Phil Winder wrote:
> On Jul 10, 6:19 pm, Joerg <notthisjoerg...@removethispacbell.net>
> wrote:
>> Phil Winder wrote:
>>> On Jul 9, 11:55 pm, Joerg <notthisjoerg...@removethispacbell.net>
>>> wrote:
>>>> Phil Winder wrote:
>>>> [...]
>>>>> Hi all,
>>>>> I just though I would update you on what I have found sine you all
>>>>> took the time to help me.
>>>>> I have implemented a new microcontroller that has simultaneous
>>>>> sampling and a slightly higher sampling rate.  I could then
>>>>> interpolate the data with pretty good results using a simple padding +
>>>>> band pass filtering technique.  The higher the SNR the better it
>>>>> worked.
>>>>> However, I have hit a great big wall.  It all boils down to the fact
>>>>> that I have used 2 rows of transducers to make the spacing 1
>>>>> wavelength.
>>>> If it's any consolation, we have all hit that wall. One wavelength is a
>>>> bit coarse.
>>>>> For the following results, Consider the situation where x is the
>>>>> horizontal plane, y is the vertical plane and z is the distance
>>>>> between the source and the target.  If the target is slightly elevated
>>>>> in the y plane, the top and bottommost transducers would receive an
>>>>> echo at different times.  Furthermore, due to multipath dispersion I
>>>>> am also receiving further echoes from different y directions.  So to
>>>>> counteract this, I would have to scan not only in the x plane, but in
>>>>> the y plane too, and this was accomplished by summing all of the
>>>>> results in the y direction to produce a plot of the targets in the x
>>>>> plane.  However, by delaying the signals in the y plane, the x plane
>>>>> in some situations became erroneous.  It looks like I am getting some
>>>>> sort of aliasing in the x plane.  I think that this is because of
>>>>> instead of having a beam pattern from 4 transducers, I am getting 2 x
>>>>> 2 transducer patterns, so not only do I now have a very very wide beam
>>>>> width, I will have some nasty sidelobes too (since if you just
>>>>> consider the 2 transducers, the spacing is 2 x wavelength.)
>>>>> On the up side, the hardware side of it works great!
>>>> At least now you are getting a good feel on how much HW performance you
>>>> need. Might want ot try a real (external) ADC at some point.
>>>>> So all around, this was pretty much a disaster, and I am not looking
>>>>> forward to remaking all of the hardware.  So for beta 2 I will need:
>>>>> o to source some smaller transducers so that I can get 1/2 x
>>>>> wavelength spacing in a linear fashion. Possibly go higher in
>>>>> frequency to get a better z resolution.
>>>>> o use a dedicated ADC with 8 transducers, rather than 4.  Get
>>>>> something with a faster sampling rate too.
>>>>> o remake the hardware :(
>>>>> The hardest thing I see is sourcing the peizoceramics from somewhere.
>>>>> Does anyone know of where I can get any cheaply online?  Self enclosed
>>>>> transducers would be ideal, but I would be willing to mess with the
>>>>> naked ceramics myself if I had too.
>>>> I know PZT vendors but our stuff is always full custom volume
>>>> production. IOW they dice, mount, backfill to our specs. It's all in the
>>>> MHz range and I am not too familiar with 40kHz stuff. If it is the usual
>>>> thickness excitation you could buy a bunch of cheap transducers, disect
>>>> them and ten dice them with a diamond blade. Be careful, this is
>>>> dangerous. Maybe leave the dicing to professionals who operate older
>>>> dicing saws for wafers. They'll balk at first, don't want to contaminate
>>>> their machines, so this may require holding a wad of cash in front of
>>>> them ;-)
>>>> If this is on a shoestring budget you might ask around in robotics
>>>> forums, see if someone has done it before. They often try to obtain
>>>> better directivity for navigational purposes. Just don't get any raw
>>>> PZT5H if it's not polarized. Polarization requires a HV source.
>>>> Oh man, it's 4:00pm and we can't see the sun anymore. Only smoke. <cough>
>>>> --
>>>> Regards, Joerg
>>>> http://www.analogconsultants.com/
>>>> "gmail" domain blocked because of excessive spam.
>>>> Use another domain or send PM.
>>> Holy smokes!
>>> Thanks for the thoughts, I would definitely not be able to do the
>>> polarisation myself.  And like you said, these things are usually
>>> bought it pretty big numbers....
>>> But what I could do is try and dismantle one of these transducers I
>>> have, maybe even cut a few down a little bit and see how they
>>> perform.  Its not ideal, but it could work.
>> Be very careful with eye protection, venting and stuff. And you can't do
>> it dry, we always used wet saws.
>>
>>> The only other option that i have been persuing is using 20kHz (or
>>> even less).  That means 1 wavelength at 17mm and Ive found some
>>> electret microphones transducers that measure 4mm wide so I would be
>>> able to get half wavelength there.
>> Keep in mind that most animals will go crazy at that frequency. Whenever
>> I have some ferrite going off on a sub-harmonic the shepherd leaves the
>> room and gives me "the looks". The rottie is a lot less sensitive, just
>> snores through it.
>>
>>> By the way I presume that you are working underwater since at 1MHz
>>> there's a wavelength of 0.3mm.  A tad small.
>> Yes, we deal with very small wavelengths. Mostly human body ultrasound.
>>
>> --
>> Regards, Joerg
>>
>> http://www.analogconsultants.com/
>>
>> "gmail" domain blocked because of excessive spam.
>> Use another domain or send PM.
> 
> Joerg, Well I was actually talking about the transducer unit, not the
> ceramic itself.  I thought if I could dismantle the outer shell, it
> may shave a few mm off.  I would have thought the ceramic would be too
> brittle to cut anyway.
> 

The shell is usually very thin, the disk is almost the same diameter.

[...]

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Jul 10, 6:19 pm, Joerg <notthisjoerg...@removethispacbell.net>
wrote:
> Phil Winder wrote:
> > On Jul 9, 11:55 pm, Joerg <notthisjoerg...@removethispacbell.net>
> > wrote:
> >> Phil Winder wrote:
>
> >> [...]
>
> >>> Hi all,
> >>> I just though I would update you on what I have found sine you all
> >>> took the time to help me.
> >>> I have implemented a new microcontroller that has simultaneous
> >>> sampling and a slightly higher sampling rate.  I could then
> >>> interpolate the data with pretty good results using a simple padding +
> >>> band pass filtering technique.  The higher the SNR the better it
> >>> worked.
> >>> However, I have hit a great big wall.  It all boils down to the fact
> >>> that I have used 2 rows of transducers to make the spacing 1
> >>> wavelength.
> >> If it's any consolation, we have all hit that wall. One wavelength is a
> >> bit coarse.
>
> >>> For the following results, Consider the situation where x is the
> >>> horizontal plane, y is the vertical plane and z is the distance
> >>> between the source and the target.  If the target is slightly elevated
> >>> in the y plane, the top and bottommost transducers would receive an
> >>> echo at different times.  Furthermore, due to multipath dispersion I
> >>> am also receiving further echoes from different y directions.  So to
> >>> counteract this, I would have to scan not only in the x plane, but in
> >>> the y plane too, and this was accomplished by summing all of the
> >>> results in the y direction to produce a plot of the targets in the x
> >>> plane.  However, by delaying the signals in the y plane, the x plane
> >>> in some situations became erroneous.  It looks like I am getting some
> >>> sort of aliasing in the x plane.  I think that this is because of
> >>> instead of having a beam pattern from 4 transducers, I am getting 2 x
> >>> 2 transducer patterns, so not only do I now have a very very wide beam
> >>> width, I will have some nasty sidelobes too (since if you just
> >>> consider the 2 transducers, the spacing is 2 x wavelength.)
> >>> On the up side, the hardware side of it works great!
> >> At least now you are getting a good feel on how much HW performance you
> >> need. Might want ot try a real (external) ADC at some point.
>
> >>> So all around, this was pretty much a disaster, and I am not looking
> >>> forward to remaking all of the hardware.  So for beta 2 I will need:
> >>> o to source some smaller transducers so that I can get 1/2 x
> >>> wavelength spacing in a linear fashion. Possibly go higher in
> >>> frequency to get a better z resolution.
> >>> o use a dedicated ADC with 8 transducers, rather than 4.  Get
> >>> something with a faster sampling rate too.
> >>> o remake the hardware :(
> >>> The hardest thing I see is sourcing the peizoceramics from somewhere.
> >>> Does anyone know of where I can get any cheaply online?  Self enclosed
> >>> transducers would be ideal, but I would be willing to mess with the
> >>> naked ceramics myself if I had too.
> >> I know PZT vendors but our stuff is always full custom volume
> >> production. IOW they dice, mount, backfill to our specs. It's all in the
> >> MHz range and I am not too familiar with 40kHz stuff. If it is the usual
> >> thickness excitation you could buy a bunch of cheap transducers, disect
> >> them and ten dice them with a diamond blade. Be careful, this is
> >> dangerous. Maybe leave the dicing to professionals who operate older
> >> dicing saws for wafers. They'll balk at first, don't want to contaminate
> >> their machines, so this may require holding a wad of cash in front of
> >> them ;-)
>
> >> If this is on a shoestring budget you might ask around in robotics
> >> forums, see if someone has done it before. They often try to obtain
> >> better directivity for navigational purposes. Just don't get any raw
> >> PZT5H if it's not polarized. Polarization requires a HV source.
>
> >> Oh man, it's 4:00pm and we can't see the sun anymore. Only smoke. <cough>
>
> >> --
> >> Regards, Joerg
>
> >>http://www.analogconsultants.com/
>
> >> "gmail" domain blocked because of excessive spam.
> >> Use another domain or send PM.
>
> > Holy smokes!
> > Thanks for the thoughts, I would definitely not be able to do the
> > polarisation myself.  And like you said, these things are usually
> > bought it pretty big numbers....
> > But what I could do is try and dismantle one of these transducers I
> > have, maybe even cut a few down a little bit and see how they
> > perform.  Its not ideal, but it could work.
>
> Be very careful with eye protection, venting and stuff. And you can't do
> it dry, we always used wet saws.
>
> > The only other option that i have been persuing is using 20kHz (or
> > even less).  That means 1 wavelength at 17mm and Ive found some
> > electret microphones transducers that measure 4mm wide so I would be
> > able to get half wavelength there.
>
> Keep in mind that most animals will go crazy at that frequency. Whenever
> I have some ferrite going off on a sub-harmonic the shepherd leaves the
> room and gives me "the looks". The rottie is a lot less sensitive, just
> snores through it.
>
> > By the way I presume that you are working underwater since at 1MHz
> > there's a wavelength of 0.3mm.  A tad small.
>
> Yes, we deal with very small wavelengths. Mostly human body ultrasound.
>
> --
> Regards, Joerg
>
> http://www.analogconsultants.com/
>
> "gmail" domain blocked because of excessive spam.
> Use another domain or send PM.

Joerg, Well I was actually talking about the transducer unit, not the
ceramic itself.  I thought if I could dismantle the outer shell, it
may shave a few mm off.  I would have thought the ceramic would be too
brittle to cut anyway.

Frank, yeah I'm the original poster.  Firstly im in the UK.  Secondly
I am in air and thirdly 1" is far too large.  Im looking for sub 5 mm,
so less than about 1/4".  Small I know.  Good idea about the maths, I
might have to look into that.  The Speed of sound in air is about 342
m/s, the wavelength at 40 kHz is about 8.5mm.

That is cheap though, I think I got mine when they were selling the ex
RHOS non-compliant parts off.  Picked them up for about &#4294967295;1 each.

Thanks guys.

Phil

Phil Winder wrote:
> On Jul 9, 11:55 pm, Joerg <notthisjoerg...@removethispacbell.net>
> wrote:
>> Phil Winder wrote:
>>
>> [...]
>>
>>> Hi all,
>>> I just though I would update you on what I have found sine you all
>>> took the time to help me.
>>> I have implemented a new microcontroller that has simultaneous
>>> sampling and a slightly higher sampling rate.  I could then
>>> interpolate the data with pretty good results using a simple padding +
>>> band pass filtering technique.  The higher the SNR the better it
>>> worked.
>>> However, I have hit a great big wall.  It all boils down to the fact
>>> that I have used 2 rows of transducers to make the spacing 1
>>> wavelength.
>> If it's any consolation, we have all hit that wall. One wavelength is a
>> bit coarse.
>>
>>
>>
>>> For the following results, Consider the situation where x is the
>>> horizontal plane, y is the vertical plane and z is the distance
>>> between the source and the target.  If the target is slightly elevated
>>> in the y plane, the top and bottommost transducers would receive an
>>> echo at different times.  Furthermore, due to multipath dispersion I
>>> am also receiving further echoes from different y directions.  So to
>>> counteract this, I would have to scan not only in the x plane, but in
>>> the y plane too, and this was accomplished by summing all of the
>>> results in the y direction to produce a plot of the targets in the x
>>> plane.  However, by delaying the signals in the y plane, the x plane
>>> in some situations became erroneous.  It looks like I am getting some
>>> sort of aliasing in the x plane.  I think that this is because of
>>> instead of having a beam pattern from 4 transducers, I am getting 2 x
>>> 2 transducer patterns, so not only do I now have a very very wide beam
>>> width, I will have some nasty sidelobes too (since if you just
>>> consider the 2 transducers, the spacing is 2 x wavelength.)
>>> On the up side, the hardware side of it works great!
>> At least now you are getting a good feel on how much HW performance you
>> need. Might want ot try a real (external) ADC at some point.
>>
>>> So all around, this was pretty much a disaster, and I am not looking
>>> forward to remaking all of the hardware.  So for beta 2 I will need:
>>> o to source some smaller transducers so that I can get 1/2 x
>>> wavelength spacing in a linear fashion. Possibly go higher in
>>> frequency to get a better z resolution.
>>> o use a dedicated ADC with 8 transducers, rather than 4.  Get
>>> something with a faster sampling rate too.
>>> o remake the hardware :(
>>> The hardest thing I see is sourcing the peizoceramics from somewhere.
>>> Does anyone know of where I can get any cheaply online?  Self enclosed
>>> transducers would be ideal, but I would be willing to mess with the
>>> naked ceramics myself if I had too.
>> I know PZT vendors but our stuff is always full custom volume
>> production. IOW they dice, mount, backfill to our specs. It's all in the
>> MHz range and I am not too familiar with 40kHz stuff. If it is the usual
>> thickness excitation you could buy a bunch of cheap transducers, disect
>> them and ten dice them with a diamond blade. Be careful, this is
>> dangerous. Maybe leave the dicing to professionals who operate older
>> dicing saws for wafers. They'll balk at first, don't want to contaminate
>> their machines, so this may require holding a wad of cash in front of
>> them ;-)
>>
>> If this is on a shoestring budget you might ask around in robotics
>> forums, see if someone has done it before. They often try to obtain
>> better directivity for navigational purposes. Just don't get any raw
>> PZT5H if it's not polarized. Polarization requires a HV source.
>>
>> Oh man, it's 4:00pm and we can't see the sun anymore. Only smoke. <cough>
>>
>> --
>> Regards, Joerg
>>
>> http://www.analogconsultants.com/
>>
>> "gmail" domain blocked because of excessive spam.
>> Use another domain or send PM.
> 
> Holy smokes!
> Thanks for the thoughts, I would definitely not be able to do the
> polarisation myself.  And like you said, these things are usually
> bought it pretty big numbers....
> But what I could do is try and dismantle one of these transducers I
> have, maybe even cut a few down a little bit and see how they
> perform.  Its not ideal, but it could work.
> 

Be very careful with eye protection, venting and stuff. And you can't do 
it dry, we always used wet saws.


> The only other option that i have been persuing is using 20kHz (or
> even less).  That means 1 wavelength at 17mm and Ive found some
> electret microphones transducers that measure 4mm wide so I would be
> able to get half wavelength there.
> 

Keep in mind that most animals will go crazy at that frequency. Whenever 
I have some ferrite going off on a sub-harmonic the shepherd leaves the 
room and gives me "the looks". The rottie is a lot less sensitive, just 
snores through it.


> By the way I presume that you are working underwater since at 1MHz
> there's a wavelength of 0.3mm.  A tad small.
> 

Yes, we deal with very small wavelengths. Mostly human body ultrasound.

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Thu, 10 Jul 2008 01:36:11 -0700 (PDT), Phil Winder <philipwinder@googlemail.com> wrote:
> On Jul 9, 11:55 pm, Joerg <notthisjoerg...@removethispacbell.net>
> wrote:
>> Phil Winder wrote:
--snip--
>> > I have implemented a new microcontroller that has simultaneous
>> > sampling and a slightly higher sampling rate.  I could then
>> > interpolate the data with pretty good results using a simple padding +
>> > band pass filtering technique.  The higher the SNR the better it
>> > worked.
>> > However, I have hit a great big wall.  It all boils down to the fact
>> > that I have used 2 rows of transducers to make the spacing 1
>> > wavelength.
--snip--
>> > The hardest thing I see is sourcing the peizoceramics from somewhere.
>> > Does anyone know of where I can get any cheaply online?  Self enclosed
>> > transducers would be ideal, but I would be willing to mess with the
>> > naked ceramics myself if I had too.

Phil,

Assuming you're the original poster (attributions sometimes get lost
in the clipping), could you use something like these:

  All Electronics
  www.allelectronics.com
  XDR-24 Matsushita #0D24K2 Ultrasonic Transducer
  0.95"dia x 0.38"
  $1.25, or 10/$10

I _think_ these are 24KHz rather than 40KHz, and I've forgotten the
speed of sound in water so I don't know how 1" compares to that
particular wavelength... but they _are_ cheap. How about a 6x6 array
for $36? <grin!>

As to the wavelength-dependent spacing, is there some mathematical
way to resolve the ambiguities and get useful results from multiple
transducers located at more-than-wavelength displacements?


Frank McKenney
--
    The world is divided into two groups of people: Those to whom
    "No user serviceable parts inside" is a warning, and those to
     whom it is an open challenge and provocation!
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)

On Jul 9, 11:55 pm, Joerg <notthisjoerg...@removethispacbell.net>
wrote:
> Phil Winder wrote:
>
> [...]
>
> > Hi all,
> > I just though I would update you on what I have found sine you all
> > took the time to help me.
> > I have implemented a new microcontroller that has simultaneous
> > sampling and a slightly higher sampling rate.  I could then
> > interpolate the data with pretty good results using a simple padding +
> > band pass filtering technique.  The higher the SNR the better it
> > worked.
> > However, I have hit a great big wall.  It all boils down to the fact
> > that I have used 2 rows of transducers to make the spacing 1
> > wavelength.
>
> If it's any consolation, we have all hit that wall. One wavelength is a
> bit coarse.
>
>
>
> > For the following results, Consider the situation where x is the
> > horizontal plane, y is the vertical plane and z is the distance
> > between the source and the target.  If the target is slightly elevated
> > in the y plane, the top and bottommost transducers would receive an
> > echo at different times.  Furthermore, due to multipath dispersion I
> > am also receiving further echoes from different y directions.  So to
> > counteract this, I would have to scan not only in the x plane, but in
> > the y plane too, and this was accomplished by summing all of the
> > results in the y direction to produce a plot of the targets in the x
> > plane.  However, by delaying the signals in the y plane, the x plane
> > in some situations became erroneous.  It looks like I am getting some
> > sort of aliasing in the x plane.  I think that this is because of
> > instead of having a beam pattern from 4 transducers, I am getting 2 x
> > 2 transducer patterns, so not only do I now have a very very wide beam
> > width, I will have some nasty sidelobes too (since if you just
> > consider the 2 transducers, the spacing is 2 x wavelength.)
>
> > On the up side, the hardware side of it works great!
>
> At least now you are getting a good feel on how much HW performance you
> need. Might want ot try a real (external) ADC at some point.
>
> > So all around, this was pretty much a disaster, and I am not looking
> > forward to remaking all of the hardware.  So for beta 2 I will need:
> > o to source some smaller transducers so that I can get 1/2 x
> > wavelength spacing in a linear fashion. Possibly go higher in
> > frequency to get a better z resolution.
> > o use a dedicated ADC with 8 transducers, rather than 4.  Get
> > something with a faster sampling rate too.
> > o remake the hardware :(
>
> > The hardest thing I see is sourcing the peizoceramics from somewhere.
> > Does anyone know of where I can get any cheaply online?  Self enclosed
> > transducers would be ideal, but I would be willing to mess with the
> > naked ceramics myself if I had too.
>
> I know PZT vendors but our stuff is always full custom volume
> production. IOW they dice, mount, backfill to our specs. It's all in the
> MHz range and I am not too familiar with 40kHz stuff. If it is the usual
> thickness excitation you could buy a bunch of cheap transducers, disect
> them and ten dice them with a diamond blade. Be careful, this is
> dangerous. Maybe leave the dicing to professionals who operate older
> dicing saws for wafers. They'll balk at first, don't want to contaminate
> their machines, so this may require holding a wad of cash in front of
> them ;-)
>
> If this is on a shoestring budget you might ask around in robotics
> forums, see if someone has done it before. They often try to obtain
> better directivity for navigational purposes. Just don't get any raw
> PZT5H if it's not polarized. Polarization requires a HV source.
>
> Oh man, it's 4:00pm and we can't see the sun anymore. Only smoke. <cough>
>
> --
> Regards, Joerg
>
> http://www.analogconsultants.com/
>
> "gmail" domain blocked because of excessive spam.
> Use another domain or send PM.

Holy smokes!
Thanks for the thoughts, I would definitely not be able to do the
polarisation myself.  And like you said, these things are usually
bought it pretty big numbers....
But what I could do is try and dismantle one of these transducers I
have, maybe even cut a few down a little bit and see how they
perform.  Its not ideal, but it could work.

The only other option that i have been persuing is using 20kHz (or
even less).  That means 1 wavelength at 17mm and Ive found some
electret microphones transducers that measure 4mm wide so I would be
able to get half wavelength there.

By the way I presume that you are working underwater since at 1MHz
there's a wavelength of 0.3mm.  A tad small.

Best regards,
Phil

Phil Winder wrote:

[...]

> Hi all,
> I just though I would update you on what I have found sine you all
> took the time to help me.
> I have implemented a new microcontroller that has simultaneous
> sampling and a slightly higher sampling rate.  I could then
> interpolate the data with pretty good results using a simple padding +
> band pass filtering technique.  The higher the SNR the better it
> worked.
> However, I have hit a great big wall.  It all boils down to the fact
> that I have used 2 rows of transducers to make the spacing 1
> wavelength.
> 

If it's any consolation, we have all hit that wall. One wavelength is a 
bit coarse.


> For the following results, Consider the situation where x is the
> horizontal plane, y is the vertical plane and z is the distance
> between the source and the target.  If the target is slightly elevated
> in the y plane, the top and bottommost transducers would receive an
> echo at different times.  Furthermore, due to multipath dispersion I
> am also receiving further echoes from different y directions.  So to
> counteract this, I would have to scan not only in the x plane, but in
> the y plane too, and this was accomplished by summing all of the
> results in the y direction to produce a plot of the targets in the x
> plane.  However, by delaying the signals in the y plane, the x plane
> in some situations became erroneous.  It looks like I am getting some
> sort of aliasing in the x plane.  I think that this is because of
> instead of having a beam pattern from 4 transducers, I am getting 2 x
> 2 transducer patterns, so not only do I now have a very very wide beam
> width, I will have some nasty sidelobes too (since if you just
> consider the 2 transducers, the spacing is 2 x wavelength.)
> 
> On the up side, the hardware side of it works great!
> 

At least now you are getting a good feel on how much HW performance you 
need. Might want ot try a real (external) ADC at some point.


> So all around, this was pretty much a disaster, and I am not looking
> forward to remaking all of the hardware.  So for beta 2 I will need:
> o to source some smaller transducers so that I can get 1/2 x
> wavelength spacing in a linear fashion. Possibly go higher in
> frequency to get a better z resolution.
> o use a dedicated ADC with 8 transducers, rather than 4.  Get
> something with a faster sampling rate too.
> o remake the hardware :(
> 
> The hardest thing I see is sourcing the peizoceramics from somewhere.
> Does anyone know of where I can get any cheaply online?  Self enclosed
> transducers would be ideal, but I would be willing to mess with the
> naked ceramics myself if I had too.
> 

I know PZT vendors but our stuff is always full custom volume 
production. IOW they dice, mount, backfill to our specs. It's all in the 
MHz range and I am not too familiar with 40kHz stuff. If it is the usual 
thickness excitation you could buy a bunch of cheap transducers, disect 
them and ten dice them with a diamond blade. Be careful, this is 
dangerous. Maybe leave the dicing to professionals who operate older 
dicing saws for wafers. They'll balk at first, don't want to contaminate 
their machines, so this may require holding a wad of cash in front of 
them ;-)

If this is on a shoestring budget you might ask around in robotics 
forums, see if someone has done it before. They often try to obtain 
better directivity for navigational purposes. Just don't get any raw 
PZT5H if it's not polarized. Polarization requires a HV source.

Oh man, it's 4:00pm and we can't see the sun anymore. Only smoke. <cough>

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Jun 27, 6:40 pm, Joerg <notthisjoerg...@removethispacbell.net>
wrote:
> Phil Winder wrote:
> > On Jun 27, 3:05 am, "Fred Marshall" <fmarshallx@remove_the_x.acm.org>
> > wrote:
> >> "Phil Winder" <philipwin...@googlemail.com> wrote in message
>
> >>news:21ae1e6d-1e0c-42e1-a6d3-32a7c510e80c@e39g2000hsf.googlegroups.com...
>
> >> Phil,
>
> >> It's not quite clear to me what you're trying to accomplish by steering the
> >> receive beam.  It would be nice to know.
>
> >> As has been pointed out, 1 wavelength spacing is problematic to a degree
> >> because the beam pattern for omni elements would repeat every 90 degrees.
> >> If the elements aren't omni then the situation is somewhat better.
>
> >> Staggering the elements puts two elements behind the others.  That's a
> >> built-in delay.  How much is it?  It means the broadside beam may not be the
> >> main lobe unless the staggered distance is also 1 wavelength or unless
> >> there's some delay associated with summing the forward elements.  It's
> >> surely a more complicated arrangement than a line array.
>
> >> Have you computed a theoretical beam pattern?  If you assume omni elements
> >> it's easiest to do and then you can either calculate or just "adjust" the
> >> result for the element beam patterns.
>
> >> Fred
>
> > @ Joerg: Ahh, got you.  You mean do more than one transmit and receive
> > cycle, but add a slight delay to the receive on the second and
> > subsequent receives. Thanks.
>
> Yep, and adding delay to the transmit pulses is often easier than
> sloshing the ADC clock around. Especially if it ain't a flash converter.
>
> > @ Fred: I just fancied having a go thats all!  I did think about
> > mounting a single rx/tx onto a servo/stepper motor, but I decided that
> > it wasn't very elegant.  Plus I was interested in beamforming, so I
> > gave it a shot.  Eventually I would like to mount it onto a robot
> > possibly, or maybe just use it as a real time show-off piece!
>
> > The elements are not behind each other, they are stacked on top of
> > each other.  If looking directly at the array, the x spacing is 3 x 1
> > wavelength and the y spacing is 1 x 1 wavelength.  So the patter looks
> > like the pattern on a football (if they were circular pieces of
> > leather!). Or like a parallelogram filled with 4 circular transducers.
> > Ooh, forgot I had some images on the web! (http://www.philwinder.com/uploads/2008/04/img_0001.JPG
> > orhttp://www.philwinder.com/wordpress/2008/04/25/phased-array-pcb-v01-f...
> > )
>
> That's too much spacing for good beamforming.
>
> > I have calculated the beam pattern for a linear array, but not for
> > this stacked arrangement.  I probably should, but intuitively I
> > thought that the x spacing was conserved, so it shouldn't be a problem
> > unless the target is much lower or higher than the transmitters.  What
> > I should do really is scan not only the 4 X transducers, but the 2 Y
> > transducers too.  But for now I am making sure that they are level.
>
> --
> Regards, Joerg
>
> http://www.analogconsultants.com/
>
> "gmail" domain blocked because of excessive spam.
> Use another domain or send PM.

Hi all,
I just though I would update you on what I have found sine you all
took the time to help me.
I have implemented a new microcontroller that has simultaneous
sampling and a slightly higher sampling rate.  I could then
interpolate the data with pretty good results using a simple padding +
band pass filtering technique.  The higher the SNR the better it
worked.
However, I have hit a great big wall.  It all boils down to the fact
that I have used 2 rows of transducers to make the spacing 1
wavelength.

For the following results, Consider the situation where x is the
horizontal plane, y is the vertical plane and z is the distance
between the source and the target.  If the target is slightly elevated
in the y plane, the top and bottommost transducers would receive an
echo at different times.  Furthermore, due to multipath dispersion I
am also receiving further echoes from different y directions.  So to
counteract this, I would have to scan not only in the x plane, but in
the y plane too, and this was accomplished by summing all of the
results in the y direction to produce a plot of the targets in the x
plane.  However, by delaying the signals in the y plane, the x plane
in some situations became erroneous.  It looks like I am getting some
sort of aliasing in the x plane.  I think that this is because of
instead of having a beam pattern from 4 transducers, I am getting 2 x
2 transducer patterns, so not only do I now have a very very wide beam
width, I will have some nasty sidelobes too (since if you just
consider the 2 transducers, the spacing is 2 x wavelength.)

On the up side, the hardware side of it works great!

So all around, this was pretty much a disaster, and I am not looking
forward to remaking all of the hardware.  So for beta 2 I will need:
o to source some smaller transducers so that I can get 1/2 x
wavelength spacing in a linear fashion. Possibly go higher in
frequency to get a better z resolution.
o use a dedicated ADC with 8 transducers, rather than 4.  Get
something with a faster sampling rate too.
o remake the hardware :(

The hardest thing I see is sourcing the peizoceramics from somewhere.
Does anyone know of where I can get any cheaply online?  Self enclosed
transducers would be ideal, but I would be willing to mess with the
naked ceramics myself if I had too.

Thanks,
Phil Winder

Phil Winder wrote:
> On Jun 27, 3:05 am, "Fred Marshall" <fmarshallx@remove_the_x.acm.org>
> wrote:
>> "Phil Winder" <philipwin...@googlemail.com> wrote in message
>>
>> news:21ae1e6d-1e0c-42e1-a6d3-32a7c510e80c@e39g2000hsf.googlegroups.com...
>>
>> Phil,
>>
>> It's not quite clear to me what you're trying to accomplish by steering the
>> receive beam.  It would be nice to know.
>>
>> As has been pointed out, 1 wavelength spacing is problematic to a degree
>> because the beam pattern for omni elements would repeat every 90 degrees.
>> If the elements aren't omni then the situation is somewhat better.
>>
>> Staggering the elements puts two elements behind the others.  That's a
>> built-in delay.  How much is it?  It means the broadside beam may not be the
>> main lobe unless the staggered distance is also 1 wavelength or unless
>> there's some delay associated with summing the forward elements.  It's
>> surely a more complicated arrangement than a line array.
>>
>> Have you computed a theoretical beam pattern?  If you assume omni elements
>> it's easiest to do and then you can either calculate or just "adjust" the
>> result for the element beam patterns.
>>
>> Fred
> 
> @ Joerg: Ahh, got you.  You mean do more than one transmit and receive
> cycle, but add a slight delay to the receive on the second and
> subsequent receives. Thanks.
> 

Yep, and adding delay to the transmit pulses is often easier than 
sloshing the ADC clock around. Especially if it ain't a flash converter.


> @ Fred: I just fancied having a go thats all!  I did think about
> mounting a single rx/tx onto a servo/stepper motor, but I decided that
> it wasn't very elegant.  Plus I was interested in beamforming, so I
> gave it a shot.  Eventually I would like to mount it onto a robot
> possibly, or maybe just use it as a real time show-off piece!
> 
> The elements are not behind each other, they are stacked on top of
> each other.  If looking directly at the array, the x spacing is 3 x 1
> wavelength and the y spacing is 1 x 1 wavelength.  So the patter looks
> like the pattern on a football (if they were circular pieces of
> leather!). Or like a parallelogram filled with 4 circular transducers.
> Ooh, forgot I had some images on the web! ( http://www.philwinder.com/uploads/2008/04/img_0001.JPG
> or http://www.philwinder.com/wordpress/2008/04/25/phased-array-pcb-v01-finished/
> )
> 

That's too much spacing for good beamforming.


> I have calculated the beam pattern for a linear array, but not for
> this stacked arrangement.  I probably should, but intuitively I
> thought that the x spacing was conserved, so it shouldn't be a problem
> unless the target is much lower or higher than the transmitters.  What
> I should do really is scan not only the 4 X transducers, but the 2 Y
> transducers too.  But for now I am making sure that they are level.
> 

-- 
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

On Jun 27, 3:05 am, "Fred Marshall" <fmarshallx@remove_the_x.acm.org>
wrote:
> "Phil Winder" <philipwin...@googlemail.com> wrote in message
>
> news:21ae1e6d-1e0c-42e1-a6d3-32a7c510e80c@e39g2000hsf.googlegroups.com...
>
> Phil,
>
> It's not quite clear to me what you're trying to accomplish by steering the
> receive beam.  It would be nice to know.
>
> As has been pointed out, 1 wavelength spacing is problematic to a degree
> because the beam pattern for omni elements would repeat every 90 degrees.
> If the elements aren't omni then the situation is somewhat better.
>
> Staggering the elements puts two elements behind the others.  That's a
> built-in delay.  How much is it?  It means the broadside beam may not be the
> main lobe unless the staggered distance is also 1 wavelength or unless
> there's some delay associated with summing the forward elements.  It's
> surely a more complicated arrangement than a line array.
>
> Have you computed a theoretical beam pattern?  If you assume omni elements
> it's easiest to do and then you can either calculate or just "adjust" the
> result for the element beam patterns.
>
> Fred

@ Joerg: Ahh, got you.  You mean do more than one transmit and receive
cycle, but add a slight delay to the receive on the second and
subsequent receives. Thanks.

@ Fred: I just fancied having a go thats all!  I did think about
mounting a single rx/tx onto a servo/stepper motor, but I decided that
it wasn't very elegant.  Plus I was interested in beamforming, so I
gave it a shot.  Eventually I would like to mount it onto a robot
possibly, or maybe just use it as a real time show-off piece!

The elements are not behind each other, they are stacked on top of
each other.  If looking directly at the array, the x spacing is 3 x 1
wavelength and the y spacing is 1 x 1 wavelength.  So the patter looks
like the pattern on a football (if they were circular pieces of
leather!). Or like a parallelogram filled with 4 circular transducers.
Ooh, forgot I had some images on the web! ( http://www.philwinder.com/uploads/2008/04/img_0001.JPG
or http://www.philwinder.com/wordpress/2008/04/25/phased-array-pcb-v01-finished/
)

I have calculated the beam pattern for a linear array, but not for
this stacked arrangement.  I probably should, but intuitively I
thought that the x spacing was conserved, so it shouldn't be a problem
unless the target is much lower or higher than the transmitters.  What
I should do really is scan not only the 4 X transducers, but the 2 Y
transducers too.  But for now I am making sure that they are level.

Thanks,
Phil

"Phil Winder" <philipwinder@googlemail.com> wrote in message 
news:21ae1e6d-1e0c-42e1-a6d3-32a7c510e80c@e39g2000hsf.googlegroups.com...

Phil,

It's not quite clear to me what you're trying to accomplish by steering the 
receive beam.  It would be nice to know.

As has been pointed out, 1 wavelength spacing is problematic to a degree 
because the beam pattern for omni elements would repeat every 90 degrees. 
If the elements aren't omni then the situation is somewhat better.

Staggering the elements puts two elements behind the others.  That's a 
built-in delay.  How much is it?  It means the broadside beam may not be the 
main lobe unless the staggered distance is also 1 wavelength or unless 
there's some delay associated with summing the forward elements.  It's 
surely a more complicated arrangement than a line array.

Have you computed a theoretical beam pattern?  If you assume omni elements 
it's easiest to do and then you can either calculate or just "adjust" the 
result for the element beam patterns.

Fred