Frequency (ƒ) 107 – 108 Hz
Radio wavelength (λ) 3 -30 m
Commonly used frequency (ƒ) is 27.12 MHz and wavelength 11 m.
It this current two circuits are used. Machine circuit is coupled with the patient circuit leading to resonance phenomenon, in this way patient is treated.

A.  Machine circuit:

The basic oscillator circuit consists of condenser, inductance, and the currents of different frequencies are obtained by selecting suitable condenser and inductance. It a current of very high frequency is required, the condenser and inductance are very small. While to produce a current of lower frequency a larger condenser and inductance is used.

B.  Patient circuit:

When SWD is applied by the condenser field method, the electrodes in the patient tissues form a capacitor, the capacitance of which depends upon the size electrodes and distance material between them. When the oscillator and resonator circuits are in tune with each other there is maximum power transfer to the patient.
The indicator light on equipment either comes ON or changes color. An ammeter wired into the resonating current shows a maximum reading which is diminished by turning the knob controlling the variable capacitor.

Therapeutic effects of SWD:

1.   Effect on inflammation:

When SWD is applied in an inflammatory condition, the arterioles and capillaries dilate resulting in an increase blood flow to the area, availability of oxygen and nutritive materials increase and also bringing in more antibodies and WBCs. The dilatation of arterioles and capillaries increase the exudate in the tissues and this is followed by increased absorption which together increases the blood flow to the area and assist in the removal of waste products. These effects help in the resolution of inflammation.

Acute condition:

In acute condition SWD is applied with caution to the treatment area in which there is already vasodilatation and exudation of the fluid as an increased these processes may aggrevate the symptoms.

Sub acute condition:

In sub acute condition stronger doses may be applied with considerable benefits.

Chronic condition:

In chronic condition a thermal dose with longer duration must be used to be effective.


  • Rheumatoid arthritis
  • Chronic osteoarthritis
  • Tendinitis
  • Capsulitis
  • Pelvic inflammatory diseases

2.   Relief of pain:

Low back pain affects approximately 60 – 80 % of adults. These low backache patients’ response quickly to SWD treatment. SWD is effective in the treatment of low back pain. The mechanism of pain relief can be explained by the following suggestions.
Sedative effect due to mild degree of heating removal of noxious chemical which are the waste products of metabolism due to the increase blood flow
Counter irritation effect due to the strong superficial heating which blocks the pain transmission at the pain gate.
Relief of pain also occur due to resolution of inflammation by SWD

3.   Effects on infection:

In bacterial infection the body’s own defensive mechanism (immunity) comes into action in the form of increased exudation of fluid into the tissues, vasodilatation causing increased blood flow, concentration of WBCs and antibodies. Heating the tissues by SWD increases these processes and therefore increases (enhance) the body’s own defense mechanism.


  • Boils
  • Abscess
  • Carbuncle etc

4.   Effects on traumatic condition:

Increased exudation of fluid, increased metabolism and increased blood flow help in the removal of waste products and increased availability of nutritive material which enhance healing process.
In acute traumatic condition the caution should be made (exercised).
For joint stiffness which occurs through trauma, SWD is applied in stronger dose to cause a thermal effect in the tissue which enhances the extensibility of the collagen fibers. This makes it easy for the physical therapist to mobilize the joint. Hamstring flexibility can be greatly improved by applying SWD with stretching exercises.


  • Recent ankle injury
  • Meniscus injury in the knee
  • Post traumatic stiffness of the knee joint etc

5.   Induction of muscle relaxation:

As we know that heating of the tissues induces muscle relaxation. When SWD is applied over spasmodic muscles, the muscle become relax and the pain is relieved because spasm is directly related to pain. The increase of tissue temperature up to 42°C is being found to cause a decrease of the firing rate of type II muscle spindles efferent and γ – efferent and increase firing rate of type Ib fibers from the Golgi tendon organs. These changes in nerve fibers decrease the firing rate of α – motor neurons and thus reduce the muscle spasm.


  • Spasm of the post vertebral muscles
  • Low back pain

Dangers of SWD:

v          Burn due to many factors
·         Concentration of electric field
·         Excess current
·         Impaired blood flow
·         Scald over dose
·         Over dose
v    Precipitation of Gangrene
v    Electric shock
v    Sparking
v    Giddiness
v    Damage to eye
v    Damage to equipments

Contra – Indications and Precautions:

Ø    Patient with implanted (total hip replacement etc) or with TENS
Ø    Pacemaker
Ø    Metal in the tissue
Ø    Impaired thermal sensation
Ø    Pregnancy
Ø    Hemorrhage
Ø    Ischemic tissues
Ø    Malignant tumors
Ø    Recent radiotherapy
Ø    Over the testes
Ø    Eyes
Ø    Growing epiphysis
Ø    Venous thrombosis
Ø    Fever
Ø    Patient with active tuberculosis
Ø    Patient at risk:
    o                  Small children
    o                  Mentally retarded patients