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By Beth Bacheldor

Researchers Create 3D-Printed Smart Milk Cap

Several University of California Berkeley engineers, in collaboration with colleagues at Taiwan's National Chiao Tung University, have created a prototype of a 3D-printed smart cap for milk cartons that is designed to wirelessly monitor the freshness of the milk products. The smart cap uses 3D-printed plastic with embedded RF passive circuit electronics and can be used to wirelessly monitor the quality of liquid food (milk and juice, for instance).

According to a recent article published in Microsystems & Nanoengineering, the researchers used a 3D printer to make a smart milk-carton cap fitted with a cone-shaped capacitor and a flat spiral-shaped inductor. Together, the two electrical components formed a resonant circuit known as an inductor-capacitor (LC) tank. The cap was screwed onto a carton of fresh milk, which was briefly turned upside-down so that some of the liquid became trapped between the capacitor's upper and lower electrodes. The carton was then stored at room temperature—22 degrees Celsius (71.6 degrees Fahrenheit)—for 36 hours. Another carton of fresh milk was similarly fitted with a smart cap and stored at 4 degrees Celsius (39.2 degrees Fahrenheit).

The researchers used a wireless inductive reader to monitor the LC tank's resonant frequency in real time. As the milk trapped inside the capacitor gap began to spoil, the value of the LC tank's resonant frequency began to drop. When a carton of milk was stored at room temperature for 36 hours, the printed sensor's peak resonance frequency dropped by 4.3 percent. In comparison, a carton of milk kept in refrigeration at 4 degrees Celsius saw a relatively minor 0.12 percent shift in frequency over the same time period.

According to the researchers, the preliminary results from testing the prototype smart cap "demonstrate the good consistency of these 3D-printed devices with the analytical expectations and indicate the possible performance enhancements and system integration based on the 3D structures." The positive results, the authors note in their article, indicate that "3D devices with embedded metallic components can open up a new class of applications in devices (beyond the passive wireless sensors) that benefit from 3D structures with embedded metallic conductors."

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