Updated: Feb 9, 2021
The idea is to develop a mobile application in iOS and Android that turns your phone into a portable personal sonar or ultrasound device.
The app would scan the environment for noise and determine the background frequencies. Then it selects a frequency that has the least interference (background noise).
It will generate and emit this sound frequency, then listens for a bounce-back (reflective wave). Using an algorithm for sonar-based signal identification, it should be able to create a low-grade ultrasound image.
Ultrasound frequencies range from 20 kHz to several gigahertz. Most iOS and Android devices speakers can emit up to 44 kHz. This would give us a little bit of range to work with. We could also overcome this range limitation by adding a BLE sound emitter that has a high-frequency range.
At the moment, I am not sure what an app like this would be useful for but I'll leave that to the community to decide.