PING and cloth

Vega256

Hi guys,

Simple question regarding the PING ultrasonic distance sensor. Does cloth reflect the ultrasonic signal emitted by the PING?

Franklin

To some extent it will.

GordonMcComb

Depends on the cloth. Most cloth will absorb sound, and not reflect it, though it also depends on whether the cloth is draped or perpendicular to the wave fronts. Some cloth, like that used for speaker grills, is actually "transparent" to sound waves. Your Pings will bounce right through to whatever is behind it.

-- Gordon

Tracy Allen

I was involved in a project that used ultrasonic tags for monitoring the presence of people in locations where they might be exposed to air pollution. The tags had to be placed under clothing or in cloth bags, so the paper includes empirical data about signal strength under layers of cotton and nylon.

An Ultrasound Personal Locator for Time-Activity Assessment, Internl J Occup and Environ Health, 15 (2): 122-132, 2009.

Duane Degn

I've been playing with adding an ultrasound senor to my Scribbler 2 for the last few days. I though I'd share some of my observations concerning ultrasound and cloth.

Our living room couch sits a couple of inches off the ground. Just high enough for the S2's IR sensors not to see it. I've noticed the couch appears to be invisible to the sonar sensor even though the sonar sensor is at just about the ideal height to see the couch.

The sensor does see the couch after it has made contact with the couch. The location of the ultrasound sensor is such that it is the part of the robot to make "first contact" with the couch. It appears the senor compresses the material and padding against the wood frame of the couch. The sensor is finally triggered once it pressed against the frame of the couch.

One problem this caused was that after the sensor was triggered it would back up a bit and perform a 360 degree scan searching for the clearest path (the farthest reading). The couch would again be invisible to the sensor so the robot would repeat the previous action of getting stopped by the couch.

I realize "invisible" isn't really the correct term to use with how the sensor saw the couch. If the couch had been invisible, the robot would have seen the wall behind the couch (which it did not).

I modified the program to have the S2 turn around if a second ultrasound trigger occurred soon after the first one. This fixed the problem of the robot getting stuck at the couch.

I think this a case where the cloth/padding initially absorbed the ultrasound but then because transparent once compressed.

Edit: I was using a MaxBotic ultrasound sensor. There appears to be a problem using Ping sensors with a S2.