Additive Printing of Wearable EDA Sensors on In-Mold Electronics on Automotive Platform
Authors: Lall Pradeep , Jang Hyesoo , Miller Scott 
Published: November 2023

Additive fabrication techniques for fabricating printed circuit boards obviate the necessity for costly equipment, such as etching vessels or photomasks for eliminating metallization and photoresist. Software-driven design and fabrication enable production flexibility as well as expedited tool modifications and design enhancements. Furthermore, additive printing methods can be utilized on various substrates, vehicles, and polymers with diverse geometries and textures, while previous methods need to have complex and costlier processes. On the regards that it allows for more flexibility and creativity in designing PCBs, this affords engineers the opportunity to devise diverse applications, such as wearable biosensors like an EDA sensor to monitor and measure various aspects of the human body’s health and stresses. Wearable biosensors can tract parameters of biosignals which can provide useful information for medical assessment of drivers. Previous investigations have examined the development of additively printed wearable biosensors owing to their potential for adaptability and integration. Nonetheless, there are reservations about the stability of current wearable biosensor technology when it is exposed to flexural strain. They have some challenge to overcome many harsh environments condition which various mechanical stress involve to. To circumvent stability issues, it is imperative to develop a superior fabricating technique and assessment of reliability. In this research paper, additive fabrication methods were used to create printed circuit boards (PCBs) for wearable biosensors without expensive equipment or processes. These methods allow us to design and modify PCBs quickly and easily using software, as well as print PCBs on different materials and shapes, such as thermoformable substrates that can be molded by heat and pressure. We focused on electrodermal activity (EDA) sensors that measure skin conductance for driver monitoring. The EDA sensor measures skin conductance for driver monitoring purposes. We printed EDA sensor circuits on thermoformable substrates using a direct-write printing technique with an nScrypt printer. The thermoformable substrate is a material that can be molded by heat and pressure into different shapes such as curved or flat surfaces. Correspondingly, we thermoformed the PCBs into various shapes for reliability testing. We evaluated the biosensor’s performance by analyzing the biosignals under different harsh conditions such as thermoformed shape, temperature, humidity, and human body status (resting, walking, etc.) with respect to driving scenarios such as normal driving and emergency braking. We also tested and evaluated the sensor’s accuracy and reliability in these conditions considering many aspects of characteristics of the sensors by comparing it with a reference device (Max30009 and 3M electrode). The results showed that our additive PCB-based EDA sensor could successfully measure skin conductance with acceptable error margins. The sensor also demonstrated good mechanical robustness when thermoformed into different shapes in the car. In conclusion, we have developed an EDA sensor using additive fabrication techniques for printed circuit boards. Our sensor can monitor driver’s stress level with high reliability and flexibility.