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My problem is that I have to control (turn on and off) one LASER that is placed inside an aluminium can (not like soda can, but one 2 mm thick).

So the question is if there's any way to do that wirelessly. I've been thinking about Bluetooth and Zigbee but in my initial research I've found data may not be able to 'go through' the aluminium.

I've been thinking about IR, but it may not fit my idea because I have a camera shoting pics of the can, so the IR led may affect the images.

Any thoughts on that? Any other solution? Is there some tech that I could look for that would suit my problem?

Thanks in advance

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If that can is completely closed it's impossible to do this with RF. Not with a 2mm thickness. – stevenvh Jun 5 '12 at 16:12
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One wireless method you could look into is magnetically coupled windings, similar transformer, or RFID, or NFC. Even if it works, communication distance will not be great. 2mm of aluminium will contribute to shorted turn effect, unfortunately. BTW, is there a reason why you can't make a penetration in the aluminium tube and run a cable, or an optical fiber, or an antenna feed? – Nick Alexeev Jun 5 '12 at 16:31
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Variation on Turbo J answer. Hall effect transistor circuit on the inside of the can and solenoid winding on the outside. That will penetrate the can. – kingchris Jun 5 '12 at 17:31
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Schroedinger's Laser? – Olin Lathrop Jun 5 '12 at 18:09
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No, I didn't misunderstand you. | You need to provide a more complete description of your requirement so that people (not me) do not waste time trying to answer the wrong question. | if you want to "latch the LASER on" a very simple electronic circuit can take the output from a reed relay or hall cell and use that to operate it. For simple on/off control a neodymium magnet will "reach through" 2mm of Al. As magnet diameter increases the depth of field at a given strength will increase. As you have a battery supply for the LASER this can be used to power the on/off latching circuit as well. – Russell McMahon Jun 7 '12 at 2:34
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3 Answers

up vote 3 down vote

Sound waves (or ultrasound) should be able to get through the can. Use a speaker and microphone (or ultrasonic transducers).

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The environment where it will be used can (and mostly will be) very noisy, so do you think it would still be doable? I am thinking about filters that I know a little about but I'd never implemented none and wouldn't know if it would even help. – Bergamin Jun 6 '12 at 21:00
It is probably still doable. The solution will depend on the characteristics of the background noise (dB, frequencies, intermittent/continuous). You need to make the signal stand out from the noise, either using a quiet frequency band or by something like repeating a 10-bit on/off pattern until it is received. For the latter case, longer patterns will give fewer false positives, but will have more delay before turning on. You will need to tune the number of bits and repetitions to your environment. – Justin Jun 7 '12 at 12:02
up vote 1 down vote

Simple solution: Big coil outside and reed contact inside the can. A strong magnetic field should be able to penetrate 2mm alu. Might need some experimentation to learn what is "strong enough".

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Thanks for the idea. I know nothing about reed contact but wouldn't it open if the magnetic field goes off? I know that I didn't wrote it, but my can will enter a duct once the laser is turned on, so I wouldn't be able to keep the magfield on. – Bergamin Jun 6 '12 at 21:09
@Bergamin: Why wouldn't you be able to keep the magfield on? Run some wires to the coil, or RF control power to the coil. – Shamtam Jun 6 '12 at 22:51
Think of the reed contact as sort of a power button. – Turbo J Jun 7 '12 at 8:52
up vote 0 down vote

You can make the can/casing the antenna.

Create a design where the cylinder is cut/sectioned midway its length. Join/mate the halves mechanically in some fashion (say threaded) to provide a hermetic seal. This allows you to easily assemble into and access the contents of the casing. Make sure though that the halves are electrically not connected to each other (the mating parts made of plastic, and the seal made of a rubber gasket) and with a very thin distance between the halves.

The two halves can now be used as a radio dipole antenna. The entire length of the cylinder is one-half the wavelength for the signal. This idea will work if your application will have the cylinder length in some convenient radio frequency.

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