Beamforming

Status
Not open for further replies.

epilot

Member
Hi friends.

Today when I was reading a paper on the net I saw a small word obout sonar and radar beamforming, then I did a search via google. I noticed that this job is down with "delay" and phase shifting of acoustic beams,
even I saw a thread here;that a guy suggested to another to use this way and use 10 ultrasonic transducers to avoid direct rotating his trasducers.

Well after reading some words in the field; I am not sure how making delay or phase shifting can curve abeam( like what a lens does for one or more light beams)!!!
My idea is that a device that makes a delay or phase shifting does not do a such job, but it delays the time of output beam, if my guess is right, then how it acts like a lens?!

Thanks for any input
 

Attachments

  • untitled.JPG
    39.1 KB · Views: 118
no it creates a time dependent interference pattern which changes the direction of the wave/beam.
( i assume it only works with sonar )
 
Works with light too, but light can be focused so much...why bother? Just use a spinning mirror.

It uses constructive and destructive interference. You have a lot of work ahead of you, mostly in how you must have complete control of the transducers involved. (I think I was the one that put forth the idea).

1. You could have a panhead
2. You could have an array instead of a panhead
3. You could use an array with beamforming to artificially focus your beam with an array of wide beamwidth transducers

3. is by far the hardest. The only place you are going to find such material is by studying/googling ACTIVE submarine beamforming sonars in the military, as opposed to passive sonars which just listen and coincidentally are used much more often because it is easier to hide due since you don't have to transmit a signal that could get intercepted.
 
Last edited:
_nox_ said:
no it creates a time dependent interference pattern which changes the direction of the wave/beam.
( i assume it only works with sonar )
Click to expand...


Yes, it uses time delay to change the directivity, but How?
How does time delay Curve and change the ANGEL of beam??
 

First, what is a "spinning mirror"? Are you meaning a rotating mirror? What is a "panhead"?

Yes I have head that it use constructive and destructive interference, but again How it doeas the job. 2 or more transducers will make constructive and destructive interference without any beamformer device too.
What is the relationship between "directing" and constructive and destructive interference while the interference only cancels the destructive part.
 

I meant for lasers (and lasers only, which is out of reach of most people because of the parts and precision required) that since you can focus a laser beam so much and since lasers reflect off of mirrors, it's better to jsut use one laser beam (instead of an array) and a spinning mirror (instead of panhead) to redirect the beam wherever you want.

A panhead is like your neck and your eyes. Your neck spins your eyes so you can use your eyes to see in different directions. Panning is a term used in movie filming like when you pan the camera. It is just a motorized spinning platform or head that the sensors sit on.

I'm not "quite" sure how beamforming works exactly, but I imagine it's like this:

You have 3 sensors each with a 60 degree beam width facing semi-circular outwards. The sensors are 40 degrees apart (20 degree overlap in the beams.). You send out an sinusoid with an equal amplitudes and frequencies at the same time from all 3 sensors. The difference is the left/right sensor has 180 degrees phase shift (not quite the same as time delay since this is a finite-time signal- the left/right signals are inverted versions of the center signal). The left and right beams overlap 20 degrees on either side of the center 60 degree beam. They superimpose (add up) on 20 degrees of both sides of the center beam. Since they are 180 phase shifted (or inverted), they add up to zero. It ends up that the center beam now appears as only 60-20-20=20 degrees wide. Beam forming is used to artificially narrow down the wide sonar beam (beam width is dependent on frequency and frequency affects resolution and effective range so it's a constraint you can't mess around with too much).
 
Last edited:
Introduced in 1948, the Panhead is much quieter and cleaner than the Knucklehead and also began the revolution of the twin-V design.

**broken link removed**
 
phased array radars are pretty common military applactions of this technique.

note that for ultrasonic you may have a problem because the transducers are usually pretty directional. You will not have much power to the sides. look at the datasheets and select transducers with the widest possible "beam".

I have experimented with using differential flight times to determine deflection angle of the relecting object. it sort of works but I need to find much wider angle devices to make it worth while.
 


Hi dknguyen,

I have read all those links, but I could not to get my response.
Beamforming is used in the military radars to avoid from rotating radars,
now suppose a radar that does not rotate but can detect the thing that are in the back of it, so again how does beamforming and delaying cause focusing at that angles?
 
What is your idea about this delay circuit? the delay amount is determined by R5 and R6.
 

Attachments

  • 8.JPG
    20.5 KB · Views: 113

If you have several overlapping beams and you delay or phase shifting the beams properly, you can get destructive interference (180 degree phase shift with respect) in the overlapping areas which artificially makes the beam narrower (only the non-overlapping beam remains and it's sides have been shaved off due to the destructive interference from overlapping with the phase shifted beams on the sides). It is only a time delay for infinite-time signals. In practice, where there are only finite time signals, it's a phase shift rather than a time delay. (For sinusoids they are the same for infinite time signals).

I'm not sure how much beamforming is used with radar. It seems to me it is more often used for sonar. Beamforming does not curve, bend or focus the beam the way you are thinking. What it does is use destructive interference cancel out the sides of the beam leaving a narrower center beam. It "shaves" off the sides of the beam with destructive interference.

A radar that beamforms and can see things behind it probably as a circular arrangment of sensors, so there really is no front or back.
 
Last edited:
Status
Not open for further replies.
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…