beamwidth?

[Tom]

First, I am very glad to have found this forum. I have spent the last three days reading all the posts. I started a sidescan project before finding you guys so I am committed to my current approach. I own a Wesmar SS110 video system that works, but has more limitations than I am happy with.


My question: In one of the early posts Jan discussed 8 degree transducers and rejected them for a beam width being too narrow. I don't see how this is possible. Am I missing something? According to Dan Fountains calculations using 20* transducers produces a 4.8* beamwidth. My calculation using 8* transducers will produce 1.8* beamwidth?!?!?

[Jan]

Re: beamwidth?

Tom,


I rejected the 8° beamwidth when that would have been the overall beamwidth... using 1 transducer.


Now I am using 12 rectangular(?) elements which gives me a total length of about 35cm which is about 1° (My initial calculation came to something like 0.6°... I think... was some time ago)


The narrower the beam the better it is.


Fishfinder transducers are designed to create cone shaped beams, and that is not what a sidescan can use.


Sidescan needs a flat pie shaped beam. (like the fans used to cool ones face ... so to say)


Sidescan is looking at it surrounding through very narrow slits and not through round holes.


You want only to see what is straight in front of the transducer and not also what is left and right of it.


It will become very difficult to determine if an echo came from the left, middle or right.


And when it came from the left or right you have to know how much from the left or right.


As you see, this will be more or less impossible to do.


That is the reason why it is better to use flat fan shaped beams.


The 'flatter" the better.


The shape of the 'fan' should be something like 60° up/down and 1° left/right.


Hope this helps.


Best regards, Jan.

[Tom]

Re: beamwidth?

>Tom,


>I rejected the 8° beamwidth when that would have been the overall beamwidth... using 1 transducer.


>Now I am using 12 rectangular(?) elements which gives me a total length of about 35cm which is about 1° (My initial calculation came to something like 0.6°... I think... was some time ago)


>The narrower the beam the better it is.


>Fishfinder transducers are designed to create cone shaped beams, and that is not what a sidescan can use.


>Sidescan needs a flat pie shaped beam. (like the fans used to cool ones face ... so to say)


>Sidescan is looking at it surrounding through very narrow slits and not through round holes.


>You want only to see what is straight in front of the transducer and not also what is left and right of it.


>It will become very difficult to determine if an echo came from the left, middle or right.


>And when it came from the left or right you have to know how much from the left or right.


>As you see, this will be more or less impossible to do.


>That is the reason why it is better to use flat fan shaped beams.


>The 'flatter" the better.


>The shape of the 'fan' should be something like 60° up/down and 1° left/right.


>Hope this helps.


>Best regards, Jan.


Using four 8* transducer will be OK? If I understand the acoustical technology placing four two inch tranducer elements in a line and connecting to the trigger pulse will provide the narrow fan shaped beam? My calculations indicate an exposure of only 3 meters wide at 100 meter distance and about 5 meters at 150 meter distance. I suspect this will be near the limit of my range using 1000W output.

[Jim]

Re: beamwidth?

>>Tom,


>>I rejected the 8° beamwidth when that would have been the overall beamwidth... using 1 transducer.


>>Now I am using 12 rectangular(?) elements which gives me a total length of about 35cm which is about 1° (My initial calculation came to something like 0.6°... I think... was some time ago)


>>The narrower the beam the better it is.


>>Fishfinder transducers are designed to create cone shaped beams, and that is not what a sidescan can use.


>>Sidescan needs a flat pie shaped beam. (like the fans used to cool ones face ... so to say)


>>Sidescan is looking at it surrounding through very narrow slits and not through round holes.


>>You want only to see what is straight in front of the transducer and not also what is left and right of it.


>>It will become very difficult to determine if an echo came from the left, middle or right.


>>And when it came from the left or right you have to know how much from the left or right.


>>As you see, this will be more or less impossible to do.


>>That is the reason why it is better to use flat fan shaped beams.


>>The 'flatter" the better.


>>The shape of the 'fan' should be something like 60° up/down and 1° left/right.


>>Hope this helps.


>>Best regards, Jan.


>


>Using four 8* transducer will be OK? If I understand the acoustical technology placing four two inch tranducer elements in a line and connecting to the trigger pulse will provide the narrow fan shaped beam? My calculations indicate an exposure of only 3 meters wide at 100 meter distance and about 5 meters at 150 meter distance. I suspect this will be near the limit of my range using 1000W output.


Tom-


Check out two posts from Sture on 8/1/99 for a quick review on transducers and ranges. Hope this helps!


Jim

[Jim]

Re: beamwidth?

>>>Tom,


>>>I rejected the 8° beamwidth when that would have been the overall beamwidth... using 1 transducer.


>>>Now I am using 12 rectangular(?) elements which gives me a total length of about 35cm which is about 1° (My initial calculation came to something like 0.6°... I think... was some time ago)


>>>The narrower the beam the better it is.


>>>Fishfinder transducers are designed to create cone shaped beams, and that is not what a sidescan can use.


>>>Sidescan needs a flat pie shaped beam. (like the fans used to cool ones face ... so to say)


>>>Sidescan is looking at it surrounding through very narrow slits and not through round holes.


>>>You want only to see what is straight in front of the transducer and not also what is left and right of it.


>>>It will become very difficult to determine if an echo came from the left, middle or right.


>>>And when it came from the left or right you have to know how much from the left or right.


>>>As you see, this will be more or less impossible to do.


>>>That is the reason why it is better to use flat fan shaped beams.


>>>The 'flatter" the better.


>>>The shape of the 'fan' should be something like 60° up/down and 1° left/right.


>>>Hope this helps.


>>>Best regards, Jan.


>>


>>Using four 8* transducer will be OK? If I understand the acoustical technology placing four two inch tranducer elements in a line and connecting to the trigger pulse will provide the narrow fan shaped beam? My calculations indicate an exposure of only 3 meters wide at 100 meter distance and about 5 meters at 150 meter distance. I suspect this will be near the limit of my range using 1000W output.


>Tom-


>Check out two posts from Sture on 8/1/99 for a quick review on transducers and ranges. Hope this helps!


>Jim


Sorry- The "1" key didn't hit twice. Make that 8/11/99 for Sture's posts.


Jim

[Jan]

Re: beamwidth?