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)
Real Life Beamforming with substandard arrays. Need help forming some sort of solution.
Started by ●June 25, 2008
Reply by ●July 10, 20082008-07-10
Reply by ●July 10, 20082008-07-10
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.
Reply by ●July 11, 20082008-07-11
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 �1 each. Thanks guys. Phil
Reply by ●July 12, 20082008-07-12
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.
