electricity and magnetism

Application of electricity and magnetism in medicine
High- Frequency electricity In Medicine
There are many method used in the thermal treatment include :
1- short wave
2- Ultrasound wave
3- microwave
4- infrared wave
5- electrical stimulation
Micro wave diathermy. Is different from short- wave diathermy, in short
wave diathermy the tissue to be heated is part of resonance circuit where
the tissue to be heated is placed between two capacitor plates that have an
oscillating electric field across them. The changing electric field forces the
ions in the tissue to move back and forth . they thus acquire kinetic energy
, Part of kinetic energy dissipated when the ions collide with molecules in
the tissues. While in micro wave diathermy the tissue absorbs
electromagnetic waves that are incident up on it. microwave diathermy is
used to heat joints , tendon sheaths , and muscles
The use of frequencies near 30 MHz for heating is called short-wave
diathermy . Long - wave diathermy , at frequencies near 10 KHz , is no
longer used . In short-wave diathermy two methods are used to get the
electromagnetic energy into the body : the capacitance method and the
inductance method . short-wave diathermy is used in the treatment of
arthritis , traumatic injuries , strains , and sprains . However, it does have
limitations . The amount of energy absorbed depends upon the frequency
of the microwaves , the energy is absorbed best at frequencies near 20 GHz
and poorly at lower frequencies near 100 MHz and at higher frequencies
around 1000 GHz . Because the energy is deposited more effectively in
tissue with high water content , microwave energy is absorbed better in
muscle tissue than in fatty tissues , which have less water . And because
of the large amount of energy deposited in surface fatty layers . For this
reason microwave diathermy is frequently used.
Low-frequency electricity and magnetism in medicine
When electrical conductor is moved perpendicular to magnetic field , a
voltage is induced in the conductor proportional to the product of the
magnetic field and the velocity of the conductor (Faraday s Law). This Law
also holds for conducting fluid moving perpendicular to the magnetic field
. Blood acts as conducting fluid . If it passes with mean velocity (v)
through magnetic field (B) as shown in ( fig. 11-9 page 245 ) . a voltage
(V) is induced between the electrodes such that .
V = B d v
Where (d) is the diameter of the blood vessel . since (V, B, d ) can all be
measured , the mean velocity can obtained . The volume flow of blood (Q
) through the vessel can then be calculated , since ( Q) is the product of the
mean velocity times the area of the vessel ( ?d2/ 4 ) or
? d2 V
Q = x
4 B d
Example : A magnetic blood flow meter is positional across a blood
vessel ( 5 * 10-3 m ) in diameter. With a magnetic field of (3*10-2 T) an
induced voltage of ( 15*10-6 v ) is measured
a-Find the velocity in the vessel.
From V= B d v
V 1.5*10-5
v = = = 0.1 m/sec
B d (3*10-2) (5*10-3)
b- Assuming all the blood travels at the mean velocity, what is the
volume flow rate ?
? d2 V
Q = x = 1.9 cm3/sec
4 B d
Electrocardiography (ECG ) is the process of recording the electrical
activity of the heart over a period of time using electrodes placed on a
patient s body. These electrodes detect the tiny electrical changes on the
skin that arise from the heart muscle depolarizing during each heartbeat.
Electricity Waves - Energy Travel over a Long Distance
Electric force can transform into different types of energy waves, such as
heat, radiation, radio and micro waves; and these energy waves can travel
along distance. A changing magnetic field will induce a changing electric
field and vice-versa, the two are linked. These changing fields form
electromagnetic waves. Electromagnetic waves can travel not only through
air and solid materials, but also through space.
The human nervous system can create electric energy waves that can be
measured with scientific instruments. The human body produces infra-red
radiation that, with night vision equipment, can be seen from miles away.