Scientists at the United Technologies Research Center (UTRC) and the University of Connecticut have developed “smart” sensors designed to be embedded into machine parts and alert users of minute damage or wear.

The sensors are created using an advanced 3D-printing method called direct write technology.

Typically, 3D printing — also known as additive manufacturing — involves using lasers to fuse layers of a fine metal powder into a solid object. With direct write technology, a paste-like material comes out of a nozzle, like ink from a pen, and can be applied to various substrate materials.

“Direct write technology is capable of depositing fine traces of conductive, semi-conductive, insulating, resistive, or magnetic materials onto 3D surfaces,” said Sameh Dardona, an associate director of research and innovation at UTRC and lead researcher on the project.

“The technology will impact how we manufacture and integrate sensors into products as it enables us to directly deposit the sensing materials into surfaces without the need for housing, substrates, or brackets.”

Both the direct write method and the smart sensor components were developed in the direct write lab at UTRC.

The method

With direct write technology, the researchers are able to integrate miniscule lines of conductive silver filament — only 15 microns wide and 50 microns apart, thinner than the average human hair — into a machine as it is being constructed.

Like a string threaded into a piece of clothing, the tiny sensors are interwoven throughout the machine. They can detect very minute damage in areas that can’t usually be reached by sensors, alerting users of damage before it can cause serious problems.

“The beauty of this method is that the patterns are deposited directly onto existing machine components, allowing seamless integration of sensing functionality into existing machinery,” said Anson Ma, an associate professor of chemical and biomolecular engineering at UConn, who worked on the project.

The lines of silver filament are organized in parallel lines, each coupled with a tiny 3D-printed resistor. The silver filament is capable of conducting electricity, so when a voltage is applied, the interconnected parallel lines form an electrical circuit.

“As wear occurs, part of these parts get damaged, resulting in a change in the electrical signal,” said Ma. “This strategy opens up the possibility of sensing wear without taking the machinery apart during normal operations, enhancing safety and minimizing machine downtime.”

When the component is damaged, the electrical circuit is broken. Damage can therefore be detected remotely and in real time by reading the voltage levels.

Applications

The microsensors could be embedded, for example, into ceramic and polymer coatings of jet engine turbine fan blades, which are consistently subject to immense pressure and heat.

Microscopic damage — such as a crack in the protective coating — could have a significant impact on the component’s function, but could be literally invisible to the naked eye. Embedded sensors, however, would allow mechanics to keep track of even the most miniscule damage as it occurs and fix it before they can create more significant damage.

The sensors could be embedded into any technology that involves moving parts and is subject to wear.

“This changes the way we look at manufacturing,” Dardona said in a statement. “We can now integrate functions into components to make them more intelligent.”

“These sensors can detect any kind of wear, even corrosion, and report that information to the end user. This helps us improve performance, avoid failures, and save costs.”

Dardona envisions these sensors being used in aerospace, automotive and industrial machines — industries where there is a need to accurately monitor the condition of machine components in real time.

The direct write technology can also be used to create more than just sensors. The team used the same process to create unique machine components that have magnetic coatings or magnetic material embedded inside them.

They developed a polymer-bonded magnetic ink that can be shaped in arbitrary and unusual forms, allowing for the creation of unusual magnetic components.

“For magnet fabrication, we have formulated a functional ink containing magnetic particles and photopolymer, which solidifies upon exposure to UV light,” said Ma.

“We first lay down some inks following a desired pattern using the direct write method, and then apply UV to (partially) solidify that layer. We repeat the process to create a 3D object with arbitrary shapes as designed in the digital file.

“The key is to control the flow properties of the ink such that the deposited ink would retain the shape until UV-induced solidification takes place.”

Ma believes that this magnet technology has a wide range of industrial applications.

“Magnets can be used to create an electric current in a generator or alternator, enhance the performance of electromagnetic devices such as inductors, and track the speed or the position of a moving piston or a rotating shaft,” he said.

Once this technology is in the hands of designers and engineers, there is no telling how many applications it could have.

In a statement, Dardona noted that embedding magnetic material directly into components could lead to visionary product designs that are more aerodynamic, lighter and efficient.

“Printed magnets will have applications in sensing and actuation,” said Dardona. “The printing process can fabricate magnet designs that are not possible using existing subtractive or machining techniques.”

Dardona has applied for a patent for the sensor technology.

Collaboration is key

Both Dardona and Ma emphasized that the collaboration between UTRC and UConn has been very productive, and that the project could not have been completed without the unique contributions of both parties.

The project was funded and managed by Dardona’s team at UTRC. Dardona said that the relationship with UConn was formed because of the university’s unique expertise in ink rheology and formulation.

“This has been an extremely fruitful collaboration between university (academia) and industry,” said Ma.

“Our university research group focuses on the fundamental understanding and formulation of functional inks with appropriate properties for high fidelity printing, while our industrial partner (UTRC) is leading the sensor design and applying this technology to tackle important technical challenges related to wear sensor and magnet applications.”

Such collaborations also provide students a unique opportunity to gain real-world research experience.

As part of the collaboration, Alan Shen, a doctoral student at UConn, was embedded into Dardona’s research team. Serving as a lead researcher on both of the projects, he assisted in the development, testing and retesting of these new technologies for the past three years.

“It’s also very rewarding for our students,” Ma said in a statement.

“Students involved in these projects are fully integrated into the research team. It’s not only great from a workforce development perspective; it also gives students a chance to work closely with professional engineers in a beautiful facility like UTRC.”