On a different wavelength, Nader Engheta leads a community in light

Science & Technology

Nader Engheta was puzzled when he got a call from the psychology department about a fish.

In the early 1990s, Engheta, a newly minted associate professor of electrical engineering in Penn's School of Engineering and Applied Science, was a respected expert in radio wave technologies. But in recent years, his work had been expanding into subjects at once more eccentric and fundamental.

Engheta's interest in electromagnetic waves was not limited to radio frequencies, as a spate of fresh publications could attest. Some studies investigated a range of wave interactions with a class of matter known as a "chiral media," materials with molecular configurations that exhibit qualities of left or right "handedness." Others established practical electromagnetic applications for a bewildering branch of mathematics called "fractional calculus," an area with the same Newtonian roots as calculus proper but a premise as eyebrow-raising as the suggestion a family might literally include two-and-a-half children.

Electromagnetic waves are organized on a spectrum of wavelengths. On the shorter end of the spectrum are high-energy waves, such as X-rays. In the middle, there is the limited range we see as visible light. And on the longer end are the lower-energy regimes of radio and heat.

Researchers tend to focus on one kind of wave or one section of the spectrum, exploring quirks and functions unique to each. But all waves, electromagnetic or not, share the same characteristics: They consist of a repeating pattern with a certain height (amplitude), rate of vibration (frequency), and distance between peaks (wavelength). These qualities can define a laser beam, a broadcasting voice, a wind-swept lake, or a violin string.

I’ve always known that knowledge does not have boundaries. Research fields have boundaries, but they are artificial. You can work across different fields. Nader Engheta, Penn Engineering professor and 2023 Franklin Medal winner

Engheta has never been the kind of scholar to limit the scope of his curiosity to a single field of research. He is interested in waves, and his fascination lies equally in the physics that determine wave behavior and the experimental technologies that push the boundaries of those laws.

So, when Edward Pugh, a mathematical psychologist studying the physiology of visual perception, explained that green sunfish might possess an evolutionary advantage for seeing underwater, Engheta listened.

Soon, the two Penn professors were poring over microscope images of green sunfish retinas.

The eyes of this fish contain photoreceptors structured to perceive polarized light, or light waves that oscillate in a uniform direction. Human eyes contain no such structures, unable to differentiate between light waves that vibrate across multiple planes—as ordinary sunlight does—and light that travels neatly within a single plane—as sunlight might after bouncing off a firm surface. For us, the fish's brackish underwater environment is too murky and blurred to navigate by sight. But some marine species may use polarized light we cannot see to pilot themselves away from danger and toward nourishment.

Pugh, a vision scientist, had questions about optics. Do these photoreceptors work like polarization-preserving optical fibers? Engheta, radio antennae expert, dove into cell biology for answers.

Three decades later, in 2023, the Franklin Institute awarded Engheta the Benjamin Franklin Medal, one of the world's most prestigious recognitions for achievements in science and technology. A laureate in electrical engineering, Engheta received the honor "[f]or transformative innovations in engineering novel materials that interact with electromagnetic waves in unprecedented ways."

This short citation indexes a flood of peerless scientific contributions that were just over the horizon for Engheta at the time he was studying sunfish. Over the next few years, he and Pugh established a new field they called "bio-inspired polarization imaging," designing and building a camera that could see like a fish, one so finely tuned it could capture not only clear underwater views, but detailed fingerprints on the surface of glass objects. The work Engheta would go on to do as the 21st century neared would take a very different direction, proving foundational for several major new avenues of research.

More than just a surprising advance in technology, the sunfish episode illustrates the key components of Engheta's unique success—an openness to inspiration, virtuosity in technical skill, a knack for collaboration, and disregard for disciplinary confines. It also marks a decisive step forward on his path to light.

The transistor radio belonged to his older brother, who was building it from parts.

"As a child growing up in Iran, I was always curious about how things worked," says Engheta. "I had never seen anything like this radio and needed to know how it could function without being connected to anything."

His brother's explanation of how portable music resulted from electromagnetic and mechanical waves transformed into electronic signals led him a few years later to the University of Tehran, where he earned a degree in electrical engineering with highest honors, and then to the United States for his graduate work.

Nader's contributions to his field comprise a breadth and impact that is not often seen from one individual. Vijay Kumar, Nemirovsky Family Dean of Penn Engineering

It may seem that this origin story about a radio is just that—an origin story about a radio.

But the radio is background noise. This moment showcases a personality porous to the world, with a fastidious sense of purpose when it comes to learning more.

Engheta's career-defining impacts on optics do not occur despite his pedigree in radio, but in relation to it, and his professional leap from one side of the electromagnetic spectrum to the other was entirely in keeping with the spirit of his scientific approach.

Artur Davoyan, assistant professor of mechanical and aerospace engineering at UCLA who spent three years as a postdoctoral fellow in Engheta's lab at Penn, describes Engheta's relationship to subject matter expertise as a means, not an end.

"Nader is an authority on an astonishing number of topics," says Davoyan. "He's extremely agile when it comes to giving perspective on science, the go-to person if you want a fresh look at any problem. This is because his motivation is never to simply master a field. His ultimate goal is to satisfy the unique creativity he was born with, and his greatest contribution to science has been to show people around him how to operate from this same place of curiosity and joy. He flourished when he began theorizing and designing materials for tailoring light because it was the perfect playground to exercise this way of thinking to its full extent."

"I’ve always known that knowledge does not have boundaries," says Engheta. "Research fields have boundaries, but they are artificial. You can work across different fields."

He pauses and reflects for a few seconds. Smiles.

"In fact, innovation often occurs at the boundary points between fields. These fields may have disparate languages and priorities—but they also have interesting commonalities you can find if you know how to look."

Knowing how to look is one thing. Understanding two distinct forms of science and communicating between them is another. Engheta is perhaps most celebrated for his seminal work linking electronics and optics, two fields so alien in approach they may as well exist on different planets.

In the early 2000s, when nanotechnology was beginning to hit its stride, scientists were newly able to control and fabricate patterns at the atomic level, and light researchers were exploring ways to manipulate light by shaping structures at nanoscale. Fresh from his fishy foray into the optics of visual systems, Engheta realized he could leverage nanotechnology to apply his expertise in radio frequency concepts to visible light.

In a study that would help develop and expand a burgeoning area of research called "metamaterials," Engheta introduced a tiny metallic particle with strong light scattering properties to a material at nanoscale.

He called it an antenna.

Engineers unvaryingly describe the crossover language Engheta developed to communicate between radio and light science in reverential, aesthetic terms: "elegant," "beautiful," "stunning." His analysis of this metallic nanoparticle imagined it as an analog of a classical circuit, drawing parallels between its light-scattering properties and the functions of resistor, inductor, and capacitor that are the ABCs of electronics.

Ahmad Hoorfar, professor of electrical and computer engineering at Villanova University and Engheta's lead sponsor for the Franklin Medal, stresses the impact of this work.

"That you can make circuit elements at optical frequencies," he explains, "means that all the design that people have done for the previous 50 to 70 years in electronics was suddenly available to optics. This work built bridges that provided a wealth of resources. It's a brilliant idea that both simplified and improved optical science."

Mark Brongersma, professor in the Department of Materials Science and Engineering at Stanford University and a frequent collaborator of Engheta's, affirms the significance of Engheta's interdisciplinary approach.

"Nader knew how antennae work in the radio frequency regime," says Brongersma, "and was able to provide a different, incredibly impressive perspective of how to engineer these metallic structures to manipulate light."

This different perspective was not limited to the inclusion of a single miniscule particle. Engheta envisioned adding more—couples or whole arrays of these particles. Today, these are called "metasurfaces," artificially mixed and modified two-dimensional structures that scatter and transform the way light propagates.

Penn's rich history of Franklin Medal Laureates includes a distinguished lineup of researchers who have made groundbreaking contributions to their respective fields. Among the recipients are Katalin Karikó and Drew Weissman (2022), Doug Wallace (2017), Charles Kane and Eugene Mele (2015), William Labov (2013), Peter Nowell (2010), Ruzena Bajcsy (2009), Aravind Joshi (2005), Robert Newnham (2004), Robin Hochstrasser (2003), Ralph Brinster and Shiriki Kumanyika (1997), Alan MacDiarmid (1993), Eli Burstein (1979), Mildred Cohn (1975), Britton Chance (1966), and Ezra Krendel (1960).

Contributions from the cohort of researchers and innovators range from mRNA technology to topology research, sociolinguistics, cancer genetics, robotics, and more. These exceptional laureates exemplify Penn's enduring dedication to innovative research and scientific excellence.

"With this," adds Brongersma, "we can steer light. We can focus it. Light manipulation science impacts so many important technologies around us—from solar energy harvesters, to sensors, to visual displays for television and augmented reality devices. All of these are limited by our ability to tailor light at nanoscale. Metamaterials are advancing that ability, in large part thanks to Nader."

Acknowledged today as the "father" of metamaterials, Engheta defines this complex field of study with his signature lucidity.

"The materials that make up the periodic table all interact with light in conventional ways," he says. "The idea of metamaterials is to make materials that do unconventional things with light."

In simple terms, metamaterials alter the electromagnetic properties of one material through the precisely shaped inclusion of another. All three elements matter—the properties of the main material, the properties of the inclusion, and above all, the geometry introduced.

"What's amazing," says Engheta, "is that the electromagnetic properties of the resulting metamaterial can be entirely different from those that comprise it."

Greater than the sum of their parts, metamaterials offer a neat allegory for Engheta's approach to engineering: Distinct viewpoints, thoughtfully wrought and combined, produce outcomes more valuable than each could have individually imagined.

It's a rare form of creativity in science to focus more on the questions asked than the answers expected.

Engheta is known for asking two questions in particular: "What if?" and "Why not?"

These questions express a philosophy of science as committed to education as it is to research.

"Nader's contributions to his field comprise a breadth and impact that is not often seen from one individual," says Vijay Kumar, Nemirovsky Family Dean of Penn Engineering. "He is also one of the kindest and most engaging teachers and caring mentors that we have on our faculty."

The generation of engineers who trained with him before going off to lead their own labs affirm this, highlighting the influence of his supportive, outside-the-box thinking.

"I chose Penn Engineering because of Nader's approach to science," says Davoyan. "He looks at problems from unexpected angles. He finds inquiries no one is making. I was also working on optics and metamaterials, and he was a huge name in the field. But, if he had worked in a different area altogether, I still would have come to learn from him."

Mario Mencagli, assistant professor of electrical and computer engineering at the University of North Carolina at Charlotte and another of Engheta's former postdoctoral fellows at Penn, underlines his singular commitment to understanding.

"He likes to go deep," says Mencagli. "We were building new technologies and improving their capabilities, but that was never enough. We had to also understand the physics behind what was happening. I learned a lot from this. Sometimes, we were almost trying to get lost, to simplify a problem to such a degree we could discern the physical laws behind it. Once you’ve achieved that level of depth, you can really build."

More than a peculiar commitment to rigor, Engheta's orientation echoes that of his hero, Nikola Tesla. A theoretical physicist, he approaches this work as a technologist, rejecting standard distinctions between scientist and engineer—the former, a student of the fundamental laws of nature, the latter, a builder of technologies optimized for nature's constraints. Engheta has made his mark with daring theoretical interventions that push limits of what's scientifically possible and tools that bring these new understandings of the world into being.

Humeyra Caglayan, professor of experimental optics and photonics at Tampere University in Finland, recalls her postdoctoral research with Engheta in exactly these terms.

"As physicists, we are always looking to understand how things work," says Caglayan. "But sometimes, it's enough for us to leave it at that. Nader, though, always wants to frame this effort as leading to a technology that can be used within our lifetimes. That is very unique."

Andrea Alù, distinguished professor at the City University of New York, Einstein Professor of Physics at the Graduate Center, CUNY and founding director at the Advanced Science Research Center, CUNY, has consistently co-published with Engheta since his undergraduate days as a visiting student at Penn.

"We work well together because we both enjoy the curiosity in and of itself," says Alù. "Results are not enough. Until we really grasp something, we’re not satisfied. Nader is a disciple of extreme clarity, and I learned this from him. When people read Nader's papers, they’re excited, and really absorb things from them."

Alan Willner, distinguished professor of electrical and computer engineering at USC and expert in optical science, agrees.

"Whenever you talk to Nader, your brain tingles with the number of new ideas flying around. And his brilliance is inseparable from his empathy. He boils things down to the most fundamental issues. With warmth, kindness, and encouragement, he can masterfully explain anything to anyone, and there are layers to his explanation. If you know a little, you come away learning a lot. If you know a lot, you still come away learning a lot."

A balancing act of innovation—"‘The crazier, the better,’ he’d say," laughs Mencagli—and genuine connection, Engheta's career, like his conversation, is incapable of following predictable paths.

"His ‘by the ways’ are famous," says Brongersma. "You’ll ask him a question and he’ll start answering, but before he finishes the answer, and he’ll say, ‘by the way,’ and another dimension will come into play. In five minutes or so, you’ll get back to the original conversation, but there could be one or more ‘by the ways’ before it all gets neatly addressed and resolved."

This is the grammar of a person interested in getting to the heart of things. And in Engheta's science, heart carries a double meaning.

His mentees and colleagues speak with equal passion about his personal gestures of care and his professional encouragement to think freely about the science that inspires them. Gifts for new babies mingle with mathematical dilemmas, and inquiries about friends and family flow freely alongside advances in experiment design.

Engheta's research continues to inspire and push limits. He is currently developing metamaterials to serve as hardware for analog computers, which already display potential to one day break the speed and energy-efficiency ceilings of the digital revolution. His curiosity has resulted in devices that harness physics few thought possible. Metal and semiconductor combinations cancel each other's light scattering and work together as a kind of invisibility cloak. A field he founded known as "epsilon-near-zero metamaterials" provides tools for stretching light waves between two distant points in such a way they behave as one, achieving astounding simultaneity.

Even as his work continues to be honored at the highest levels, Engheta maintains his reputation for curiosity and gratitude towards all those around him, as open today to out-of-left-field queries as he was the day the sunfish crossed his desk.

"Everyone has something to contribute," he says, "every question is welcome."

Andrea Alù is distinguished professor at the City University of New York, Einstein Professor of Physics at the Graduate Center, CUNY, and founding director at the Advanced Science Research Center, CUNY. He was a visiting undergraduate student at Penn in 2002. His Ph.D. dissertation at the University of Roma Tre, Italy, was co-advised by Engheta, and he was a postdoctoral fellow in Engheta's group in the Department of Electrical and Systems Engineering from 2007 to 2008.

Mark Brongersma is the Stephen Harris Professor in the Department of Materials Science and Engineering, as well as Applied Physics, at Stanford University.

Humeyra Caglayan is professor of experimental optics and photonics at Tampere University. She was a postdoctoral fellow at Penn Engineering in the Department of Electrical and Systems Engineering from 2011 to 2013.

Artur Davoyan is assistant professor of mechanical and aerospace engineering at UCLA. He was a postdoctoral fellow at the University of Pennsylvania School of Engineering and Applied Science in the Department of Electrical and Systems Engineering from 2012 to 2015.

Nader Engheta is H. Nedwill Ramsey Professor of Electrical and Systems Engineering at Penn Engineering, with secondary appointments in the departments of Bioengineering, Materials Science and Engineering, and Physics and Astronomy in the School of Arts & Sciences.

Ahmad Hoorfar is professor of electrical and computer engineering and the founder and director of the Antenna Research Laboratory at Villanova University.

Vijay Kumar is Nemirovsky Family Dean of Penn Engineering and Professor in the Department of Mechanical Engineering and Applied Mechanics with secondary appointments in the Departments of Electrical and Systems Engineering and Computer and Information Science.

Mario Mencagli is assistant professor of electrical and computer engineering at the University of North Carolina at Charlotte. He was a postdoctoral fellow at the Penn Engineering in the Department of Electrical and Systems Engineering from 2017 to 2019.

Alan Willner is a distinguished professor of electrical and computer engineering and the Andrew & Erna Viterbi Professorial Chair at USC.