Friday, June 14, 2019

Michael Faraday - Predictor of Radio?

Michael Faraday [1791-1867], an English chemist and physicist who, in 1831, converted magnetism into electricity.  By varying magnetic forces, Faraday was able to generate electrical currents in a wire - known today as electro-magnetic induction.  This phenomenon is taken for granted today but was considered as "magic" in his day as there was no such thing as electricity, only DC current was available generated by voltaic cells.

Faraday [and Clerk Maxwell, who mathematically translated Faraday’s work] led the way to modern day wireless theory. Without Faraday, there would be no radio! Faraday’s work laid the ground work for electromagnetic radio wave propagation.

When 13 years old, he worked for a bookseller and soon became a book apprentice. This work exposed him to science and resulted in his interest in chemistry and simple electricity.  Faraday was a ‘deep’ thinker, a great questioner, and an imaginative person.

In 1812, he became a student of Sir Humphry Davy, who was a lecturer at the Royal Academy, where Faraday was a ‘bookman’ for him [took notes then bounded Davy’s lectures].  Faraday soon went to work for the Academy assisting lecturers by maintaining their electrical equipment. As time progressed and his science knowledge increased, he also became a sought after lecturer and began devoting time to research and experimentation. While with Humphry, he was interested in Ampere’s work [first to measure electrical current] and eventually picked up where Ampere left off.  Since electricity produced magnetism, Faraday set out to see if magnetism would produce electricity.  He was successful and published several papers and lectured regarding magnetism generating electricity.

Faraday lived in a time where other scientists were suspicious of other scientist, and he was suspected of taking credit of research conducted by others. Faraday was not University educated but a self-educated man.  As of a result, his educated contemporaries were suspicious, jealous and resented his standing in the scientific world.

Faraday was a humble, over sensitive person and decided to record his views on electromagnetism. He wrote his views in a sealed document to show future scientist the validity of his discoveries but especially his theories.

In 1832, he submitted a sealed document to the Royal Society. The Society deposited the document in a locked strong box where it remained secured and unopened for over 100 years!  In 1937, the Royal Society opened the box and examined Faraday’s handwritten notes where he predicted the existence of electromagnetic waves. 

Faraday inventing radio technology is certainly a giant leap of the imagination but it does show his strong skills as an experimenter and his understanding of electromagnetic wave field theory [relationship between light and electricity, that space was filled with electric/magnetic lines-of-force]. Thus, one can easily say that Faraday ushered in the "radio era" !

Faraday’s Sealed Letter:

Royal Institution
March 12, 1832

Certain of the results of the investigations which are embodied in the two papers entitled ‘Experimental Researches in Electricity’ lately read to the Royal Society, and the views arising therefrom, in connexion with other views and experiments lead me to believe that magnetic action is progressive, and requires time, i.e. that when a magnet acts upon a distant magnet or piece of iron, the influencing cause (which I may for the moment call magnetism) proceeds gradually from the magnetic bodies, and requires time for its transmission, which will probably be found to be very sensible.

I think also, that I see reason for supposing that electric induction (of tension) is also performed in a similar progressive way.

I am inclined to compare the diffusion of magnetic forces from a magnetic pole to the vibrations upon the surface of disturbed water, or those of air in the phenomenon of sound; i.e. I am inclined to think the vibratory theory will apply to these phenomena as it does to sound, and most probably to light.

By analogy, I think it may possibly apply to the phenomenon of induction of electricity of tension also.

These views I wish to work out experimentally; but as much of my time is engaged in the duties of my office, and as the experiments will therefore be prolonged, and may in their course be subject to the observation of others, I wish, by depositing this paper in the care of the Royal Society, to take possession as it were of a certain date; and so have right, if they are confirmed by experiment, to claim credit for the views at that date; at which time as far as I know, no one is conscious of or can claim them but myself.

M. Faraday

Monday, January 7, 2019

The Coherer

Have you ever heard of a device called the Coherer?  The Coherer is an early radio signal detector that was used over 100 years ago. It evolved as a replacement for the Hertz detector [copper loop conductor with an air gap].   We know that Hertz was the first to detect electromagnetic waves in 1888 proving Maxwell’s earlier mathematical predictions. The Coherer, a primitive form of radio receiver, was a significant participant in the very early days of wireless.

Branly in his Lab
Professor Eduard Branly discovered the Coherer around 1890. His device transformed the development of wireless technology as Marconi used it in his first wireless transmission system later in 1896. 

Branly was a French Physicist that resumed research on electromagnetic conductors began by others earlier in the 1880s. His research centered on iron filings [in powder form]; and their reaction to electromagnetic waves. The Coherer is essentially a small glass tube with two pieces of metal with wires attached to each end thus forming electrodes.  The two metal pieces are placed in proximity to each other to form an air gap where iron or copper filings were positioned.
Branly's Coherer

In his early experiments, Branly found that the metal filings, while lying on a glass plate, changed their resistance when in proximity to a strong electromagnetic wave [signal oscillations]. He explained this phenomenon by stating that the filing’s “cohered” [stick together, hold together].   Branly was also a medical scientist who researched different theories about how nerves carry messages from the skin to and from the brain.  His research found that nerves are not continuous fibers but neurons. Neurons are a bunch of cells gathered closely but are not connected. He equated this neuron phenomenon to describe the coherer effect.

Branly encapsulated the filings in a glass tube.  He attached a battery circuit and a galvanometer [type of an amp meter] to the coherer; then discharged a Leyden jar whose electromagnetic wave [oscillations] made the loose metal filings cohere; that is, form a low resistance circuit, moving and sticking the filings together to act like a conductor. This completed the circuit allowing the current to flow [as the galvanometer would indicate]. Disrupting the filings [separating the loose filings] would stop current flow until another Leyden jar discharged was conducted for them to cohere again.

This device conceptually opened the door to wireless transmission as Branly showed that it could detect electromagnetic waves. The coherer is considered a key element in the development of wireless, and earned Branly a Noble Prize in 1921. This technology became the standard for early wireless telegraphy receivers until the “cat whisker” detector was discovered to be a better detector in 1906.
Facsimile of Lodge's coherer circuit
Circuit Digram
In the mid 1890s, the English Physicist Olive Lodge experimented with Branly’s coherer. Lodge found that it was superior to his detector device and experimented with it for his wireless transmission system. Lodge was a noteworthy wireless scientist who conducted many important wireless experiments prior to Marconi arriving on the scene.  Lodge improved Branly’s device by adding a “tapper” that shook and loosened the filings after they cohered in between transmissions [clear the filings when the oscillations ceased].  The Lodge coherer circuit included a bell that would ring when the filings cohered; stop ringing when the electromagnetic wave dissipated, then the tapper cleared [shook] the filings apart for the next transmitting/receiving sequence.  Lodge is also responsible for naming the device the “Coherer”.

Gugliemo Marconi, experimenting with his wireless system, used the Branly’s coherer and the tapper that Lodge developed to transmit and receive wireless Morse code. He also improved the device by adding vacuum chamber to the coherer, thus making it easier for the filings to cohere. Marconi first successful radiotelegraphy transmission and reception occurred in 1896 [about 40 miles], which resulted in his first radio Patent.  He was also responsible for the first transatlantic radio transmission in 1906.
Marconi's Coherer