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Optical rectenna

Optical rectenna is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Optical rectenna rather than just read about it. In short: An optical rectenna is a rectenna (rectifying antenna) that works with visible or infrared light. A rectenna is a circuit containing an antenna and a diode, which turns electromagnetic waves into direct current electricity.

Optical rectenna — main illustration
Optical rectenna — illustration

Key takeaways

  • Optical rectenna belongs to physics; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Optical rectenna to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Optical rectenna from memory before moving on to harder problems.

Reference excerpt

An optical rectenna is a rectenna (rectifying antenna) that works with visible or infrared light. A rectenna is a circuit containing an antenna and a diode, which turns electromagnetic waves into direct current electricity. While rectennas have long been used for radio waves or microwaves, an optical rectenna would operate the same way but with infrared or visible light, turning it into electricity. While traditional (radio- and microwave) rectennas are fundamentally similar to optical rectennas, it is vastly more challenging in practice to make an optical rectenna. One challenge is that light has such a high frequency—hundreds of terahertz for visible light—that only a few types of specialized diodes can switch quickly enough to rectify it. Another challenge is that antennas tend to be a similar size to a wavelength, so a very tiny optical antenna requires a challenging nanotechnology fabrication process. A third challenge is that, being very small, an optical antenna typically absorbs very little power, and therefore tend to produce a tiny voltage in the diode, which leads to low diode nonlinearity and hence low efficiency. Due to these and other challenges, optical rectennas have so far been restricted to laboratory demonstrations, typically with intense focused laser light producing a tiny but measurable amount of power. Nevertheless, it is hoped that arrays of optical rectennas could eventually be an efficient means of converting sunlight into electric power, producing solar power more efficiently than conventional solar cells. The idea was first proposed by Robert L. Bailey in 1972. As of 2012, only a few optical rectenna devices have been built, demonstrating only that energy conversion is possible. It is unknown if they will ever be as cost-effective or efficient as conventional photovoltaic cells. The term nantenna (nano-antenna) is sometimes used to refer to either an optical rectenna, or an optical antenna by itself. In 2008 it was reported that Idaho National Laboratories designed an optical antenna to absorb wavelengths in the range of 3–15 μm. These wavelengths correspond to photon energies of 0.4 eV down to 0.08 eV. Based on antenna theory, an optical antenna can absorb any wavelength of light efficiently provided that the size of the antenna is optimized for that specific wavelength. Ideally, antennas would be used to absorb light at wavelengths between 0.4 and 1.6 μm because these wavelengths have higher energy than far-infrared (longer wavelengths) and make up about 85% of the solar radiation spectrum (see Figure 1).

… excerpt ends here. Continue reading the full article.

Illustrations

Optical rectenna: Figure 1. Spectral irradiance of wavelengths in the solar spectrum. The red shaded area shows the irradiance at sea level. There is less irradiance at sea level due to absorption of light by the atmosphere.
Figure 1. Spectral irradiance of wavelengths in the solar spectrum. The red shaded area shows the irradiance at sea level. There is less irradiance at sea level due to absorption of light by the atmosphere.
Optical rectenna: Figure 3. Image showing the skin effect at high frequencies. The dark region, at the surface, indicates electron flow where the lighter region (interior) indicates little to no electron flow.
Figure 3. Image showing the skin effect at high frequencies. The dark region, at the surface, indicates electron flow where the lighter region (interior) indicates little to no electron flow.

Worked examples

Example 1 — a first encounter with Optical rectenna

Start with the simplest possible case. Write down what Optical rectenna claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Optical rectenna before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Optical rectenna ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Optical rectenna

In research
Optical rectenna appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Optical rectenna in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Optical rectenna is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antennas, Solar cells, Solar energy, so understanding it makes those chapters shorter.
In everyday life
Look for Optical rectenna outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Optical rectenna in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Optical rectenna means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Optical rectenna out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Optical rectenna in simple terms?

An optical rectenna is a rectenna (rectifying antenna) that works with visible or infrared light. A rectenna is a circuit containing an antenna and a diode, which turns electromagnetic waves into direct current electricity.

Why does Optical rectenna matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Optical rectenna?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Optical rectenna.

Tags

  • Antennas
  • Solar cells
  • Solar energy

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