*Solar Rectennas: Analysis and Design DOI: http://dx.doi.org/10.5772/intechopen.89216*

*Recent Wireless Power Transfer Technologies*

and the diode [5].

inexpensive and available. Why solar rectennas?

ciency during the day.

rectennas such as [6]:

challenging.

part of a solar rectenna.

**2. History of rectennas**

rectennas rather than the solar irradiation.

which is hard to achieve using the planar MIM diodes.

maximum power transfer and hence higher efficiency.

higher.

illumination) than current solar cells [4]. Rather than the low efficiency, solar rectennas overcome the other drawbacks of PVs which include the dependence on the bandgap energy and the narrowband operation (visible region only). However, several challenges contribute to make the actual conversion efficiency much lower than expected such as the poor coupling between the optical antenna

Each photon in semiconductor solar cells produces electron hole pair to generate electrical power. However, the device absorbs only those photons that have energy higher than the band gap energy. This limits the conversion efficiency to 44% or even less in real devices. On the other hand, classical rectifiers receive the electromagnetic energy and convert it into DC power with a conversion efficiency reaching 100%. Solar rectennas are designed to operate in a similar way with the expectation to obtain very high efficiencies at a wide range of the electromagnetic spectrum. The field of solar rectennas appears to be promising and attractive due to the fact that high efficiency is theoretically obtainable and the material used is

• Solar rectennas can achieve as high as the efficiency of solar cells or even

• The material of solar rectennas is widely available in the form of thin films, and the fabrication process is inexpensive compared to conventional solar cells.

• Solar rectennas demonstrate versatility over PV devices by exceeding effi-

• Other forms of infrared such as waste heat can also be harvested by solar

In contrast, there are several drawbacks and challenges associated with solar

• When converting visible light, the time constant must be in the range of 0.1 fs,

• The leakage current of the diode must be as small as 1 μA, which is quite

• A strong matching between the antenna impedance and the diode's to ensure

It is obvious that the technology of solar rectennas is still young in the early stage of research and faces numerous challenges and limitations. Thus, in this chapter, the theoretical understanding is presented highlighting the development of each

In the last century, the story of solar rectenna begun when electrical power has been transferred without the use of wires. This technique is called wireless power

**178**

transmission (WPT). It is worth to mention that all the rectenna systems conceived at that time were working at microwave frequencies with efficiencies exceeding 80% at a single frequency.

A brief historical background on this technique is presented here:


**Figure 1.** *The first optical rectenna proposed by mark [8].*

that consists of nickel-nickel oxide-nickel diode is used to convert terahertz fields into electrical current. Furthermore, other research studies [13] are interested to study the impacts of geometrical parameters on the antenna performance.

**181**

**Figure 2.**

**4. Nanoantennas**

*Block diagram of optical rectenna [8].*

*Solar Rectennas: Analysis and Design*

**3. Basics of solar rectennas**

electric fields, respectively.

the value of the surface current.

Generally, power losses result in from this reradiation.

*DOI: http://dx.doi.org/10.5772/intechopen.89216*

The structure and the operation theory of nanoantennas have been presented in this section. The same as the response of the conventional RF antenna to the electromagnetic wave, nanoantenna responds to the visible light and IR. Induced AC current, which is formed on the surface of the antenna, interacts with the incident wave and oscillates with it in the same frequency. The presence of a feeding gap in the antenna can help to collect the solar power, and then DC power is produced by rectifying the oscillated AC current with the aid of a specific diode-based rectifier. Based on the theory of boundary conditions, the tangential electric field vanishes on the antenna surface and is equal to zero (Et = 0). This is fundamental to the traditional RF antenna, where metals are considered to have ideal electrical conductivity. In other words, Es = −Ei, where Es and Ei are scattered electric and incident

In contrast, the operation of nanoscale antennas is based on the optical and IR regimes. In this case, metals are considered to be non-ideal conductors since they exhibit lower conductivity. Thus, the expression Et has to be taken into account. This expression can be presented by multiplying the value of surface impedance by

**Figure 2** shows the block diagram of a typical optical rectenna, in which the solar antenna receives the electromagnetic wave within a proper frequency band to deliver it to the low-pass filter (LPF) [8]. The latter, which is placed between the antenna and diode (rectifier), is used to prevent the reradiation of the higher harmonics that generated from the rectification process by the nonlinear diode.

Furthermore, the LPF matches the impedance between the antenna and the subsequent circuitry. The DC LPF smoothly delivers the rectified signal to DC and then passes it to the external load. In general, MIM diode is considered being the most common rectifier in the solar rectenna system; based on the electron tunneling process, the rectification is generally occurring through the insulator layer.

Mirrors and lenses are usually utilized to control light propagation. However, they are unable to concentrate the light in a tiny area (smaller than λ/2), whereas antennas can easily confine the electromagnetic wave in subwavelength (beyond the

After that, there was a significant interest by researchers to study nanoantennas coupled to MIM diode for solar power-harvesting applications or THz sensing, which cannot be covered here due to space limitations.
