Ceramic Additive ManufacturingElectronics

MITRE partners with Lithoz to 3D print underwater acoustic transducers

Three-way partnership also includes MSI Transducers Corp

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Lithoz, one of the leaders and pioneers in advanced ceramic 3D printing technology, is making its technology available to MITRE to develop more advanced underwater acoustic transducers for communication systems. MITRE and MSI Transducers Corp are collaborating on this project that shows how ceramic 3D printing is emerging as a key option for the future of communication systems, on land, and now underwater as well.

Currently, the interest in underwater acoustic communication and monitoring is growing rapidly as more and more underwater monitoring systems are deployed around the world. Compact and autonomous underwater sensing platforms rely on acoustic transducers for transmitting and receiving signals in marine environments. These systems may be constrained to battery power and thus critically limited by less efficient or sensitive transducers. Transducers that use piezo-composites as an active layer exhibit improved efficiency and sensitivity, but have been commercially restricted by manufacturing processes that constrain possible transducer geometries to those that can be molded or cut.

MITRE and Lithoz have partnered to 3D print ceramic underwater acoustic transducers for communication systems
A traditional underwater acoustic transducer

Additive manufacturing can overcome the shortcomings in conventional manufacturing techniques to create novel-shaped transducers with augmented properties. Enhanced sensitivity and sidelobe reduction may be achieved through the spatial distribution of the printed material that leverages AM’s ability to print voids and lattice shapes easily and iteratively without expensive tooling redesign. However, printing these shapes repeatably using a benchmark material has not yet been accomplished.

MITRE, a not-for-profit organization that works across federal, state and local governments, as well as industry and academia, did not possess the expertise and equipment to print piezoelectric material. Thus a three-way partnership was established between MITRE, MSI Transducers Corp. and Lithoz-America, LLC. This collaborative agreement enabled MITRE to develop and implement a finite element transducer model to design transducer geometries for specific performance benefits.

MSI brought to the table a wealth of knowledge on piezoelectric material processing, packaging and testing. Lithoz contributed with AM hardware and material development expertise to develop printable piezoelectric materials and geometries. Introductions to both Lithoz and MSI were made possible through the extensive network of Bridging Innovation partnerships that MITRE maintains.

Starting in FY19, the collaborative research team achieved success by manufacturing and testing the first AM samples, which had measured material and piezoelectric results that were the same or better than conventionally manufactured materials. This success served as a major project milestone and gave confidence that the printed material could compare well to conventional material and thus would be suitable in underwater transducers.

In FY20, the team began focusing on novel geometries that would realize performance benefits over conventional geometries. Early indications based on preliminary printed samples suggest that these structures will be printable and open the door to previously unreached and novel performance.

3D printed ceramic structures, magnified X20

Inspired by the R&D 100-winning FUSE antenna, another MITRE-developed capability, the company’s researchers set out to determine how to “print” transducers, the sensors that send and receive acoustic signals underwater.

The research team demonstrated a technology that can create novel transducers with improved properties, such as sensitivity, directionality, and bandwidth. These can be applied to unique undersea missions not well-served by conventionally manufactured transducers, including the activities of small maritime robots known as autonomous underwater vehicles (AUVs).

“This innovation will enable pioneering ways to build transducers with capabilities that were previously only hypothetical,” said MITRE’s Chief BlueTech Strategist Nick Rotker. “It opens up the transducer design space to enable more capable and more-efficient platforms to gain a better understanding of what’s going on within our oceans.”

It’s one thing to obtain greater insights under the surface. It’s another thing to do it undetected. That requires advanced acoustic transduction properties to project data in a highly focused direction, making it challenging for third parties to receive it. MITRE researchers developed a novel geometric technique to achieve this in a single transducer.

“It’s the difference between shining a flashlight versus a laser pointer, only with sound,” explained MITRE’s Justin Tufariello, the project’s principal investigator. “Rather than advertising your presence to everyone in the area, a platform can now more covertly transfer acoustic data. That brings many potential applications, especially within the national security communities.”

To explore that potential, the prototype is undergoing testing by a U.S. Department of Defense sponsor.

In addition to military applications, the increasing use of AUVs to perform data collection for a variety of purposes amplifies the challenges of underwater acoustics—and the need for solutions. The platforms often carry sensors to monitor the environment, measuring things like temperature and mapping the ocean floor with sonar. But AUVs can’t use the same transducers that large vehicles like submarines do, because of the signal processing and electrical power requirements of those arrays.

The 3D printed sensors created by MITRE and Lithoz provide these vehicles with customizable transducer options. For small-hulled vehicles, they can offer significant improvements over conventionally manufactured transducers, a process that’s remained static for decades.

The patent-pending technology earned a finalist spot in 2023’s R&D 100. Tufariello and his colleagues also presented findings at the Acoustical Society of America meeting in May.

Ballard Smith, one of MITRE’s independent R&D program leads involved in our transducer research since its beginnings, said the project’s success goes beyond technical accomplishments.

“This work showcases the importance of knowing the problem space and connecting the right partners to rapidly develop impactful capabilities that could revolutionize undersea operations,” Smith said.

From conception to prototype, the collaborative research team followed a rigorous development and evaluation process, refining the technology along the way. That included proving the additively manufactured transducers work as well as conventionally manufactured ones, under the same challenges.

For example, they had to ensure the structures could hold up under pressure. So, they tested both additively and conventionally manufactured prototypes at the world-renowned Woods Hole Oceanographic Institution, one of our non-profit BlueTech partners. Their hydrostatic chamber can simulate the pressure of the ocean to 10,000 pounds per square inch—just over four miles deep. With roughly 99% of the ocean less than that depth, the testing confirmed the transducer’s durability for use in a wide range of underwater applications.

Additionally, the effort leveraged MITRE’s modeling and simulation expertise to understand the strengths and limitations of different components early in the development process, saving time and effort during prototyping. Our Advanced Manufacturing Lab offered support as well.

The research opens exciting opportunities to expand and advance innovation in the maritime environment.

“We hope this effort will open other cost-effective possibilities for different types of ceramic 3D printing, so we can continue to propel the field of underwater research forward,” Tufariello said.

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