I'm designing an air ultrasound range finder that bounces ultrasound signals off a person's head to measure the distance of the device from the head. The goal is to get ~1mm accuracy as a device is actively being moved away from a person's head (range of distances is 0mm to ~250mm) so I need a pretty good update rate (>30 Hz). Of course, there are also some issues with the reflectance of the scalp and of the occlusion caused by a person's hair.
- How do I determine the best frequency transducer to use? I was thinking 40 kHz due to the low size components and the market availability.
- Should I go for narrow beam or wide beam? I think narrow beam would have better reflectance, but wouldnt they only work for specific ranges?
- When I mount these transducers onto this device, do they need to be at an angle relative to each other to optimize the reflection? Or can their transmit axis just be normal to the same plane?
- What kind of signal processing should I use? Obviously low bandwidth ultrasound transducers will have a fairly broad waveform, so I think correlation won't work too well. But will a threshold method be accurate enough? Maybe there are other methods I haven't considered?