In a world continuously increasing in the number of electronic devices, the need for cooling fans increases and so does its contribution to noise pollution. This project explores a solution to this problem by designing an acoustic metamaterial that attenuates the fan noise from a Sofasco fan, whose fundamental blade pass frequencyis approximately 800 Hz. According to Ping, two Helmholtz resonators (HRs) that are parallel side branched to a waveguide whose distance is less than a wavelength will have a hybrid resonance at the difference average. This approach did not work with the first generation samples, but the use of two parallel HRs was used in future designs. According to Sang-Hyun, the attenuation increases logarithmically for each parallel HR side branched to a waveguide. Using Sang-Hyun method, a second generation sample was designed that achieved a transmission loss of 45 dB, but it had an airflow loss of 75%. Other second generation designs explored decreasing the airflow loss, but none of the methods were successful. The third generation design has a waveguide shaped as a truncated sector, which increases the cross-sectional area of the waveguide as well as the airflow. The best sample of the third generation design had a transmission loss of 30 dB with an airflow loss of 45%. In an attempt to further decrease the airflow loss, the fourth generation design placed two HRs connected in series with each other (dual HRs) a side branch to the waveguide. The airflow loss was reduced to less than 1% with transmission loss of approximately 18 dB at 496 Hz and 1250 Hz. This design also led to a transmission loss of approximately 8 dB from 582 Hz to 1000 Hz. This design was never modified to achieve the fan frequency of800 Hz, but this can be achieved using design equations for dual HRs.
