Title: A Smartphone Application that Detects and Analyzes Raman Backscattering to Distinguish Between Substances
Subcategory: Optics / Raman Scattering
Grade level: High School - Grades 9-12
Academic Level: Ordinary
Project Type: Building / Engineering
Awards: Global Finalist
Affiliation: Google Science Fair
Materials: Camera, smartphone, infrared light source
Techniques: MANOVA, ANOVA, and Tukey statistical tests
Description: The objectives of this project were to determine whether a smartphone’s CCD camera could detect Raman backscattering and then to write an application that could process that backscattering data for the purpose of distinguishing between substances. To perform the experiment, a box was built into which a smartphone could be inserted at a fixed distance from a sample and a fixed difference from near infrared light sources. The box could then be used to take normal and irradiated pictures of a sample. Next, a smartphone application was built that could process the pictures, and by using a sufficiently large array of pixel data it takes into account quantum randomness effects and sources of interference. The application then translated each pixel’s RGB data into a Core Graphics context and compared two 100 element arrays of essentially three dimensional picture data to derive pixel differential data indicative of the frequency of the inelastically backscattered light.
In physics, backscatter (or backscattering) is the reflection of waves, particles, or signals back to the direction from which they came. It is a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror. Backscattering has important applications in astronomy, photography, and medical ultrasonography. The opposite effect is forward scatter, e.g. when a translucent material like a cloud diffuses sunlight, giving soft light. Backscattering can occur in quite different physical situations, where the incoming waves or particles are deflected from their original direction by different mechanisms and among others: Inelastic collisions between electromagnetic waves and the transmitting medium like in Raman scattering.
An inelastic collision, in contrast to an elastic collision, is a collision in which kinetic energy is not conserved due to the action of internal friction.
Raman scattering or the Raman effect is the inelastic scattering of a photon by molecules which are excited to higher vibrational or rotational energy levels. It was discovered in 1928 by C. V. Raman and his student K. S. Krishnan in liquids, and independently by Grigory Landsberg and Leonid Mandelstam in crystals. The effect had been predicted theoretically by Adolf Smekal in 1923.
When photons are scattered from an atom or molecule, most of them are elastically scattered (Rayleigh scattering), such that the scattered photons have the same energy (frequency and wavelength) as the incident photons. A small fraction of the scattered photons (approximately 1 in 10 million) are scattered inelastically by an excitation, with the scattered photons having a frequency and energy different from, and usually lower than, those of the incident photons. In a gas, Raman scattering can occur with a change in energy of a molecule due to a transition to another (usually higher) energy level. Chemists are primarily concerned with this "transitional" Raman effect.
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