Re: [DIYbio] Re: Interested in Automated Cell Culturing?

The emitter is inside the microwave oven. Mine has 1400 watts, which seems to be plenty of power to boil water.

You need the diode. It converts the gigahertz frequencies into DC that the motor can use.

A dipole antenna is simply two conductors whose length determines the frequency at which the antenna is resonant. For collecting power, you don't actually need to be resonant. You'd collect less power, but there is 1400 watts to play with, and the motor only needs 50 milliwatts or so.

The microwave oven frequency is 2.45 GHz. A wavelength is thus 12.24 centimeters. A half-wave dipole would thus be 6.12 centimeters across, with each leg being a bit over 3 centimeters long. Cut each lead of the diode down to 1.2 inches and you have your rectifying antenna for 2.45 GHz.

Other antenna structures can be used, such as the quad discussed here. Better diodes might also be useful, as the ones we used are not that good at 2.45 GHz, and if you want to actually draw more power than you need to light an LED, a better diode might be a good idea. I think I said 1N914, but on further recollection we probably used a 1N34A (it was a long time ago). A 1N60 diode is about 60 cents.

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On Sat, Jul 6, 2013 at 6:15 PM, Nathan McCorkle <nmz...@gmail.com> wrote:

Would you need a diode? Would you need to decouple the motor from the
antenna, how would you tune it's resonant frequency? If you can't
change the motor circuit's resonant frequency, where can you get a
high-enough power tunable microwave emitter?

On Sat, Jul 6, 2013 at 5:40 PM, Simon Quellen Field <sfi...@scitoys.com> wrote:
> We used to build microwave leak detectors by putting an LED across the leads
> of a 1N914 diode. The diode's leads were just the right length to make a
> resonant dipole antenna for the microwaves. If there was enough energy in
> the rectenna to light the LED, the seals on the microwave were deemed
> inadequate. If you placed it inside the microwave, the LED got too much
> current and became a Dark Emitting Diode (DED).
>
> If instead of the LED, you put a small DC motor, it would spin. If it spins
> too fast you can add a resistor. Put a magnet on the motor's axle, and you
> have a magnetic stirrer. Put all of that in a housing and you're good to go.
> No integrated circuits required.
>
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>
>
> On Sat, Jul 6, 2013 at 4:35 PM, John Griessen <jo...@industromatic.com>
> wrote:
>>
>> On 07/06/2013 06:00 PM, jarlemag wrote:
>>>
>>> Could you explain the physics of that in a bit more detail?
>>>
>>> - JP
>>>
>>> kl. 23:57:10 UTC+2 lørdag 6. juli 2013 skrev Cathal Garvey (Phone)
>>> følgende:
>>>
>>>     Along same lines I've often wondered about a microwave-powered
>>> stirbar. As in, magnetic strip/plate under flask, magic bar in
>>>     flask absorbs microwaves and self-propels. Would be great for keeping
>>> temperature even in drinks, let alone flasks of broth..
>>
>>
>> Magic might be required, but you can kinda sort of imagine a tortuous path
>> to getting microwave energy, running a computer programmed gizmo,
>> balancing
>> heating vs stirring power somehow would be tough...
>>
>> It's all so much easier to imagine a time slicing do this, do that, do
>> this,
>> do that kind of machine without much magic required.  You'd use a
>> no-permanent
>> magnet stir bar -- just paramagnetic iron with a plastic wrap.  Move that
>> for a while with
>> magnetic fields, stop that, blast with microwave energy field, stir again,
>> repeat while necessary.
>>
>> And sure, Arduino IDE can be used to develop it.
>>
>>
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-Nathan

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