Recharging Robot Fish

I think you can have a much greater range than that. At a few KHz, the salt water won't have too much loss. You could use a non or less ionic material to in place of the salt. If you used Fluorinert, the fish could be a lot heavier but you wouldn't be able to sell the kit for $29.95 on late night TV.

The limiting factor on the AC field strength is mostly the losses you are willing to live with. Imagine the tank is on a stand that is about as tall as the tank its self. If this stand is also the coil assembly and contains a large core pointed vertically, the field strength inside the tank could be quite high even at the half way up point.

You need to design the electronics to make very good use of the energy you have. Doing the tail motion seems to me to be the hardest part of the whole design.

that

barrier.

How about using pure water and a metal plate above and below the tank. The fish could be conductive on the top and bottom to pick up the power. Thsi would let you go to a low enough frequency that the FCC doesn't care. You would have a huge AC voltage between the plates but They can be well defended against people touching them.

IIRC, 1% salt water has a resistivity of 3 Ohm-Meters. and Skindepth is about 500*sqrt(R/F)

Skindepth = 500*sqrt(3/20K) = 6M

If your tank is 1 meter tall, this reduces the field at the top by a factor of exp(1/6) = 1.18 in other words it is less than 20% reduction from this.

Wow! What an idea... The fish convert the ethanol directly to electricity. Maybe I might see fish like that someday in my lifetime..

Best to get fire insurance with that tank... :) D from BC

Mmm...it's approx. $800CAD for a 24" LCD computer monitor... A 24" monitor is about 22"x13". That would back-display a boring tank size.. Big tanks will need larger LCD displays (arrays) costing more money..

Also, there's no true 3D view..

I think the robot fish still have a chance. D from BC

barrier.

Salt water AC conductance?? I thought stuff like salt water permeability and reluctance would be pop up.

Can an induction heater heat up salt water? I think this is related to charging batteries by induction. D from BC

I think all you need to do is fit each fish with a little tin-foil hat. :-)

Ed

ultrasonics ?

Colin =^.^=

Why not do it to the tourists? Tell them its to keep the fish from reading their minds. ;-)

I don't think anything but the resistivity of salt water will matter to the losses at 20KHz for lowish power levels.

It won't be very good at it but if you apply a big enough dB/dT you will get some heating from the currents.

The question is the losses you get from the salt water. It looks like they are small enough to allow inductive charging to work quite well.

I assume that the coil on the bottom of the tank will be resonated by a capacitor in series with it. This means that the semiconductor driving it won't have to handle very high voltages.

Series resonance is a nice way to get high ac current for high magnetic strength. I'd have to read up on resonant switchers and linear power oscillators again..

I might try a 20Khz smps supply circuit with a U core. D from BC

It'll be the Finding Nemo jewelry cleaner too :)

The nice thing about the EM method is that the charging coil is inside the robot fish... With ultrasonic, wouldn't the transducer(s) need to be on the outside of the robot fish? (The robot fish should look like a fish with scales.) D from BC

well you could make the outside of the fish transparent to the frequency used I would imagine. or make the scales individual tiny transducers. (mems)

or how about subsonic then ? you could cyclicly pressurize the water and an air bladder in the fish would expand etc. this could power a small generator, maybe even a piezo, or better still the expansion could cuase the fishtail to flex one way and back making the fish swim purly mechanicaly.

or how about a dc field ? electric eels can create it so why not, or you could even have 3 layers of fluid, a conductive one to say mimic the air, a thin insulating indistinguishable from either the top or bottom layer, and the water below. as the fish pokes its head through to the top layer - zap it gets instant recharge. make it so its naturaly boyant and has to swim down under power.

I thought normal radio waves werent too good under water - hence submarines are a job to keep intouch with. they have to use those fancy 1km long waves.

or maybe nuclear powered is the way togo ?

how much power are we talking about anyway ?

with your coils on the bottom, they could just swim close to the botom to get recharged rather than 'die'.

Colin =^.^=

Great ideas! Except for nuclear :( I got a chuckle from the quasi -hydraulic solution. Modulate the water pressure.. :)

I have no idea what the power consumption of the robot fish will be.. If I start now...I might know in about 3 years... I'll do an archive search and do a post reply in 2010. :)

D from BC