Wireless, 3D-Printed Smart Cap Detects Spoiled Food Using Embedded Sensors

A team of engineers from UC Berkeley along with colleagues at Taiwan’s National Chiao Tung University has further extended the scope of 3D printing technology by using the novel technique to create electrical parts such as capacitors, inductors, resistors, and integrated wireless electrical sensing solutions.

UC Berkeley engineers created a ‘smart cap’ using 3D-printed plastic with embedded electronics to wirelessly monitor the freshness of milk.(Photo and schematic by Sung-Yueh Wu)

The researchers 3D-printed a wireless smart cap for a carton of milk that was able to detect signs of spoilage through integrated sensors. The study has been published in Microsystems & Nanoengineering, a new open-access journal in the Nature Publishing Group.

Over the past decade, significant developments have resulted in the fabrication of a wide range of 3D-printed products, such as medical implants, prosthetics, vehicle components, toys, food and building materials, except sensitive electronic parts.

In the realm of 3D printing, polymer materials are widely used as they are flexible enough to be made into different types of shapes. However, a major drawback of these materials is that they do not conduct electricity well, and hence, does not prove to be ideal candidates for electronic devices. In order to overcome this issue, the research team used wax and polymers to build a system. This wax would then be removed, leaving empty tubes into which liquid metal was introduced and subsequently cured. In their experiments, the researchers introduced silver in the hollow tubes.

Our paper describes the first demonstration of 3D printing for working basic electrical components, as well as a working wireless sensor. One day, people may simply download 3D-printing files from the Internet with customized shapes and colors and print out useful devices at home.

Liwei Lin, a professor of mechanical engineering and co-director of the Berkeley Sensor and Actuator Center

The function of different types of electrical components was determined by the metal’s shape and design. For example, flat plates were converted into capacitors and thin wires functioned as resistors. However, there was no clear understanding as to whether these metal pieces are indeed useful. In order to resolve this mystery, the research group incorporated the electronic parts within a plastic milk carton cap to track any sign of spoilage. A resonant circuit was then formed by integrating the smart cap with an inductor and a capacitor. Upon flipping the carton quickly, some amount of milk was allowed to get trapped in the capacitor gap of the cap and the whole milk carton was left unopened at room temperature of approximately 71.60F for a period of 36h.

The resonant circuit was able to perceive the differences in electrical signals, which occur when bacterial levels are very high. These changes in electrical signals were occasionally tracked using a wireless radio-frequency probe at the beginning of the experiment and every 12h thereafter for up to 36h. It was observed that as the milk degrades its property changes slowly, resulting in differences in its electrical properties. The smart cap was able to detect these changes wirelessly and discovered that the peak vibration frequency of the milk kept at room temperature reduced by 4.3% after a span of 36h. Conversely, a milk carton kept in refrigeration at 39.20F temperature underwent a minor 0.12% change in frequency during the course of 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. 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.

Lin informed that as 3D printers become better and cost-effective, there would be a wide range of options for electronics; however, people printing out their own computers and smartphones is still a far-fetched idea.

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 customization.

Lin also informed that his laboratory is exploring ways to advance this technology for health applications, for instance implantable instruments with integrated transducers, which can track drug concentrations, muscle strain, and blood pressure.

The study’s co-lead authors are Chen Yang, UC Berkeley research specialist, and Sung-Yueh Wu, visiting Ph.D. student, who are both working in Lin’s lab. Wu is also a student of Wensyang Hsu, study co-author and a professor of mechanical engineering at National Chiao Tung University.


Stuart Milne

Written by

Stuart Milne

Stuart graduated from the University of Wales, Institute Cardiff with a first-class honours degree in Industrial Product Design. After working on a start-up company involved in LED Lighting solutions, Stuart decided to take an opportunity with AZoNetwork. Over the past five years at AZoNetwork, Stuart has been involved in developing an industry leading range of products, enhancing client experience and improving internal systems designed to deliver significant value for clients hard earned marketing dollars. In his spare time Stuart likes to continue his love for art and design by creating art work and continuing his love for sketching. In the future Stuart, would like to continue his love for travel and explore new and exciting places.


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