Serious question. Trying to figure out if there is any research/guidelines on selecting the frequency of a vibrator for a portable electronic device. This is safety related wearble device for first responders/cops/etc. I know lower frequency is better but is there a frequency that really starts to fall off when it comes to coupling vibrations though a belt or jacket/vest?
I've googled around a bit but all I'm finding is things related to measureing vibrations from heavy machinery and such.
Also, maybe this is more of a biology question?