Wireless Power Transmission via Modulated Laser Irradiation of Pyroelectric Thin Films

Abstract

The paper highlighted one of the benefits of thin film pyroelectrics versus bulk systems, namely, the ability to withstand large electric fields. When using considering a PEC technique that uses cyclic charging and discharging, this benefit becomes apparent upon inspection of the cycle (Figure 1a) and work (W) equationFor maximum power density each PEC cycle should experience as large of a ΔD as possible, enabled by large pyroelectric coefficients, and be subjected to as wide a ΔE as possible. The electrocaloric community has exploited this benefit, showing a number of material systems with excellent energy conversion potential under high applied fields. [2][3][4][5][6] Thin film pyroelectrics also have the benefit of low thermal mass, which enables faster energy conversion at higher cycle frequencies thus producing higher power. [7] Equation (2) relates the work to power simplywhere P and f are the cycle power and frequency, respectively. Bhatia et al. showed that the strongest correlation to PEC power density came from cycle frequency and not material properties.Using an electrically driven resistive heater, Bhatia et al. demonstrated energy conversion cycles at 1 kHz obtaining record high power densities of 3 W cm −3 . [8] This is in contrast to a majority of studies using bulk pyroelectrics where power densities were limited to <200 mW cm −3 due to systems relying on fluid flow over pyroelectric structures for transient temperature variations. [9,10] Radiatively stimulated PEC has been under consideration since the 1960s. A thermo-dielectric energy system utilizing concentrated solar energy was patented in 1960. [11] In 1982, NASA commissioned a study on using PEC on rotating satellites, where periodic solar incident energy would provide the time variant temperature. [12] Targeting applications where PEC was optically driven, Zabek, et al., showed that using micropatterned top electrodes on a free-standing polymer pyroelectric improved PEC performance by 380% by enabling greater optical absorption by the material while only minimally affecting the capacitance. [13] Thermal energy harvesting was demonstrated using a heat lamp and off-the-shelf pyroelectric material at a frequency of <0.5 Hz, resulting in harvested energies in the milliwatt range. [14] Thin film pyroelectrics, which have the greatest potential for high power and efficiency conversion, have infrequently been used for real conversion cycles.Distributed, small sensor systems show promise for creating a more connected human experience through the internet of things, yet their energy needs are not being satisfied by current on-sensor storage mechanisms, such as batteries, or energy harvesting approaches. One alternative is to wirelessly transmit power to sensor nodes. Over short distances (<10 cm) this is accomplished via inductive or capacitive coupling. Long distance transmission (>10 m) requires a low-divergence signal source, such as a laser, and a receiver that can convert either light or heat into electricity. Pyroelectric thin films receivers...

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