Synthesis between the printed spiral coil and the planar interdigital capacitor for near-field wireless energy transfer (WET) is proposed. The proposed amalgamated design is intentionally positioned under several displacements, namely, planar offsets at the z-axis as well as lateral offsets at both the x-and y-axes to investigate tolerance capability. This is particularly crucial in practical circumstances, whereby a perfect alignment between primary and secondary resonators is not usually achieved unless with the integration of magnet plates to aid seamless position latching, otherwise complex adaptive matching circuits are needed to compensate for displacements. At a fixed axial transfer distance of 25 mm, the corresponding maximum simulated and measured transfer efficiency is 73.01% and 71.84%, respectively, under perfect alignment. Sustainable power transfer efficiency (PTE) is demonstrated during a 360 • planar clockwise rotation with the step size of 45 • and the measured variation ratio is 0.02 while the feasibility of preserving PTE until 0.6 quotients of lateral displacement and axial distance is validated when up to 15-mm lateral offsets occur either from x or y reference planes. It can thus be concluded that the printed spiral resonator proposed appears to be a good candidate to rectify planar and lateral displacements featuring simplicity and space-saving robust structure that necessitates only a minimized footprint, thus paving the way for adaptation in WET applications, such as consumer electronics and implanted medical devices.

A printed spiral resonator without external lumped elements is proposed. Instead of employing surface-mount device capacitors, the series-parallel capacitive plates are designed and etched on the same substrate to achieve simultaneous conjugate matching between a pair of symmetrical near-field coupled resonators. Simulations are conducted with the aid of CST Microwave Studio. The proposed design displayed satisfactory tolerance toward planar displacement at z-axis plane, lateral displacement at x-and y-axis planes, as well as concurrent planar and lateral displacement. Positioned at perfect alignment with a transfer distance of 15 mm, the simulated and measured maximum power transfer efficiency achieved are 79.54% and 74.96%, respectively. The variation ratio for planar displacement acquired is 0.29% when receiving resonator is rotated from −180 • till 180 • with a step size of 15 •. Under rotational angle from 0 • till 180 • , the measured average variation ratio for lateral displacement at x-and y-axis up to 15 mm is 20.14%. The feasibility of sustaining power transfer efficiency under various offsets depicts the possibility of integrating the proposed simple design for low power wireless energy transfer applications, such as wireless charging for handheld devices in consumer electronics and implanted biomedical devices.

Accomplishing equilibrium in terms of transfer efficiency for dual-band wireless energy transfer (WET) system remains as one of key concerns particularly in the implementation of a single transmitter device which supports simultaneous energy and data transfer functionality. Three stages of design method are discussed in addressing the aforementioned concern. A single layer dual-band printed spiral resonator for non-radiative wireless energy transfer operating at 6.78 MHz and 13.56 MHz is presented. By employing multi-coil approach, measured power transfer efficiency for a symmetrical link separated at axial distance of 30 mm are 72.34% and 74.02% at the respective frequency bands. When operating distance is varied between 30 mm to 38 mm, consistency of simulated peak transfer efficiency above 50% is achievable.

A flexible microstrip grid array antenna designed on polydimethylsiloxane (PDMS) substrate and copper conductive fabric as the patch and ground plane is presented. The proposed rectangular geometry designed at 15 GHz is made of 19 cells with 22 radiating elements. The proposed antenna achieves almost 40% wideband characteristics at −10 dB reflection coefficient from 11.10 GHz until 16.2 GHz with measured maximum gain of 14.0 dBi in normal state. Analysis on performance of antenna at bend state with various value of bend radius has been done. The measured reflection coefficient shows low sensitivity to bending effect where the antenna operates well at designed frequency which is at 15 GHz. Due to these criteria, it is a suitable candidate for wearable applications.

With the adoption of single coil approach, printed spiral resonator design strategy for near-field wireless energy transfer is presented. A pair of symmetrical resonators operating at high frequency band specifically 6.78 MHz and 13.56 MHz is designed. Simulated power transfer efficiency (PTE) of over 88% are obtained for both frequencies when coupled spiral resonators separated at a distance of 25 mm is integrated with hybrid compensation network topology. The variance of PTE between both frequencies is about 0.04.