Efficient, compact, wireless battery design

Wireless batteries or rectennas – rectifying antennas – are conceived for converting wireless RF power into DC power Although power conversion efficiencies exceeding 80% have been reported for high (20dBm) rectenna input power levels, wireless batteries will be most beneficial at large distances from sources that will radiate at power levels limited by national and international regulations. Therefore, the challenge is in maximizing the power conversion efficiency of wireless batteries for low input power levels, say 0dBm and below. By directly conjugate matching a rectifying circuit to a microstrip patch antenna, the need for a matching network between the two no longer exists. Thus the efficiency of the wireless battery will improve. Moreover, this matching technique automatically uppresses the reradiation of harmonics by the microstrip patch antenna since the harmonics will be mismatched. Thus, the impedance matching and filtering network encountered in traditional wireless battery designs has become obsolete. With the aid of analytical models developed for antenna and rectifier, single-layer, internally matched and filtered PCB rectennas have been designed for low input power levels. An efficiency of 52% for 0dBm input power has been realized at 2.45GHz for a wireless battery realized on FR4, showing an improvement – next to the size and complexity reduction - of more than 10% over a traditional rectenna design. A series connection of these wireless batteries is shown to be able to power a standard household wall clock

Accuracy improvement of cavity model effective patch dimensions using a single full-wave iteration

An accuracy improvement procedure for microstrip patch antenna design is presented. The classical cavity model of a patch antenna is discussed with emphasis on the fringe fields and the compensation for these fringe fields in the form of effective patch dimensions. The effective patch dimensions are improved using a single full-wave simulation, drastically increasing accuracy at the cost of only a small increase in computation time. Using the input impedance of the patch antenna determined via a full-wave simulator, effective patch dimensions are adjusted for each single mode, matching the cavity model results to the full-wave results. It is found that adjustment of non-resonant modes cause a shift in amplitude of the input impedance and a adjustment of a resonant mode results in a shift in frequency. The error in predicted impedance decreases from 75% to 5%. An example is given where an exotic input impedance is required, to match the antenna directly to a nonlinear system. This shows that this method results in fast, efficient, reliable and optimal microstrip patch antenna design

Analytical models for low-power rectenna design

The design of a low-cost rectenna for low-power applications is presented. The rectenna is designed with the use of analytical models and closed-form analytical expressions. This allows for a fast design of the rectenna system. To acquire a small-area rectenna, a layered design is proposed. Measurements indicate the validity range of the analytical models