Vibration Detector Mimics Spider’s Sensory Organ

Even though spiders typically sport eight tiny eyes, many of the arachnids can’t see very well. To locate prey or prospective mates, web crawlers instead rely in part on exquisitely sensitive “slit organs” on their legs to detect mechanical vibrations from nearby food and friends.

Inspired by these spidey sensors, researchers in South Korea have built a slit-based, wearable device capable of measuring a person’s heart rate and recognizing human speech (Nature 2014, DOI: 10.1038/nature14002). The team thinks the easy-to-manufacture sensor could one day be an ultrasensitive interface between humans and computers.

A spider’s slit organs are a series of parallel grooves in the arachnid’s exoskeleton. When vibrations exert stress on these grooves, they deform and cause embedded nerve cells to fire.

To mimic this architecture, Mansoo Choi and the late Kahp-Yang Suh of Seoul National University, Tae-il Kim of Sungkyunkwan University, and coworkers coated a 10-µm-thick viscoelastic pad of polyurethane acrylate with a 20-nm-thick layer of platinum. Then they generated parallel cracks—or “slits”—in the assembly by wrapping it around a rod.

The resultant sensor detects vibrations with its nanoscale cracks: The oscillations cause them to deform, altering the device’s electrical resistivity.

Pressed to a volunteer’s wrist, the millimeters-wide sensor measured a difference in pulse rate before and after exercise, the researchers showed. When pressed to a volunteer’s neck, the device detected vibration patterns from four words uttered by the person. More important, it was able to distinguish among these words with 98% accuracy.

This is a “remarkably simple, yet high-performance, type of strain gauge,” says John A. Rogers, a sensor expert and materials scientist at the University of Illinois, Urbana-Champaign. “The opportunities for this sort of functionality are significant in applications ranging from health monitoring to prosthetic control.” A coauthor of the new study now works as a postdoc in Rogers’s lab.

Choi tells C&EN his team hopes to commercialize the slit sensor. But first, the researchers will need to run long-term stability tests and replace platinum with a cheaper material while maintaining the device’s sensitivity.