Microwave diathermy involves irradiating tissues with electromagnetic radiation between 300-30000 MHz. It can heat tissues effectively to a depth of around 3-4 cm due to strong absorption by water molecules. Common frequencies used are 2450, 915, and 433.9 MHz. Therapeutic effects include pain relief, reduced muscle spasm, and increased tissue extensibility. Treatment involves 20 minutes of mild, comfortable warmth applied daily or every other day. Contraindications include malignant tissues, metal implants, and pregnancy.

1. Sreeraj S R

2. Definition
Irradiation of tissues with radiation in the shorter wireless part of the spectrum (Hertzian
rays) i.e. the wave length is between infra red and short wave diathermy.
The general frequency of microwave is between 300 to 30000MHz with wave length of 1 m
to 1 mm.
Frequently used frequency and wavelength are,
Frequency Wavelength
2450 MHz 12.25 cm
915 MHz 32.7 cm
433.92 MHz 69 cm
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3. Electromagnetic spectrum
1 101 102 103 104 105 106 107 108 109 1010 1011
1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022
Radio & TV
Infra Red
Microwaves
Gamma-
Rays
X-Rays
Ultra
Violet
Microwaves
Non-ionising Radiation
(generally not so bad)
Ionising
Radiation
(generally bad)
Frequency (Hertz)Sreeraj S R

4. Fan and cathode
Heater control
circuits
Power
supply
from
mains
Magnetron
Mains
Intensity
control
Reflector
Emitter
Antenna
Coaxial cable
Production
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5. Magnetron
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6. Microwave Diathermy Unit
A= Power Switch
B=Timer
C=Output Meter (indicates output in watts)
D= Power Output Level Knob
E= Amber Light-Warming up / Red Light- Ready
Sreeraj S R

7. Physical behaviour
Reflection
Refraction
Absorption, Grotthus Law
the half-value depth for microwave is often
given as 3 – 4 cm.
absorption of microwaves is much lower in fat
(half-value about 3.5 cm) and higher in the
vascular muscle tissue (half-value about 0.7
cm).
Sreeraj S R

8. Applicators
Circular Shaped Applicators
MaximumTemperature At Periphery
Rectangular Shaped Applicators
MaximumTemperature At Center
Contact applicators
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9. Physiological effects
Consequence of tissue heating due to
o Ionic movement
o Dipole rotation
o Molecular distortion
Strongly absorbed by tissues of high water
content
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10. Physiological effects
Effects on metabolism
Effects on blood supply
Effects on nervous tissue
Effects on muscular tissue
Effects on sweat glands
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11. Therapeutic Effects
Relief of pain
Reduce muscle spasm
Promote healing
Infection
Increase the extensibility
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12. Dosage
20 min for vascular adjustment
If significant heating required 30 min would
be reasonable
Intensity: the patient should feel mild and
comfortable warmth.
Frequency: daily or on alternating day.
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13. Contra-indications
Over malignant tissues.
Over ischemic tissues
Over wet dressings
Metal implants.
Pacemaker.
Over growing bone.
Male gonads: repeated
irradiation can cause sterility.
Hemorrhage.
Tuberculous joints.
Impaired thermal sensation.
Unreliable patients.
The eyes: cause cataract.
Recent radiotherapy.
Hypersensitivity to heat
Acute infection or inflammation.
Obesity: with 2450MHz
microwave, there is danger of
producing an excessive heat in
the subcutaneous fat layer.
Analgesic therapy: the thermal
sensation diminished.
Venous thrombosis.
Pregnancy: heat applied to pelvis
or hip in pregnancy may cause
hemorrhage or miscarriage.
Menstruation.
Acute dermatological conditions.
Severe cardiac conditions.
Blood pressure abnormalities.
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14. Principles of Application
Preparation of patient
Preparation of apparatus
Preparation of part to be treated
Setting up- Emitter should be positioned so that radiations strike the
surface at right angles
Instruction and warning
Application
Termination
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15. Difference between SWD & MWD
SWD MWD
Frequency and
wavelength
• Frequency of 10 t0 100 MHz
• Wavelength of 3 to 30 m
• Frequency of 300 to 30,000 MHz
• Wavelength of 1 m to 1 mm
Therapeutic frequency
and wavelength
• Frequency of 27.12 MHz and
• wavelength of greater than 11
m
• Frequencies of 2450, 915 and 433.9 MHz
• wavelengths of 122.5, 330 and 690 mm
respectively
Circuits used • Machine circuit (produce HFC
and amplify its intensity)
• Patient circuit
• Magnetron
• Transducer circuit (with antenna &
reflector)
Fields used • Electrostatic and Electro-
magnetic
• Electro-magnetic
Factors affecting heat
absorption
• Water content
• spacing
• size of the condenser
• laws of reflection, refraction,
absorption and inverse square
• water content
• frequency
• Distance
• laws of reflection, refraction, absorption
and inverse square
Depth of penetration • deep, up to 50 mm or 7 cm • more superficial than SWD, up to 3-4
cm.
Sreeraj S R

16. Difference between SWD & MWD
SWD MWD
Advantages can heat through joints • can localize heat accurately
• can do selective heating
Limitations • Complex application
• risk of deep tissue burn
• intensity can’t be monitored
• Can’t be used to heat deep
structures
• 1 aspect of body can be treated at a
time
Treatment time
and intensity
• 20 Minutes
• Intensity - Mild comfortable
warmth
• Frequency is daily or alternate
days
• 20 Minutes
• Intensity - Mild comfortable
warmth
• Frequency is daily or alternate days
Factors
affecting heat
absorption
• Water content
• spacing
• size of the condenser
• laws of reflection, refraction,
• absorption and inverse square
• water content
• frequency
• Distance
• laws of reflection, refraction,
absorption and inverse square
Sreeraj S R

17. References
1. Electrotherapy Explained by Low and Reed
2. Textbook of Electrotherapy by Singh Jagmohan
3. http://en.wikipedia.org/wiki/Cavity_magnetron
4. http://www.powershow.com/view/13fe42-
MzA2M/Shortwave_and_Microwave_Diathermy_powerpoint_ppt_present
ation
5. Microwave Diathermy by Sagar Naik. physio4all
6. http://hyperphysics.phy-astr.gsu.edu/hbase/ems2.html#c4
7. Sheila Kitchen, S. and Bazin, S. (1996). Clayton’s electrotherapy (10th ed).
Philadelphia:W.B. Saunders Company.
Sreeraj S R