bipolar pulsing to remove Earth Field

[Carl-NC]

What i ment to say is, Earths magnetic field alone (in absence of any anomaly) will not be detectable, moving coil thru the relatively homogenous field will not induce anything in it no matter how sensitive detector is.

A wire or coil moving through any magnetic field, whether it's homogeneous or distorted, will induce a current, if the field has any component normal to the wire/coil. This is a fundamental of electromagnetics.

The Fisher-style transmitter, as done in the Impulse, is not a good PI transmitter, at least as we normally do PI. However, there is a variation of this circuit that does make a good PI transmitter. I am working on this now, and may use it in the Hammerhead III design.

- Carl

[Tepco]

A wire or coil moving through any magnetic field, whether it's homogeneous or distorted, will induce a current, if the field has any component normal to the wire/coil. This is a fundamental of electromagnetics.

- Carl

Fundamental of electromagnetic is, rate of change. Anything moving in static field whit no gradient will induce just nothing! No rate of change, no voltage induced, fundamental of induction. Earth field is more or less static, maybe not for intercontinental sweep, but in any practical condition (no anomalies) it is.

[mickstv]

How high do you want to go with the PPS? Is 5000 good enough? 10,000 maybe?
Have a look at the Tinkerers TEM, it shortens the decay time considerably.

Tinkerer

Hi Tinkerer, I have been following the TEM, and it looks promising. What I'm trying to do is design a detector from scratch without copying other designs, mainly using a analog design with a processor to control all the timing.

I have managed to get a rough bipolar design on paper and will be breadboarding it tomorrow. Fingers crossed it works.



Mick

[Carl-NC]

Fundamental of electromagnetic is, rate of change. Anything moving in static field whit no gradient will induce just nothing! No rate of change, no voltage induced, fundamental of induction.

A motionless coil in a static field will produce no current. But a motionless coil in a changing magnetic field will produce a current. Likewise, a moving coil in a static magnetic field will also produce a current. If the coil is moving, the field does not have to be distorted.

[Aziz]

A motionless coil in a static field will produce no current. But a motionless coil in a changing magnetic field will produce a current. Likewise, a moving coil in a static magnetic field will also produce a current. If the coil is moving, the field does not have to be distorted.

*LOL*
Perfect, we have something like the perpetuum mobile or the zero point module (ZPM).


The very large power lines rotate with the earth rotation (1667 km/h). The earth field can be considered to be stationary or static. Why don't we get the free energy?

Aziz

[Carl-NC]

The very large power lines rotate with the earth rotation (1667 km/h). The earth field can be considered to be stationary or static. Why don't we get the free energy?

We do. Several hundred nanoamps, in fact.

[Tinkerer]

We do. Several hundred nanoamps, in fact.

The Earth's magnetic field is geo-stationary. It rotates with the earth.

The EF is most noticeable when we tilt the coil. The tilting can easily produce an angular velocity of several meters.

Let's say we have a coil with 20 turns, moving with an angular velocity of 2 meters in the Earth's magnetic field of 0.5 Gauss.

Does anybody know the exact mathematical formula to calculate this?

Tinkerer

[mickstv]

Don't mock the Birds Nest

Here's the breadboard of the design I have come up with. Two TX pulses 50us and a spacing of roughly 60us. Also two sample points one after each TX pulse. The TX is running on 6 volts and the rest of the amps and switches are running 0-12 volts, this was a quicker method to get the design working. Frontend amp is running at about 200 in gain and the integrator is running at about 700 in gain.

The pot at the bottom of the picture is used to balance the EF, once it's set you never need to change it.





Uploaded with ImageShack.us

[6666]

Hi Mick
do you have a mudmap of your creation ?
Is it a H bridge ?

[Carl-NC]

The Earth's magnetic field is geo-stationary. It rotates with the earth.

Yeah, I know... tongue-in-cheek. However, geomagnetically induced currents from solar storms can induce enough "free energy" to bring down the power grid.

Let's say we have a coil with 20 turns, moving with an angular velocity of 2 meters in the Earth's magnetic field of 0.5 Gauss.

Does anybody know the exact mathematical formula to calculate this?

"Angular velocity of 2 meters" is unclear... if the Earth field is horizontally uniform you need to either be raising/lowering or tilting the loop in the field. (Sorry Tepco, you're right, a loop moving through a constant B field produces nothing; I was thinking of a simple wire, but a coil self-cancels.) If changing the height of the loop you need to know more about the magnetic field flux; if tilting the loop then you have a time-varying loop area (flux density) which is easier to calculate if all you know is the point flux. In either case, E = -N*dB/dt.

[mickstv]

Hi Mick
do you have a mudmap of your creation ?
Is it a H bridge ?

I do have a partial circuit, but it needs a lot more work before I maybe make it avaiable. I won't call it a H-bridge only because it has two N-channel fets and no P-channel ones. Also the frontend runs on a single voltage rail. The next area I have to tidy up is the fet drive circuit. Then setup a second set of sample points for ground balance.

I can see some big benefits including double the signal level, so you don't have to run the first amp hard to pickup smaller targets. Also you can run a short receive period because you no longer need the late samples at 150-250us for the EF balance.




Mick

[6666]

Hi Mick
looking forward to seeing both yours and Carls idea on bipolar pulsing
this sort of takes me back to the days of germanium trannies
and pulsing r/c actuators , it will be interesting to see
if any of the actuator principles can be applied here.
cheers

[Tepco]

Hello Tepco,

What ever it is, it exists and needs to be eliminated.

I agree with you on the Fisher half bridge transmitter. I built it using bipolar transistors
and fets, but could never get the delay down. The diodes that make it work also kill the signal .It works good as a continous wave transmitter.

As Carl stated, an h-bridge might make it all practical. Here is one I am going to try next.
see attached patent. The schematic has a mistake or two

Whit more than few errors on schematic, patent is regular full-bridge, whit zener clamped flyback, interestingly intended to operate whit coil inside metal housing, reminding me to another, passively dumped coil, Ellen Ott, US6326790 and few others.

In Fisher style arrangement, there is no flyback pulse, pulse energy is “recovered” via reverse diodes, making it highly efficient. This process will not “kill” the target signal, just there is no delay adjustment possible. If TX pulse is,say,20uS to ramp up to some peak current, recovery time will be about the same, then sampling can take place, so minimal sampling time is limited by TX pulse width and it is fixed for given configuration. Naturally, higher drive voltage is needed to ramp up coil current in shorter pulse, but most of the coil energy is recovered later instead to be wasted in flyback. Whit this approach, very high reactive current can be circulated thru the coil, loss is only resistive and switching, allowing operation at high frequency and reasonable current consumption. Only, sampling time is now not limited by coil parameters, like in classic PI, but whit recovery time, so using ,say, 20uS sampling delay this will not be good for small gold or fine jewelry, but very useful for “relics hunting” or something coin sized and larger.
There are many solutions for bridge driver, but as usual, every one came whit some advantages and some limitations.

Simplest approach is dedicated half bridge drive Ic, like IR 2111 or 2112, later can accept independent drive for upper and lower FET, but 2111 (8pin chip) is also useful, driven whit square wave to turn on upper or lower FET, and disable pin used to terminate pulse and turn off both FETs. Advantage is, this is simple, and will handle low duty cycle signals. This will work nice in classic half-bridge, like in Fisher, (coil connected to mid point of two bus capacitors). Disadvantage is, coil will now float at some (maybe relatively high) voltage, requiring good CMRR amplifier, but at least AC coupled, and logic control and power stage must share same GND.

Also, unipolar flyback can be generated, now whit coil connected to V+ like this: first, lower fet is commanded on for say 100uS to “charge” the coil, then turned off and upper fet is turned on, now effectively “short circuiting” the coil and preventing energy release. (during this time, another coil in induction balance can sense target polarity, he, hybrid, and extract information for GB) Then upper fet is turned off, generating flyback. Important is, IRF is 600V rated, (1200V versions exist), FET must be whit lower breakdown or IC will fail.

Unfortunately, no bipolar flyback can be generated this way, even if FETs are diode isolated (to isolate internal diodes), negative voltage is not tolerated, chip will be destroyed instantly if it goes below GND.

Another alternative is using gate drive transformer(s). Normally, transformers are limited to 50% duty cycle, but whit additional circuitry can handle asymmetrical signals. Main limitation here is core size required for low frequency (few hundred Hz), but even this is acceptable for experiments. Otherwise, almost bulletproof, now FETs can be isolated for bipolar flyback, control and power can float at any level, coil can be ground referenced etc.

I hope this (bit long ) writing can be useful to some degree. Best regards.

[mickstv]

Here's a picture of the preamp output taken at 50us per div. the artefact's seen before the start of the TX are due to poor fet switching. I can start sampling at about 10-12us. I have found that if I reduce the gain by half the sample time can start as early as 6-8us so I'll need to modify the frontend and use two stages.

[Altra]

Mick

That looks great, keep us posted.

I just finished the h-bridge idea from the patent US6130489
it works, but lots of components. And some quirks. I'll post
a schematic and some screen shots tommorrow.

Regards