Exploring Infrasound - Tornado Early Warning Detection Project Using Raspberry Pi Pico and a Python Supervisory Program

Inspired by the possibility of building an early warning system for tornadoes, Dev developed an infrasound detector. Tornadoes are rare in his area, but his detector found other infrasound activity using sensor circuitry based on a Raspberry Pi Pico, combined with a Python supervisory program that stores data on a computer for analysis.

- Dev Gualtieri

Just as there are invisible spectra of light, there are inaudible sounds. The human eye can't see infrared light at low frequencies and ultraviolet light at high frequencies. For audio, our ears can't detect the high ultrasound frequencies that are useful for things such as television remote controls and medical imaging. Sound also has an inaudible low-frequency component called infrasound.

A few electronic device designs have been published for making ultrasound audible. Most of these use heterodyning to shift the ultrasonic frequencies down to the audible range. The principal purpose of these circuits is to listen to the echolocation calls of bats, which occur at frequencies up to about 200kHz, but more typically between 20kHz and 60kHz. Electronics for such devices are a simple design problem for Circuit Cellar readers, but microphones with sensitivity at ultrasonic frequencies can be quite expensive. The inexpensive ultrasound receivers used in remote controls are not suitable for broadband ultrasonic detection, since they respond to a single frequency, 40kHz, with just a kilohertz bandwidth. If you don't live near a bat cave or highly wooded area, there will be little ultrasound activity.

Winds blowing over uneven terrain, ocean waves crashing onto shorelines, and erupting volcanoes generate infrasound waves that can travel long distances. Heavy vehicles and machinery are other sources of infrasound. Sound is a pressure wave that expands and compresses air over each cycle, and energy is lost during this expansion-compression cycle. Low-frequency waves have fewer cycles per distance than higher-frequency waves, so infrasound travels farther. Nuclear weapons are no longer being tested, but the infrasound from nuclear explosions were detected worldwide. Before supersonic flights of Concorde jets were discontinued, it was discovered that their infrasound emission interfered with the navigation of homing pigeons.