Researchers at UC Berkeley and Taiwan's National Chio Tung University have created a low-cost electronic sensor that's able to wirelessly monitor the freshness of milk. The team created the electronic components for the sensor using a 3D-printing method, which it believes could have a big impact on the industry.

To create sensitive electronic components by means of 3D-printing, the team fabricated polymer structures containing hollow microchannels and cavities. The designs include injecting holes that allow the moulds to be filled with liquid metal paste, which solidifies to form the components.

The researchers made various electronic components using this method, including resistors, inductors and capacitors. It was the need to test their components that gave rise to the milk cap idea.

The team combined a capacitor and inductor to create a resonant circuit, which was then placed inside the cap. The design of the cap is such that quickly flipping the carton causes a small amount of the liquid to gather in the capacitor gap, allowing the team to monitor changes in the electrical signals in response to increased levels of bacteria.

The team observed the test carton at room temperature (71.6°F / 22°C), taking measurements every 12 hours for 36 hours. As time went on, the peak vibration frequency of the milk dropped by 4.3 percent, indicating significantly increased bacteria levels. A test carton, placed in a refrigerator, saw a much smaller frequency drop of just 0.12 percent over the same period of time.

While we're unlikely to see the sensor make its way into milk cartons any time soon, the team believes that its new method of creating electronic components could one day have a big impact on the industry.

"This 3D-printing technology could eventually make electronic circuits cheap enough to be added to packaging to provide food safety alerts for consumers," said team member Liwei Lin. "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."

While this is the first time we've seen 3D-printing used in exactly this manner, other research is also focusing on creating low-cost sensors to keep an eye on whether food is still safe to eat. Earlier this year, MIT highlighted its work on a carbon nanotube-based sensor that can detect when unrefrigerated meat starts to decay.

The findings of the UC Berkeley-lead research were published in the journal Microsystems and Nanoengineering.

Source: UC Berkeley

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