Period and Frequency

Period

• The actual time required to complete a single cycle.

• The time from the start of one cycle to the start of the next cycle.

Basically the period is just the time that it takes to do something. From start to finish.

For example:

1. The earth rotates once every 24 hours. The period is 24 hours.

2. A shift at work is 8 hours. The period is 8 hours.

Units

Because we are talking about the time to complete a cycle then the units will always be time units. I.e. Microseconds, milliseconds, Seconds, minutes and hours.

Typical values for the ultrasound period will be: 0.1 μsec to 0.5 μsec = 0.0000001 sec to 0.0000005 sec

The period will be determined by the sound source and will not be changeable by the Sonographer.

Frequency

The frequency then is the number of cycles that occur during a specific amount of time.

An example would be the Summer Olympics

What is the frequency of the summer olympics?

• Twenty-five times per century

• Two-and-one-half times per decade

• Once per four years

In Ultrasound the frequency of the wave will be the number of cycles that the wave experiences per second.

The frequency will be determined by the sound source and will not be changeable by the Sonographer.

Units

Because frequency explains how quickly or how slowly something cycles our units will be cycles per second (unit of time)

Typical values for the ultrasound frequency will be: 2 MHz to 12 MHz

Remember that the frequency of the beam will effect both the penetration and the axial resolution (image quality).

Equations:

Frequency (MHz, million cycles per second) = 1 (cycle) / Period (second/s)

F = 1 / Period

Example:

The period of a beam is 0.5 μsec what is the frequency? Frequency = 1 cycle / 0.5 μsec = 2 MHz (million cycles per second)

Period (second/s )= 1 (cycle) / Frequency (MHz, million cycles per second)

 

Period = 1 / Frequency

Example:

With a 5 MHz transducer what would the period be? Period = 1 cycle / 5 MHz = 0.0000002 sec = 0.2 μsec

Period and Frequency

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Your answers are highlighted below.
Question 1
Cycle is always measured in
A
time.
B
frequency.
C
MHz
D
distance between a specific point in two consecutive waves.
Question 2
Which statement is not true of ultrasound frequency?
A
It effects both penetration and the axial resolution.
B
It is the number of cycles that the wave experiences per second.
C
It is not changeable by the Sonographer.
D
It is unrelated to wavelength.
Question 3
Typical values for the ultrasound period will be:
A
0.1 MHz to 0.5 MHz
B
0.1 μsec to 0.5 μsec
C
2 MHz to 12 MHz
D
0.0000001 μsec to 0.0000005 μsec
Question 4
The period of a beam is 0.3 μsec what is the frequency?
Question 5
With a 2 MHz transducer what would the period be?
A
1 second
B
.5 μsec
C
.2 μsec
D
2.5 MHz
Question 6
Which of the following is not a good definition for period?
A
The time that passes from the end of one cycle to the beginning of the next cycle.
B
The time from the start of one cycle to the start of the next cycle.
C
The actual time required to complete a single cycle.
D
The time that it takes to do something from start to finish.
Question 7
If you multiply frequency (MHz) by period (μsec) of a wave...
A
The answer is unpredictable.
B
The answer will be the propagation speed (mm).
C
The answer will always be 1 second.
D
The answer will be the wavelength.
Question 8
Typical values for the ultrasound frequency will be:
A
0.1 μsec to 0.5 μsec
B
.2 MHz to 1.2 MHz
C
2 MHz to 12 MHz
D
.2 μsec to 1.2 μsec
Question 9
With a 5 MHz transducer what would the period be?
A
2.5 μsec
B
2 μsec
C
2.2 μsec
D
0.2 μsec
Question 10
The period of a beam is 0.4 μsec what is the frequency?
A
5 Mhz
B
2 MHz
C
0.5 MHz
D
2.5 MHz
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I am the founder and lead Instructor here at ExamRefresh.com. I strive to help those that are entering the field of Ultrasound to be the best that they can be. Ultrasound is my passion.

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Comments

  1. Would like some information about relationships such as if frequency increases than period decreases. If density increases than stiffness decreases.

    • I was just talking about this subject with another member. I think in the next few days I will create an article with all the direct and indirect relationships I can think of. These are one of the most important aspects of the physics exam.

  2. Sana Shamshad says:

    So basically frequent is how many periods are present in a particular duration of time???
    I hope I understood correctly…

  3. Val-Monique Flournoy says:

    I passed my exam today, thank you for sharing your knowledge!

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