In an article published in ACS Applied Materials & Interfaces, researchers have presented an infrared (IR)-based highly flexible soft optoelectronic sensor with pigmented cladding that is efficient in multimodal sensing.
Compared with optoelectronic sensors based on the visible spectrum, this novel method makes the sensor more suitable for low-powered devices as the IR-spectrum signal allows it to operate with a fraction of the power than what would have been initially used.
The reliability of soft optoelectronic sensors that can perform multimodal sensing makes them a desirable option for applications involving strain sensors. However, the constant electrical power input required to transmit the light signal through the core of these strain sensors is a drawback that results in excessive power consumption for low-powered devices. The present work demonstrates that utilizing an IR-spectrum signal for signal propagation can effectively counter the problem.
The soft optoelectronic sensors were highly resilient due to using pigmented elastomers as the fiber optics or waveguides cladding. These strain sensors were installed into a soft robotics gripper that could control its contact force despite severe extrinsic disturbances.
Improving the Performance of Soft Robotics
Soft robotics has promoted tremendous interest in creating devices that can interact safely with humans and the environment. However, since these devices are incredibly deformable, much work has been put into designing stretchable and soft strain sensors to assess the deformation effectively.
The optoelectronic sensors employ numerous operating theories and are ideally reliable, precise, resistant to interfering noise sources, and suitable for low-powered devices. However, physical and non-physical disruptions occurring in the environment where these soft strain sensors are operated can impact their measurements. Therefore, research on reducing the impact of environmental disturbances on soft optoelectronic strain sensors is crucial to make them appropriate for practical applications.
The waveguides in fiber optics typically consist of two components: a core that directs light and cladding that shields the core from interference. A cladded fiber that can detect excessive strains of up to 300% can be fabricated by carefully choosing the materials for the core and cladding and co-extrusion of both the materials. Such optical linear strain sensors are frequently used for sensing the deformation of linear actuators such as the McKibben actuators.
The soft optoelectronic sensors were made robust for sensing operations by the IR resilient pigments utilized in fiber optics for the cladding material of the waveguides. These pigments also helped block the optical penetration of IR and visible light.
The researchers proposed a viable production process for the pigmented soft waveguides in fiber optics and investigated their optical properties for multimodal deformation sensing.
The researchers also characterized the power consumption of IR- and visible-based waveguides in fiber optics and studied the impact of noise interferences on pigmented and non-pigmented soft waveguides.
The current paper also introduced a soft pneumatic gripper with implanted IR-based pigmented soft waveguide in fiber optics for its resilience to outside interference and grasping applications.
Fabricating and Enhancing the Resilience of the Optoelectronic Sensor
The existing soft optoelectronic sensors were made of an optical waveguide in fiber optics, a photodiode (PDE), and a light-emitting diode (LED). However, in the current work, the visible spectrum PDE and LED were substituted with IR-based ones to reduce power consumption, making them suitable for low-powered devices. The working principle of soft optoelectronic sensors requires the PDE and LED to be constantly active to detect variations in the flowing optical signal.
The energy requirement problem in soft robotics was resolved using longer wavelength signals with lesser energy expenditure, such as IR wavelengths. Using an IR signal instead of a visible wavelength signal affected the resilience of the sensor as IR-based spectrum light can flow through diverse mediums, such as the cladding of the sensor, more effortlessly than visible light.
The researchers built an IR-based soft optoelectronic sensor suitable for low-powered devices. The sensor was protected from interference effects and was resilient to infrared and visible spectrum disturbances.
Aside from the sun, there are relatively few external IR optical sources in the environment that can disturb a single IR-based soft optoelectronic sensor. However, multiple IR-based strain sensors working in proximity interfered with each other as each signal leaked from the cladding and created cross-interference between each sensor. Therefore, the researchers added black silicone pigments to the cladding of the soft waveguides in the fiber optics.
They also developed a soft robotics pneumatic gripper using IR-based resilient, soft optoelectronic strain sensors for measuring the contact force of the fingers. Each finger consisted of a PneuNet actuator with rigid reinforcements onto which hybrid optical fibers were fixed. These hybrid optical fibers consisted of rigid fibers connected to a soft core.
The soft robotics gripper was highly responsive to external optical disturbances. The suggested resilient and sensorized IR-based soft robotics pneumatic gripper grasped various objects and measured and controlled its grasping force. The soft robotics gripper could follow the desired reference command even in the presence of an external IR source acting as a disturbance.
IR-Based Soft Optoelectronic Sensors and the Way Ahead
The paper primarily focused on introducing pigments to the cladding of soft optoelectronic sensors, enhancing their resilience and ability to prevent optical interferences. As a result, the researchers produced soft and stretchable optoelectronic sensors that were robust, efficient in multimodal sensing, and suitable for low-powered devices.
The visible spectrum-based LED and PDE employed in previous soft optoelectronic sensors resulted in significant power consumption due to their constant operation.
The researchers substituted the visible spectrum PDE and LED with IR-based ones, which resulted in the sensor using only a tiny fraction of the power of a comparable visible spectrum sensor.
The cladding of the soft waveguide in fiber optics was coated with black silicone pigments to make the sensor extraordinarily robust and suitable for low-powered devices. The silicone made the cladding highly resistant to interferences by preventing the external and internal IR signals from passing through the cladding.
The sensors proposed in the present paper were integrated into a soft robotics gripper that could sense contact force.
The gripper controlled the contact force despite extrinsic IR optical disturbances.
The soft optoelectronic strain sensor is a promising candidate for various applications due to its low power requirements and remarkable resilience.
J. Babar and R. Hugo. (2022) Low-Powered and Resilient IR-Based Pigmented Soft Optoelectronic Sensors. ACS Applied Materials & Interfaces. https://pubs.acs.org/doi/10.1021/acsami.2c07318