MarkT:
Where is the link to the datasheet?From those spec's it sounds like a bare transducer - that won't do anything very useful.
For ultrasonic ranging you need to fire a high power pulse of 40kHz (at perhaps 30 to 50V using a tuned step-up transformer) through the transducer to create a "ping". You then disconnect the drive electronics and attach a sensitive analog amplifier to listen for the returning echoes. The delay from send to receive gives the distance.
So unless the device comes with a transmitter and receiver electronics it isn't going to do what you think I'm afraid.
Hmm, well I hope I ordered the right thing!
Here's the link to the eBay page:
http://www.ebay.com/itm/280724584131?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
So am I going to need additional electronics to get this thing working?