# Piezo for sonar

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#### Bern1937

##### New Member
This is for underwater use.

I am starting a project which is the same thing only different from several others. . I am looking for the latest thoughts on piezo elements. Do I do my own water proofing or what is a good combination of the water proof ones. How do you mount them for the best efficiency in coupling energy to the water. I want to use a separate speaker and microphone, and have them separated several inches. They can be the same, but is there better combinations if I use different elements? If so, what is a good one for transmitting and also receiving? Maximum depth/distance I will be going is a few feet, so I shouldn’t need a lot of power. I think the higher the freq. the better, but not sure just where needed yet. I am thinking in the ball park of 50 to 100 KC. —– So what is the latest and greatest? Is piezo the best way to go, for a good price. — Thanks

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#### dknguyen

##### Well-Known Member
Why don't you just buy a transducer? Or when you say piezo element, do you actually mean a transducer? At least to me, when you say piezo element it sounds like you want to build your own transducer.

http://www.futurlec.com/Ultrasonic_Sensors.shtml

Higher frequency isn't better, just different. Higher frequency makes a narrower beam that doesn't travel as far while lower frequency makes a wider beam that travels farther. However, you are in water which conducts sound much better than air so you have a lot more freedom than in air.

Your frequency is also decided by the transducer that you use and hobbyists don't have too many choices. Your frequency will be decided by what you can buy that is waterproof and cheap enough.

I would use the same type of transducer for receiving and transmitting (whether you end up using separate transmitter and receiver, or single transceiver) because then the transmission and reception peaks will be matched.

I am unable to tell if you're interested in ultrasonics or if you just want to get something that works:
https://www.amazon.com/Waterproof-Ultrasonic-Distance-Measuring-Transducer/dp/B01J5KZU8M

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#### Bern1937

##### New Member
Frequency, in my case does matter, in that it will have an effect on resolution, chirp time, and dead time. If I go with two transducers, I can play some games with them that will effect these issues.

Your comment on using the same type for both is very valid, however I don't know if some types make better receivers than others, or not significant. And yes I would want their frequency to match.

Your lead to the Diymore unit is very close and I have looked at it before. A couple of issues that I don't know if I can control is being able to start a cycle on my command, and controlling the chirp and dead time.

Planning on getting one and doing some hacking to see what can be done. The main issue here is they need to work underwater.

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#### Bern1937

##### New Member
The one big issue I failed to mention in last reply, "Sonar" All of this is underwater.

My mistake: Sonar is in either air or water. To me it is underwater only. Sorry>

The Diymore unit is for air. I would also have to change to waterproof transducers. This is why I am thinking about water proof piezos.

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#### dknguyen

##### Well-Known Member
The one big issue I failed to mention in last reply, "Sonar" All of this is underwater.

My mistake: Sonar is in either air or water. To me it is underwater only. Sorry>

The Diymore unit is for air. I would also have to change to waterproof transducers. This is why I am thinking about water proof piezos.
Is there a language barrier here? The transducers near the bottom of the page on the first link are waterproof...and the DIYmore unit also uses a waterproof transducer...

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#### Bern1937

##### New Member
Hey dknguyen, thanks for all.

I am not sure if waterproof and underwater means the same. I know of items where they say waterproof, but still not useable underwater. Just means OK to have in the rain. I just don't know.

#### dknguyen

##### Well-Known Member
Hey dknguyen, thanks for all.

I am not sure if waterproof and underwater means the same. I know of items where they say waterproof, but still not useable underwater. Just means OK to have in the rain. I just don't know.
You should be able to use them underwater. You will just have reallllllllllyyyy long range because water conducts sound so well and the frequency is so low. When working underwater, you can use much higher frequencies than you can in air, but you don't have to. Using a much higher frequency lets you trade your super long range which might not be needed for a narrower beam width, which might be more useful.

https://www.maxbotix.com/Tutorials/underwater-ranging.htm

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#### Bern1937

##### New Member
Like the ones labeled water proof in the Futurlec cat. they say do not use underwater

#### dknguyen

##### Well-Known Member
Like the ones labeled water proof in the Futurlec cat. they say do not use underwater
That doesn't matter. As long as water can't get in and you seal all the electrical connections so water can't get in, you will be fine. Sonar doesn't seem to be quite as picky as you think it is.

How deep does this have to work? Because water pressure is probably the biggest problem you're going to run into that might damage the sensor.

#### Bern1937

##### New Member
After looking at the pricing in the MaxBotix catalog, I'm back to looking at water proof piezo

#### Bern1937

##### New Member
The sensors will never be under a few inches of water.

#### dknguyen

##### Well-Known Member
After looking at the pricing in the MaxBotix catalog, I'm back to looking at water proof piezo
It's like I'm talking to a wall. It seems to me that you are more in love with the idea of waterproofing your own piezo than actually wanting to know if there's a easier, cheaper, or more efficient way.

First you ignore the fact that I linked you waterproof sensors and say that those sensors won't work because they aren't waterproof.

Then you ignore all the cheap transduceres and modules I sent you and say that the expense of the MaxBotix is making your mind turn back to waterproofing your own piezo.

The transducers in my first reply are $5 for a pair and the DIYmore ranging module is$16. If price is what you're concerned about, you're not going to beat those two.

The sensors will never be under a few inches of water.
Any sensor that is designed for air but is waterproof should work then.

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#### Bern1937

##### New Member
Looks like its time order some of Futurlic USTR60-10H.

You think that if this unit is sealed with a good sealer of some type, it would be good to go?

Wiring to it should not be a problem to water proof.

#### dknguyen

##### Well-Known Member
You think that if this unit is sealed with a good sealer of some type, it would be good to go?
Yes. That's what other people have done. It just needs to have enough power to move the membrane back and forth against the water pressure while not becoming full of water. It's not very different from doing it in air. Just that underwater, very high frequencies (up to 2MHz, maybe more) won't dissipate as quickly as in air so you can use those too if you want. You'll lose some performance because air and water have different impedances and the sensor is probably only impedance matched for air or water. But \$5 is hard to beat.

Also, underwater conditions can be more variable like the effects of water, pressure, and water composition so you might have to measure and compensate for that depending on what you're doing. The advantage is your sound transmission is much much better.

Move your effort from how to design the transducer to how to make a circuit to drive and receive the piezo and compensate for water conditions. Or I suppose you could just buy the electronics but you'll probably only be able to find one designed for air and have to and calibrate it for that. A good one for underwater would do the things like temperature, depth/water pressure measurements compensate for those but I don't think you'll find an affordable one.

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#### Bern1937

##### New Member
Thanks for all, dknguyen,

I think I have had it for the day. I am in Idaho, where are you? Got a few things going tomorrow and I need my beauty sleep. Hasn't done much yet, but you never know. Worth to keep trying.