Oscillations

The string oscillates up and down in periodic motion, causing surrounding air molecules to oscillate and produce sound waves.

What happens when a guitar string is plucked?

The vibrating string makes air molecules oscillate, which generates sound waves.

What role do air molecules play in sound production from a guitar string?

Around an equilibrium position.

Around what does the guitar string vibrate when plucked?

When the string starts from its initial position, moves to one extreme, then the other extreme, and finally returns to the initial position.

What defines one complete oscillation of a vibrating string?

Periodic Motion

Any motion that repeats itself at regular time intervals, such as a vibrating guitar string or a child swinging on a swing.

(T) - Period in oscillatory moment

• The time to complete one oscillation

• It is constant in the absence of friction

Second (s)

S.I unit of time

Frequency (f)

• Number of events per unit time

• For periodic motion, it is the number of oscillations per unit time.

f = 1/T

Mathematical representation of the frequency

1 complete oscillation

1 cycle in oscillatory motion

20 Hz to 20,000 Hz

The range of human hearing

ultrasound

These machines emit frequencies higher than the upper limit of human hearing, giving them the description of…

Ultrasound machines

_________________ are used for in pregnancy to perform a non-invasive medical diagnosis of the fetus by creating images of the womb.

high-frequency sound waves, ionizing radiations like X-rays

Ultrasound gets considered safe for both mother and fetus because it uses ____________________ instead of __________________.

2 MHz to 18MHz

The frequency range of ultrasound used in fetal imaging.

Transducer probe

Component of the ultrasound machine that generates sound waves

It emits high-frequency sound waves that reflect off tissues at different speeds.

How does the ultrasound transducer create images?

Returning echoes are processed by a computer to form real-time images.

What happens to the echoes from the tissues in ultrasound imaging?

Yes, it is true.

Is it true that sound waves travel differently through fluids, soft tissues, and bones, giving high contrast in soft tissue structures where X-rays are less effective;

making these devices extremely useful in imaging soft tissues like fetus.

2D ultrasound

Type of the prenatal ultrasound scan that produces flat grayscale images

3D ultrasound

• Type of the prenatal ultrasound scan that produces detailed surface images of the fetus.

• Visualizes fetal facial features and limbs.

• Detects the surface anomalies like cleft lip.

4D ultrasound

• Type of the prenatal ultrasound scan that produces detailed surface images of the fetus, moving (real-time) 3D images.

• Also gets called “Real-time 3D ultrasound.“

• Allow observations of fetal movements like yawning or kicking.

As early as 5 to 6 weeks of pregnancy.

How early can fetal heartbeat be detected via ultrasound?

Doppler ultrasound

A special mode of the ultrasound devices that measures blood flow in the umbilical cord and fetal blood vessels to check oxygen and nutrient supply to detect any growth restrictions or oxygen deficiency.

Sonography

Another name for ultrasound imaging, whose etymology basically means writing with the sound.

Piezoelectric crystals

• Special materials inside the transducer probe that generate sound waves when an electric current is applied, and produce electrical signals when they receive returning echoes.

• They convert electrical energy into ultrasound waves and then back into electrical signals when echoes return.

• They enable the two-way process of sending sound waves into the body and receiving echoes to form images.

Hertz (Hz)

S.I. unit of frequency

Definition of Hertz

1Hz = 1/s

Below 720 mW/cm^2

The typical safe intensity of ultrasound used in medical imaging, which is considered safe for the diagnostic use without any tissue damage

The gel eliminates air pockets between the probe and skin, allowing efficient transmission of sound waves.

Why is a gel applied to the abdomen during ultrasound?

Around 4 to 5 weeks, by visualizing the gestational sac.

What is the earliest week that ultrasound can confirm pregnancy?
And how?

Crown-Rump Length

The measurement from the top of the fetus’s head (crown) to the bottom of the buttocks (rump), used in early pregnancy (6–13 weeks) to accurately estimate gestational age and due date.

Amniotic Fluid Index (AFI)

• The ultrasound measurement of amniotic fluid volume

• Abnormal levels indicate risks like growth restriction or birth defects.

Amniotic fluid

• A protective liquid surrounding the fetus in the amniotic sac.

• Cushions the fetus from external shocks.

• Allows free movement, aiding muscle and bone development.

• Maintains a constant temperature.

• Prevents amniotic sac from sticking to the fetus.

• Assists in lung and digestive system development through fetal swallowing and breathing practice.

Nuchal Translucency (NT) scan

Scan that measures the fluid (and its thickness) at the back of the fetal neck (11–14 weeks) to screen for chromosomal abnormalities like Down Syndrome.

Nuchal Translucency (NT)

A collection of fluid under the skin at the back of the fetal neck.

Down Syndrome

• A genetic condition

• Caused by the presence of an extra copy of chromosome 21 (trisomy 21)

• Results in developmental delays, characteristic facial issues, and potential health issues such as heart defects and hearing problems.

Edwards Syndrome

• A genetic disorder

• Caused by the presence of an extra copy of chromosome 18 (trisomy 18)

• It is characterized by severe developmental delays, congenital heart defects, low birth weight, distinctive facial features (such as small jaw and prominent occiput), and often life-threatening complications.

• Most affected infants have a high mortality rate within the first year of life.

Abnormal NT measurement

A thicker-than-normal NT which indicates chromosomal abnormalities, heart defects, or other genetic conditions.

Mid-pregnancy scan

• Also called anatomy scan

• Done around 18 to 22 weeks

• In order to assess fetal organs, growth, and structural abnormalities.

resolution, penetration

Higher frequency = better __________ but lower __________

Usually after 14-16 weeks

Around what weeks can the ultrasound device detect the sex of the fetus?

Gestational age

The age of the pregnancy measured in weeks, usually counted from the first day of the mother’s last menstrual period (LMP).

Estimated Date of Delivery (EDD)

The predicted date when the baby is expected to be born, typically around 40 weeks of gestation. It can be refined using CRL measurements in early pregnancy.