I am requesting help to construct an ultrasonic device that emits sound at about 25Khz. Unlike most ultrasonic devices, I want the device to carry sound over 100 feet (or 30 meters) and still be over 140 decibels at 100 feet (or 30 meters).
Does anyone know how I can do this? Plans? Actual devices? Please reply.
All I know of this is that the sirens on fire engines can do this for miles.