A Sensor That Won’t Crack Under Pressure

In order for our robots to get smarter and our interactions with computers to become more natural and immersive, improvements in existing sensor technologies are needed. In particular, flexible pressure sensors are in need of some upgrades — these devices have the ability to collect environmental data that is analogous to the information that we receive through our skin as we touch any number of surfaces. Needless to say, the sense of touch is a crucial factor in our everyday experiences, so replicating it is a top priority in many fields.

Recent efforts have focused on developing better flexible piezoresistive films that are able to sense pressure changes. These films have been favored due to their desirable mechanical properties that give them stability and durability under many conditions. This is typically achieved by embedding some type of conductive nanoparticle into an elastic matrix. But despite their favorable qualities, pressure sensitive films have limits to the amount of stress they can take before they fail, and furthermore, they lack the high level of sensitivity that is required by some applications.

To improve the stress tolerance of the sensors, researchers have created them with pyramidal, dome-shaped, wrinkled, and hierarchical configurations. While these approaches have been met with a great deal of success, the fabrication processes that are involved are very complex, limiting the practicality of these technologies.

An innovative sensor design pioneered by researchers at Xi’an Jiaotong University and Ningbo University has shown that it is tolerant to extremely high levels of stress, and also that it is very sensitive, making it useful for a wide range of applications. But unlike previous pressure sensing technologies, this device can be fabricated via a simple and inexpensive process. For this reason, the sensor may eventually find practical applications in areas ranging from medical devices to vehicle load detection.

The sensing film that makes up the device is composed of a non-toxic, flexible polymer called polydimethylsiloxane with embedded multiwalled carbon nanotubes, which exhibit exceptional electromechanical performance. But the real innovation was introducing microslits into the film. These slits permit large amounts of deformation in the material without breakage, enabling it to achieve ultrahigh levels of stress tolerance. And importantly, these microslits are very easy and inexpensive to introduce into the design with a simple screen printing process.

Sensors based on the team’s microslit design were created and tested in a series of real-world experiments to validate their methods. A number of prototype devices were demonstrated to be capable of wind direction detection, sensing robot movement, and monitoring human health with the help of these pressure sensors. It was even proven that the films could withstand ultrahigh pressures of over 400 kPa in a vehicle load detection experiment. But that is nothing compared to the theoretical maximum pressure of 2.477 MPa that the sensor can handle.

In total, the effectiveness and durability of the sensor was tested in more than 50,000 load/unload cycles. Given the utility and the simple fabrication method, this sensor looks like a promising candidate to power the next generation of intelligent systems.