Engineers at the University of California-Berkeley have developed a so-called “smart cap” using 3D-printed plastic and containing embedded electronics. They recently demonstrated that the device can wirelessly monitor the freshness of milk, according to an article published Monday, July 20, 2015, in the online international journal Microsystems & Nanoengineering. 3D additive manufacturing (AM) techniques can make 3D resistors, capacitors, and inductors, along with circuits and passive wireless sensors. These structures are injected with silver particles and solidified to form metallic elements and interconnects.

Smart cap
The proposed “smart cap” for rapid detection of liquid food quality featuring wireless readout: (a) the smart cap with a half-gallon milk package and the cross-sectional schematic diagram; (b) sensing principle with the equivalent circuit diagram.
The “smart cap” has an embedded inductor-capacitor tank as the wireless passive sensor and can monitor the quality of milk and juice wirelessly, the article stated. “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 degrees F) for 36 hours,” according to a university news report. The result shows a 4.3-percent resonance frequency shift from milk stored in the room temperature environment for that period. This work establishes an innovative approach to construct arbitrary 3D systems with embedded electrical structures as integrated circuitry for various applications, including the demonstrated passive wireless sensors, the article explained. UC Berkeley researchers have been working with researchers from Taiwan’s National Chiao Tung University on practical applications for 3D printed electronic circuits and wireless sensors. The belief is that the “smart cap” approach could be used on other food industry applications to help make sure food products are fresh and safe to eat. “This 3D-printing technology could eventually make electronic circuits cheap enough to be added to packaging to provide food safety alerts for consumers,” said senior author Liwei Lin, a professor of mechanical engineering and co-director of the Berkeley Sensor and Actuator Center. “You could imagine a scenario where you can use your cellphone to check the freshness of food while it’s still on the store shelves.” The co-lead authors of the study were UC Berkeley research specialist Chen Yang and visiting Ph.D. student Sung-Yueh Wu, both of whom work 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.

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