ACI's Piezo fiber composites for energy harvesting and vibration dampening applications.

Energy harvesting is great for a green economy, but it can also be used in recreational settings.

Vibration energy harvesting (VEH) is a leading energy harvesting technique used to power micro-circuits.

Unique VEH applications are playing a growing role in consumer markets, such as sporting goods, where self-powered systems are being incorporated to increase structural stability, control and performance of certain equipment.

Sporting Industry

HEAD Sports, a manufacturer and marketer of premium sporting goods, has taken advantage of a particular energy harvesting technology to maximize performance in tennis rackets and skis, called active vibration control (AVC).

The foundation technology is developed by Advanced Cerametrics (ACI) and involves the ability to make any ceramic into flexible fibers, which help to optimize the performance of the piezo and reverse piezo effect for energy harvesting and vibration dampening.

“The piezo effect is the energy harvesting part,” explains Jerry Ruddle, executive vice president and general manager of Advanced Cerametrics. “ACI’s uniquely flexible piezo fiber composite is not heavy and brittle like traditional piezo ceramics, and can be integrated into various products. When subjected to vibrations and mechanical movement, the fibers create voltage that is useful in microcircuits.”

Dampening Vibrations

Both aspects of piezo and reverse piezo are used in the design and delivery of the functionality in the HEAD racket and skis.

By capturing the mechanical movement and vibration in the ski and racket structures – both torsional and vibrational forces – a voltage is generated (the piezo effect). That voltage is then taken through a circuit and applied back to a piezo fiber composite that dampens the vibration (the reverse piezo effect), which in turn, “quiets” the product for better stability, control and performance.

The mechanical energy produced from the ball hitting the racket and the ski moving along the snow is converted by VEH into electric energy. This process contributes to passive vibration dampening, and enables the active dampening as well.

As Ruddle explains, “The vibrations are dampened by taking the voltage to a circuit and then back to the structure to help stiffen it. The dampening and stiffening is done by applying a voltage to the piezo composite, creating a mechanical force within the fiber and reducing the vibrations.”

Dampening vibration in the tennis racket produces a better feel and control of the racket, and reduces the energy that could cause tennis elbow. In the ski, the structure is tuned to different conditions, such as soft snow vs. ice, giving the ski a better controllable edge.

Controllable Edge

“A more controllable edge helps to better cut turns and increases ski speed because inefficient ski chatter is reduced,” says Ruddle.

Ruddle also points out that an increase in the width of today’s skis has caused higher torsional forces, which creates twisting in the skis, decreasing the controllable edge. AVC helps to quiet the torsional forces with the dampening effect, recycling the energy back to the structure to produce the perfect edge grip.

The skis and racket both incorporate a closed-looped system with no external power source, and use passive and active vibration dampening techniques with the piezo fibers. The design process for each product involves understanding the vibration characteristics of the structure and designing the piezo fiber composites to address where those vibrations are occurring.

Vibration dampening has caught on in other sports as well, showing up in hockey sticks. “ACI is also working with other sporting good companies to incorporate the advantages of piezo fiber composites,” Ruddle says.

Perpetual, Green & Clean

While VEH has brought product success to the sporting good industry, Ruddle emphasizes that VEH is a growing renewable technology for powering other applications, such as self-powered wireless sensors and sensor networks for industrial process and condition-based monitoring for predictive maintenance, building automation and environmental management, infrastructure monitoring (e.g. bridges) and transportation systems (aviation, rail, automotive).

“We can take the piezo fiber composites and deliver the power to modules (the Harvestor) that eliminate wire and battery power in many low micro circuit applications,” Ruddle says. “The energy is harvested from ambient vibrations from the application or the environment and is delivered like a battery would deliver power – but it’s perpetual, it’s green and it’s clean.”

According to Ruddle, with perpetual power, as long as there is some vibration or mechanical energy input from the environment, then the Harvestor power module will continue to operate, which eliminates the various costs related to battery replacement, wire and weight.

“In our day-to-day environment, there is so much vibration and mechanical energy that can be captured and utilized for good purpose,” Ruddle adds. “We will continue to see expanding application and adoption of vibration energy harvesting.”