Infrasound refers to sound waves below 20 Hz that cannot be heard by humans but can be felt. It can produce anxiety, sorrow, or chills in people and carries far distances with little loss of strength. Examples of natural infrasound sources include volcanoes, earthquakes, and ocean waves. Ultrasound refers to sound waves above 20 kHz that cannot be heard but can be used in medical imaging devices to produce images of internal tissues and structures. Ultrasound works by transmitting sound waves that bounce off internal tissues and are received back by the transducer to form an image. It is used for fetal imaging, cardiac imaging, and assessing blood flow through Doppler techniques.

1. Infrasound / Ultrasound Tina [25] & Sheryl [26]