Ultrasonic Sensor for Car Interior

[NivagSwerdna]

Someone broke the interior sensor on my Renault Espace today and I'm trying to work out exactly what the part is...

In the Espace there are at least two ultrasonic interior sensors (one on each side at the back), might be some further forward as well... not sure about that.

Anyway this device when taken out of its housing is 9.8mm diameter and 7.1mm high so quite like MUS-40S or MUS-40E?

Are these either Transmitters (presumably to flood the cabin) or Receivers (to detect pertubations)?  How can I work out if I have a damaged Transmitter or Receiver?

Should I replace the pair? 

Thanks in advance

[SeanB]

Probably will work with either, so just buy the transmitter and put it in, it will at least work there as either transmitter or receiver, with only slightly less sensitivity if you have it wrong.

[NivagSwerdna]

I found a picture of MA40S4S on ebay which seems to look almost identical to mine but has a red dot.  Do you think red dot means sender?  or does polarity matter with these and it marks +ve?

"S" for Sender? j = September 2003?

(Excuse the ignorance... never used these before)

[fzabkar]

https://www.murata.com/en-us/products/productdata/8797589340190/MASPOPSE.pdf?1450668610000
https://www.murata.com/en-us/products/productdata/8797589274654/MASPOPRE.pdf?1450668610000

The S part is a transmitter (sender) while the R part is a receiver.

[NivagSwerdna]

Do these things have polarity?  What is the intention of the red dot on these EBAY ones (which I don't have on my damaged one)?

[fzabkar]

The datasheet states that you should not apply a DC voltage to avoid migration, so the device cannot be polarised.