrication process of the device using micromachining technology. The sensor element measures 11.0 mm × 15.0 mm × 0.4 mm. We experimentally evaluated the device characteristics by using silicon rubber and polyurethane resin samples with different hardnesses, and we verified the hardness detection performance. The fabricated tactile sensor detected differences in hardness in the range of 10 3–10 5 N/m.

A comparative study of steel- and carbon-fibre cement as piezoresistive strain sensors

Carbon-fibre (15 μm diameter) cement is a better piezoresistive strain sensor than stainless steel-fibre (8 μm diameter) cement at a similar fibre volume fraction, as shown by a higher signal-to-noise ratio and better reversibility upon unloading, albeit having a lower gauge factor (particularly under tension). Steel-fibre cement containing 0·36 vol% fibres is a better piezoresistive strain sensor than that containing 0·72 vol% fibres, as shown by better reversibility upon unloading and the higher gauge factor under compression. The difference in performance of carbon- and steel-fibre cement is attributed to a difference in piezoresistivity mechanism.

A comparative study of steel- and carbon-fibre cement as piezoresistive strain sensors

Carbon-fibre (15 μm diameter) cement is a better piezoresistive strain sensor than stainless steel-fibre (8 μm diameter) cement at a similar fibre volume fraction, as shown by a higher signal-to-noise ratio and better reversibility upon unloading, albeit having a lower gauge factor (particularly under tension). Steel-fibre cement containing 0·36 vol% fibres is a better piezoresistive strain sensor than that containing 0·72 vol% fibres, as shown by better reversibility upon unloading and the higher gauge factor under compression. The difference in performance of carbon- and steel-fibre cement is attributed to a difference in piezoresistivity mechanism.

Simulation and fabrication of piezoresistive membrane type MEMS strain sensors

Two piezoresistive ( n-polysilicon) strain sensors on a thin Si 3N 4/SiO 2 membrane with improved sensitivity were successfully fabricated by using MEMS technology. The primary difference between the two designs was the number of strips of the polysilicon patterns. For each design, a doped n-polysilicon sensing element was patterned over a thin 3 μm Si 3N 4/SiO 2 membrane. A 1000×1000 μm 2 window in the silicon wafer was etched to free the thin membrane from the silicon wafer. The intent of this design was to fabricate a flexible MEMS strain sensor similar in function to a commercial metal foil strain gage. A finite element model of this geometry indicates that strains in the membrane will be higher than strains in the surrounding silicon. The values of nominal resistance of the single strip sensor and the multi-strip sensor were 4.6 and 8.6 kΩ, respectively. To evaluate thermal stability and sensing characteristics, the temperature coefficient of resistance [TCR=(Δ R/ R 0)/Δ T] and the gage factor [GF=(Δ R/ R 0)/ ε] for each design were evaluated. The sensors were heated on a hot plate to measure the TCR. The sensors were embedded in a vinyl ester epoxy plate to determine the sensor sensitivity. The TCR was 7.5×10 −4 and 9.5×10 −4/°C for the single strip and the multi-strip pattern sensors. The gage factor was as high as 15 (bending) and 13 (tension) for the single strip sensor, and 4 (bending) and 21 (tension) for the multi-strip sensor. The sensitivity of these MEMS sensors is much higher than the sensitivity of commercial metal foil strain gages and strain gage alloys.

A high-performance planar piezoresistive accelerometer

The micromachined piezoresistive accelerometer is now 20 years old. Design variations have been investigated, but commercial devices have generally maintained a consistent topology with incremental improvements. In this paper, a new approach is introduced to the design and construction of this device that offers functional and manufacturing advantages. Piezoresistive accelerometers are described that combine deep reactive ion etching and oblique ion implantation to form self-caging proof masses and flexures with vertical sidewalls and sidewall piezoresistive strain sensors. These devices deflect in-plane rather than out-of-plane, which allows one to form multiaxis accelerometers on one substrate. Performance is comparable to inexpensive commercial capacitive accelerometers and is limited by 1/f noise. The design, fabrication, and experimental characterization is presented. This new topology provides the foundation for a new category of piezoresistive accelerometers.

Development of new capacitive strain sensors based on thick film polymer and cermet technologies

In this work, the strain sensing characteristics of new thick film capacitive sensors are presented. New cermet and polymer dielectric pastes based on lead–zirconate–titanate (PZT) and polyvinylidene fluoride (PVDF) have been developed. The screen printing technique has been used to fabricate the sensors on 96% alumina substrates. Various strain gauge characteristics have been studied, including the electrical properties of both the cermet and polymeric films. Both the cermet and polymer sensors exhibit good dielectric properties with gauge factors comparable to piezoresistive strain sensors. An application circuit based on integrated bipolar arrays incorporating the new capacitive strain sensors was designed and tested. The output from this circuit is a frequency that is proportional to the applied strain.

Short carbon fiber reinforced epoxy coating as a piezoresistive strain sensor for cement mortar

Epoxy containing 10 vol.% short carbon fibers and applied as a coating (0.2 mm thick) directly on cement mortar was found to be an effective piezoresistive strain sensor for tensile strain up to 0.042% and compressive strain down to −0.11%. Exceeding these strain limits caused damage in the coating. The strain sensitivity (reversible fractional increase in electrical resistance per unit strain) was 94–97 and 20–24 when the strain was contraction and expansion, respectively. The irreversible fractional increase in resistance per unit strain was 0.5–2.3 and 15–69 when the strain was contraction and expansion, respectively; it increased with increasing magnitude of strain. The resistance change was almost totally reversible when the strain was contraction, but was only partly reversible when the strain was expansion. The sensor in coating form was similar to that in bulk form in the electromechanical behavior.

Short-carbon-fiber-reinforced epoxy as a piezoresistive strain sensor

Epoxy containing 5.5 vol.% short carbon fibers was found to be piezoresistive strain sensor, such that the magnitude of the reversible fractional increase in electrical resistance per unit strain was 6-23 under tension and 29-31 under compression. These values are much higher than those of previously reported composite piezoresistive materials. The reversible fractional increase in resistance was positive under tension and negative under compression, but the irreversible fractional increase in resistance was positive under both tension and compression. Both reversible and irreversible fractional increases in resistance increased in magnitude with increasing stress/strain amplitude. The reversible portion was due to piezoresistivity, while the irreversible portion was due to damage.

Atomic resolution with an atomic force microscope using piezoresistive detection

A new detection scheme for atomic force microscopy (AFM) is shown to yield atomic resolution images of conducting and nonconducting layered materials. This detection scheme uses a piezoresistive strain sensor embedded in the AFM cantilever. The cantilever is batch fabricated using standard silicon micromachining techniques. The deflection of the cantilever is measured directly from the resistance of the piezoresistive strain sensor without the need for external deflection sensing elements. Using this cantilever we achieved 0.1 Årms vertical resolution in a 10 Hz–1 kHz bandwidth.

Polysilicon strain sensors using shear piezoresistance

The conventional piezoresistive strain sensor uses either the longitudinal or transverse piezoresistive effect. However, in addition to the change in resistance, an electric field is developed perpendicular to the current flow. This yields a voltage output, similar to that found in Hall measurements, which is proportional to strain instead of magnetic field. The magnitude of this voltage is also determined by the angle of the applied strain. This paper examines the use of this effect in producing a compact pressure sensor in polysilicon films. A theoretical model is described for both the change in resistance and the perpendicular voltage, due to a shear strain, for a polysilicon device and a comparison with experimental results shows reasonable agreement.

Silicon Force Transducer for Extraluminal Measurement of Oviduct Contractile Activity

A miniature, implantable force transducer has been developed for the extraluminal measurement of segmental smooth muscle contractility and has been applied to the oviduct in the Macaca mulatta. The force transducer makes use of a commercially available piezoresistive silicon strain sensor bonded to a flexible metal strip. The device is housed in a tissue compatible, gas sterilizable tubule upon which are placed sutures for subsequent extraluminal attachment to an organ.