Can Ultrasonic range finder, pass through thin plastic/metal?

Hello guys. i am planning on working with some ultrasonic range finding sensors on the following weeks, for two projects

  1. measure the fuel level, in a fuel tank (tank wall is very thin , about 10mm or something)
    2)develop a parking sensor module.

I have no prevous experiance on that subject, and so i have no idea, if the sensors will be able to work, if a thin metal/plastic is in front of it…

for (1) the reason is that the sensors, will be mounted above the fuel tank, so they will have to pass through the walls… but with a quick search around the internet, it seems that this is the way to do it…

for (2), i have seen that OEM car makers, drill holes on the bumpers… and so i wonder, if ultrasonic works with a thin metal layer, why not with a thin plastic??
Also, on the specs of some sensors i see something like “blind distance = 2cm”… does it have anything to do?? thanks!!

Can Ultrasonic range finder, pass through thin plastic/metal?

I've never tried it, but I don't think so.

It might go through thin-thin-thin plastic like plastic wrap, but I'll bet aluminum foil reflects more than it passes-through, so you'd probably detect the distance to the foil.

Low-frequencies pass-through materials easier than high-frequencies. Have you ever noticed how a bass from a loud stereo passes through walls better than the rest of the music?

No

tank wall is very thin , about 10mm or something

10 mm (1 cm)? More likely "or something".

The sensor will not respond to reflecting surfaces closer than the blind distance.

Sound will reflect from just about any surface, so you will probably have false echos to handle. For most materials, sound energy that is not reflected is transmitted, and the ratio depends very strongly on the material. Very thin plastic like food wrap will reflect only weakly and may be OK.

Experiment and see!

well its propapbly less than 10mm :D

So as i understand, if i mount the sensor above the fuel tank, then BOTH the tank wall , and the "fuel" will reflect the sound back. but since the wall will be in less distance than the blind spot, then the sensor will ignore it...?

So as i understand, if i mount the sensor above the fuel tank, then BOTH the tank wall , and the "fuel" will reflect the sound back.

No!!! Is your tank made of plastic wrap? :stuck_out_tongue: You are not going to read anything useful through the walls of a fuel tank and the reflections from fuel tank will screw-up the readings even if it's too close to get a usable reading.

:D In theory you might be able to make a "sonic" fuel detector, especially if it's a metal tank... i.e. If you tap on the tank (or hit it with a solenoid) an empty tank will make a different sound than a full tank, and in theory you could detect the difference in sound. But, that would be a silly thing to do, since there are well-known ways to measure fuel level that are known to work.

I dont understand... ultrasonic sensors are supposed to be a legit and widly used tecnhique to mesure fuel tank levels... I suppose it would be much easier if i had a sensor at hadn to test it :D

But metal or not, sound passes through it.. and technically speaking, sound should be able to pass though metal easier than plastic...

(how does something like this work? http://www.philippi-online.de/index.php5?url=produkte.php5&m1id=2&sprache=en&kat1_nr=3&kat2_nr=5 )

widly used tecnhique to mesure fuel tank levels…

When positioned inside the tank.

AWOL: When positioned inside the tank.

they advertise that its the best non-invasive technique :P also, it says you are supposed to mount it above the tank... :D

Well, if that's what they advertise, they must know.

If the sensor receives multiple echoes, it responds to the first, not the second, or third. Also think about the amplitude of the reflections. A reflection from the outside of the tank is going to be huge compared to anything that has to anything that has to pass through the wall TWICE and be reflected from the liquid.

JohnLincoln: If the sensor receives multiple echoes, it responds to the first, not the second, or third.

Some of the Devantech devices record multiple echoes. However, as noted, the passage through tank, vapour, vapour and tank again is going to make for small returns.

It seems that allot of people tend to aggre that it will not pass through:P and at best if it passes it will have low ennergy left... ultrasonic is 40Khz.. that means 0.8cm weavlength... so even if the wall is less than 0.8, it has to pass twice..

Newer cars use "electromagnetic" sensors to do it without drilling the bumpers... any ideas how could this be done ??

Good afternoon everybody,

I apologize to jump in this late after the last reply. In my profession I use probes on daily basis, especially 4 Mhz transducers. I use these for scanning welds, this way they get worn out very fast and to prevent this we glue a plastic "shoe" on the transducer.

Works like a charm!

You just need a good couplant in order to prevent air to be trapped underneeth. We don't want air to be in between as it acts due to the huge difference in sound velocity as a mirror.

The lower the frequency the easier it passes through air and higher grain materials. Even so, the amount of energy passing is the easiest part. Getting is back with high enough energy is the difficult part.

I am actually investigating to glue on of these probes to the bottom plating of my boat...

Regards

settra: they advertise that its the best non-invasive technique :P also, it says you are supposed to mount it above the tank... :D

non-invasive.? you are thinking you can measure through metal, then through air. not going to be a simple sensor.

step #1) drill a hole in the tank for the new sensor...... option #2) using a hole in the top of the tank such as an inspection hole... install new bracket to hold the sensor. now, if you look UP.... option #3) mount the sensor on the bottom of the tank so that the fluid and wall act as a single unit. the sensor will detect the distance from the sensor through the tank wall and to the top of the fluid, up to the air gap. expect two returns. one from the tank wall, second from the level of the tank that does not have foam or other filler.

settra: It seems that allot of people tend to aggre that it will not pass through:P and at best if it passes it will have low ennergy left... ultrasonic is 40Khz.. that means 0.8cm weavlength... so even if the wall is less than 0.8, it has to pass twice..

Newer cars use "electromagnetic" sensors to do it without drilling the bumpers... any ideas how could this be done ??

you install the radiator, it creates a magnetic field, for cars, this goes out to about 3 feet for the parking sensor application. then you attach the antenna.

settra: It seems that allot of people tend to aggre that it will not pass through:P and at best if it passes it will have low ennergy left... ultrasonic is 40Khz.. that means 0.8cm weavlength... so even if the wall is less than 0.8, it has to pass twice..

Newer cars use "electromagnetic" sensors to do it without drilling the bumpers... any ideas how could this be done ??

it is not that 'people agree' it is that you cannot pass some frequencies through some materials. lasers can put holes through a couple feet of metals., but some cannot even burn the same metal. it is the frequency or some such. airplane radar is not behind metal, that would block the signal, but materials that are transparent to that specific frequency. every notice you can hear your neighbor's stereo but only the beat, not the high squeaky bits ? the walls of the house and air gaps act like filters. to some frequencies. same reason that submarines don't use high frequency radio while submerged. if you noticed, this thread has been filling up with posts of people who cannot offer solutions, only offering that they do not know how to do it. The best advise I can offer is to read up on the technology you want to use. there is no mainstream sensors we have multiple channels of sources for. If I was to do a fuel tank sensor, I would try to figure out the Rocket fuel tank sensor. and probably use a car sensor that has a plastic 'face' to protect it from weather.

I know this is old, but I ran into it while searching various ultrasonic sensing methods and how it works. This app note by TI is useful info about Ultrasonic sensor mounting limitations.

http://www.ti.com/lit/an/snaa266a/snaa266a.pdf