A coatable, light-weight, fast-response nanocomposite sensor for thein situacquisition of dynamic elastic disturbance: from structural vibration to ultrasonic waves

Abstract

Inspired by an innovative sensing philosophy, a lightweight nanocomposite sensor made of a hybrid of carbon black (CB)/polyvinylidene fluoride (PVDF) was developed. The nanoscalar architecture and percolation characteristics of the hybrid were optimized, in order to fulfil in-situ acquisition of dynamic elastic disturbance from low-frequency vibration to high-frequency ultrasonic waves. Dynamic particulate motion induced by elastic disturbance modulates the infrastructure of CB conductive network in the sensor, with introduction of the tunneling effect, leading to dynamic alteration in piezoresistivity measured by the sensor.Electrical analysis, morphological characterization, and static/dynamic electro-mechanical response interrogation were implemented, to advance insight into the sensing mechanism of the sensor, and meanwhile to facilitate ascertainment of an optimal percolation threshold. At the optimal threshold (~ 6.5 wt%), the sensor exhibits high-fidelity, fast-response, and highsensitivity to ultrafast elastic disturbance (in an ultrasonic regime up to 400 kHz) yet with an ultralow magnitude (of the order of micrometer). Performance of the sensor was evaluated, against conventional piezoelectric transducer and strain gauge, showing excellent coincidence, yet a much greater gauge factor and frequency-independent piezoresistive behaviours. Coatable to a structure and deployable in a large quantity to form a dense sensor network, this nanocomposite sensor has blazed a trail for implementing in-situ sensing for vibration-or ultrasonic wave-based structural health monitoring, by striking a compromise between "sensing cost" and "sensing effectiveness".

On a Highly Reproducible, Broadband Nanocomposite Ultrasonic Film Sensor Fabricated by Ultrasonic Atomization‐Assisted Spray Coating

“…CB with an average particle diameter of 30 nm (Black Pearl 2000, Cabot Corp., USA) was chosen as the nanofiller for the proposed nanocomposite ultrasonic sensor due to its reported high sensitivity to ultrasonic waves [ 22,24,25 ] and its relatively low aspect ratio and large specific surface area, which would assist its dispersion in spraying inks. Uniform dispersion of nanofillers would not only avoid clogging of spraying nozzles, allowing successful fabrication of sensors at various nanofiller contents, but would also lead to establishment of well‐structured quantum tunneling networks inside sensors, maximizing the responses of sensors to the high‐frequency microscopic strains that are generated by ultrasonic waves.…”

“…In the early days, several types of hot‐pressed sensors with broadband frequency responses were introduced. [ 20,22 ] Although the method of hot pressing is versatile and easy to operate, the resultant sensors require much time to cure and are relatively thick (i.e., ≈200 μm) with low physical flexibilities. Manually spray‐coated sensors benefit from requiring short curing times and having good flexibilities and sufficiently high sensitivities.…”

“…The spraying ink for the proposed sensor was prepared by mixing CB nanofillers, which have been shown to possess a high sensitivity to ultrasonic waves, [ 22,25 ] with PVP, whose amphiphilic groups would assist the dispersion of the CB nanofillers in the sensor and, in turn, give rise to evenly distributed quantum tunneling paths. Ethanol was chosen as the solvent, because its rapid evaporation would enhance the coalescence of sensor films.…”

A Spray-on, Nanocomposite-Based Sensor Network for in-Situ Active Structural Health Monitoring

“…Limited by these facts, a new breed of piezoresistive sensors based on nanocomposites, flexible and small, with low density, high sensitivity, and a broad sensing band, have been developed and fabricated using hot pressing in our previous study [30,31]. Under applied strains, the tunneling effect among nanofiller particles induces a dynamic alteration in the piezoresistive properties of the sensor.…”

Real-Time Deflection Monitoring for Milling of a Thin-Walled Workpiece by Using PVDF Thin-Film Sensors with a Cantilevered Beam as a Case Study

“…Ye et al [ 14 ] developed a PVDF-based sensor to detect the change of maximum displacement from an ionic exchange polymer metal composite actuator in real-time. Zeng et al [ 15 ] developed a sensor that was a hybrid of carbon black and PVDF for use in in situ acquisition of dynamic elastic disturbances of low frequency vibrations. Ma et al [ 11 ] mounted the PVDF sensor on the milling cutter to measure the cutting forces in a machining process.…”