Imaging Using EM Waves

Attenuation and Absorption: As waves pass through a medium, their intensity $I$ decreases exponentially according to the Beer-Lambert Law: $I = I_0 e^{-\mu x}$, where $\mu$ is the attenuation coefficient and $x$ is the thickness.

Spatial Resolution: The ability to distinguish two close objects is limited by diffraction. According to the Rayleigh Criterion, the minimum resolvable distance is proportional to the wavelength $\lambda$.

Scattering: When EM waves encounter particles smaller than their wavelength, they scatter (Rayleigh scattering). This is crucial for imaging structures that do not reflect light directly.

Phase Information: Advanced imaging techniques use the phase shift of the wave (how much it is delayed) rather than just its intensity to visualize transparent or low-contrast objects.

Wavelength-Scale Matching: Always check if the wavelength $\lambda$ is smaller than the object being imaged. If $\lambda > \text{object size}$, diffraction will blur the image beyond recognition.

Energy Calculations: Remember that energy is inversely proportional to wavelength ($E = \frac{hc}{\lambda}$). Shorter wavelengths (X-rays) are more dangerous but offer higher resolution.

Contrast Analysis: If a question asks why a certain wave type is used, identify the physical property that creates contrast (e.g., density for X-rays, temperature for IR, water content for Microwaves).

Common Units: Be comfortable converting between nanometers (visible), micrometers (IR), and centimeters (Radio) to assess resolution limits.