Listen to Protons With a Homemade Magnetometer

When will you receive MRI scanning, the machine uses a phenomenon called nuclear magnetic resonance (NMR). Some types of atomic nuclei, including nuclei hydrogen atoms in a water molecule – cmake one hesitate in a magnetic field, and these vibrations can be detected using coils of wire. MRI scanners use intensive magnetic fields which create resonances in tens and hundreds megahertz. However, another instrument based on NMR includes much lower frequency vibrations: proton precession magnetometeroften used to measure the Earth's magnetic field.

Proton precession magnetometers have been around for decades and were once often used in archeology And mineral exploration. High-end models can cost thousands of dollars. Then, in 2022, German engineer Alexander Mumm developed very simple circuit for cut down. I recently built a circuit for it and can prove it using less than a pound of 22-gauge magnetic wire; two common integrated circuits; A metal-oxide-semiconductor field-effect transistor or MOSFET; multiple discrete components; and two empty 113 gram bottles Morton Seasoning BlendThe Earth's magnetic field can be measured very accurately.

The frequency of the signal emitted by protons precessing in the Earth's magnetic field lies in the audio range, so with a pair headphones and two amplifier integrated circuits [middle right]you can detect the signal from water in condiment bottles wrapped in coils [bottom left and right]. A MOSFET [middle left] allows you to quickly control the coils. The amplification circuit is powered by a 9-volt battery, and a 36-volt battery charges the coils.James Provost

How to MRI scannerproton precession magnetometer measures vibrations hydrogen nuclei– that is, protons. Like other subatomic particles, protons have a quantum property called rotateanalogue of classical angular momentum. In a magnetic field, protons oscillate like tops, with their axes of rotation forming a cone—a phenomenon called precession. A proton precession magnetometer causes many protons to oscillate in unison and then measures their oscillation frequency, which is proportional to the intensity of the surrounding magnetic field.

Weak strength Earth's magnetic field (at least compared to an MRI machine) means that the protons swaying under its influence do so at sound frequencies. Move synchronously enough, and the spinning protons induce a voltage in the nearest sensor coil. Amp it up and run it through some headphonesand you will receive a beep. So, with the right circuitry, you can literally hear the protons.

The first step is to make the pickup coils, which requires bottles of Morton seasoning mix. Why Morton Seasoning Blend? Two reasons. First, a bottle this size will allow you to wrap about 500 turns of wire around each with about 450 grams of 22 gauge wire. Secondly, there are small protrusions on each end of the bottle, which provides a great coil shape.

Why two bottles and two coils? This is necessary to suppress electromagnetic interference, mainly coming from power lines, which is invariably picked up by the coils. When two opposing winding coils are connected in series, such external noise tends to cancel out. However, the signals from the precessing protons in the two coils will amplify each other.

Do not attempt this indoors or near objects containing iron.

The proton magnetometer has three modes. The first is designed to supply direct current through the coils. The second mode turns off the current source and allows the magnetic field it creates to collapse. The third is the listening mode, in which the coils are connected to a sensitive audio amplifier. By filling each bottle with distilled water and passing a constant current (a few amps) through these coils, you line up the spins of the many protons in the water. Then, with the circuit in listening mode, you use the coils to detect the synchronous oscillations of the oscillating protons.

Mumm's circuit switches from one mode to another in the simplest way: using a three-position switch. One position enables DC polarization mode. The following allows the magnetic field created during polarization for camber, and the third position is for listening.

How to Avoid Harmful Sparks

The second option may seem simple – just disconnect the coils, right? But if you do, the same principle that makes spark plugs spark will cause damage high voltage through the switch contacts when the magnetic fields around the coils are destroyed.

A proton precession magnetometer is primarily a multistage analog amplifier.James Provost

To avoid this, Mumm's circuit uses a MOSFET to act as a power transistor. Zener diodeused in many power control circuits to allow only current above a set value to pass. threshold voltage flow. This limits the voltage that appears across the coils when the current is turned off just enough so that the magnetometer can quickly switch from polarizing mode to listening mode without causing damage.

To pick up a strong signal, the listening circuit must also be tuned to resonate at the expected proton precession frequency, which will depend on the Earth's magnetic field at your location. You can roughly determine what it is using the online version geomagnetic field calculator. You will get the field strength and then multiply it by gyromagnetic ratio protons (42.577 MHz at Tesla). For me it came out to about 2 kilohertz. Having estimated the inductance of the coils by their diameter and number of turns, I then selected a capacitor of suitable capacitance in parallel with the coils to make tank circuit which resonates at this frequency.

You can customize your tank circuit using frequency generator and oscilloscope. Or, as Mumm suggests, attach a small speaker to the output of the circuit. Then bring the speaker close to the pickup coils. This will create magnetic feedback and the circuit will oscillate on its own –loud! You just need to measure frequency of this tone and then adjust reservoir capacitor to bring this self-hosted OSgeneration at the frequency you want tune in.

My first attempt to hear protons had mixed success: sometimes I heard sounds, sometimes I didn’t. What helped make this thing work stably was the understanding that proton magnetometers do not tolerate large magnetic field gradients. Therefore, do not try to do this indoors or anywhere near iron-containing objects: water pipes, cars or even the ground. It is best to use a wide open space outside, with the coils raised off the ground. The second thing that helped was adding more power in polarization mode. Although the 12-volt battery works fine, the 36-volt battery performs much better.

Having figured all this out, I can now easily hear protons. These sounds are clearly proton sounds because they disappear if I empty the bottles of water. And, using free audio analyzer software called Spectrum LaboratoryI confirmed that the frequency of these tones matches the magnetic field at my location by about 1 percent. While not a practical field instrument, any kind of proton precession magnetometer under $100 is nothing to scoff at.