Acoustics is the science that is concerned with the effects, transmission, reception, control, and production of sound. The headphones people use in listening to podcasts and songs, as well as the sonic camouflage that are in submarines, involve the process of sound transmission and it is an important part of how people engage with their surroundings. As such, there are acoustic metamaterials created to manipulate, direct, and control the soundwaves as they pass through various mediums. They are designed in a way that they can be placed in a structure to transmit or dampen sound.
Traditional vs. sharkskin-inspired acoustics
Traditional acoustic metamaterials, though, exhibit unconventional capability in terms of control acoustic waves. Although they have enabled various applications, such as waveguiding, topological insulation, nonreciprocal propagation, logic operation, cloaking, and superlensing, most of these paradigms are dependent on architected structures that have fixed configurations. This means that they are often made of hard plastic or metal that, once fabricated, their properties can no longer be changed. An example of this would be an acoustic device that is fabricated to dampen the outgoing sound in a submarine to achieve stealthiness. In case a different condition occurs like a submarine ally wants to communicate, using the same acoustic device will not allow external transmission of sound. But there are emerging acoustic metamaterials that now have a special ability to enable the switching of the fabricated acoustic metamaterials.
The smart material that allows the change in acoustic transmission
Kyung Hoon Lee from the University of Southern California, Los Angeles Sonny Astani Department of Civil and Environmental Engineering and team recently created a smart acoustic that is inspired by sharkskin denticles. They said that the smart material allows the shifts in the acoustic transmission.
Lead author Qiming Wang said that with traditional types of acoustic metamaterials, you design one structure and you also achieve one property. With their sharkskin-inspired smart acoustic, though, they were able to achieve multiple properties using only a single structure. As they were studying the new material, the researchers found that they could re-create the properties that are intrinsic to the electronic devices, like switching. This only shows the promise of a sound “computer” or “smart sound transmission.”
Explaining sharks’ dermal denticles
Marine science expert Jennifer Kennedy, who was not involved in the study, said that dermal denticles are tough scales that cover the skin of sharks and rays. These structures are what give sharks’ skin the rough feel if you run a finger from tail to head but a smooth feel from head to tail. The main function of these dermal denticles is to protect the sharks against predators. These also reduce their turbulence, allowing them to swim covertly and faster. Some swimsuit manufacturers have tried replicating sharks' denticles in their material to help swimmers cut through the water faster.
Design principle using sharkskin
In their study titled “Sharkskin-Inspired Magnetoactive Reconfigurable Acoustic Metamaterials” that appeared in the Science Partner Journals (SPJ), Wang and the team explained that their smart acoustic device also had the same dual properties as the dermal denticles. The metamaterial contains magneto-sensitive nanoparticles that bend under magnetic stimuli or a force that can change the structure on-demand and remotely. Thus, accommodating several transmission conditions. The authors said that fast-swimming sharks have skin denticles that are V-shaped and this reduces the flow of their drag. “V-shaped trenches can guide a turbulent flow to become a laminate flow,” their study reads. It was also discovered that titling the denticles by only a small angle can already increase the flow drag drastically. The team was inspired by this natural example of tuning the flow drag. So, they proposed a magnetoactive MRP array that can change the acoustic transmissions by bending reversibly the MRP’s through a remotely-controlled magnetic field.
They added that the smart acoustic metamaterial they designed is made up of iron nanoparticles mix and rubber. The iron enables the material to be responsive to the magnetic field while the rubber provides flexibility so it can flex or bend repeatedly or reversibly. To ensure that the structures are responsive to the acoustic inputs, the group also assembled the materials that allowed changes in the acoustic transmission. Compared to the traditional acoustic metamaterials, their sharkskin-inspired smart metamaterials require no pressure or direct contact to change the architecture of the materials. This was also explained in the science and technology platform Phys.org.
The team demonstrated how the acoustics mimic three main components of electronic devices, which are diode, logic gate, and switch. Their material is also being tested in air and they hope to test if the same properties will also function underwater. If that is the case, it can achieve the same features as an ultrasound range.
Acoustic insulation worldwide: statistics
The most common types of acoustic materials today are absorbers, noise barriers, and composite materials, according to acoustical soundproofing service provider Noise Control Specialist. Absorbers include fabric-wrapped acoustic panels, acoustic ceiling clouds, and acoustic foams. Noise barriers include MLV sound barrier and acoustical door seal kits. Further, composite materials include drop tile ceiling barriers, blanket enclosures, and combination acoustical blankets.
On the other hand, acoustic insulation or soundproofing is the overall ability of a structure or building to reduce the sound transmission through it. According to market research company Global Market Insights, there has been a growing demand for sound absorption material in the entertainment industry, including cinema halls, auditoriums, corporate workplaces, and music studious. These drive a positive scope for the acoustic insulation market. In 2018, the acoustic insulation market size was valued at US$12 billion.
In 2019, the market value of acoustic insulation worldwide by region were as follows: Europe (US$4.4 billion), North America ($3.2 billion), APAC ($2.7 billion), Middle East and Africa ($0.7 billion), and South America ($0.3 billion). This year, it is forecast that the largest market will still be Europe ($4.5 billion) followed by North America ($3.5 billion), APAC ($2.9 billion), the Middle East and Africa ($0.9 billion), and South America ($0.4 billion). This was published by database company Statista. By 2024, the market value for acoustic insulation will reach $5.4 billion in Europe, which is expected to be the largest market by region.
The design principle inspired by sharkskin denticles is a breakthrough in designing acoustic metamaterials.