3D printing: InfraredTags make plastics communicative

Shopping can be exhausting, for example when you first have to find the price label of a product or rush through the aisles looking for alternative products. All of this could be done at a glance while shopping – if InfraredTags were integrated into a product's packaging.

Such tags are not visible to the naked eye, but with the help of an app they are. This way, consumers can save time and nerves. Mustafa Doğa Doğan explained how such tags are integrated into products and how plastics are particularly suitable for this.

What was the research project for the InfraredTags about?

Mustafa Doğa Doğan: Imagine you are at a store browsing different items — you’d like to get further information about the products you’re considering, the unit price, recipes, calorie information, or cheaper alternatives. Even though barcodes like QR codes are really cheap to manufacture and could be used to label items, they are typically visually distracting and not as durable as other tags like RFID, so they can easily become unreadable over time.

Thus, in the last decade, researchers have investigated several ways to insert tags that are imperceptible to the naked eye. However, prior research prototypes need either custom fabrication hardware or expensive/large detection tools to achieve invisible tags.

This is why we developed InfraredTags, a method to embed markers and barcodes in the geometry of the 3D printed object that does not require complex fabrication or high-cost imaging equipment. We accomplish this by using off-the-shelf fused deposition modeling (FDM) 3D printers and a commercially available infrared (IR) transmitting filament for fabrication, and a low-cost, off-the-shelf near-infrared camera for detection.

How are the tags brought into the product?

Doğa Doğan: The main geometry of the object is 3D printed using the IR-transmitting filament, while the tag itself is created by leaving air gaps for the bits. Because the main geometry is semitransparent in the IR region, the near-infrared camera can see through it and capture the air gaps, that means the marker, which shows up at a different intensity in the image. The contrast in the image can be further improved by dual-material 3D printing the bits from an infrared-opaque filament instead of leaving them as air gaps. Our method can embed 2D tags, such as QR codes and ArUco markers, and can embed multiple tags within the object, which allows for scanning from multiple angles while tolerating partial occlusion.

What requirements do plastics have to fulfill to be suitable for this?

Doğa Doğan: The plastic should be 3D printable. For FDM 3D printing, this means that it should be available in filament spools.
More importantly, the infrared-transmitting (or infrared-translucent) plastic filament should not pass visible light such that the tag behind it cannot be directly seen by humans, but should pass near-infrared light such that an infrared camera can see it.

Which plastics do you use, what makes them special?

Doğa Doğan: Specifically, the filament we use transmits near-infrared at a much higher rate (∼45 percent) compared to visible light (0 to 15 percent), and thus appears translucent in the IR region and mostly opaque in the visible light region. This filament is PLA based, which is great because PLA is the most common 3D printing material, so we were able to use it at regular 3D printing temperatures (200-220°C) without having to modify our fabrication hardware.

What potential do you see for plastics in the future?

Doğa Doğan: Plastics are the most common material used in 3D printing. In this project, we used how plastics with special optical characteristics can be used to invisibly embed information into objects. I am excited to see different types of plastics become available to consumers for digital fabrication, which would allow more diverse and functional applications. While we only used black PLA (polylactic acid) in this project, manufacturers could produce filaments of other colors that have similar transmission characteristics to create more customized or multi-material prints in rigid and flexible forms.

It is just fascinating how so many different capabilities and object forms can be achieved using simple plastics, and I am excited to see what kinds of everyday applications our research will enable in the future.