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3D-printed ‘smart cap’ detects spoiled food

Thu 6 Aug 2015

New research released today details a new 3D printing technology, creating a wireless ‘smart cap’ for a milk carton which can monitor for spoiled liquid using integrated sensors.

Engineers at the University of California, Berkeley, in partnership with a team at the Nationl Chiao Tung University, Taiwan, published their findings in open-access journal Microsystems and Nanoengineering.


The paper titled 3D-printed microelectronics for integrated circuitry and passive wireless sensors describes “the first demonstration of 3D printing for working basic electrical components, as well as a working wireless sensor,” said senior author Liwei Lin, mechanical engineering professor and co-director at the Berkeley Sensor and Actuator Center.

“One day, people may simply download 3D printing files from the internet with customised shapes and colours and print out useful devices at home,” said Lin.

The system uses a mixture of polymers and wax, which when removed leaves hollow tubes into which liquid metal is added and cured. The researchers used silver in their latest experiments.

The electronic component was then embedded into a plastic cap to detect signs of spoilage in a milk carton. A capacitor and inductor were added to the ‘smart cap’ to create a resonant circuit. The engineers flipped the carton to allow a bit of milk into the capacitor, and left the carton unopened for 36 hours at room temperature.

The circuit was looking to detect changes in the electrical signals which accompany increasing levels of bacteria, and feed them back to a wireless radio-frequency probe every 12 hours.

The results showed that the vibration frequency of milk kept at room temperature decreased by 4.3% after 36 hours. Whereas a refrigerated carton only saw a 0.12% drop in frequency over the same time period.

“This 3D printing technology could eventually make electronic circuits cheap enough to be added to packaging to provide food safety alerts for consumers,” Lin added. “You could imagine a scenario where you can use your phone to check the freshness of food while it’s still on the store shelves.”

Lin believes that as 3D printers improve and become cheaper, the opportunities will develop also. He does however doubt the possibility of being able to print your own smartphone or computer hardware in the foreseeable future.

“That would be very difficult because of the extremely small size of modern electronics […] It might also not be practical in terms of price since current integrated circuits are made by batch fabrication to keep costs low. Instead, I see 3D-printed microelectronic devices as very promising for systems that would benefit from customisation.”

Lin continued to explain that his team are focusing on investigating uses of this technology in a healthcare setting, such as blood pressure and concentration monitors.

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