Piezoresistive Carbon Foams in Sensing Applications

Abstract

Mechanical strain sensing is ubiquitous, found in applications such as heart rate monitoring, analysis of body part motion, vibration of machines, dilatation in buildings and large infrastructure, and so forth. Piezoresistive materials and sensors based on those offer versatile and robust solutions to measure strains and displacements and can be implemented even in acceleration and pressure analyses. In this paper, we overview the most prominent piezoresistive materials, and present a case study on carbon foams as well as on their hierarchical hybrid structures with carbon nanotubes/nanofibers. Our results show highly non-linear electrical resistance and mechanical stress dependence on uniaxial strain in both types of materials up to 50% compression. The Young's moduli increase with compressive strain between 1-65 and 0.1-92 kPa for the foam and hierarchical structure, respectively. The foams have giant gauge factors (up to −1000) with large differential gauge factors (on the scale of −10) and differential pressure sensitivity of 0.016 Pa −1 (at 10% strain) making them suitable for detecting both small and large displacements with excellent accuracy of electrical readout as we demonstrate in detecting building wall displacement as well as in monitoring heart rate and flexing of fingers.

Lightweight porous silica foams with extreme-low dielectric permittivity and loss for future 6G wireless communication technologies

“…First, the carbon foam was prepared by a pyrolysis of melamine foam in a 4" quartz tube furnace under N2 flow (150 mL/min). The furnace was heated to 300 °C at a rate of 15 °C/min, then to 800 °C at a rate of 2 °C/min, and kept there for 60 min [38][39][40]. Next, a thin silica shell was synthesized on the carbon skeleton by base catalyzed sol-gel polycondensation of TEOS.…”

SU-8 cantilever with integrated pyrolyzed glass-like carbon piezoresistor

“…ε is the applied mechanical strain, and υ is Poisson’s ratio. Metal strain gauges (e.g., made of aluminum, gold, or copper) have GF of ~2, depending mainly on the dimensional change of the cross-sectional area and length corresponding to the Poisson ratio 7 . For semiconductors, the GF is more than one order of magnitude higher than the GF in metals (e.g .…”

“…For semiconductors, the GF is more than one order of magnitude higher than the GF in metals (e.g . , p-type Si has a GF of ~100) 7 . These large GF s are caused by the large change of the electrical resistivity (Δ ρ ), which, in turn, is due to the variation of the carrier density and of the mobility induced by the deformation of the band structure 8 , 9 .…”

“…Carbon allotropes, including graphite 13 – 15 , carbon nanotubes (CNTs) 16 – 18 , amorphous carbon (a-C) 4 , 19 , graphene 20 , 21 , and nanofoams 7 , have already been studied as piezoresistive materials. The diverse mechanical and electrical properties of structural allotropes are due to the different sp, sp 2 , and sp 3 hybridized bonds, thus enabling a variety of sensor applications.…”

Fiber Bragg grating based acceleration sensors: a review

“…Capacitive acceleration sensor has the advantages of high sensitivity, zero frequency response and wide dynamic range, but it is easy to be interfered by the outside world and only suitable for low-frequency fields, such as seismic detection and geological exploration (Alessandro et al , 2019; Giacci et al , 2017). Piezoresistive acceleration sensor has the advantages of small volume, low output impedance and high measurement accuracy, but it is easily affected by temperature (Kordas and Pitkanen, 2019; Liu et al , 2018). Unlike the above sensors, the resonant frequency of the current FBG accelerometer can only reach a few kilohertz.…”