Vibrating strings, energy that transforms

Rock in Rio is coming up, and it’s impossible not to think about music, fun, and, of course, a lot of energy. But what if part of that energy lies precisely in the instruments that make the music happen? That’s the question driving the research of engineer and master’s student Laura Lima, from Coppe/UFRJ, who has been investigating the potential to convert the energy present in the vibrations of a guitar’s strings into electricity.

During her master’s program in the Mechanical Engineering Program (PEM) at Coppe, Laura is researching the energy potential of mechanical vibrations produced by musical instruments. The idea is to investigate how much energy can be harnessed from these vibrations and how it can be converted into electrical energy.

This topic is part of a research area that has been gaining traction in recent years: mechanical energy harvesting, or energy harvesting. The principle involves harnessing small amounts of energy present in movements and vibrations–rather than simply letting them dissipate–to power sensors and electronic devices.

During her undergraduate studies, Laura began exploring this potential through an instrument that is a staple at major music festivals: the guitar. At the Center of Nonlinear Mechanics (Mecanon) at PEM, she investigated the energy involved in the vibration of the strings and its conversion into electrical energy.

In electric instruments, such as the guitar, pickups transform the mechanical vibration of the strings into an electrical signal, which is sent to the amplifier and then converted back into sound. Laura decided to examine this entire process and understand how much energy is involved in this transformation.

“The idea is to explore the energy available for transmitting or amplifying sound. To do this, I used a mathematical model to describe the problem and investigate the power levels transmitted by different songs. The research was based on the frequencies and amplitudes generated by each musical note, and numerical simulations were performed to evaluate the power levels associated with various musical styles,” explains Laura.

And what can the guitar reveal about energy?

To conduct her research, Laura developed a computational model capable of analyzing different songs based on the characteristics of the notes and the vibrations produced by the guitar strings.

Here are some figures to help you understand the study:

• 🎸 6 strings and 22 frets included in the model;
• 🎵 138 different notes analyzed;
• 🎶 5 musical styles compared: slow pop, soft rock, upbeat pop, blues, and hard rock;
• 📈 average, minimum, and maximum power levels associated with the songs;
• ⚡ average electrical currents generated and their relationship to the current required to power an amplifier.

And that’s when the musical genre began to make a difference.

The results showed that heavy rock and blues songs had frequencies close to 600 Hz, while the pop songs analyzed reached about 500 Hz. One explanation lies in an element well known to rock and blues fans: the guitar solo.

“These solos use high-pitched notes and, generally, a lot of distortion effects, and it’s clear that the solo makes a big difference in a song’s power output. Given that high frequencies are associated with higher-pitched sounds, and that low-pitched sounds have lower frequencies, we estimate that the higher-pitched the song, the higher the frequencies will be, and, consequently, the greater the associated energy levels,” explains Laura.

Based on the simulations, the researcher was also able to analyze the average electric currents generated by different songs and compare them to the current needed to power a standard audio amplifier.

The results have not yet been tested in a practical application, but they point to a potential that Laura intends to investigate more deeply during her master’s program, under the guidance of PEM professor Marcelo Savi, coordinator of Mecanon.

Now, the research goes beyond guitar strings and is expected to involve other musical instruments as well, either individually or in combination.

The possibility of harnessing this energy takes on yet another dimension when considering large music events. According to Laura, one of the research objectives is to assess whether renewable energy and alternative sources—such as energy obtained from the vibrations of the instruments themselves—could contribute to the energy self-sufficiency of certain electronic systems used at events, such as amplifiers.

The idea is not new to engineering. Mechanical energy harvesting is already being studied in various contexts, such as in sensors, electronic devices, and transportation systems, where movement and vibrations can be converted into useful energy.

In the case of music, however, there is something particularly interesting: what makes the audience vibrate can also generate energy.

And while the audience prepares for another edition of Rock in Rio, Laura continues to investigate, in the lab, a question that perfectly combines engineering and music: how much energy is there behind a guitar being played?