Take heed to Protons With a Home made Magnetometer

While you get an MRI scan, the machine exploits a phenomenon referred to as nuclear magnetic resonance (NMR). Sure sorts of atomic nuclei—together with these of the hydrogen atoms in a water molecule—can be made to oscillate in a magnetic subject, and these oscillations could be detected with coils of wire. MRI scanners make use of intense magnetic fields that create resonances at tens to lots of of megahertz. Nonetheless, one other NMR-based instrument includes a lot lower-frequency oscillations: a proton-precession magnetometer, typically used to measure Earth’s magnetic subject.

Proton-precession magnetometers have been round for many years and had been as soon as typically utilized in archaeology and mineral exploration. Excessive-end fashions can value 1000’s of {dollars}. Then, in 2022 a German engineer named Alexander Mumm devised a quite simple circuit for a stripped-down one. I lately constructed his circuit and may attest that with lower than half a kilogram of 22-gauge magnet wire; two frequent built-in circuits; a metal-oxide-semiconductor field-effect transistor, or MOSFET; a handful of discrete parts; and two empty 113-gram bottles of Morton seasoning mix, it’s attainable to measure Earth’s magnetic subject very precisely.

The frequency of the sign emitted by protons precessing in Earth’s magnetic subject lies within the audio vary, so with a pair of headphones and two amplifier built-in circuits [middle right], you’ll be able to detect a sign from water in seasoning bottles wrapped in coils [bottom left and right]. A MOSFET [middle left] permits for fast management of the coils. The amplification circuitry is powered by a 9-volt battery, whereas a 36-volt battery prices the coils.James Provost

Like an MRI scanner, a proton-precession magnetometer measures the oscillations of hydrogen nuclei—that’s, protons. Like different subatomic particles, protons possess a quantum property referred to as spin, akin to classical angular momentum. In a magnetic subject, protons wobble like spinning tops, with their spin axes tracing out a cone—a phenomenon referred to as precession. A proton-precession magnetometer will get many protons to wobble in sync after which measures the frequency of their wobbles, which is proportional to the depth of the ambient magnetic subject.

The weak power of Earth’s magnetic subject (a minimum of in comparison with that of an MRI machine) signifies that protons wobbling underneath its affect accomplish that at audio frequencies. Get sufficient shifting in unison and the spinning protons will induce a voltage in a close-by pickup coil. Amplify that and go it by way of some earphones, and also you get an audio tone. So with an acceptable circuit, you’ll be able to, actually, hear protons.

Step one is to make the pickup coils, which is the place the bottles of Morton seasoning mix are available. Why Morton seasoning mix? Two causes. First, this dimension bottle will will let you wrap about 500 turns of wire round every one with about 450 grams of 22-gauge wire. Second, the bottle has little shoulders molded at every finish, making for wonderful coil kinds.

Why two bottles and two coils? That’s to quash electromagnetic noise—principally coming from energy traces—that invariably will get picked up by the coils. When two counterwound coils are wired in collection, such exterior noise tends to cancel out. Alerts from precessing protons within the two coils, although, will reinforce each other.

Don’t do this indoors or wherever close to iron-containing objects.

A proton magnetometer has three modes. The primary is for sending DC present by way of the coils. The second mode disconnects the present supply and permits the magnetic subject it had created to break down. The third is listening mode, which connects the coils to a delicate audio amplifier. By filling every bottle with distilled water and sending a DC present (a number of amperes) by way of these coils, you line up the spins of many protons within the water. Then, after placing your circuit into listening mode, you utilize the coils to sense the synchronous oscillations of the wobbling protons.

Mumm’s circuit shifts from one mode to a different within the easiest way attainable: utilizing a three-position change. One place allows the DC-polarization mode. The subsequent permits the magnetic subject constructed up throughout polarization to break down, and the third place is for listening.

Avoiding Damaging Sparks

The second mode may appear straightforward to attain—simply disconnect the coils, proper? However for those who do this, the identical precept that makes spark plugs spark will put a dangerous excessive voltage throughout the change contacts because the magnetic fields across the coils collapse.

The proton-precession magnetometer is primarily only a multistage analog amplifier.James Provost

To keep away from that, Mumm’s circuit employs a MOSFET, wired to work like a high-power Zener diode, utilized in many power-regulation circuits to permit solely present above a specified threshold voltage to stream. This limits the voltage that develops throughout the coils when the present is reduce off by simply sufficient in order that the magnetometer can shift from polarizing to listening mode shortly however with out inflicting harm.

To choose up a powerful sign, the listening circuit should even be tuned to resonate on the anticipated frequency of proton precession, which is able to depend upon Earth’s magnetic subject at your location. You’ll be able to work out roughly what that’s utilizing an internet geomagnetic-field calculator. You’ll get the sector power, and you then’ll multiply that by the gyromagnetic ratio of protons (42.577 MHz per tesla). For me, that labored out to about 2 kilohertz. Estimating the inductance of the coils from their diameter and variety of turns, I then chosen a capacitor of appropriate worth in parallel with the coils to make a tank circuit that resonates at that frequency.

You could possibly tune your tank circuit utilizing a frequency generator and oscilloscope. Or, as Mumm suggests, connect a small speaker to the output of the circuit. Then convey the speaker close to the pickup coils. This may create magnetic suggestions and the circuit will oscillate on it’s personal—loudly! You merely must measure the frequency of this tone, after which alter the tank capacitor to convey this self-oscillation to the frequency you need to tune to.

My preliminary try and hearken to protons met with combined success: Typically I heard tones, typically not. What helped to get this gizmo working persistently was realizing that proton magnetometers don’t tolerate massive gradients within the magnetic subject. So don’t do this indoors or wherever close to iron-containing objects: water pipes, vehicles, and even the bottom. A large-open area outdoors is greatest, with the coils raised off the bottom. The second factor that helped was to use extra oomph in polarization mode. Whereas a 12-volt battery works okay, 36 V does significantly better.

After figuring this stuff out, I can now hear protons simply. These tones are clearly the sounds of protons, as a result of they go away if I drain the water within the bottles. And, utilizing free audio-analyzer software program referred to as Spectrum Lab, I confirmed that the frequency of those tones matches the magnetic subject at my location to about 1 %. Whereas it’s not a sensible subject instrument, a proton-precession magnetometer of any variety for lower than US $100 is nothing to sneer at.