Prof.Dr. Gehan Mosaad

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Electromagnetic Spectrum

• Prof.Dr. Gehan Mosaad

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At the end of this lecture the student must be
able to

• Define electrotherapy, electric current and
  electromagnetic spectrum (EMS)
• Understand the characteristics of electromagnetic
  radiation
• Identify the different regions of EMS
• List Physical laws governing application of
  electromagnetic radiation

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Definitions

• Electrotherapy can be defined as the treatment of
  patients by electrical means. It also means that
  electrical forces are applied to the body
  leading to physiological changes for therapeutic
  purpose.
• Electric current is the flow of electric charge
  through a medium. This charge is carried by
  moving electrons in a conductor as wire, or by
  ions in electrolyte or by both ions and electrons
  as in a plasma. The unit for measuring the rate
  of flow of electric charge is the ampere.
• Electromagnetism Electric current produces a
  magnetic field which can be visualized as
  pattern of circular field lines surrounding the
  wire.

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Electromagnetic Spectrum

• Electromagnetic spectrum
• It is the distribution of electromagnetic
  radiation according to the energy ( or according
  to wavelength or frequency).
• Electromagnetic radiation
• It is composed of electric and magnetic fields
  that are oriented perpendicular to each other and
  to the direction of travel or radiation.
• It covers a broad spectrum of wavelengths and
  frequencies.

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Characteristics of electromagnetic radiation

• All electromagnetic radiations have a constant
  velocity in space 300 million meters per second
  (speed of light)
• They transport energy through space
• They are transmitted without the need of a
  medium or conductor (self propagating).
• They are transverse waves, may be absorbed,
  reflected and/or refracted depending on the
  medium that they strike.
• Their direction of travel is always in a straight
  line.
• Electromagnetic radiation is categorized
  according to its wavelength and frequency which
  are inversely proportional to each other.

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• The relation between wavelength and frequency
• Wavelength The horizontal distance from one wave
  beak to the same point on the next wave.
• Frequency The number of cycles that occurs in
  one second (cycle /second). It is measured in
  Hertz (Hz).
• The relation between wavelength and frequency are
  governed by the formula
• Speed of light Wavelength X frequency
• Because the velocity is constant, there is
  inverse relationship between the wavelength and
  frequency for electromagnetic wave( the higher
  the frequency the shorter the wavelength).
• The radiating energy is directly proportional to
  the frequency and inversely to the wavelength

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Regions of electromagnetic spectrum

• Ionizing range
• Electromagnetic radiation such as x ray and gamma
  rays is ionized radiation.
• It can break molecular bonds to form ions and
  can easily penetrate the tissue and deposit its
  energy within the cell. If the energy is
  sufficiently high, ionizing radiation can also
  inhibit cell division and eventually killing the
  cell.
• Energy within the ionizing range is used in very
  small doses for imaging (diagnostically in X ray)
  or to destroy tissues (therapeutically in
  radiation treatment) for some forms of cancer.

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Regions of electromagnetic spectrum

• Non ionizing range
• Low frequency electromagnetic radiation is non
  ionizing and can not break molecular bonds or
  produce ions and so can be used for therapeutic
  medical applications.
• It includes
• 1- Light spectrum as visible light, infrared
  ultraviolet
• 2- Diathermy as shortwave and microwave
• 3- Electric currents as electrical stimulating
  current

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• Physical laws governing the application of
  electromagnetic radiation

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1- Reflection

• Reflection is the return of the electromagnetic
  wave from an object. When electromagnetic
  radiations strike a surface part of the energy is
  reflected back in the same plane of the incident
  angle.
• Incident angle Reflected angle
• The amount of reflection decrease when the
  radiation striking the surface at right angle.
  

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2-Refraction

• Refraction refers to the change in direction of
  the radiation vector when it passes from one
  medium to another of a different density.
• It depends on the media involved and the angle of
  incidence of the rays
• So, the rays striking the surface at right angle
  continue in the same straight lines.

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3- Absorption and penetration

• Absorption is reciprocal of penetration as the
  greater the penetration the lesser the
  absorption.
• Radiation must be absorbed to facilitate the
  changes within the body tissue. Absorption
  depends on the nature and type of tissue
• The penetration of energy into a medium is
  dependent upon
• Wavelength and frequency
• Angle of incidence
• Nature of medium
• Intensity of radiation

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4- Scattering

• Radiation passing through non-homogenous matter
  may be partly scattered.
• The amount of scattering depends on the
  wavelength of radiation. Longer wavelength
• ( lower frequency) are scattered less than the
  shorter ones (higher frequency)

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5- Inverse square law

• This law state that the intensity of radiation
  is inversely proportional to the square of the
  distance between the source of the energy and the
  tissues.
• The intensity of the energy striking the tissue
  depends on the distance between the source and
  the tissue.
• According to the formula E Es / D²
• where
• E the amount of energy received by the tissue
• Es the amount of energy produced by the
  source
• D² the square of the distance between the
  tissue and the source.

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6-Cosine law

• This law state that the intensity of radiation
  varies as the cosine of the angle of incidence.
• Effective energy Energy X cosine of the angle
  of incidence
• Electromagnetic energy is most efficiently
  transmitted to the tissue when it strikes the
  body at right angle. As this angle of incidence
  deviates away from 90 degree, the intensity of
  radiation affecting the tissue decrease.

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7-The Arndt-Schulz law

• This law state that, no physiological changes can
  occur in body tissues, if the amount of energy
  absorbed is insufficient to stimulate the
  absorbing tissues.
• According to this law, a certain minimum
  intensity of electromagnetic radiation is needed
  to initiate a biological process.
• Beyond a certain level, stronger intensity will
  have a progressively less positive effect and
  become inhibitory.

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Thank You