is it possible to use an raspberry pi to detect ultrasound of 40000 Hz ? if so what parts and what software. and i want to have a small screen that readsout the Freq. would help me a lot! Thanks for the input 
The outputs will be different and you'll need to use a screened cable to connect the meter to the transducer.
On reflection you might do better with something like this if you know how to work it:
Owon Hds1022m-n Handheld 2 Channel 20 MHz Oscilloscope + DMM | Rapid Online
Cheaper than the Keysight and much more portable - will also show you frequency as well.
There are loads of people offering cheap handheld scopes - see what you can get locally.
MK
Thanks for the help! I will look in to it. But do you know if i can use the same transducer as the one that sendes the signal?
If it is a ultrasonic tranducer, should work both ways based on https://en.wikipedia.org/wiki/Transducer
C
ah ok thanks !, im going to try this the following week, ill keep you guys updated
The transducer as suggested should do well for you. Also you may want to research underwater sonar devices such are found on subarine communications systems. Lots of good reading out there.
i have orderd a working ultrasound system and an extra transducer, its not going to arrive this week, but hope to have it next week, i have premisson to borrow a high end digital scope, so i hope this goes well
could you guys recomend me an Oscilloscope for this use ? i would like a hand held one with a battery that dont need to last that long but 10-20 min, and a DMM in one if possible. what MHz do i need? price is is not an issue.
You don't need much bandwidth since you are looking at 40kHz signals.
The nicest toys come from Fluke and Keysight:
Very nice - but over £2k
Search Results | Farnell element14
This one:
is a lot cheaper at £1053
but I'm sure you could get away with:
about £330 form Amazon
I haven't used any of these - the Fluke and Keysight models will be nicer and will behave like proper scopes - the Hantek will probably be quite good enough to see if systems are working or not and cheap enough for you not care too much if you drop one in the bilges !
MK
thanks for the input, i wasnt expecting sutch a price :Z sorry about that, but do you think this is good enough Hantek DSO1060 Digital Handheld Oscilloscope /Multimeter 60MHz 500MSa/s 2 Channels-in Oscilloscopes from Industry & Busi…
or do i need to go up on the Keysight Technologies U1602BU1602B was thinking about losing it too
i dont think i will go for the fluke, just because im gonna lose money on this deal then, so ether the keysight or the Hantek
or mabye this one 72-9360 - TENMA 72-9360 - Oscilloscope, 2 Analogue, 100 MHz, 500 MSPS, 512 kpts, 3.5 ns | Farnell element14 Norge ?
I would go for the Hantek from Amazon - under EU distance trading laws you can return it (undamaged of course) within a few days of receipt if it isn't any good for you purpose.
I would expect it to be adequate for your purpose.
http://www.eevblog.com/forum/chat/hantek-dso-1060-a-battery-powered-60mhz-dso/
Another two links with a bit more information.
MK