UC Berkeley engineers, together with colleagues at Taiwan’s National Chiao Tung University, 3D printed a wireless “smart cap” for a milk carton that detects signs of spoilage using embedded sensors.
The researchers used polymers and wax to form sensitive electronic components which are then integrated into a plastic milk carton cap to monitor signs of spoilage. The “smart cap” has a capacitor and an inductor fitted to form a resonant circuit. A quick flip of the carton allowed a bit of milk to get trapped in the cap’s capacitor gap, and the entire carton was then left unopened at room temperature (about 71.6°F) for 36 hours.
The circuit could detect the changes in electrical signals that accompany increased levels of bacteria and the researchers periodically monitored the changes with a wireless radio-frequency probe at the start of the experiment and every 12 hours thereafter, up to 36 hours. The property of milk changes gradually as it degrades, leading to variations in its electrical characteristics. Those changes were detected wirelessly using the smart cap, which found that the peak vibration frequency of the room-temperature milk dropped by 4.3% after 36 hours. In comparison, a carton of milk kept in refrigeration at 39.2°F had a minor 0.12% shift in frequency over the same time period.
Senior author Liwei Lin, a professor of mechanical engineering and co-director of the Berkeley Sensor and Actuator Center says,“This 3D-printing technology could eventually make electronic circuits cheap enough to be added to packaging to provide food safety alerts for consumers.”
Lin said his lab is working on developing this technology for health applications, such as implantable devices with embedded transducers that can monitor blood pressure, muscle strain and drug concentrations.
The co-lead authors of the study are UC Berkeley research specialist Chen Yang and visiting Ph.D. student Sung-Yueh Wu, both working in Lin’s lab. Wu is also a student of study co-author Wensyang Hsu, a professor of mechanical engineering at National Chiao Tung University.