1. Interference of sine waves can occur when two waves interact, resulting in reinforcement if they are in phase or cancellation if out of phase. 2. Interferometers use the interference of light waves to analyze gas concentrations, with displacement of fringes proportional to concentration. 3. Interference filters only transmit wavelengths that are integer multiples of the coating thickness, allowing selection of specific infrared wavelengths.

1. Biological processes that occur in a repetitive way are as ventilation of the lungs and the cardiac cycle. Waves
include the sine wave, the sawtooth wave, and the square wave-Sine wave is of special importance >> produce
any of the other patterns combining
THE CONCEPT OF A SINE
WAVE
by various different sine waves. Wave motion >>variation in pressure in the case of sound waves and variation in the electric and magnetic fields in
the case of electromagnetic radiation such as light. 1-The movement of the coil in an electrical generator produces a sine wave >>alternating
current. 2-Mechanically>>a pump with a piston moving up and down with the movement of a crankshaft (the vertical displacement d and the angle of
the crankshaft A form a right-angled triangle with the crankshaft of fixed length r as the hypotenuse). ‫الوتر‬
**
CHARACTERISTICS OF THE SINE WAVE
1-Phase
One complete rotation of the pump crankshaft> >one complete cycle on the graph (
360°)
A rotation of the crank through 90°>> a quarter of a cycle- If the two sine waves differ
by exactly one-quarter of a cycle or 90°>> out of phase.
2-Wavelength and
Amplitude
The wavelength > distance between any two corresponding points (two peaks in the same direction.)- The maximum
displacement>> amplitude- In sound waves, a large amplitude is loud and a small amplitude is quiet- With light waves a
large amplitude is bright and a small amplitude dim.
3-Frequency, Period and
Velocity
**jetta= ‫جتا‬
Velocity = Frequency x
Wavelength
The frequency of a wave >> number of complete cycles which occur in 1 second ( SI system
=hertz =Hz) i.e (10 cycles per second (10 herz)>> each cycle is one-tenth of a second. Sound>>
a velocity of
A light wave motion with a high frequency and a short wavelength is seen as blue, whereas one with a lower frequency and longer wavelength appears red. Visible light is a small
part of the electromagnetic spectrum, which also includes radio waves, infrared and ultraviolet radiation, X-rays and gamma rays .In gases such as air the reduction in velocity is so
small that the wavelength can be regarded as the velocity in a vacuum divided by the frequency .The velocity of electromagnetic radiation is constant in a vacuum for all frequencies.
For X-rays and gamma rays a unit of energy called the electron-volt (eV)- Remote electromagnetic radiation is used>> carbon dioxide and nitrous oxide analysis and in
thermography. Gamma rays and X-rays are essential to radiology and are used in radiotherapy ,and nuclear medicine. Visible light is also used in many medical instruments, e.g. in
the oximeter used to measure oxygen saturation in blood and in refractometry. Gases emit electromagnetic radiation if they are suitably excited, e.g.. bombardment by electrons,and
the wavelengths of radiation emitted are characteristic of the gas. In the SI system the second is defined in terms of the frequency of radiation emitted by atoms of caesium-133.
Sound waves are regions of high and low pressure in the air, and they travel through it at a fixed velocity (Fig.) >> depends on the wavelength
and therefore on the frequency. As a source moves away from a listener, he hears a lower pitch from the drop in frequency. These changes in frequency constitute the
Doppler effect.
330 m s-1 in air. If the velocity is fixed, then >> the higher the frequency, the shorter the wave lengh and vice versa. Sound waves of different frequencies are picked
up by the ear ,a sound wave with a high frequency has a short wavelength >> high pitched , whereas a sound with a low frequency has a longer wavelength >> low
pitched.
THE DOPPLER EFFECT
When sound waves, or other types of wave, reach a boundary between two different substances, part of the wave is transmittedand part reflected.
.
In the case of sound waves, it is the difference in density between the two materials >> the proportions of the wave which are transmitted and reflected>>
a transducer is used to transmit and receive sound waves into and out of the body>>pass between air>> gel reduces the difference in densities.
Ultrasound waves are also used to form images of body structures because the waves are reflected off boundaries and interfaces between
substances of different densities.
Ultrasound waves are also used to substances of different densities the time taken for the ultrasound wave to travel from the transducer and return which
allows the depth of a boundary or change in density to be measured. The transducer can be moved to and fro through an arc. Alternatively a transducer
comprised of many small individual crystals arranged in a line may be used to display a cross section through the body. Ultrasound therapy units generate
ultrasound of high intensity >> local heating as a treatment . If very high power is used, the pressure in the sound wave can fall to zero during the
minimum of the waveform and this can result in the rapid creation and collapse of bubbles in the tissues.( cavitation).

2. INTERFERENCE
When two or more sine waves are added together ( have the same frequency, amplitude, and phase)>>enhanced amplitude. On the other hand, if these two sine waves
are 180 degree out of phase>> zero amplitude (straight line)>> interference>>Refractomer (interferometer)>> optical devices for analysing various gases or
vapours>>concentration of halothane in oxygen in vaporizers checking. Two light beams, one through a sample chamber and one through a reference chamber
wave. Wave motions in phase>>reinforcement >>a bright fringe; or they combine out of phase >> dark fringe. The displacement of a selected fringe is directly proportional
to the concentration of gas added to the sample chamber. Small portable refractometers are commonly used in anaesthesia, but more sensitive versions also exist. The
refractometer is non-specific and may be used for measuring the concentration of a variety of different gases. On the other hand, it cannot be used to identify component gases in
a mixture and so these must be known in advance. For example, when a refractomer is used to check the performance of vaporizers, the refractometer calibration using a
halothane-oxygen mixture is not identical with that for a mixture of halothane in nitrous oxide and oxygen. (Reduction the velocity of the light passing through the sample
chamber).
INTERFERENCE FILTERS (Only radiation with a multiple of twice wavelength of the coating thickness (the two beams in phase) will pass through with little attenuation) >>
Filters of this type are useful for selecting the required wavelength of infrared radiation for use in an infrared analyser.
Interference >>(select one wavelength from a spectrum of Wavelengths). Electromagnetic radiation >> it strikes a boundary between two media. The fractions transmitted and
reflected depend on the characteristics of the media, the wavelength of the radiation and the angle of incidence. An interference filter is a block of material which is transparent to
the radiation of interest and which has been coated with a very thin layer of a different transparent material. Therefore, only radiation with a multiple of twice the coating
thickness will passthrough with little attenuation. For other wave lengths the two beams will be out of phase and the intensity of the transmitted radiation will be reduced.
Semi-silvered mirror
THE FREQUENCY SPECTRUM
A figure illustrates the results of adding sine waves with differing frequencies and amplitudes, as well as a differing phase relationship. It is
seen that the resultant waveform is no longer a sine wave but in this case is a wave pattern similar to an arterial pressure tracing. This result is
obtained simply by adding the amplitudes of the component waves at every point along their cycles. ** Spectrum=ordered array
The addition of whole ranges of sine waves, each with a different frequency, may result in quite complex waveforms and, as an example,
ECG waveform could be produced by adding a large range of frequencies. The range of these frequencies is important inthe design and use of monitoring apparatus
and may be described by a spectrum of frequencies. In such a spectrum the ECG is composed of a range offrequencies from about 0.5 to 100 Hz, while an EEG
signal has a smaller range of frequencies. The slower waves of the EEG are only about 1 to5 Hz, whereas the faster beta waves are in the range of 15 to 60 Hz. In the
EMG (electromyogram) there are sharp spikes and these indicate high frequency components. Any waveform, no matter how complex, can be produced by selecting
and adding together appropriate sine waves. The mathematical process of analysing >>Fourier analysis, and this concept helps in understanding the patterns of
biological electrical signals.
QUESTIONS
A-HOW TO USE THE INTERACTION OF TWO SINE WAVES IN ANAESTHESIA PRACTICE?