The research could help develop methods for reducing intense noise that threatens aircraft and ground crews

Newswise — Researchers from the FAMU-FSU College of Engineering and the Florida Center for Advanced Aero-Propulsion, or FCAAP, are helping to solve a safety challenge in military aviation: the extreme noise generated by supersonic jets during takeoff and landing.

The research, published in the Journal of Fluid Mechanics, demonstrates a new model for understanding how supersonic jets of air collide with the ground or other structures to create a resonant feedback loop that produces extreme noise that can reach dangerous volume levels.

The team examined jets like those found in a type of aircraft known as Short Takeoff and Vertical Landing jets, or STOVL. The ability to operate without a traditional runway gives these aircraft, such as the F-35B Lightning II, critical tactical advantages.

But as they descend toward the ground, their exhaust plumes interact with landing surfaces and generate intense noise, often exceeding 140 decibels, posing serious dangers to both aircraft structure and nearby personnel.

“Only a tiny fraction of the jet’s energy is transformed into sound, but this small fraction has a major impact,” said Farrukh S. Alvi, professor in the Department of Mechanical and Aerospace Engineering and former founding director of the Institute for Strategic Partnerships, Innovation, Research, and Education, or InSPIRE, and founding director of FCAAP. “The intense noise produced by jet engines can cause structural damage to the aircraft and damage the hearing of personnel on the ground. We are trying to understand the physics behind these supersonic jets and the noise they produce so that we can develop tools that can reduce their impacts. In fact, we have already had some success in developing techniques that can reduce jet noise.”

Why it matters

When the high-speed air coming from jet engines mixes with the ambient air, it creates large-scale disturbances that hit the ground, producing strong sound waves that propagate back toward the jet engine. This establishes a repeating, back‑and‑forth interaction and creates resonance, an example of a feedback loop, causing loud and repeating noise. For aircraft, these resonant vibrations accelerate structural fatigue and can generate hazardous low-pressure zones that can pull the aircraft toward the ground.

For crewmembers on the ground, sustained exposure to sound levels over 140 decibels can cause permanent hearing damage, even when wearing protective equipment. At peak intensities, extreme acoustic pressure can even cause organ damage.

An animation showing an aircraft using supersonic jets for a vertical landing. As it descends toward the ground, exhaust plumes interact with landing surfaces to generate intense noise, often exceeding 140 decibels, posing serious dangers to both aircraft structure and nearby personnel. (Courtesy of Myungjun Song)

A new approach to modeling jet resonance

The research team tested a supersonic, Mach 1.5 jet — 1.5 times the speed of sound — and adjusted nozzle pressure and the jet’s distance from the ground to simulate take-off/landing and make a range of measurements.

To see the airflow, they used a high‑speed camera and a specialized visualization technique called schlieren imaging that allowed them to ‘see’ the jet flow — including its large-scale disturbances and the sound waves generated in real time. At the same time, a highly sensitive microphone also recorded the sound produced by the jet.

When the jet is loud, the jet flow and the sound waves repeat at a regular rhythm, which is a characteristic of a resonant cycle. By matching images to a specific point in the cycle, the researchers developed a clear picture of the airflow and measured how fast large-scale disturbances in air moved and how sound waves traveled back toward the nozzle.

The researchers found that for many cases, the pitch — how the human brain perceives the frequency of sound waves — of the noise was primarily governed by acoustic standing waves, which appear stationary in space between the body of the plane and the ground. The findings reveal that the pitch is not primarily governed by disturbance velocity, thereby offering another perspective on the existing understanding of the resonance feedback. They also found that slower disturbances tend to be larger, consequently creating louder noise.

“That was surprising,” said postdoctoral researcher Myungjun Song, the study’s lead author. “We found that these acoustic standing waves are much more important in determining the pitch, while the size and speed of the disturbances decide the level or ‘loudness’ of the noise produced.”

The discovery offered the research team an insight. Because the disturbance speed has little effect on pitch, information about acoustic standing waves would be enough to predict the noise pitch.

The new model enables engineers to predict noise frequencies more easily during aircraft and landing pad design, a critical step toward protecting both aircraft structures and personnel from acoustic trauma.

World-class research facilities drive discovery

The experiments were conducted at FCAAP’s specialized research facilities, designed for advanced high-speed aerodynamic studies at the FAMU-FSU College of Engineering.

Researchers used the FCAAP’s STOVL facility, which offers cutting-edge flow diagnostic capabilities, and the hot jet facility, which can generate high-temperature, high-speed airflow in an anechoic chamber to allow for highly accurate acoustic measurements under realistic jet conditions.

“While jet propulsion is an important focus of our work, our research is not limited to it,” Alvi said. “The university and the college, through FCAAP, operates a polysonic wind tunnel that simulates supersonic flows up to Mach 6 — supersonic to hypersonic conditions. We also use our anechoic wind tunnel and subsonic wind tunnels for numerous other aerospace related research projects. Together, these facilities and the expertise of our researchers create a one-of-a-kind ecosystem for conducting leading-edge research in aerospace and aviation.”

An associated initiative, InSPIRE is an FSU-led effort to establish a new aerospace and advanced manufacturing hub in Bay County, Florida. The program builds on FCAAP’s foundation to develop complementary facilities for larger hypersonic wind tunnels that can handle a wider range of conditions for applied, industry-relevant research.

“In partnership with industry, InSPIRE is also integrating advanced manufacturing capabilities that will allow much more efficient test and evaluation and assist our industry partners to innovate manufacturing processes in a realistic factory-modeled setting,” said Alvi, the former director of InSPIRE. “Working with industry partners allows our researchers to use their expertise to solve the pressing and difficult problems that are directly relevant for industry.”

Research team and support

The project was a collaborative effort involving Song, the study’s lead author; Alvi; and graduate student Serdar Seçkin.

Funding was provided by the Office of Naval Research, with additional support from the National Science Foundation, the Air Force Office of Scientific Research, FCAAP, the FAMU-FSU College of Engineering and the Don Fuqua Eminent Scholar Fund.

Newswise — In the air people breathe, the water on the Earth, the stars in the sky and more, atoms are the building blocks that make up the universe. Understanding the structure of the atomic nucleus is crucial for research with implications for astrophysics and in applications such as medical imaging and data storage.

A new study conducted by Department of Physics researchers using the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University examined titanium-50 nuclei and showed that a long‑standing explanation for where magnetism in atomic nuclei comes from does not fully work for titanium‑50. The research, which was published in Physical Review Letters, suggests that scientists may need to rethink how they explain nuclear magnetism.

“What current models propose is that magnetic strength is largely generated by spin-flip excitations, that means when flipping proton or neutron spins from up to down between so-called spin-orbit partner orbitals,” said Associate Professor Mark Spieker, a co-author on the multi-institution study. “For the first time, we showed that this type of spin-flip cannot be the only mechanism that generates nuclear magnetism.”

How it works

Current nuclear models treat protons and neutrons as individual particles that can occupy fixed energy levels. A spin-flip occurs when these particles change the orientation of their spin as they jump between levels, generating magnetic strength in the process. For many years, scientists believed that this spin-flip mechanism was mainly responsible for magnetic strengths, or signals, in atomic nuclei. Advanced computer modeling also predicted this behavior.

The FSU experiments showed something unexpected: nuclear excited states that clearly showed this neutron spin-flip structure were not the ones producing the strongest magnetic signals. In other words, having more of this neutron “spin‑flip” structure did not automatically mean a stronger magnetic effect.

What they did

The researchers conducted a neutron-transfer experiment at the John D. Fox Superconducting Linear Accelerator Laboratory, using the facility’s Tandem Van de Graaff Accelerator to direct a deuteron — a nucleus made of a proton and a neutron — beam at a thin foil of titanium-49. During the reaction, the neutron from the beam was transferred to titanium-49, producing titanium-50 and leaving a residual proton.

Scientists used the Super-Enge Split-Pole Spectrograph at the Fox Lab to measure the different angles at which the proton was emitted in the reaction, allowing them to analyze how the neutron was transferred to titanium-49.

“You could say that the deuteron beam hits the titanium-49, transfers a neutron, and in this process kicks it up a set of stairs. Depending on the nucleus, that set of stairs looks very different,” Spieker said. “With the spectrograph, we can measure how high the different steps are. How high we get up the set of stairs depends on the excitation energy that we give to the nucleus.”

They combined their results with previously published electron- and proton-scattering data and with data from new photon-scattering experiments conducted at collaborating universities. By combining all these approaches, they were able to closely examine how neutrons flip their spin and how much those flips contribute to the nucleus’s overall magnetic behavior.

The researchers saw that the magnetic signal observed in their experiments was not of the same strength as models predicted — a sign that something else must be contributing to the magnetic signals they measured for titanium-50.

“Without combining all these data sets, the story cannot be stitched together cleanly,” said Bryan Kelly, a graduate student at FSU and study co-author. “Seeing the other magnetic excitations, that the other probes are sensitive to, allowed us to conclude that the spin-flip mechanism between spin-orbit partners is not the sole factor of magnetic strength generation.”

Why it matters and future directions

The study’s results challenge long-standing assumptions about the magnetic behavior of nuclei. Improving scientific understanding of the structure of atomic nuclei will refine current models used across nuclear physics and astrophysics and will help to link these with models used in high-energy physics. Such combined efforts between different fields of physics lead to a better understanding of the building blocks of ordinary matter that shape our universe.

“Developing a better understanding of the universe is exciting and fascinating on its own, and as we learn more, we can possibly apply these new insights to all sorts of new ideas,” Spieker said. “All ordinary matter is made of atomic nuclei, so the more we understand these ‘building blocks’ of nature, the more possibilities we have for what we can use them for to benefit society and drive progress.”

In future studies, the researchers plan to examine what accounts for the unexplained magnetism in titanium-50.

“This research showed that we cannot rely on magnetic strength measurements alone to understand excited states of nuclei,” Kelly said. “Magnetic strength is spread out across several nuclear states and understanding why will require further investigations of the nucleus.”

Acknowledgements

Researchers from Florida State University, the Technical University of Darmstadt in Germany and the Triangle Universities Nuclear Laboratory in North Carolina at Duke University contributed to this study.

This research was supported by the U.S. National Science Foundation, the U.S. Department of Energy Office of Science, the German Research Foundation, the Institute of Atomic Physics in Romania, the Romanian Ministry of Research and the Romanian Government.

Newswise — In medicine, security, nuclear safety and scientific research, X-rays are essential tools for seeing what remains hidden.

The materials used to create X-ray detectors can be rigid, expensive and laborious to produce. But new research led by FSU Department of Chemistry and Biochemistry Professor Biwu Ma is creating lower-cost, adaptable materials that could revolutionize X-ray detection technologies.

In two separate research studies, Ma’s group offers solutions to long-standing challenges in X-ray imaging. In the first study, published in Small, the team developed a new material that generates electric signals when exposed to X-rays, enabling direct X-ray detection. In the second study, published in Angewandte Chemie, the researchers used a related material to produce low-cost scintillators, which are materials that emit visible light when exposed to X-rays or other high-energy radiation.

“We have traditionally relied on inorganic materials for X-ray detection, but they are often rigid, expensive to manufacture and energy-intensive to produce, and they have many limitations,” Ma said. “What we have been trying to develop is a new class of materials that can address the issues and challenges faced by existing materials.”

In these studies, researchers created new hybrid materials composed of both organic and inorganic components, known as organic metal halide complexes (OMHCs) and organic metal halide hybrids (OMHHs). By tailoring the structures of these materials at the molecular level, the team enabled different forms of X-ray detection. This research represents a major step toward developing lower-cost, scalable and flexible X-ray detector technologies capable of overcoming key limitations of conventional inorganic systems.

Glassy OMHC films for direct X-ray detectors

Commercially available direct X-ray detectors are constructed using inorganic semiconductors, made from non-carbon materials, such as cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe). These materials contain toxic elements and require energy-intensive processing, making them expensive.

In the first study, the team demonstrated, for the first time, the use of OMHCs as a material for making direct X-ray detectors. These are materials composed of carbon-based semiconducting molecules that are bonded to metal halides, which are compounds made of metal and a halogen element. The specific OMHC compound developed by the team was created out of zinc, bromine, and a carbon-based molecule, enabling efficient X-ray absorption and electron transport within a single material.

Using a melt-processing approach, similar to melting plastics and allowing them to cool into a desired shape, the researchers transformed OMHC molecular crystals into amorphous, glass-like materials that can be molded into ready-to-use forms. They used these materials to make direct X-ray detectors that convert incoming X-rays into electrical signals.

Results

The resulting detectors produced strong electrical responses even at low X-ray exposure levels, making them more effective than detectors made from traditional materials. The team also evaluated the long-term stability of detectors made with the new material. After storing the detectors for four months under ambient conditions, testing showed they retained 98% of their initial performance.

OMHCs offer additional practical advantages. They are less expensive to produce than materials currently used in commercially available X-ray detectors because they can be synthesized from abundant and non-toxic raw materials. Moreover, the simple melt-processing method also makes device fabrication easier and more scalable than existing approaches.

“This is actually the first time these OMHC materials have been used to fabricate direct X-ray detectors,” said Ma. “They can be prepared in a low-cost way while delivering high performance. From a sustainability perspective, this new class of materials offer tremendous advantages over conventional materials.”

Bright, fast and flexible scintillators: X-ray components on fabric

In the second study, the team developed a new version of OMHH-based scintillators that exhibit high light yield and fast response, meaning they emit strong visible light and respond almost instantly when exposed to X-rays. OMHHs are similar to OMHCs, but a different type of chemical bond brings together organic components and metal halides into a single material.

The work builds on the team’s years of effort in the area since 2020, when they demonstrated the first ecofriendly OMHH scintillators. Earlier versions of OMHH scintillators relied on slow crystal growth processes that limited their size and flexibility, and their light emission faded relatively slowly. This latest generation of OMHH scintillators overcomes both challenges by eliminating the need for crystal growth and by dramatically speeding up the light response.

Results

By carefully designing the molecular structure, the team created a new amorphous OMHH material that shows fast response in nanoseconds. Unlike earlier versions of OMHH scintillators, in which light emission comes from metal halide centers and lingers for longer periods, the new material emits from the organic components of the material, exhibiting a faster response while maintaining excellent X-ray absorption and high light output.

Fast-response scintillators are especially important for advanced radiation detection and imaging. Their rapid light emission allows for clearer images, improved timing accuracy and reduced signal overlap, which are critical for applications such as medical imaging, security screening and real-time radiation monitoring.

The amorphous nature of the material also allows it to be easily processed into thin films and coatings. Using this approach, the team created fabric-based X-ray scintillators that can be integrated into clothing, enabling wearable and portable radiation detectors. These flexible scintillating fabrics represent a significant departure from traditional rigid detectors and open new possibilities for comfortable, adaptable and low-cost X-ray detection technologies.

Why it matters

While the two studies focused on different X-ray detection approaches, both used similar material design strategies to address major challenges in developing next-generation X-ray detection technologies.

FSU has begun filing patents to commercialize the technologies developed in Ma’s group and test them in real-world conditions. These advancements offer exciting and cost-effective solutions for next-generation X-ray detection technologies. Commercialization of these materials could benefit many fields, including medical imaging, security scanning, nuclear safety and more.

In addition to the team’s internal efforts, the group has collaborated with research institutions and industrial partners to explore diverse applications of these materials. These collaborations include Delft University of Technology (TU Delft) for photon-counting computed tomography, the University of Antwerp for luminescent dosimeters for radiotherapy, the University at Buffalo for pixelated X-ray imagers, and Qrona Technologies for X-ray microscopy technologies.

“The materials are very unique and were developed here at FSU,” Ma said. “We believe our materials and devices have tremendous potential to outperform existing technologies and address key challenges in the field.”

The research has been supported by federal funding from the National Science Foundation Division of Materials Research and Innovation and Technology Ecosystems. The lead authors of the two publications are Oluwadara Joshua Olasupo, who recently graduated with a Ph.D., and Tarannuma Ferdous Manny, a fourth-year graduate student. Collaborators from TU Delft and the University at Buffalo also contributed to the work. The research additionally involved high school students through the FSU Young Scholars Program.