# Are there materials that are opaque to infra sonic waves?

I have read that infra sonic sound waves because of their large wavelengths pass through most materials largely unabsorbed. However, are there materials that absorb infrasonic waves(could be frequency specific) very strongly? I have searched the web but have been unsuccessful in discovering an example. I asked this question writing "infrasonic waves" but if the absorption is very frequency specific(like, 'X' absorbs 20Hz very strongly) that answers my question too.

• It's not a question of materials in this case but one of design. The major application for "infrasonic" waves is earthquake protection and there are well known design strategies to shield structures from the very long wavelengths and the extreme amplitudes of such movements. I would say that these strategies can be employed well into the range of 10Hz or so, before methods to deal with "sound" become more useful. One important one would be to mount the structure on shock absorbers, since the air is a very poor medium for low frequency sound transmission. Feb 8 '16 at 6:58

Infrasonic waves propagate by physically moving the medium backwards and forwards with often quite significant amplitude. That is why you can feel amplified bass in music as well as hear it. Anything spongy will absorb infrasound to some extent. My recipe would be rigid spaced panels with soft foam interior. However, the front and rear of the panel should not be rigidly connected.

One piece of news on spiral channel absorbers

Acoustic absorption systems work by absorbing sound energy at a resonant frequency and dissipating it into heat. Traditional acoustic absorbers consist of specially perforated plates placed in front of hard objects to form air cavities; however, in order to operate at low frequencies, these systems must also be relatively thick in length, which makes them physically impractical for most applications. To remedy this, Assouar's group, whose previous work consisted of developing coiled channel systems, designed an acoustic absorber in which sound waves enter an internal coiled air channel through a perforated center hole. This forces the acoustic waves to travel through the channel, effectively increasing the total propagation length of the waves and leading to an effective low sound velocity and high acoustic refractive index. This allows them to make the absorber itself relatively thin, while still maintaining the absorptive properties of a much thicker chamber.

The question relates to materials so not sure if meta-materials would be a relevant answer. meta-materials

were first suggested for electromagnetic waves in 1968 by Soviet physicist Victor Veselago.

However there was some work published describing how to apply the concept to protect against hearthquake waves. The link provides references to test with vibration at 50Hz and absorption higher than 80%.

Provided that this work is reproduced elsewere (I could not find links) it would stand to reason that this can be incrementally improved to a point where most the energy is absorbed or actually diverted away.