Wireless module/IC that can take 100°C (212°F)???

[ManCave]

Hi all,

I have a requirement for wireless module or a chip (WiFi, BlueTooth, ...anything really) with the following specifications:

• Must be able to operate at 100°C.
• Should be small as the final design size constrain is about 1" diameter sphere

The module (with some other electronics) will be sealed and immersed in boiling water. I cannot disclose much more details as this is a project for work.

Does anyone know of one? I've searched with no luck!

Any help would be greatly appreciated!

[amyk]

Won't work - the water will attenuate most of the signal. Consider acoustic communication instead.

[Zero999]

Or IR, if there's a direct line of sight to the detector or a surface the signal can reflect off to the sensor.

[Fraser]

If playing with RF, the oscillator stability will be be a challenge as it will normally change frequency with temperature. This could be countered using a receiver with AFC to track the carrier. As others have stated, GHz frequencies and submersion in fluid are not normally good bedfellows. Some simple tests with sample transmitters and receivers in non boiling water will give you an idea of which will and will not work through such a medium. Inductive coupling as used in RFID tags is a possibility if lower frequencies are used.

Also, as has already been stated, light and sound work well for communication through fluids. If using ultrasound you will have the challenge of a transducer that will cope with 100 Degree C surface temperature, and still have a decent operating life.

Many electronic components, IC's and batteries also get a tad upset when running at 100C. You need to consider how long the device will remain submerged in fluid of such a temperature and whether heat shielding in the form of a vacuum dewar is needed. Fire brigade thermal cameras often have thermal absorption layers and liquid filled heat sinks to keep the electronics cool in hot environs. I regret I do not have the technical insight into such techniques to advise you though.

Aurora

[tonyarkles]

The module (with some other electronics) will be sealed and immersed in boiling water. I cannot disclose much more details as this is a project for work.

I'm guessing this is a temperature sensor? Will it be measuring anything else?

[ManCave]

Thank you very much all for the insight.

I did not consider the fact that water absorbs high frequency RF.

The maximum amount of water (fluid) the sensor will be immersed in is up to around 2 litres. The container may not be transparent and the specification of the design dictates non-contact measurement. Therefore laser or IR is not really an option. The receiver is non-wetted hence acoustic is not really an option either.

If you can not get line of sight environment, or can not afford the cost of ultrasonic, then consider lower frequency RF.

Also, high freq/performance RF devices don't like 100C temp, try low freq such as 13.56M or 27.12M. If I were you, I will simply use an oscillator a and gate and a low power RF amp.

RF modulation is, obviously, OOK (on off keying), and base band coding should be done in MCU, you can choose HDB3 or AMI, or so, as you wish.

The range required is short, up to about 1 meter or less. Would this be reasonably low power solution? (transmitting about once per minute)?

If playing with RF, the oscillator stability will be be a challenge as it will normally change frequency with temperature. This could be countered using a receiver with AFC to track the carrier.

I would probably use MCU to temperature compensate.

You need to consider how long the device will remain submerged in fluid of such a temperature and whether heat shielding in the form of a vacuum dewar is needed. Fire brigade thermal cameras often have thermal absorption layers and liquid filled heat sinks to keep the electronics cool in hot environs. I regret I do not have the technical insight into such techniques to advise you though.

That sounds interesting. This seems to add a lot of complexity and cost, however. Also, I would rather not restrict the time the sensor can spend in 100°C fluid. At the moment its only about 30 minutes, however I can see why this could extend in the future.

I'm guessing this is a temperature sensor? Will it be measuring anything else?

Let's say just temperature for now.

[Fraser]

I am a great believer in considering the theoretical limits of RF penetration but also looking for the real world experiences of others. Theory is often a good base line but practice is proof positive of what is possible. Many good antennas have been invented through experimentation rather than a purely theoretical approach. RF is a very unpredictable energy, especially when it comes to materials penetration.

With that in mind I did some Googling on Radio Controlled model submarines. I have always stuck to fixed and rotary wing aircraft but know that the RC submarine chaps have exactly the same issues as your project.....i.e. which frequency is best in water and what range can be expected. The TX and RX positions are reversed in your case but with careful design that should not be a major obstacle.

As already suggested, think low frequencies in the HF bands and not GHz microwave  frequencies 

Take a look here and do your own research on RC submarines 

http://www.rcgroups.com/forums/showthread.php?t=853144

Be aware that I know of no RC electronics that will operate in a 100C environment. As such you would either need to use bespoke transmitters or protect the transmitter from heat in a Vacuum Dewar. RC telemetry products used in the Quadcopters can provide excellent data communications but sadly most (all?) use GHz freqeuncies.

You could set up a water (fluid) filled test tank with a Transmitter antenna waterproofed and submerged in it and driven by an RF signal generator. Monitor the signal level at the desired distance with a sensitive wideband receiver and see which frequencies dos and do not make the distance. A practical experiment may tell you much about the challenges you face with penetration through water or other fluids. Once you know which frequencies are, and are not usable you can begin your research in to available transmitter modules and data rates. In your position I would buy some cheap data modules and see how they behave at 100C by placing them in a domestic Oven set at 100C    They may go bananas, but they may also work, albeit at a frequency different to the spec ! Regarding MCU controlled oscillator correction.... nice idea but if you want to apply the KISS principle, go with AFC in the receiver.

All this take no account of using transmitter frequencies within legal allocations. That is another topic but should be considered if this is to be a commercial product. Short range data links do have approved frequencies such as 433MHz for car key fobs, wireless alrams, telemetry etc. Wireless computer keyboards used to operate at 27MHz HF which may be an option ? It is worth checking your local licence free transmitter regulations if that is a concern for you.

Some food for thought anyway 

Aurora

[mikeselectricstuff]

Induction loop may be an option - maybe using off-the-shelf 125khz RFID coils
 

[ManCave]

Aurora,
Thank you very much for very comprehensive posts! Some great ideas there! I will definitely look into RC subs and see what can be don there as it seems like an ideal option. And thanks for the legal bit as this might be an important consideration in the project!

Mike,
This seems interesting. Do you have experience with these modules? What sort of range could I expect (in the open)?

[LaserSteve]

If the data rate is low enough, an inductive system that is crystal controlled at say 40 to 500  KHz might just work for him.  However this is going to go together with a ceramic or Teflon substrate, silver solder for reliability,  and probably will need to be inductive powered. We've had several threads on trying to find batteries that work at Boiling Water  temperatures. The Military has them, but there is not much of a civilian application, so not readily available...

While its unlikely that boiling water will stay pure for long, very pure water does not impede low frequency (less then 15 Mhz) RF that much. Its only when you have conductive ions in the solution that absorbance becomes a severe problem at low RF.

If he has room for the external coils, and his data rate is low, the same external coil that powers the board can also recover the telemetry.

The rub is finding low leakage transistors for this temperature range.

The "Down Hole" oil well logging people have the high temperature electronics worked out, that is where he needs to look. The caving and spelunking folks have inductive communications very well documented.

The other trick is to use a high RF field to drive the board, and then have the board re-radiate a modulated second harmonic of the excitation frequency. This is used in a lot of exotic environments, such as helicopter rotors, lathe heads, and railroad cars.

A lot of RFID tags are glass encapsulated, I'm not sure if any of those have external modulation though. A few, precious few, of them are programmable.

He's also going to have to learn about glass to metal hermetic seals if any sensor probes need to touch the water.

"Will it float"... :-)

Steve

[mzzj]

If the data rate is low enough, an inductive system that is crystal controlled at say 40 to 500  KHz might just work for him.  However this is going to go together with a ceramic or Teflon substrate, silver solder for reliability,  and probably will need to be inductive powered. We've had several threads on trying to find batteries that work at Boiling Water  temperatures. The Military has them, but there is not much of a civilian application, so not readily available...

And I have recommended also previously Tadiran high temperature lithium batteries. TLH series is specified to +125C operation but regularly used up to 140C and I have seen some used shortly(hours, not days) up to 160 or 180C.
Or Tadiran SL-560 up to 130C specification
http://www.tadiranbatteries.de/pdf/lithium-thionyl-chloride-batteries/SL-560.pdf

[mikeselectricstuff]

Mike,
This seems interesting. Do you have experience with these modules? What sort of range could I expect (in the open)?

Range is of the order of 2x the diameter of the two antenna coils, if roughly co-axial.
Ferrites can be  used to improve a bit.
If orientation is random then it's a bit less predictable.

[Zero999]

If you just want to measure the temperature of some water in a vessel from a distance then why not just monitor the emitted thermal radiation? IR thermometers are widely available.

While its unlikely that boiling water will stay pure for long, very pure water does not impede low frequency (less then 15 Mhz) RF that much. Its only when you have conductive ions in the solution that absorbance becomes a severe problem at low RF.

This is true but there will also be a limit to how fast the ions can move around, which means that above the plasma frequency the ions will stop absorbing and allow the radiation to pass through, hence why salt water is fairly transparent to near IR (800nm) radiation. Unfortunately other modes of absorption probably kick in above the plasma frequency which will no doubt depend on the ionic contaminants and their concentration.

[filssavi]

I know that you have already discarded it but ultrasonic would be pretty though to use in this scenario, if the water is boiling the bubbles of steam vapour rupturing at the liquid/gas interface will make a ton of acoustical noise and you will not be able to hear a thing, maybe filtering a lot can make things work, but I don't think it will be that good anyway

[ManCave]

Hi Guys!

Thank you all again for involvement and valuable advice!!! I've done some research and managed to narrow it down to the standard low MHz RF for the moment as per Aurora's suggestion on RC subs and LaserSteve's mention of low impedance at low MHz frequencies. I was hoping to get some commercial modules as I wanted to avoid building an actual transmitter/receiver circuits from scratch as this is nether my field of expertise nor of the interest. I've done some RF stuff before, but quite a long time ago, so time to refresh I guess .

RFID solutions seem to pose several issues, mainly with the coil size to range ratio. Since I'm limited to under an inch coil size and require range of about 0.5m, it does not seem to  be a viable solution. Also the orientation is random complicating things even more.

If you just want to measure the temperature of some water in a vessel from a distance then why not just monitor the emitted thermal radiation? IR thermometers are widely available.

Unfortunately no line of sight measurements are acceptable in this application, and the sensor has to be immersed in the fluid, but thank you for your idea!

And I have recommended also previously Tadiran high temperature lithium batteries. TLH series is specified to +125C operation but regularly used up to 140C and I have seen some used shortly(hours, not days) up to 160 or 180C. Or Tadiran SL-560 up to 130C specification

Thanks for the recommendation. I have also looked at these previously but unfortunately the smallest they do is 1/2AA which is too big. Do you know any high temp cells of up to 1/2AAAA size or prismatic to fit into about a 1" sphere?

[Fraser]

Wow, a 1" sphere is a pretty small space in which to work, especially at HF frequencies.

A question...... does the sphere have to sink or can it float on the surface of the water with its sensor on its bottom. If it is allowed to float you can have a small monopole antenna sticking out of the top and use 433MHz with ease. The 1" sphere is very small to work within though. You may need to do a revisit on the customers requirements, manage expectations and determine maximum dimensions that can be coped with.

Aurora

[Marco]

RFID antennas are large because they have to transfer energy ... you could try a small solenoid on ferrite.

[Fraser]

An interesting little product found here:

http://embedded-lab.com/blog/?p=5436

Looks versatile and worthy of investigation. I would cook it in an oven at 100C and see how it performs    If it copes.....maybe look at how well ~400MHz copes with a fluid submersed antenna.

Foe examples of fluid RF thermometers you have only to look at wireless swimming pool thermometers. The common designs have the electronics housed on a buoy that floats on the fluids surface and the sensor extends to a suitable depth in the fluid. Keeping the electronics on the surface will reduce the thermal stress and also allow common UHF/SHF telemetry systems to be used. Food for thought ?

Aurora

[Marco]

This thesis has some method for ferrite solenoid based near field communication on page 62, it's only math without experiment though. Cheap experiment to do though. Get two inductors and two caps with a resonance of say 10 kHz, drive one with a function generator and attach a scope to the other ... see what you get.

[ManCave]

A question...... does the sphere have to sink or can it float on the surface of the water with its sensor on its bottom. If it is allowed to float you can have a small monopole antenna sticking out of the top and use 433MHz with ease. The 1" sphere is very small to work within though. You may need to do a revisit on the customers requirements, manage expectations and determine maximum dimensions that can be coped with.

Thanks for the suggestion, It is allowed to float, but the antenna would have to be something like a 1cm length or so max...

This thesis has some method for ferrite solenoid based near field communication on page 62, it's only math without experiment though. Cheap experiment to do though. Get two inductors and two caps with a resonance of say 10 kHz, drive one with a function generator and attach a scope to the other ... see what you get.

Thanks Marco, I had a brief look. Might give it a shot. I think the first thing I'm going to do is to make (or buy) a 27MHz  transmitter/receiver (standard hobby RC stuff) and see if it can transmit within my conditions. I'll take it from there!

Thanks all for suggestions!

[Fraser]

Just so you know, 418MHz and 433Mhz telemetry transmitters often use a tuned mini loop antenna rather than a whip. The antenna loop may be vertical or horizintal. These are often to be found in car central locking transmitters so the whole transmitter can be very small indeed. It is whether it can cope with 100C that I do not know. Some of my 433MHz transmitter PCB's are ceramic. These types may cope with higher temperatures ? Such transmitters and receivers are so cheap these days that they may be worth experimenting with.

Take a look here.... one of my favourite suppliers of such modules:

http://www.rfsolutions.co.uk/

http://www.rfsolutions.co.uk/acatalog/FM_Radio_Modules.html

http://www.rfsolutions.co.uk/acatalog/FM_Hybrid_Transmitter___Receiver_Modules.html

http://www.rfsolutions.co.uk/acatalog/FM_RTFQ10_433.html

Sadly 27MHz needs decent sized antenna dimensions even for a short range link. It could be quite a challenge to build a functional 27MHz antenna into a 1" sphere.


Aurora

[ManCave]

Thanks, Aurora!!! You are incredibly fast!

some nice info there and all confirmed. £3 for a 433MHz transmitter module, I would indeed class that as cheap! I guess I'll be ordering some soon

[amyk]

Finding something that fits the temperature range isn't the problem here - standard automotive temperature range is -40C to +125C - signal attenuation is.

[mrpackethead]

oddly was looking at this the other day..

Don't completely discount 2.4Ghz in water.   Using COTS gear, you might achieve ranges of 15-20cm, which depending on your application might fit the bill ok.  It really does depend a lot on whats in the water.. Fresh water and salt water behave differently for example.

Heres a paper on the topic.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355409/

[Gribo]

There are automotive rated transceivers out there for sub 1GHz transmissions (CC1101-Q1 for example). If the data rate and range requirement are low enough, you can use crystals rated for such temperatures, even with the loose tolerance rating, 40-100ppm instead of 10-40ppm required by the transceiver, albeit with reduced sensitivity and blocking performance.