jlarkin@highlandsniptechnology.com wrote:
> On Sat, 17 Jul 2021 09:34:38 -0700 (PDT), Lasse Langwadt Christensen
> <langwadt@fonz.dk> wrote:
>
>> lørdag den 17. juli 2021 kl. 18.31.44 UTC+2 skrev jla...@highlandsniptechnology.com:
>>> On Sat, 17 Jul 2021 12:22:48 -0400, Phil Hobbs
>>> <pcdhSpamM...@electrooptical.net> wrote:
>>>
>>>> George Herold wrote:
>>>>> On Friday, July 16, 2021 at 1:25:54 PM UTC-4, Phil Hobbs wrote:
>>>>>> So we have this application that requires a circuit to maintain
>>>>>> intimate contact with a curved biological surface, namely the
>>>>>> abdomen of a pregnant woman.
>>>>>>
>>>>>> Flex is the obvious thing, but since the curvature is relatively
>>>>>> gentle, we're thinking of using thin FR4. We can get a 4-layer
>>>>>> board with overall thickness of 0.4 mm. The board needs to be about
>>>>>> 20 x 100 mm, and we can make it pretty spidery--each of the
>>>>>> individual detector/TIA pairs can be on its own paddle with a long
>>>>>> skinny "cable" attaching it to one end of the board.
>>>>>>
>>>>>> Have any of you lot tried something like that?
>>>>>>
>>>>> Nope, but a crazy idea, can you cut some slots and such in FR4 such
>>>>> as to make it more bendable at two or three places? Do you need
>>>>> bendiness on more than one axis?
>>>>
>>>> The paddles where the components go can be stiff because they're quite
>>>> small--a photodiode (5 mm or 14 mm), an SC70 op amp, a SOT23 bootstrap
>>>> FET, two resistors and a couple of bypass caps. It's mostly the
>>>> survival of the 'cable' parts that I'm concerned about. If necessary I
>>>> can probably use wires and leave the FR4 to do the gross mechanical
>>>> locating.
>>>>
>>>> The whole thing is going to be potted in black silicone
>>>> rubber (with the PDs visible, of course) because I'm looking at a path
>>>> loss of > 200 dB electrical--with an amp of LED drive current, we expect
>>>> to get tens of picoamps of signal photocurrent, and less with a
>>>> dark-skinned mom.
>>>>
>>>> Melanin absorption causes overestimation of SpO_2, by as much as 8% @ 2
>>>> sigma at low SpO_2 values, right where it has the worst effects. The
>>>> effect mostly disappears at high SpO_2.
>>>>
>>>> We're going to be using a three-wavelength system to avoid that problem,
>>>> but even without that systematic shift, the absorption still hits the
>>>> SNR pretty badly.
>>>>
>>>> Cheers
>>>>
>>>> Phil Hobbs
>>> How about a thing like a giant spider with legs that droop down onto
>>> mom's belly? Make it look more friendly, of course. Turtle or rabbit
>>> or something.
>>> --
>>
>> octopus with sucking cups and everythign
>
> Suction cups aren't a bad idea at all.
>
> Given a super-flexy, maybe silicone insulated, multiwire cable, I
> wonder how much vacuum could slip in between the wires. Or make a
> custom thing, a silicone tube with wires loosely packed inside.

We need the black silicone part to get a good light-tight fit.

Doesn't take much light leakage to blow this measurement right out of
the water. Typical path loss is ~200-240 dB electrical.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On Sat, 17 Jul 2021 16:48:40 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>jlarkin@highlandsniptechnology.com wrote:
>> On Sat, 17 Jul 2021 09:34:38 -0700 (PDT), Lasse Langwadt Christensen
>> <langwadt@fonz.dk> wrote:
>>
>>> lørdag den 17. juli 2021 kl. 18.31.44 UTC+2 skrev jla...@highlandsniptechnology.com:
>>>> On Sat, 17 Jul 2021 12:22:48 -0400, Phil Hobbs
>>>> <pcdhSpamM...@electrooptical.net> wrote:
>>>>
>>>>> George Herold wrote:
>>>>>> On Friday, July 16, 2021 at 1:25:54 PM UTC-4, Phil Hobbs wrote:
>>>>>>> So we have this application that requires a circuit to maintain
>>>>>>> intimate contact with a curved biological surface, namely the
>>>>>>> abdomen of a pregnant woman.
>>>>>>>
>>>>>>> Flex is the obvious thing, but since the curvature is relatively
>>>>>>> gentle, we're thinking of using thin FR4. We can get a 4-layer
>>>>>>> board with overall thickness of 0.4 mm. The board needs to be about
>>>>>>> 20 x 100 mm, and we can make it pretty spidery--each of the
>>>>>>> individual detector/TIA pairs can be on its own paddle with a long
>>>>>>> skinny "cable" attaching it to one end of the board.
>>>>>>>
>>>>>>> Have any of you lot tried something like that?
>>>>>>>
>>>>>> Nope, but a crazy idea, can you cut some slots and such in FR4 such
>>>>>> as to make it more bendable at two or three places? Do you need
>>>>>> bendiness on more than one axis?
>>>>>
>>>>> The paddles where the components go can be stiff because they're quite
>>>>> small--a photodiode (5 mm or 14 mm), an SC70 op amp, a SOT23 bootstrap
>>>>> FET, two resistors and a couple of bypass caps. It's mostly the
>>>>> survival of the 'cable' parts that I'm concerned about. If necessary I
>>>>> can probably use wires and leave the FR4 to do the gross mechanical
>>>>> locating.
>>>>>
>>>>> The whole thing is going to be potted in black silicone
>>>>> rubber (with the PDs visible, of course) because I'm looking at a path
>>>>> loss of > 200 dB electrical--with an amp of LED drive current, we expect
>>>>> to get tens of picoamps of signal photocurrent, and less with a
>>>>> dark-skinned mom.
>>>>>
>>>>> Melanin absorption causes overestimation of SpO_2, by as much as 8% @ 2
>>>>> sigma at low SpO_2 values, right where it has the worst effects. The
>>>>> effect mostly disappears at high SpO_2.
>>>>>
>>>>> We're going to be using a three-wavelength system to avoid that problem,
>>>>> but even without that systematic shift, the absorption still hits the
>>>>> SNR pretty badly.
>>>>>
>>>>> Cheers
>>>>>
>>>>> Phil Hobbs
>>>> How about a thing like a giant spider with legs that droop down onto
>>>> mom's belly? Make it look more friendly, of course. Turtle or rabbit
>>>> or something.
>>>> --
>>>
>>> octopus with sucking cups and everythign
>>
>> Suction cups aren't a bad idea at all.
>>
>> Given a super-flexy, maybe silicone insulated, multiwire cable, I
>> wonder how much vacuum could slip in between the wires. Or make a
>> custom thing, a silicone tube with wires loosely packed inside.
>
>We need the black silicone part to get a good light-tight fit.
>
>Doesn't take much light leakage to blow this measurement right out of
>the water. Typical path loss is ~200-240 dB electrical.
>
>Cheers
>
>Phil Hobbs

Seems like a suction puck would be ideal. Of course, mom's skin
diffuses light.

--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.

jlarkin@highlandsniptechnology.com wrote:
> On Sat, 17 Jul 2021 16:48:40 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> jlarkin@highlandsniptechnology.com wrote:
>>> On Sat, 17 Jul 2021 09:34:38 -0700 (PDT), Lasse Langwadt Christensen
>>> <langwadt@fonz.dk> wrote:
>>>
>>>> lørdag den 17. juli 2021 kl. 18.31.44 UTC+2 skrev jla...@highlandsniptechnology.com:
>>>>> On Sat, 17 Jul 2021 12:22:48 -0400, Phil Hobbs
>>>>> <pcdhSpamM...@electrooptical.net> wrote:
>>>>>
>>>>>> George Herold wrote:
>>>>>>> On Friday, July 16, 2021 at 1:25:54 PM UTC-4, Phil Hobbs wrote:
>>>>>>>> So we have this application that requires a circuit to maintain
>>>>>>>> intimate contact with a curved biological surface, namely the
>>>>>>>> abdomen of a pregnant woman.
>>>>>>>>
>>>>>>>> Flex is the obvious thing, but since the curvature is relatively
>>>>>>>> gentle, we're thinking of using thin FR4. We can get a 4-layer
>>>>>>>> board with overall thickness of 0.4 mm. The board needs to be about
>>>>>>>> 20 x 100 mm, and we can make it pretty spidery--each of the
>>>>>>>> individual detector/TIA pairs can be on its own paddle with a long
>>>>>>>> skinny "cable" attaching it to one end of the board.
>>>>>>>>
>>>>>>>> Have any of you lot tried something like that?
>>>>>>>>
>>>>>>> Nope, but a crazy idea, can you cut some slots and such in FR4 such
>>>>>>> as to make it more bendable at two or three places? Do you need
>>>>>>> bendiness on more than one axis?
>>>>>>
>>>>>> The paddles where the components go can be stiff because they're quite
>>>>>> small--a photodiode (5 mm or 14 mm), an SC70 op amp, a SOT23 bootstrap
>>>>>> FET, two resistors and a couple of bypass caps. It's mostly the
>>>>>> survival of the 'cable' parts that I'm concerned about. If necessary I
>>>>>> can probably use wires and leave the FR4 to do the gross mechanical
>>>>>> locating.
>>>>>>
>>>>>> The whole thing is going to be potted in black silicone
>>>>>> rubber (with the PDs visible, of course) because I'm looking at a path
>>>>>> loss of > 200 dB electrical--with an amp of LED drive current, we expect
>>>>>> to get tens of picoamps of signal photocurrent, and less with a
>>>>>> dark-skinned mom.
>>>>>>
>>>>>> Melanin absorption causes overestimation of SpO_2, by as much as 8% @ 2
>>>>>> sigma at low SpO_2 values, right where it has the worst effects. The
>>>>>> effect mostly disappears at high SpO_2.
>>>>>>
>>>>>> We're going to be using a three-wavelength system to avoid that problem,
>>>>>> but even without that systematic shift, the absorption still hits the
>>>>>> SNR pretty badly.
>>>>>>
>>>>>> Cheers
>>>>>>
>>>>>> Phil Hobbs
>>>>> How about a thing like a giant spider with legs that droop down onto
>>>>> mom's belly? Make it look more friendly, of course. Turtle or rabbit
>>>>> or something.
>>>>> --
>>>>
>>>> octopus with sucking cups and everythign
>>>
>>> Suction cups aren't a bad idea at all.
>>>
>>> Given a super-flexy, maybe silicone insulated, multiwire cable, I
>>> wonder how much vacuum could slip in between the wires. Or make a
>>> custom thing, a silicone tube with wires loosely packed inside.
>>
>> We need the black silicone part to get a good light-tight fit.
>>
>> Doesn't take much light leakage to blow this measurement right out of
>> the water. Typical path loss is ~200-240 dB electrical.
>>
>> Cheers
>>
>> Phil Hobbs
>
> Seems like a suction puck would be ideal. Of course, mom's skin
> diffuses light.

Has to fit a very wide range of shapes comfortably though. The idea is
for it to bend under its own weight with no issues. Flex does that OK,
but it's inconvenient to put much circuitry on, as well as being expensive.

It's certainly possible with the FR4 paddle-and-skinny-stem
approach--the issue is how long the FR4 and copper will survive in the
stem part. We'll see!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

On Sat, 17 Jul 2021 16:46:18 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>jlarkin@highlandsniptechnology.com wrote:
>> On Sat, 17 Jul 2021 12:22:48 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> George Herold wrote:
>>>> On Friday, July 16, 2021 at 1:25:54 PM UTC-4, Phil Hobbs wrote:
>>>>> So we have this application that requires a circuit to maintain
>>>>> intimate contact with a curved biological surface, namely the
>>>>> abdomen of a pregnant woman.
>>>>>
>>>>> Flex is the obvious thing, but since the curvature is relatively
>>>>> gentle, we're thinking of using thin FR4. We can get a 4-layer
>>>>> board with overall thickness of 0.4 mm. The board needs to be about
>>>>> 20 x 100 mm, and we can make it pretty spidery--each of the
>>>>> individual detector/TIA pairs can be on its own paddle with a long
>>>>> skinny "cable" attaching it to one end of the board.
>>>>>
>>>>> Have any of you lot tried something like that?
>>>>>
>>>> Nope, but a crazy idea, can you cut some slots and such in FR4 such
>>>> as to make it more bendable at two or three places? Do you need
>>>> bendiness on more than one axis?
>>>
>>> The paddles where the components go can be stiff because they're quite
>>> small--a photodiode (5 mm or 14 mm), an SC70 op amp, a SOT23 bootstrap
>>> FET, two resistors and a couple of bypass caps. It's mostly the
>>> survival of the 'cable' parts that I'm concerned about. If necessary I
>>> can probably use wires and leave the FR4 to do the gross mechanical
>>> locating.
>>>
>>> The whole thing is going to be potted in black silicone
>>> rubber (with the PDs visible, of course) because I'm looking at a path
>>> loss of > 200 dB electrical--with an amp of LED drive current, we expect
>>> to get tens of picoamps of signal photocurrent, and less with a
>>> dark-skinned mom.
>>>
>>> Melanin absorption causes overestimation of SpO_2, by as much as 8% @ 2
>>> sigma at low SpO_2 values, right where it has the worst effects. The
>>> effect mostly disappears at high SpO_2.
>>>
>>> We're going to be using a three-wavelength system to avoid that problem,
>>> but even without that systematic shift, the absorption still hits the
>>> SNR pretty badly.
>
>> How about a thing like a giant spider with legs that droop down onto
>> mom's belly? Make it look more friendly, of course. Turtle or rabbit
>> or something.
>
>Fun possibilities spread out before us. ;)
>
>The idea is to keep it really low-profile, mostly for the mom's comfort.
>
>We're looking at all sorts of ways to improve heat-sinking of the LEDs
>for the same reason. A watt of dissipation in a small area right
>against your skin, insulated by 0.1 W/m/K elastomer, could get old
>pretty fast.

This may sound odd, but this may be a perfect application for water
cooling, using distilled water. A pair of pretty small tubes should
suffice, because of the very large thermal capacity of water. I'd
guess that a one square inch radiator will suffice to reject the heat
to the air.

Joe Gwinn

On Sunday, July 18, 2021 at 2:20:14 AM UTC+10, jla...@highlandsniptechnology.com wrote:
> On Sat, 17 Jul 2021 09:34:26 +0200, Gerhard Hoffmann <dk...@arcor.de>
> wrote:
> >Am 17.07.21 um 04:45 schrieb Phil Hobbs:
> >> Spehro Pefhany wrote:
> >>> On Fri, 16 Jul 2021 21:21:19 -0400, Phil Hobbs
> >>> <pcdhSpamM...@electrooptical.net> wrote:
> >>>
> >>>>
> >>>>
> >>>> 1. Serious 4-layer flex circuit$$
> >>>> 2. Rigid-flex circuit$$$$$
> >>>> 3. Semi-flexible FR4.
> >>>
> >>> There is more than one kind of flex (either as part of rigid-flex or
> >>> alone). If you need to survive dynamic flexing there are rules to
> >>> follow and things to specify or it will die early.
> >>>
> >>
> >> It isn't a printhead application--the bending will be quite gentle and
> >> relatively infrequent.
> >>
> >> Any references for the flex rules?
> >
> >Around 2003, we made these XFP transceivers:
> >
> ><
> >https://www.flickr.com/photos/137684711@N07/51316513581/in/dateposted-public/lightbox/
> > >
> >
> >ROSA and TOSA are attached with a flexible Kapton tape.
> >The metal bar behind the solder location was absolutely
> >necessary to make it work.
> >
> >I don't think that FR4 might work. Epoxy does not like to bend
> >nor does glass fiber around a tight corner. I don't think that
> >Kapton costs too much, they use it in mass market things like
> >printers and there even seem to be pre-fabricated "cables".
> >
> >BTW, these ROSA/TOSA tapes were a major 3D electromagnetics
> >simulation nightmare. Endless HFSS and ADS runs.
> >The hot signals and GND had to flip sides somewhere,
> >at 10 GBPS without damaging the eye diagrams.
> >
> >I had some bad mechanical experience recently with Rogers TMM-6.
> >Bends easily and then breaks suddenly. It feels somehow like a
> >rubber eraser. Then we made a multilayer with TMM6 + FR-4.
> >The board house swapped the sides. The uwave synthesizer and the
> >microstrips ended up on FR-4, the DC stuff on TMM-6. :-((
> >
> We did some boards with mixed lams, microwave for the top layer and
> FR4 for the rest. They were curled like potato chips.

You do need to make the stack symmmetrical. Microwave for the top and bottom layers and FR4 in the middle. The people who made out boards in the late 1980's insisted on that.
> https://www.dropbox.com/s/mw0gka15okd4qgo/Spinner.AVI?dl=0
>
> I'm ordering some fast boards now with Isola called out for the top
> dielectric and FR4 optional for the rest, but with a flatness
> requirement.

Pay an extra layer of Isola on the bottom as well. That way you might get a flat board.

--
Bill Sloman, Sydney

On 18/07/21 01:14, Phil Hobbs wrote:
> It's certainly possible with the FR4 paddle-and-skinny-stem approach--the issue
> is how long the FR4 and copper will survive in the stem part.  We'll see!

Sounds like you might need some self-diagnostics to spot
incipient or intermittent track failures.

On Sat, 17 Jul 2021 20:14:07 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>jlarkin@highlandsniptechnology.com wrote:
>> On Sat, 17 Jul 2021 16:48:40 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> jlarkin@highlandsniptechnology.com wrote:
>>>> On Sat, 17 Jul 2021 09:34:38 -0700 (PDT), Lasse Langwadt Christensen
>>>> <langwadt@fonz.dk> wrote:
>>>>
>>>>> lørdag den 17. juli 2021 kl. 18.31.44 UTC+2 skrev jla...@highlandsniptechnology.com:
>>>>>> On Sat, 17 Jul 2021 12:22:48 -0400, Phil Hobbs
>>>>>> <pcdhSpamM...@electrooptical.net> wrote:
>>>>>>
>>>>>>> George Herold wrote:
>>>>>>>> On Friday, July 16, 2021 at 1:25:54 PM UTC-4, Phil Hobbs wrote:
>>>>>>>>> So we have this application that requires a circuit to maintain
>>>>>>>>> intimate contact with a curved biological surface, namely the
>>>>>>>>> abdomen of a pregnant woman.
>>>>>>>>>
>>>>>>>>> Flex is the obvious thing, but since the curvature is relatively
>>>>>>>>> gentle, we're thinking of using thin FR4. We can get a 4-layer
>>>>>>>>> board with overall thickness of 0.4 mm. The board needs to be about
>>>>>>>>> 20 x 100 mm, and we can make it pretty spidery--each of the
>>>>>>>>> individual detector/TIA pairs can be on its own paddle with a long
>>>>>>>>> skinny "cable" attaching it to one end of the board.
>>>>>>>>>
>>>>>>>>> Have any of you lot tried something like that?
>>>>>>>>>
>>>>>>>> Nope, but a crazy idea, can you cut some slots and such in FR4 such
>>>>>>>> as to make it more bendable at two or three places? Do you need
>>>>>>>> bendiness on more than one axis?
>>>>>>>
>>>>>>> The paddles where the components go can be stiff because they're quite
>>>>>>> small--a photodiode (5 mm or 14 mm), an SC70 op amp, a SOT23 bootstrap
>>>>>>> FET, two resistors and a couple of bypass caps. It's mostly the
>>>>>>> survival of the 'cable' parts that I'm concerned about. If necessary I
>>>>>>> can probably use wires and leave the FR4 to do the gross mechanical
>>>>>>> locating.
>>>>>>>
>>>>>>> The whole thing is going to be potted in black silicone
>>>>>>> rubber (with the PDs visible, of course) because I'm looking at a path
>>>>>>> loss of > 200 dB electrical--with an amp of LED drive current, we expect
>>>>>>> to get tens of picoamps of signal photocurrent, and less with a
>>>>>>> dark-skinned mom.
>>>>>>>
>>>>>>> Melanin absorption causes overestimation of SpO_2, by as much as 8% @ 2
>>>>>>> sigma at low SpO_2 values, right where it has the worst effects. The
>>>>>>> effect mostly disappears at high SpO_2.
>>>>>>>
>>>>>>> We're going to be using a three-wavelength system to avoid that problem,
>>>>>>> but even without that systematic shift, the absorption still hits the
>>>>>>> SNR pretty badly.
>>>>>>>
>>>>>>> Cheers
>>>>>>>
>>>>>>> Phil Hobbs
>>>>>> How about a thing like a giant spider with legs that droop down onto
>>>>>> mom's belly? Make it look more friendly, of course. Turtle or rabbit
>>>>>> or something.
>>>>>> --
>>>>>
>>>>> octopus with sucking cups and everythign
>>>>
>>>> Suction cups aren't a bad idea at all.
>>>>
>>>> Given a super-flexy, maybe silicone insulated, multiwire cable, I
>>>> wonder how much vacuum could slip in between the wires. Or make a
>>>> custom thing, a silicone tube with wires loosely packed inside.
>>>
>>> We need the black silicone part to get a good light-tight fit.
>>>
>>> Doesn't take much light leakage to blow this measurement right out of
>>> the water. Typical path loss is ~200-240 dB electrical.
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> Seems like a suction puck would be ideal. Of course, mom's skin
>> diffuses light.
>
>Has to fit a very wide range of shapes comfortably though. The idea is
>for it to bend under its own weight with no issues. Flex does that OK,
>but it's inconvenient to put much circuitry on, as well as being expensive.
>
>It's certainly possible with the FR4 paddle-and-skinny-stem
>approach--the issue is how long the FR4 and copper will survive in the
>stem part. We'll see!

Print heads did that.

--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.