A new technology developed by a professor at the U.S. Air Force Institute of Technology (AFIT) has the potential to transform industries from healthcare to aerospace. Using liquid crystals and light, Dr. Hengky Chandrahalim has devised an innovative sensor that detects sound and vibration without contact.
“Our sensor is an example of optoacoustic technology, which means it detects sound by combining optics and acoustics,” said Dr. Chandrahalim, who’s been at AFIT since 2017. “Instead of using traditional electronics or mechanical elements to sense sound, it listens using light. By marrying optics and acoustics in a novel way, we’ve created a sensor that can detect sound waves simply by observing how they change the behavior of light passing through a liquid crystal.”
Dr. Chandrahalim’s invention, titled Noncontact Liquid Crystalline Broadband Optoacoustic Sensors, recently received a patent. It directly addresses some of the limitations related to acoustic sensors, which convert sound waves into electric signals and then process those signals to extract information. A microphone in a smartphone is modern-day example of an acoustic sensor.
“Traditional acoustic sensors, such as those used to detect sound waves, vibrations or ultrasound often have a fundamental limitation,” Dr. Chandrahalim said. “Their size needs to be comparable to the sound wavelengths they’re trying to detect. This means that detecting lower-frequency sounds, which have longer wavelengths and require physically larger sensors. For sensors that must operate across a broad range of frequencies, the result is often bulky and impractical equipment. This becomes a significant challenge in many Air and Space Force applications, where systems are subject to strict constraints on size, weight, power and cost.
“Another motivating factor was the limitation of contact-based sensing. For example, ultrasound imaging typically requires the sensor to be in direct contact with the body, often using gel to ensure good coupling. But in situations where the surface is wounded, contaminated or sensitive, direct contact can be uncomfortable, risky or simply not possible. A noncontact method of detecting sound would offer significant advantages in both safety and usability.”
Identifying those limitations, Dr. Chandrahalim pondered the idea of dramatically shrinking acoustic sensors while making them non-contact and adding versatility. The inventor worked with a graduate student, Major Michael T. Dela Cruz, over 18 months to build a reliable and efficient prototype.
“Our sensor acts like an optical eardrum,” the inventor said. “It watches how light changes in response to sound, offering a new and elegant alternative to conventional sound detection, one that is lightweight, non-invasive and highly versatile. Our optoacoustic liquid crystal sensor does not need to touch what it is sensing. It can operate in open air, and it uses optical measurements instead of electrical signals.
“Liquid crystals presented a compelling solution. These materials, commonly used in display technology, exhibit optical properties that respond to mechanical changes such as pressure from sound waves. By using them as a sensing medium, we realized it was possible to detect acoustic signals by observing how light transmitted through the liquid crystal changes, enabling a completely noncontact sensing approach. Even better, the entire system could be miniaturized onto a chip-scale platform, offering significant reductions in size, weight, and cost.”
The inventor sees the acoustic sensor playing an important role for the warfighter.
“First, it addresses one of the most critical challenges in defense systems: the need to reduce size, weight, power consumption and cost,” Dr, Chandrahalim said. “Second, the sensor’s appearance is another strategic advantage. It resembles a simple piece of transparent glass and can be easily integrated into windows, panels or other clear surfaces without drawing attention. This makes it ideal for discreet monitoring in both combat and surveillance scenarios.
“Furthermore, because the sensor detects sound using light rather than electronics, it is naturally immune to electromagnetic interference. This is a critical benefit in modern military operations, where electronic warfare and jamming are common threats.”
Looking past the warfighter, there are other applications in which the invention will thrive. Dr. Chandrahalim offered up the medical field as just one example.
“This technology has the potential to significantly improve how doctors diagnose and monitor patients by offering a noncontact, gentle and highly sensitive way to detect physiological signals,” Dr. Chandrahalim said. “In current medical practice, many diagnostic tools rely on sensors that must physically touch the body. While this is effective in many cases, it presents challenges for patients with open wounds, burns, infections or other conditions that make contact painful or unsafe. Our liquid crystal-based optoacoustic sensor overcomes this limitation by detecting sound and vibration through light, without needing to touch the skin. This opens the door to a new generation of non-invasive diagnostic tools.
“By removing the need for physical contact and enabling compact, accurate and real-time sensing, this technology could transform how clinicians gather information about a patient’s condition — leading to earlier detection, improved patient comfort, more accurate diagnoses and more economical care.”
So, what’s next for the AFIT professor and his invention?
“We have not yet licensed this patent to a company, but we’re actively working toward that goal,” he said. “Looking ahead, our ultimate vision for this patented technology is to ensure it reaches its full potential and delivers meaningful benefits for both national defense and society at large.”
United States Patent Office Patent: #11, 366, 054 B2
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