Why We’re Interested in Fish Movement

If fish could speak, they would probably call for measures to protect their existence, their habitats, and the ecological balance of aquatic systems. Since they cannot, their only option is to swim to places where they can live and reproduce in healthy conditions. Where they go thus indirectly tells us how clean and accessible our rivers and oceans are. By tracking fish, marine biologists, aquatic ecologists, limnologists (inland water ecologists), conservationists, and fisheries experts can gather valuable data.

Many fish species are endangered due to overfishing, habitat loss (e.g., due to dams or the construction of offshore wind farms), pollution, and climate change. Fish tracking helps identify critical habitats such as spawning grounds and optimize protective measures.

High-Tech Underwater

Fish tracking relies on high-tech solutions. A widely used method is acoustic telemetry: fish are fitted with transmitters that emit uniquely coded ultrasonic signals. These signals are picked up by hydrophones and enable precise, real-time positioning of the animals.

One of the biggest challenges is ensuring that the transmitters have a sufficient and long-lasting energy supply—beyond the limited lifespan of microbatteries. To solve this, the Pacific Northwest National Laboratory (PNNL), a U.S. Department of Energy research facility, developed and tested various biomechanical energy harvester designs together with Smart Material GmbH.

MFC Technology – An Aerospace Innovation

The design and realization of these biomechanical harvesters are based on Macro Fiber CompositeTM (MFC) technology from Smart Material GmbH. Originally developed by NASA engineers, this technology involves sawing piezoceramic wafers into rectangular rods and embedding them between adhesive layers, electrodes, and polyimide films. This structure compensates for the ceramics' inherent brittleness.

Multifunctional Properties of MFC Film

MFCs can be applied as thin, surface-conforming films—usually by gluing—or embedded within composite structures. When electrically actuated, the MFC functions as an actuator, bending or deforming structures, counteracting vibration, or generating it. When mechanically stressed, it serves as a sensitive strain transducer, detecting forces, deformations, noise, and vibration. MFCs can also be designed to harvest electrical energy from mechanical vibrations.

Variants and Structure: From Standard to Bimorph

In addition to standard versions with single-layer piezoceramics, Smart Material also manufactures complex laminate structures, such as bimorph transducers, and can integrate electronic components into the MFCs. A key strength of MFC technology lies in its cost-effective manufacturing process, which produces components with consistent and repeatable electromechanical properties.

Suitable piezoelectric materials include:

• Conventional lead zirconate titanate ceramics (PZT 5H, 5A)
• Single-crystal ferroelectrics (e.g. PMN-PT)
• Lead-free ceramics (e.g. KNN)

Energy from Motion – MFC as Kinetic Energy Converter

Thanks to its flexibility, robustness, and environmentally friendly encapsulation, the MFC is ideal as a kinetic energy converter, particularly for non-resonant applications. Application-specific designs can be implemented as required.

Smart Material GmbH offers evaluation kits, electronic circuits, and components to facilitate rapid prototyping and application development of MFC-based generators.

Prototypes in Field Tests: Real-World Fish Tracking

For fish tracking applications, the biomechanical energy harvester is implanted under the fish’s skin, where it converts the bending motion of the fish into electricity. To do so, the harvester must be:

• Highly miniaturized and flexible
• As thin as possible
• Able to generate enough power for the application
• Stable over long periods

Lab-on-a-Fish: The Future Is Already Swimming

Development is ongoing. A prototype "Lab-on-a-Fish" biosensor has already been created, capable of collecting a wide range of data, including:

• Location
• Heart rate
• Tail movement
• Calorie consumption
• Environmental temperature, pressure, and magnetic field

MFC – Now Used Across Industries

Macro Fiber Composite (MFC) technology was originally developed for controlling vibration and deformation in high-performance aerospace structures.

Today, it is applied across numerous technology fields:

• Shape control for wings, spoilers, rudders, and other CFRP/GFRP structures
• Vibration control in aerospace, automotive, industrial, and consumer applications
• De-icing systems for unmanned aerial vehicles
• Structural Health Monitoring (SHM) including acoustic spectroscopy and guided wave transceivers
• Flexible force and strain sensors for dynamic conditions

Conclusion

Macro Fiber Composite technology enables the integration of piezoelectric functionality into conventional material composites. It allows for the development of a new generation of highly functional components, assemblies, and technological solutions—from sensors and actuators to generators.

As demonstrated by the implantable fish energy harvester, MFC technology is exceptionally flexible and adaptable to a wide variety of customer-specific applications.

Charging batteries via mechanical deformation is a key milestone on the path toward fully energy-autonomous microsystems. With ongoing advances in integrated electronics, MFCs are poised to play a central role in next-generation innovations.