I am trying to make an inexpensive modem for underwater data collection.
I have been reading some posts and documentation on the Internet and I found a good candidate to put efforts on. On the link below there is a good document from the University of California San Diego showing a complete project for a 2400 low cost piezo modem using a piezo cylinder part number SMC26D22H13111 ~ (SMC26D22H13SMQA). I can see it works up to distance of 1000 ft (at 2400bps) but my application is to send high volumes of data (mainly). So, my initial idea was to increase the throughput to a higher speed than the one on the original project.
https://ai2-s2-pdfs.s3.amazonaws.com/95ad/cd9feb4176d1c9235b95bfbaf0bcaa8602f4.pdf
My intention is to raise the speed from 2400 bps up to 14400 bps. My knowledge of electronics is limited so my question is (and I know is a broad one!), where should I concentrate the changes on the original electronic project to achieve a higher throughput?
One possible way that I see is by increasing the frequency of transmission but I am not sure what would be the implications.
Thanks,
Matthew

 

You might find this interesting: http://www.mdpi.com/1424-8220/12/4/4237/pdf

 

Thank you, Albert. Captured and archived.
If am reading the chart correctly, makes not much sense comparing [13] and [34]
5MHz yielding more distance than 100KHz
Can someone explain ?

 

@LambdaPi first you need to decide how far you want to transmit your data. Once you are decided on that you need to check seawater attenuation for that frequency, as you will see, as higher frequency as you get higher the attenuation will be.

Take a look on the graph below. It will tell you how many dBs are lost per kilometer for a specific frequency. This will also help you to chose how much acoustic power you will need...

 

Your chart is too small to read.

 

The source is ----> http://resource.npl.co.uk/acoustics/techguides/seaabsorption/physics.html

 

Thank all for the inputs.
I am now looking into the electronics.
@raphael B => We are looking for transmissions no longer than 400m deep.

 

Thank all for the inputs.
I am now looking into the electronics.
@raphael B => We are looking for transmissions no longer than 400m deep.

In addition to the information furnished so far - bear in mind that ultrasonics find a few applications in cleaning and plastic welding, to name just a couple.

In cleaning solutions, ultrasonic waves of sufficient power cause the formation of "cavitation" bubbles. these form and then implode, which causes a shock wave that knocks the dirt off. EPE published an Australian SC article for an ultrasonic doodad to sort out marine life that adheres to boat hulls. Cavitation is also in the vocabulary of people who deal with ship propellers. How much "welly" can give it is limited by cavitation around the propeller. This will also be a limiting factor if you turn up the wick on your data sender.

Ultrasonic plastic welding basically rubs the 2 bits of plastic together to produce heat - the movement is mere microns, so not much impact on finished precision.