HOW DOES ULTRASOUND WORK TO CREATE A PICTURE OF MY BABY?
The handheld device that the ultrasound technician places on your pregnant belly is called a transducer. It contains piezoelectric materials that can convert electrical energy into sound. When ultrasound was first invented, these materials were natural crystals, like the quartz used in analogue watches, but today’s ultrasound transducers usually contain human-made ceramics, such as lead zirconate titanate.
The first thing the technician does is cover your belly with a gel, to prevent air from getting between the transducer and your skin, as air bubbles can block ultrasound waves.
When the transducer is turned on, the electrical current that runs to the piezoelectric crystals makes them contract and expand more than 20,000 times per second, causing a vibration that generates a sound. At a pitch or frequency of 3-12 million Hertz, the sound is too high for you or your baby to hear – hence ‘ultrasound’. Humans can only hear up to 20,000 Hertz.
4 The technician uses the transducer to direct a beam of ultrasound waves into your body. The waves travel through your tissues at a speed of around 1,540 metres per second and so very quickly find your uterus and baby in their path. Anywhere there is a change or break in tissue structure, the ultrasound waves are reflected back at the transducer.
5 The transducer picks up the reflected waves and converts them into electrical signals. Depending on where the waves were reflected, the distance each one has to travel to reach the transducer is slightly different and these differences can be used to build the image you see on the screen. The stronger the reflected wave (amplitude) and the quicker it reaches the transducer, the higher the resolution of the image.
6 Computer software processes the information transmitted in the electrical signals. It does this very rapidly, meaning you see the picture of your baby in real time.