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Skin Communication

February 1, 2021

When I was in elementary school, I read a circuit construction article about a one transistor "lie detector" in a hobby electronics magazine. This circuit measured skin resistance, and the theory of operation was that the sweat of a nervous person telling a falsehood would decrease the skin resistance. I was fortunate in having a neighbor who was an electronics technician who had a part-time television repair business, and he supplied the components for this, and other, circuits. The functioning of that circuit wasn't that reliable, and the utility of "lie detection" is quite controversial.

The direct current (DC) resistance of human skin is generally very high, of the order of 10 k-ohm to many megohms, depending on skin dryness. I just used an ohmmeter to measure the skin resistance between the tip of my thumb and the tip of my index finger (also known as the forefinger, pointer finger, and trigger finger) as 2.5 megohms. To establish contact, I used an electrode gel of the same type as used for electrodes for electrocardiography.

The electrical impedance of skin, the resistance seen when the excitation is alternating current (AC) rather than direct current, is far different. Alternating current passes more easily through cell membranes, so the resistance of skin (R=V/I) is small when frequency-excited. When current is allowed to pass through the skin, the overall body resistance from head-to-foot is just a few hundred ohms.[1]

The difference in effect of direct current (DC) and alternating current (AC) was brought to public attention in the early days of electrification in the so-called war of the currents, in which Thomas Edison's (1847-1931) DC electric system was promoted as safer than the George Westinghouse (1846-1914)/Nikola Tesla AC system. Since transformers could be used in the AC system, and not the DC system, AC power proved victorious in 1892 through the merger of Edison Electric with its AC rival to form General Electric.

Thomas Edison and George Westinghouse around the time of the war of the currents

Thomas Edison and George Westinghouse around the time of the war of the currents. Edison was well known to the public, and there were even two biographical films about him in 1940, Young Tom Edison, staring Mickey Rooney (920-2014), and Edison, the Man, staring Spencer Tracy (1900-1967).[2-3] Westinghouse deserves to be better known. His invention of the railway air brake saved many lives. His early experiments in 1884 with a natural gas well at the backyard of his home in Pittsburgh, Pennsylvania, showed that this dangerous mine gas could be made useful.[4] (Photograph of Thomas Edison, c. 1882, left. and photograph of George Westinghouse, 1884, right, both from Wikimedia Commons.)

Skin conductivity means that you can exchange data with a handshake, or by a finger touch. Why would this be important, since Bluetooth is the usual method for short-range data communication? The reason is an analogy to the difference between using an actual credit card at a point-of-sale terminal and using your credit card for an online transaction. The physical card is always more secure.

Credit cards (image by Photographer Lotus Head)

Credit card numbers have an included check digit that detects any single-digit error and nearly all transpositions of adjacent digits.

The check digit is computed using the Luhn algorithm, patented in 1960 by IBM computer scientist, Hans Peter Luhn.[5] The algorithm is a simple check for mistyped information.

The patent has long since expired, so the method is in common use for many number cards.

(Wikimedia Commons image by Photographer Lotus Head.)

The idea of the human body as a conduit to transfer data from a worn device containing things such as passwords has been a topic of research by Shreyas Sen, an associate professor of electrical and computer engineering and his research team at Purdue University (West Lafayette, Indiana). They've published their research results in a series of recent papers.[6-11]

Their method, which they've named BodyWire-HCI, doesn't use radio frequencies. Instead, it's a baseband transmission in which an electric field is modulated by a data stream at frequencies below 1 MHz.[6,8] Data will only pass through the conductive communication path of the human body.[6] While radio frequency signals from Bluetooth can be detected at 30 feet, signals from the BodyWire-HCI approach require physical touch.[7-9]

Wrist band transceiver

A prototype wristband device is used for touch communication with a laptop computer.

The device appears bulky in this image, but it can be shrunk to a more aesthetic size.

(Purdue University photo by John Underwood.)

The human-side transceiver for this touch signalling could be a wristband device that makes contact with the skin (see photo).[7] Applications include opening doors presently opened with a card reader, and payment terminals.[7] A local area network could even be implemented within the body so implanted medical devices such as pacemakers and insulin pumps can communicate with a handheld smartphone.[7] As Sen says, a pocket-based device is also feasible,
"You wouldn’t have to bring a device out of your pocket. You could leave it in your pocket or on your body and just touch."[7]

This work was funded by the National Science Foundation and the Air Force Office of Scientific Research.[7,9] As could be expected, the Purdue research group has applied for patents on this technology.[7]

Skin data communication with a car door handle (Purdue University Engineering)

Keyless entry.

Skin data communication with a car door handle would allow access without transmission of radio frequency signals exposed to hackers.

(Screenshot of a Purdue Engineering YouTube Video.[11])


  1. Raymond M. Fish and Leslie A. Geddes, "Conduction of Electrical Current to and Through the Human Body: A Review," Eplasty, vol. 9: no. 44 (October 12, 2009). This is an open access paper with a PDF file here.
  2. Young Tom Edison (1940), Norman Taurog, Director, on the Internet Movie Database.
  3. Edison, the Man (1940), Clarence Brown, Director, on the Internet Movie Database.
  4. Pioneering Natural Gas Innovations at the Westinghouse Memorial Website.
  5. H.P. Luhn, "Computer for verifying numbers," U.S. Patent No. 2,950,048, August 23, 1960 (via Google Patents).
  6. Shovan Maity, David Yang, Scott Stanton Redford, Debayan Das, Baibhab Chatterjee, and Shreyas Sen, "BodyWire-HCI: Enabling New Interaction Modalities by Communicating Strictly During Touch Using Electro-Quasistatic Human Body Communication," ACM Transactions on Computer-Human Interaction, vol. 27, no. 6 (November, 2020), Article no. 39, https://doi.org/10.1145/3406238.
  7. Kayla Wiles, "Tech makes it possible to digitally communicate through human touch," Purdue University Press Release, December 3, 2020.
  8. Debayan Das, Shovan Maity, Baibhab Chatterjee, and Shreyas Sen, "Enabling covert body-area network using electro-quasistatic human body communication," Scientific Reports, vol. 9, Article no. 4160 (March 11, 2019), doi: 10.1038/s41598-018-38303-x. This is an open access paper with a PDF file here.
  9. Kayla Wiles, "Your body is your internet – and now it can't be hacked," Purdue University Press Release, March 12, 2019.
  10. Shreyas Sen, Shovan Maity and Debayan Das, "Turning the Body Into a Wire," IEEE Spectrum, November 24, 2020.
  11. Digital Communication through Human Touch, YouTube Video by Purdue Engineering, December 3, 2020.

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