3D Printed Graphene Piezoresistive Microelectromechanical System Sensors to Explain the Ultrasensitive Wake Tracking of Wavy Seal Whiskers

Abstract

Many marine animals perform fascinating survival hydrodynamics and perceive their surroundings through optimally evolved sensory systems. For instance, phocid seal whiskers have undulations that allow them to resist noisy self-induced vortex-induced vibrations (VIV) while locking their vibration frequencies to wakes generated by swimming fishes. In this study, fully 3D-printed microelectromechanical systems (MEMS) sensors with high gauge factor graphene nanoplatelets piezoresistors are developed to explain the exquisite sensitivity of whisker-inspired structures to upstream wakes. The sensors are also used to measure natural frequencies of excised harbor (Phoca vitulina) and grey (Halichoerus grypus) seal whiskers and determine the effect of whisker orientation on the VIV, which can explain the possible natural orientation of whiskers during active hunting. Experimental investigations conducted in a recirculating water flume show that whisker-inspired sensors successfully sense an upstream wake located up to 10× the whisker diameter by locking to the frequency of the wake generator, thus mimicking the sensing mechanism of the seal whisker. The combination of VIV reduction and frequency-locking with the upstream wake generator demonstrates the whisker-inspired sensor's high signal-to-noise ratio, indicating its efficiency in long-distance wake sensing as well as its potential as an alternative to visual and acoustic sensors in underwater robots.

Wavy Whiskers in Wakes: Explaining the Trail‐Tracking Capabilities of Whisker Arrays on Seal Muzzles

“…Its increase or decrease represents the vortex's rotation intensity variation [44] Q = 3D-Printed MEMS Cantilever Sensor: The fully 3D printed MEMS sensor designed for whisker testing (total sensor length 43 mm, width 30 mm, Figure 10A1) was composed of a MEMS cantilever structure (length 10 mm, width 10 mm, aspect ratio 100, thickness 0.1 mm) and a supporting fixture (length 30 mm, width 25 mm, thickness 3 mm), both printed using the "Grey Pro" material (flexural modulus ≈ 2.2 GPa) of the 3D printer named Formlabs Form 3. A high gauge factor Graphene nanoplatelets piezoresistor sensing element (thickness 7 nm, Figure 10A1) was formed at the hinge through a drop-casting process, which involved dropping a dilute conductive graphene dispersion [45,46] into serpentine grooves (depth 0.1 mm, width 1 mm) of the MEMS cantilever structure. A 3D-printed seal whisker structure ("Grey Pro") was then embedded into a hole of a 3Dprinted whisker holder ("Grey Pro") and surrounded with the hot-melt adhesive.…”

The role of bio-inspired micro-/nano-structures in flexible tactile sensors

“…Mammalian whiskers are an essential class of tactile sensors that complement the skin's function to detect the wind direction with high sensitivity and navigate around localized obstacles. 84,85 Javey et al developed highly sensitive electron whiskers by coating CNT-AgNP composite films on hair-like PDMS fibers. Inspired by mammalian whiskers, different configurations of E-whisker arrays were designed and successfully demonstrated for 2D and Fig.…”

Structured carbon nanotube–elastomer nanocomposites with a morphing–contact mechanism for an advanced underwater perception warning system

“…However, compared with conventional flexible sensors that work in the air environment, 10–12 rigorous requirements in terms of material composition, surface wettability and device structure are needed for underwater sensory systems. 13–15 To date, extensive efforts have been dedicated to developing functional hydrogels, 16 ionogels, 17 superhydrophobic aerogels, 18 waterproof conductive fabrics 19 and piezoresistive 20 and piezoelectric 21 electronic devices for underwater sensing applications.…”