Earth's field NMR

Jump to navigation Jump to search

WikiDoc Resources for Earth's field NMR


Most recent articles on Earth's field NMR

Most cited articles on Earth's field NMR

Review articles on Earth's field NMR

Articles on Earth's field NMR in N Eng J Med, Lancet, BMJ


Powerpoint slides on Earth's field NMR

Images of Earth's field NMR

Photos of Earth's field NMR

Podcasts & MP3s on Earth's field NMR

Videos on Earth's field NMR

Evidence Based Medicine

Cochrane Collaboration on Earth's field NMR

Bandolier on Earth's field NMR

TRIP on Earth's field NMR

Clinical Trials

Ongoing Trials on Earth's field NMR at Clinical

Trial results on Earth's field NMR

Clinical Trials on Earth's field NMR at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Earth's field NMR

NICE Guidance on Earth's field NMR


FDA on Earth's field NMR

CDC on Earth's field NMR


Books on Earth's field NMR


Earth's field NMR in the news

Be alerted to news on Earth's field NMR

News trends on Earth's field NMR


Blogs on Earth's field NMR


Definitions of Earth's field NMR

Patient Resources / Community

Patient resources on Earth's field NMR

Discussion groups on Earth's field NMR

Patient Handouts on Earth's field NMR

Directions to Hospitals Treating Earth's field NMR

Risk calculators and risk factors for Earth's field NMR

Healthcare Provider Resources

Symptoms of Earth's field NMR

Causes & Risk Factors for Earth's field NMR

Diagnostic studies for Earth's field NMR

Treatment of Earth's field NMR

Continuing Medical Education (CME)

CME Programs on Earth's field NMR


Earth's field NMR en Espanol

Earth's field NMR en Francais


Earth's field NMR in the Marketplace

Patents on Earth's field NMR

Experimental / Informatics

List of terms related to Earth's field NMR


Nuclear magnetic resonance (NMR) in the geomagnetic field is conventionally referred to as Earth's field NMR (EFNMR). Note that the same acronym is used for electric field NMR.

EFNMR is a special case of low field NMR.

When placed in a constant magnetic field and stimulated (perturbed) by a pulsed or alternating magnetic field, NMR active nuclei (such as 1H or 13C) resonate at frequencies characteristic of the isotope. The resonant frequencies and signal strengths are proportional to the strength of the applied magnetic field. Thus in the 21 tesla magnetic field that may be found in high resolution laboratory NMR spectrometers, protons resonate at 900 MHz. However in the Earth's magnetic field the same nuclei resonate at audio frequencies of around 2 kHz, generating very weak signals.

The location of a nucleus within a complex molecule affects the chemical environment experienced by the nucleus. Thus different hydrocarbon molecules containing NMR active nuclei in different positions within the molecule produce slightly different patterns of resonant frequencies. Analysis of the frequency spectrum allows the structure of the molecule to be determined.


Applications of EFNMR include:

  • EFNMR spectrometers, which use the principle of NMR spectroscopy to analyse molecular structures in a variety of applications, from investigating the structure of ice crystals in polar ice-fields, to rocks and hydrocarbons in the field.

The advantages of the Earth's field instruments over conventional (high field strength) instruments include the portability of the equipment giving the ability to analyse substances on site, and their lower cost. The much lower geomagnetic field strength, that would otherwise result in poor signal-to-noise ratios, is compensated by homogeneity of the Earth's field giving the ability to use much larger samples. Their relatively low cost and simplicity make them good educational tools.

Examples (illustrated) are the TeachSpin and Terranova MRI instruments.

Mode of operation

Free Induction Decay (FID) is the magnetic resonance due to Larmor precession that results from the stimulation of nuclei by means of either a pulsed dc magnetic field or a pulsed resonant frequency (rf) magnetic field, somewhat analogous respectively to the effects of plucking or bowing a stringed instrument. Whereas a pulsed rf field is usual in conventional (high field) NMR spectrometers, the pulsed dc field method of stimulating FID is usual in EFNMR spectrometers and PPMs.

Since the FID resonant frequency of NMR active nuclei is directly proportional to the magnetic field affecting those nuclei, we can use widely available NMR spectroscopy data to analyse suitable substances in the Earth's magnetic field.

For more context and an explanation of NMR principles, please refer to the main articles on NMR and NMR spectroscopy.

Proton EFNMR frequencies

The geomagnetic field strength and hence precession frequency varies with location and time.

Larmor precession frequency = magnetogyric ratio x magnetic field
Proton magnetogyric ratio = 42.576 Hz/μT (also written 42.576 MHz/T or 0.042576 Hz/nT)
Earth's magnetic field: 30 μT near Equator to 60 μT near Poles, around 50 μT at mid-latitudes.

Thus proton (hydrogen nucleus) EFNMR frequencies are audio frequencies of about 1.3 kHz near the Equator to 2.5 kHz near the Poles, around 2 kHz being typical of mid-latitudes.

Examples of molecules containing hydrogen nuclei useful in proton EFNMR are water, hydrocarbons such as natural gas and petroleum, and carbohydrates.


Early EFNMR instruments were developed in the 1950s using thermionic valve (vacuum tube) circuits. Sir Peter Mansfield's first acquaintance with NMR was an undergraduate project to develop a transistorized EFNMR spectrometer in the late 1950's [1]. Following that introduction to NMR, he went on to invent an MRI scanner, for which he shared a Nobel prize.

See also

External links

Template:WH Template:WS