Recycled Cardboard Paper for Ambient Radio Frequency Energy Harvesting
Developers of electronics for the Internet of Things are considering nonstandard substrate materials like recyclable, low-cost, and eco-friendly cardboard paper
From the MDPI website:
The use of waste cardboard paper material for constructing a rectenna was investigated based on a simple fabrication scheme, ready to easily dismantle the fabricated objects. The electrical traces in all designs were realized with a commercial copper tape of thickness 35 μm. The copper tape is meant to be removed easily from the surface of objects. The cardboard substrates and the fabrication process introduced constraints in the design of a rectenna.
The first step was to extract the loss tangent and relative permittivity of the material. There are many types of cardboard materials, depending on their thickness, surface rough- ness, and air gaps. This paper provided the details of the characterization method for four different material substrates. The identified RF properties were used in the design of the antenna and the rectifier, respectively. A microstrip patch antenna was designed to resonate in the 2.45 GHz ISM band. This paper confirmed that an increase in the captured EM waves leads to higher PCE by designing a dual-band microstrip patch antenna at 900 MHz and 1800 MHz bands. The limitation in the bandwidth of the microstrip patch antenna was corrected by designing a monopole antenna of broadband width.
This article reviews the design and experimental results of a 2D-rectenna for scavenging radio-frequency energy at 2.45 GHz on various cardboard paper substrates for both the antenna and rectifier. Four types of recycled cardboard material, each with different thicknesses, air gaps, and surface roughness, are selected for characterization. A linearly polarized rectangular microstrip patch antenna with microstrip transmission feeding is adopted for ease of fabrication.
At 2.45 GHz, the antenna has a simulated and measured global gain of 2.98 dB and 2.53 dB, respectively, on a 2.2 mm thick cardboard material. The rectifying element consists of a voltage-doubler configuration connected through a T-matching network to the antenna. At low RF input power (−10 dBm), the maximum available DC output power is experimentally evaluated at 1.73 μW, 7.5 μW, and 8.5 μW for HSMS-2860, HSMS- 2850, and SMS7306-079L diodes, respectively. The respective rectifiers with diodes SMS7306-079L, HSMS-2850, and HSMS-2860 exhibit optimal load values of 2 kΩ, 2.6 kΩ, and 8 kΩ. The rectifier designed using the SMS7306-079L diode experimentally reaches a maximum power conversion efficiency (PCE) of 14.2% at −5 dBm input power when the optimal load value is 1.5 kΩ.
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