A team of engineers and material scientists in the Paul M. Rady Department of Mechanical Engineering at ���������� Boulder has developed a new technology to turn thermal radiation into electricity in a way that literally teases the basic law of thermal physics.

The breakthrough was discovered by the , led by Assistant Professor Longji Cui. Their work, in collaboration with researchers from the National Renewable Energy Laboratory (NREL) and the University of Wisconsin-Madison, was recently . 

The group says their research has the potential to revolutionize manufacturing industries by increasing power generation without the need for high temperature heat sources or expensive materials. They can store clean energy, lower carbon emissions and harvest heat from geothermal, nuclear and solar radiation plants across the globe.

In other words, Cui and his team have solved an age-old puzzle: how to do more with less.

“Heat is a renewable energy source that is often overlooked,” Cui said. “Two-thirds of all energy that we use is turned into heat. Think of energy storage and electricity generation that doesn’t involve fossil fuels. We can recover some of this wasted thermal energy and use it to make clean electricity.”

Breaking the physical limit in vacuum

High-temperature industrial processes and renewable energy harvesting techniques often utilize a thermal energy conversion method called thermophotovoltaics (TPV). This method harnesses thermal energy from high temperature heat sources to generate electricity. 

But existing TPV devices have one constraint: Planck’s thermal radiation law. 

PhD student Mohammad Habibi showcasing one of the group's TPV cells used for power generation. Habibi was the leader of both the theory and experimentation of this groundbreaking research.

“Planck’s law, one of most fundamental laws in thermal physics, puts a limit on the available thermal energy that can be harnessed from a high temperature source at any given temperature,” said Cui, also a faculty member affiliated with the Materials Science and Engineering Program and the Center for Experiments on Quantum Materials. “Researchers have tried to work closer or overcome this limit using many ideas, but current methods are overly complicated to manufacture the device, costly and unscalable.”

That’s where Cui’s group comes in. By designing a unique and compact TPV device that can fit in a human hand, the team was able to overcome the vacuum limit defined by Planck’s law and double the yielded power density previously achieved by conventional TPV designs. 

“When we were exploring this technology, we had theoretically predicted a high level of enhancement. But we weren’t sure what it would look like in a real world experiment,” said Mohammad Habibi, a PhD student in Cui’s lab and leader of both the theory and experiment of this research. “After performing the experiment and processing the data, we saw the enhancement ourselves and knew it was something great.”

The zero-vacuum gap solution using glass

The research emerged, in part, from the group’s desire to challenge the limits. But in order to succeed, they had to modify existing TPV designs and take a different approach.

“There are two major performance metrics when it comes to TPV devices: efficiency and power density,” said Cui. “Most people have focused on efficiency. However, our goal was to increase power.”

The zero-vacuum gap TPV device, designed by the Cui Research Group.

To do so, the team implemented what’s called a “zero-vacuum gap” solution into the design of their TPV device. Unlike other TPV models that feature a vacuum or gas-filled gap between the thermal source and the solar cell, their design features an insulated, high index and infrared-transparent spacer made out of just glass. 

This creates a high power density channel that allows thermal heat waves to travel through the device without losing strength, drastically improving power generation. The material is also very cheap, one of the device’s central calling cards.

“Previously, when people wanted to enhance the power density, they would have to increase temperature. Let’s say an increase from 1,500 C to 2,000 C. Sometimes even higher, which eventually becomes not tolerable and unsafe for the whole energy system,” Cui explained. “Now we can work in lower temperatures that are compatible with most industrial processes, all while still generating similar electrical power than before. Our device operates at 1,000 C and yields power equivalent to 1,400 C in existing gap-integrated TPV devices.”

The group also says their glass design is just the tip of the iceberg. Other materials could help the device produce even more power.

“This is the first demonstration of this new TPV concept,” explained Habibi. “But if we used another cheap material with the same properties, like amorphous silicon, there is a potential for an even higher, nearly 20 times more increase in power density. That’s what we are looking to explore next.”

The broader commercial impact

Assistant Professor Longji Cui (middle) and the Cui Research Group. 

Cui says their novel TPV devices would make its largest impact by enabling portable power generators and decarbonizing heavy emissions industries. Once optimized, they have the power to transform high-temperature industrial processes, such as the production of glass, steel and cement with cheaper and cleaner electricity.

“Our device uses commercial technology that already exists. It can scale up naturally to be implemented in these industries,” said Cui. “We can recover wasted heat and can provide the energy storage they need with this device at a low working temperature.

“We have a patent pending based on this technology and it is very exciting to push this renewable innovation forward within the field of power generation and heat recovery.” 

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It’s been six years since the launch of startup company , co-founded by Professor Mark Rentschler of the Paul M. Rady Department of Mechanical Engineering. The company has seen great success, including the development of a medical device designed to enable more efficient procedures in the small bowel region.

Today, with the help of a $4.5 million award through the Anschutz Acceleration Initiative (AAI), Rentschler and his colleagues are working to bring two new products to the market that will transform these types of procedures even further.

“We brought our first product out on the market in 2024,” said Rentschler, also a faculty member in biomedical engineering (BME) and robotics. “We are planning to bring a second and third product to the market in 12-18 months, and we are extremely excited to get these devices in the hands of interventional endoscopists.”

Professor Mark Rentschler holding Aspero Medical's patented Ancora-SB balloon overtube.

In 2023, Aspero received clearance from the Food and Drug Administration (FDA) to market and sell the Ancora-SB device. The product is used during endoscopy procedures to diagnose and treat small bowel diseases.

According to Rentschler, operating within the small intestine can be time consuming and technically challenging. Equipped with a patented micro-textured balloon, the Ancora-SB overtube is designed to provide more traction and anchoring consistency than smooth latex or smooth silicone balloon overtube competitors.

“Balloon overtubes for small bowel procedures have been around for about a decade,” said Rentschler. “We’re not looking to change the small bowel enteroscopy procedure, but instead improve balloon anchoring performance during these procedures in the small bowel.”

Ancora-SB has allowed Aspero to prove their worth in hospitals. Their next products expand on this concept, of course, with additional features that can facilitate a less invasive interventional procedure than traditional open surgery.

The next generation balloon overtube will be used to remove cancerous lesions in the large bowel region. It features an extra working channel that allows for an additional tool to be utilized alongside the visualization scope. This offers physicians more control, access, and stabilization when maneuvering through the colon and performing advanced interventional procedures.

“Conceptually, these devices will enable triangulated surgery with two tools and centralized visualization so that physicians can more efficiently perform surgery from inside the lumen,” Rentschler said. “Instead of historically invasive procedures, where the patient is cut open, and the cancerous bowel region is removed, we’re assisting physicians as they remove the cancer from the inside of the lumen during an outpatient procedure.

“It's much less invasive, with potentially tremendous cost savings, and numerous benefits for the patient.”

Aspero’s third product will be another balloon overtube, this time with a working channel that enables minimally invasive cancer removal in the esophagus and stomach regions of the gastrointestinal tract. 

Rentschler showcasing all three of the medical devices in Aspero Medical's multi-product platform, including their two new highly anticipated devices.

Rentschler and his team say the two upcoming devices have the potential to replace a large, and growing, number of today’s conventional surgical procedures in the gastrointestinal region by enhancing safety and efficiency while reducing patient recovery time. Moving procedures from inpatient surgery to outpatient endoscopy can generate potential cost savings of up to 50 percent or more.

“Everyone knows this is the direction we need to go. Clinical outcomes from these types of procedures are incredibly strong, but the techniques and devices aren’t widely available yet,” said Rentschler. “We are creating products that help physicians and patients feel safe and comfortable without overcomplicating things. The paradigm is rapidly shifting, and we endeavor to push endoscopy forward.”

The company is currently finalizing the design of the second product. It’s about six months further along in development than the third product, but Rentschler says they are looking to have both devices FDA cleared by the end of 2026. 

When all three devices hit the market, Aspero will look to market a portfolio of products, rather than a single tool. But further innovation is on the horizon, this time incorporating the Ancora balloon technology with a robotic element.

“Ancora is a multi-product platform focusing on the small bowel, large bowel, stomach and esophageal regions,” Rentschler said. “Our next potential venture will be in flexible robots. We’ll continue with our balloon overtubes, but as anchoring platforms to be used with flexible robotic endoscopy systems.”

Until then, Rentschler and company are full steam ahead on these next products. The $4.5 million AAI grant is being offered over a four year span, but they anticipate spending that money much sooner so they can get the devices out on the market and begin positively impacting patients and physicians everywhere.

But that’s not their only goal. With a lot of Colorado involved in the company’s revolutionizing technology, Rentschler hopes to also tell another story.

“I started Aspero Medical with Dr. Steven Edmundowicz at ���������� Anschutz. We’ve received a number of grants from the state of Colorado and everyone involved is invested in our vision,” said Rentschler. “We believe that a rising tide raises all boats, and when we think of Aspero, we want it to be a successful Colorado story.”

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Watch Jacob Segil, CEO of Afference and research professor in the Paul M. Rady Department of Mechanical Engineering, showcase a new piece of haptic technology in an episode of Freethink's Hard Reset docuseries that will "redraw the borders of reality."

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