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Intensity Of Electromagnetic Waves01:22

Intensity Of Electromagnetic Waves

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The energy transport per unit area per unit time, or the Poynting vector, gives the energy flux of an electromagnetic wave at any specific time. For a plane electromagnetic wave with E0 and B0 as the peak electric and magnetic fields and traveling along the x-axis, the time-varying energy flux can be given by the following equation:
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Sound Intensity00:58

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The loudness of a sound source is related to how energetically the source is vibrating, consequently making the molecules of the propagation medium vibrate. To measure the loudness of a source, the physical quantity of interest is the intensity. This is defined as the energy emitted per unit of time per unit of area perpendicular to the sound wave's propagation direction. Since the total energy is greater if the source vibrates for a longer duration and over a larger area, dividing the...
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Intensity and Pressure of Sound Waves01:05

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The intensity of sound waves can be related to displacement and pressure amplitudes by using their wave expressions and the definition of intensity. The critical step to achieve this is to write the power delivered by the particles on the wave as the product of force and velocity and simplify the force per unit area as the pressure. The velocity of the medium's particles can be derived from the displacement.
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Sound Intensity Level00:53

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Humans perceive sound by hearing. The human ear helps sound waves reach the brain, which then interprets the waves and creates the perception of hearing. The loudness of the environment in which a person is located determines whether they can distinguish between different sound sources.
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Interaction of EM Radiation with Matter: Spectroscopy01:12

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Electromagnetic (EM) radiation can be considered an oscillating electric and magnetic field propagating through a medium that can interact with matter in its path. The electric field in the radiation can interact with electrical charges in the atoms or molecules in the matter. On the other hand, the magnetic field can interact with the magnetic field in the atomic nucleus. The study of the interaction between electromagnetic radiation and matter is termed spectroscopy. Spectroscopy is the study...
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Spectrophotometry: Introduction01:16

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Spectrophotometry is the quantitative measurement of the absorption, reflection, diffraction, or transmission of electromagnetic radiation through a material as a function of the intensity and wavelength of the radiation. A spectrophotometer is a device used to measure the change in the radiation intensity caused by its interaction with the material.
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Updated: Dec 31, 2025

Scattering And Absorption of Light in Planetary Regoliths
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Intensity measurements in scattering media.

Joseph R Lakowicz1, Jonathan D Dattelbaum1, Ignacy Gryczynski1

  • 1Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, MD 21201, USA.

Sensors and Actuators. B, Chemical
|January 2, 2020
PubMed
Summary

This study introduces a new fluorescence measurement method for highly scattering media. It uses dual-lifetime fluorophores to enable accurate intensity readings, even in challenging sample conditions.

Keywords:
FluorescenceFrequency-domainIntensityModulationSensing

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Area of Science:

  • Biomedical Optics
  • Fluorescence Spectroscopy
  • Photonics

Background:

  • Quantitative fluorescence intensity measurements are challenging in highly scattering media like biological tissues.
  • Existing methods often struggle with signal attenuation and scattering effects.
  • Developing robust techniques is crucial for applications in diagnostics and imaging.

Purpose of the Study:

  • To present a novel method for accurate quantitative fluorescence intensity measurements in highly scattering media.
  • To overcome limitations of direct intensity measurements in complex biological samples.
  • To validate the method using a scattering phantom and biologically relevant fluorophores.

Main Methods:

  • Utilizes frequency-domain (FD) fluorometry with two fluorophores: one with nanosecond decay time and a reference with microsecond lifetime.
  • The reference fluorophore is positioned externally to simulate sensing devices against skin.
  • Amplitude modulation at an intermediate frequency quantifies the target fluorophore's fractional intensity.

Main Results:

  • Successfully obtained quantitative fluorescence intensity measurements in 0.5% intralipid, a medium more scattering than skin.
  • Demonstrated accurate measurements for various concentrations of fluorescein and the pH sensor 6-carboxyfluorescein (6-CF).
  • Low-frequency modulation proved effective for quantitative measurements despite scattering interference.

Conclusions:

  • The developed dual-lifetime fluorophore method enables reliable quantitative fluorescence measurements in highly scattering environments.
  • This technique offers a general solution for overcoming challenges in direct intensity measurements in complex media.
  • The findings have significant implications for optical sensing and bio-imaging applications.