Classifying Recyclable Materials by Frequency

The purpose of our experimentation was to determine if plastic, glass and tin containers could be sorted by differences in the frequency content of the sounds they produce when they strike a Formica surface. We ran our trials using recyclable containers from a typical family's recycling bin. We tested the same number of containers, 12, of each of the following materials: plastic, glass and steel. Each container was pushed three times off the edge of a 31.5cm high ledge and left to fall onto the Formica surface. The frequency content of the sound produced was analyzed using the Logger Pro software. To begin our analysis, we divided the frequency band of 0Hz to 2000Hz into four smaller frequency bands: 0Hz to 500Hz, 500Hz to 1000Hz, 1000Hz to 1500Hz, and 1500 Hz to 2000Hz. We then summed the amplitudes of each frequency band, including 0Hz to 2000Hz, for each trial. The sums of the four smaller bands were then represented as a percentage of the entire frequency band. We found that the tin containers are easily identifiable. They had much less activity, than the plastic and glass containers did, in the 0Hz - 500Hz band. We performed a two-sample t-test, in order to see if our data was significant. We can be 95% confident that our data was not due only to chance variation. In conclusion, we have found that it is definitely possible to sort tin, plastic and glass containers by using only the frequency content of the sound the material produces when it strikes a Formica surface.

Research Done By:

Amy May

Vicki Niebrzydowski
Sterling Heights