1. THE PROBLEM
A transmission antenna is a device capable of converting electromagnetic radiation into electrical currents and vice versa, or, as defined by the IEEE in 1983, an antenna is a means of radiating or receiving radio waves.
Currently, various manufacturers offer antennas that operate on microwaves (region of the electromagnetic spectrum corresponding to wavelengths of the order of 1–30 millimeters), and on radio waves (wavelengths from centimeters to kilometers).
Figure 1. Frequencies and wavelengths of the electromagnetic spectrum
The question that arises is: Is there currently any commercial supply of antennas for the wavelengths corresponding to the visible spectrum? And if not, is it possible to manufacture antennas for those wavelengths and corresponding frequencies?
The answers are No and YES. There is no offer, and YES, in theory it is possible to manufacture antennas that operate in the bands corresponding to visible light, after all these bands are part of the electromagnetic spectrum. But... there is always a but, there is a small problem: The dimensions of the antennas go hand in hand with the wavelengths on which they operate.
Dipole antennas, for example, are designed with arms, or poles, each about ¼ the length of the electromagnetic wavelength on which they operate, see figure 2.
Figure 2. Pole length and related electric field
And it turns out that the wavelength of visible light, in green, for example, is of the order of 520 nanometers, that is, 0.52 microns, 0.00052 millimeters!
To get an idea of the construction problem, a typical bacterium measures about 3 microns, so inside an Escherichia coli, for example, it would fit aligned around 12 dipole antennas, see fig 3.
Fig 3. Twelve dipole antennas aligned within of a typical bacterium: Escherichia coli
The technology had to wait for the arrival of nanotechnology. But that is the second part of this story, which I intend to develop in parts.
