The Body Magnetic
October 15, 2015
As anyone who's gotten an electrical shock from a switch plate knows, the human body conducts electricity. This also demonstrates that the human body can store electrical charges generated by walking across carpet fabric in low humidity. If you have an ohmmeter at home, you can measure your own electrical resistance, which is the reciprocal of conductance.
For safety reasons, however, it's required that you never do any such measurements across the torso, as from one hand to another. The battery voltages of most of today's ohmmeters are small, but application of any current through the torso can be dangerous. Also, do not puncture your skin to do this measurement, since one known fatality has occurred this way.
I just measured my resistance from the thumb to little finger of my right hand. The value I got, about 20 megohm (20 MΩ), is higher than what would be expected. I needed to use a sensitive ohmmeter, since I obtained no reading on a less expensive, 2 megohm fullscale, meter. Typical values for dry skin are in the 100 kΩ range, with wet skin being in the 1 kΩ range. The contact area was just the sides of the probe tips. Using larger area electrodes, perhaps with brine or a conductive paste, might have given a lower value.
Electricity was an exciting thing in the early days after its discovery. There was the idea that electricity was the vital force of living creatures, as presented in modern adaptations of Mary Shelley's Frankenstein (1818). Shelley's original book didn't mention electricity, but the concept was worked into a revised 1831 edition.
The scientific basis for this comes from Luigi Galvani's discovery that electrical excitation caused movement in the legs of a dissected frog (see figure). Such reanimation of a dead organism was, of course, sensational.
Since both electricity and magnetism are easily observed natural phenomena, it was inevitable that someone would postulate the existence of an "animal magnetism." Animal magnetism, proposed by the German physician, Franz Mesmer, wasn't magnetism in the sense that physicists understand the term. It was supposedly an invisible natural force generated by animals. Animal magnetism had supposed medicinal properties, and people were persuaded to believe in its existence from the late 18th century into the early 20th century, along with many other primitive medical theories.
The human body does exhibit real magnetism, albeit at a very low level. Fortunately, modern science now has sensitive SQUID magnetometers that allow detection of very small magnetic fields. SQUIDS are based on the interference of quantum states in Josephson junctions embedded in superconducting materials. Magnetic regions of the brain have been magnetically imaged in a technique called magnetoencephalography.
The X-men villain, Magneto,
uses the supposed magnetism of blood hemoglobin as a weapon by drawing it out of the body. Hemoglobin, however, is not ferromagnetic, it's just weakly paramagnetic, so it's barely attracted to even the strongest magnets.
Transformers are devices that use the Faraday law of induction to transmit electrical energy through a magnetic medium by converting an oscillating current to an oscillating magnetic field, conducting it through the magnetic medium, and then converting it back to an oscillating electrical current. A simple transformer, as shown in the figure, does this with two coils and a core of high magnetic permeability. For greater efficiency, the core is typically wrapped into itself to form a closed ring.
A team of electrical engineers at the University of California, San Diego, has just shown that the human body can act as the magnetic core of a signal transformer. They demonstrated a communication technique in which data signals can be sent from one bodily appendage to another. A presentation on this research was made at the end of August at the 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Milan, Italy.[2-3]
There were two motivations for this research. The primary motivation was the desire to extend the lifetime of battery-operated transmitters by reducing as much as possible the power required to transmit data between personal monitoring devices. Bluetooth radio, the conventional method, requires considerable power, since the power losses through the body are large at Bluetooth frequencies. The research team has shown that, in theory, 10 million times lower power than Bluetooth would be required in their system.
A secondary motivation was data security. Unlike Bluetooth, which has a communications range away from the body, the magnetic communication system has a strong signal at the body that decreases dramatically away from the body. Says Jiwoong Park, an electrical engineering Ph.D. student at UCSD and first author of the study,
"Increased privacy is desirable when you're using your wearable devices to transmit information about your health."
This technique, which utilizes magnetic fields many times smaller than those of MRI imagers and wireless implant devices, should not have an associated health risk. One limitation, however, is the need to have a coil wrapped around a body part. While this is not a problem for smart watches, headbands and belts, patch sensors to detect heart rate, for example, would not work.
- Resistance is Futile, 1999 Darwin Awards Web Site.
- Web Site of the 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (2015, Milan, Italy).
- Liezel Labios, "Magnetic Fields Provide a New Way to Communicate Wirelessly," University of California San Diego Press Release, September 1, 2015
- Web Site of the University of California San Diego Center for Wearable Sensors.
Permanent Link to this article
Linked Keywords: Electric shock; electrical shock; light switch; switch plate; human body; electricity; electric charge; carpet; textile; fabric; humidity; ohmmeter; electrical resistance; multiplicative inverse; reciprocal; electrical conductance; safety; torso; hand; battery; voltage; electric current; skin; death; fatality; thumb; little finger; ohm; megohm; kΩ contact area; electrode; brine; electrodermal activity; skin resistance; electric current; Wikimedia Commons; Inkscape; vitalism; vital force; animal; living creature; Mary Wollstonecraft Shelley; Frankenstein (1818); science; scientific; Luigi Galvani; galvanism; legs; dissection; dissected; frog; experiment; textbook; magnetism; natural phenomena; animal magnetism; German; physician; Franz Mesmer; physicist; invisibility; invisible; nature; natural; force; medicine; medicinal; 18th century; 20th century; theory; SQUID; magnetometer; magnetic field; interference; quantum state; Josephson junction; superconductivity; superconducting material; brain; magnetic field imaging; magnetoencephalography; Cooper pair; electron; quantum tunnelling; insulator; insulating; Nobel Prize in Physics; Brian Josephson; Inkscape; X-men; villain; Magneto; blood; hemoglobin; weapon; ferromagnetism; ferromagnetic; paramagnetism; paramagnetic; magnet; transformer; Faraday law of induction; energy; oscillation; oscillating; solenoid; coil; magnetic core; permeability; energy conversion efficiency; annulus; toroid; electrical engineering; electrical engineer; University of California, San Diego; signal; communication; data; bodily appendage; research; 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society; Milan, Italy; battery lifetime; transmitter; electric power; Bluetooth radio; frequency; Jiwoong Park; Doctor of Philosophy; Ph.D.; author; UCSD Jacobs School of Engineering; data security; privacy; health; magnetic resonance imaging; MRI; wireless; implant device; smart watch; headband; belt; dermal patch; sensor; heart rate; 1999 Darwin Award.
Latest Books by Dev Gualtieri
Thanks to Cory Doctorow of BoingBoing for his favorable review of Secret Codes!
Blog Article Directory on a Single Page
- Levitation - March 27, 2017
- Soybean Graphene - March 23, 2017
- Income Inequality and Geometrical Frustration - March 20, 2017
- Wireless Power - March 16, 2017
- Trilobite Sex - March 13, 2017
- Freezing, Outside-In - March 9, 2017
- Ammonia Synthesis - March 6, 2017
- High Altitude Radiation - March 2, 2017
- C.N. Yang - February 27, 2017
- VOC Detection with Nanocrystals - February 23, 2017
- Molecular Fountains - February 20, 2017
- Jet Lag - February 16, 2017
- Highly Flexible Conductors - February 13, 2017
- Graphene Friction - February 9, 2017
- Dynamic Range - February 6, 2017
- Robert Boyle's To-Do List for Science - February 2, 2017
- Nanowire Ink - January 30, 2017
- Random Triangles - January 26, 2017
- Torricelli's law - January 23, 2017
- Magnetic Memory - January 19, 2017
- Graphene Putty - January 16, 2017
- Seahorse Genome - January 12, 2017
- Infinite c - January 9, 2017
- 150 Years of Transatlantic Telegraphy - January 5, 2017
- Cold Work on the Nanoscale - January 2, 2017
- Holidays 2016 - December 22, 2016
- Ballistics - December 19, 2016
- Salted Frogs - December 15, 2016
- Negative Thermal Expansion - December 12, 2016
- Verbal Cues and Stereotypes - December 8, 2016
- Capacitance Sensing - December 5, 2016
- Gallium Nitride Tribology - December 1, 2016
- Lunar Origin - November 27, 2016
- Pumpkin Propagation - November 24, 2016
- Math Anxiety - November 21, 2016
- Borophene - November 17, 2016
- Forced Innovation - November 14, 2016
- Combating Glare - November 10, 2016
- Solar Tilt and Planet Nine - November 7, 2016
- The Proton Size Problem - November 3, 2016
- Coffee Acoustics and Espresso Foam - October 31, 2016
- SnIP - An Inorganic Double Helix - October 27, 2016
- Seymour Papert (1928-2016) - October 24, 2016
- Mapping the Milky Way - October 20, 2016
- Electromagnetic Shielding - October 17, 2016
- The Lunacy of the Cows - October 13, 2016
- Random Coprimes and Pi - October 10, 2016
- James Cronin (1931-2016) - October 6, 2016
- The Ubiquitous Helix - October 3, 2016
- The Five-Second Rule - September 29, 2016
- Resistor Networks - September 26, 2016
- Brown Dwarfs - September 22, 2016
- Intrusion Rheology - September 19, 2016
- Falsifiability - September 15, 2016
- Fifth Force - September 12, 2016
- Renal Crystal Growth - September 8, 2016
- The Normality of Pi - September 5, 2016
- Metering Electrical Power - September 1, 2016
Deep Archive 2006-2008