Small antenna for RF energy scavenging applications
Creators: name: Sarosh Irani, Kashka
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400803
subject: Electrical energy generation (incl. renewables, excl. photovoltaics)
classificationCode: 400805
subject: Electrical energy transmission, networks and systems
classificationCode: 400899
subject: Electrical engineering not elsewhere classified

description: The widespread availability of Radio Frequency (RF) energy has increased due to the progression in wireless and broadcasting communication devices, which suggests the possibility to scavenge associated electromagnetic (EM) energy to feed low-powered devices. Based on RF field investigation and analysis of the maximum available power in Melbourne, Australia results show that broadcasting systems at 540 MHz (with 20 MHz bandwidth) and 100 MHz (88 – 108 MHz) are great RF scavenging sources because they provide stable RF signal levels, low propagation loss and produce maximum available power.<br><br>To collect the RF energy an antenna will be utilized. Furthermore, the antenna must be:<br><br>- Planar and omnidirectional, to pick up EM energy in all directions.<br><br>- Have a bandwidth greater than or equal to 20%, to satisfy the broadcasting system requirements.<br><br>- Matched to a 50 Ω impedance, so that no power is lost when feeding to a rectifier.<br><br>- The antennas dimensions must meet the size of a standard roof tile (432 mm x 345 mm).<br><br>The antenna will be embedded into the roof tile so that the entire rooftop can collect RF Energy. However, to meet the dimensional requirements of the roof tile the antenna must be smaller than a quarter of its wavelength or 0.22λ, at 100 MHz. Due to the dimensional constraints imposed by the size of the roof tile, the challenge remains to design a simple, low cost and efficient antenna. High Density Polyethylene (HDPE) was used as the substrate for the antenna because of its wide use in roof tiles. The substrate was provided by CME (a company who makes the roof tiles).<br><br>To reduce the size of the antenna, miniaturization techniques will need to be implemented. The problem with using any miniaturization technique is the effect it has on the radiation characteristics (bandwidth, gain and efficiency).<br><br>This thesis has focused on miniaturizing:<br><br>A semi-elliptical wideband dipole antenna using meandering slots and an external matching circuit, which will operate in the FM band (88 – 108 MHz).<br>A top loaded dipole antenna with an inductive matching loop, which will operate in the FM and UHF TV (472 – 495 MHz) bands.<br>The semi-elliptical dipole antenna, with slots and a matching circuit, had a resonant frequency of 100 MHz (a bandwidth of 1%) with a gain of 0 dBi. A size of 0.31λ x 0.25λ was achieved.<br><br>To eliminate the need for an external matching circuit, a top loaded dipole antenna with an inductive matching loop was utilized for the FM band. The fabricated antenna had a resonating frequency of 99 MHz, with a bandwidth of 1% and a gain of 1.5 dBi. That is a size of 0.22λ x 0.17λ.<br><br>Finally, a top loaded dipole antenna with a matching loop was presented for the UHF TV band (472 – 495 MHz). A bandwidth of 5% and a gain of 1 dBi were achieved. That is size of 0.27λ x 0.27λ.