Cardboard Paper Boosts Radio Frequency Energy Harvesting

The innovative use of waste cardboard paper material for constructing a rectenna has been a subject of recent investigation. Researchers have developed a simple fabrication scheme that allows for easy dismantling of the fabricated objects. The electrical traces in these designs are implemented using a commercial copper tape with a thickness of 35 μm, which can be readily removed from the object's surface. However, the use of cardboard substrates and the fabrication process present certain constraints that need to be considered in the design of a rectenna.

To begin the process, researchers focused on determining the loss tangent and relative permittivity of the cardboard material. Given the variety of cardboard types available, with differences in thickness, surface roughness, and air gaps, a detailed characterization method was established for four distinct material substrates. The identified radiofrequency (RF) properties were then utilized in the design of both the antenna and the rectifier components. Specifically, a microstrip patch antenna was engineered to resonate within the 2.45 GHz ISM band, showcasing the potential for enhanced energy capture by designing a dual-band microstrip patch antenna operating at 900 MHz and 1800 MHz frequencies.

The study delves into the design and experimental outcomes of a 2D-rectenna aimed at harvesting radio-frequency energy at 2.45 GHz using various cardboard paper substrates for both the antenna and rectifier elements. Four different types of recycled cardboard material were selected, each varying in thickness, air gaps, and surface roughness, for comprehensive characterization. A linearly polarized rectangular microstrip patch antenna with microstrip transmission feeding was chosen for its ease of fabrication and efficiency in capturing RF energy.

At the resonant frequency of 2.45 GHz, the antenna exhibited a simulated global gain of 2.98 dB and a measured gain of 2.53 dB on a 2.2 mm thick cardboard substrate. The rectifying component of the rectenna comprises a voltage-doubler configuration connected via a T-matching network to the antenna. Experimental evaluations conducted at low RF input power levels (-10 dBm) revealed maximum available DC output powers of 1.73 μW, 7.5 μW, and 8.5 μW for different diode models. The rectifiers utilizing specific diodes demonstrated optimal load values, with the SMS7306-079L diode achieving a maximum power conversion efficiency of 14.2% at -5 dBm input power when paired with an optimal load of 1.5 kΩ.

In conclusion, the exploration of waste cardboard paper as a viable material for rectenna construction presents promising results in terms of energy harvesting efficiency. By leveraging the unique properties of recycled cardboard substrates and innovative design approaches, researchers have demonstrated the feasibility of developing sustainable energy solutions using environmentally friendly materials. The study not only highlights the potential of cardboard-based rectennas in RF energy scavenging but also underscores the importance of creative thinking in addressing energy challenges through unconventional means.