Radio-frequency Rectification Research Articles

Nonlinear transport and radio frequency rectification in BiTeBr at room temperature

Materials showing second-order nonlinear transport under time reversal symmetry can be used for Radio Frequency (RF) rectification, but practical application demands room temperature operation and sensitivity to microwatts level RF signals in the ambient. In this study, we demonstrate that BiTeBr exhibits a giant nonlinear response which persists up to 350 K. Through scaling and symmetry analysis, we show that skew scattering is the dominant mechanism. Additionally, the sign of the nonlinear response can be electrically switched by tuning the Fermi energy. Theoretical analysis suggests that the large Rashba spin-orbit interactions (SOI), which gives rise to the chirality of the Bloch electrons, provide the microscopic origin of the observed nonlinear response. Our BiTeBr rectifier is capable of rectifying radiation within the frequency range of 0.2 to 6 gigahertz at room temperature, even at extremely low power levels of −15 dBm, and without the need for external biasing. Our work highlights that materials exhibiting large Rashba SOI have the potential to exhibit nonlinear responses at room temperature, making them promising candidates for harvesting high-frequency and low-power ambient electromagnetic energy.

Indium-gallium-zinc oxide Schottky diodes on softening substrates for rectifying bioelectronic circuits

Incorporating electronic components onto soft materials facilitates the development of compliant electronics suited for bioelectronic applications. In this work, we present indium-gallium-zinc-oxide (IGZO) Schottky diodes fabricated on a stimuli-responsive polymer that undergoes softening (i.e. orders-of-magnitude drop in modulus) upon exposure to physiological stimuli. These diodes rectify megahertz radio-frequency (RF) signals in half-wave rectification circuits across the softening of the polymer substrate and withstand mechanical and chemical stresses such as repeated folding up to 10 000 cycles and aging in a simulated physiological medium for up to two weeks. The effects of thermal annealing and ultraviolet-ozone treatment processes are evaluated using dynamic mechanical analysis and x-ray photoelectron spectroscopy techniques, showing that these processes lead to a large improvement in the interface properties of the platinum-IGZO Schottky contact while preserving the thermomechanical properties of the softening polymer substrate. The RF rectification capabilities of these diodes in softened and deformed states are particularly interesting for the next generation of soft wireless bioelectronics.

Reduction in RF sheath rectification with insulating antenna enclosure walls

Radiofrequency (RF) sheath rectification is one of the most prominent deleterious effects associated with ion cyclotron range of frequencies (ICRF) heating in fusion plasmas. RF sheaths and associated effects, such as impurity generation and convective cell generation, need to be mitigated to ensure that ICRF is a viable option for heating in future fusion devices. Experiments were performed on the Large Plasma Device (LAPD) at UCLA to explore the effects of using electrically-insulating antenna enclosures on RF rectified sheaths. Three different enclosure side-wall materials were used, including copper, MACOR (electrically insulating), and MACOR over copper. In the case of the MACOR–copper side walls, the non-conductive MACOR material was exposed to the bulk plasma but a layer of copper was added below to allow for image currents to flow. All three of the experiments had similar plasma density, temperature, and background magnetic field. In the case of the copper enclosure, RF rectified potentials, many times the local electron temperature, and associated formation of convective cells were observed and reported Martin M. et al (2017 Phys. Rev. Lett. 119 205002). In the experiments with MACOR and MACOR–copper enclosures, RF rectification was significantly reduced. Additionally, these latter two experiments showed no evidence of convective cell formation. Although the results from the MACOR experiment are reminiscent of the results obtained in ASDEX-U with a three-strap antenna optimized to reduce image currents on the antenna limiters Bobkov V. et al (2016 Nucl. Fusion 56 084001), the MACOR–copper experiment seems to suggest that insulating plasma facing materials have at least an equally strong impact on reducing potential rectification.

The role of rectified currents in far-field RF sheaths and in SOL losses of HHFW power on NSTX

Radio-frequency (RF) rectification is an important sheath phenomenon for wave heating of plasma in fusion devices and is proposed to be the mechanism responsible for converting high-harmonic fast-wave (HHFW) power in the National Spherical Torus eXperiment (NSTX) into a heat flux to the divertor. RF rectification has two aspects: current rectification and voltage rectification, and, while the latter is emphasized in many application, we demonstrate the importance of current rectification in analysis of the NSTX divertor during HHFW heating. When rectified currents are accounted for in first-principle models for the heat flux to the tiles, we predict a sizeable enhancement for the heat flux in the presence of an RF field: for one case studied, the predicted heat flux increases from 0.103 MW/m2 to 0.209 MW/m2. We also demonstrate how this rectification scales with injected HHFW power by tracking probe characteristics during a HHFW power ramp; the rectified current may be clamped at a certain level. This work is important for minimizing SOL losses of HHFW power in NSTX-U but may also have implications for near-field studies of ICRF antennae: ignoring rectified current may lead to underestimated heat fluxes and overestimated rectified voltages.

Radio-Frequency Rectifier for Electromagnetic Energy Harvesting: Development Path and Future Outlook

The roadmap evolution and historical milestones of electromagnetic energy conversion techniques and related breakthroughs over the years are reviewed and presented with particular emphasis on low-density energy-harvest technologies. Electromagnetic sources responsible for the presence of ambient radio-frequency (RF) energy are examined and discussed. The effective use and recycling of such an ambient electromagnetic energy are the most relevant and critical issue for the current and future practicability of wireless energyharvesting devices and systems. In this paper, a set of performance criteria and development considerations, required to meet the need of applications of ambient electromagnetic energy harvesting, are also derived from the radiating source analysis. The criteria can be calculated from a simple measurement of the I-V nonlinear behavior of RF rectification devices such as diodes and transistors, as well as linear frequency behavior (S-parameters). The existing rectifying devices are then reviewed in light of the defined performance criteria. Finally, a technological outlook of the performances that can be expected from different device technologies is assessed and discussed. Since the proposed spindiode technology would present the most promising device platform in the development of the most useful ambient energy harvesters, a special highlight of this disruptive scheme is provided in the presentation of this work.

Radio frequency rectification on membrane bound pores

Probing the interaction of biological systems with radio frequencies holdsgreat promise for research and drug screening applications. While a commonassumption is that biological systems do not operate at radio frequencies, we findthat currents due to ion transport through channels and pores in cell membranesare in the pA to nA range. These values translate via the average current⟨I⟩ = ⟨n⟩e/τd = ⟨n⟩ef to frequencies in the range of 1 MHz–1 GHz, where⟨n⟩ is the average number of ions transported andτd is the dwell time of the ions in the channel. It is thus desirable to have circuitry availablewhich facilitates radio frequency spectroscopy of ion transport. This will yield real-time invitro information on ion channel operation. Here we present measurements on the localinteraction of a radio frequency signal with single ion channels and pores. We find radiofrequency rectification and pumping on the channels and pores embedded in suspendedbilipid membranes, recorded in direct current measurements. This electromagneticmodulation can be used to probe the dynamics of ion channel conformational changes.

Radio-frequency rectification in electrogenic and nonelectrogenic cells ofChara andNitella

Electrogenic cells ofChara braunii andNitella flexilis were placed in a pulse-modulated radio-frequency electric field of up to 6000 V/m. Their vacuolar resting potentials were found to experience submillivoltdepolarizing offsets (typically 140 μV at 250 kHz) which were relatively indepencent of temperature, increased linearly with resting potential from a zero near −210mV, and had a cutoff (putatively due to ion transit times) near 5 MHz. By contrast, nonelectrogenic cells experiencedhyperpolarizing offsets (typically 1100 μV at 250 kHz) which increased in magnitude with increasing temperature, were independent of resting potential, and had a transit time cutoff near 10 MHz. The ionic mobilities inferred from these cutoff frequencies are somewhat higher than would be expected for active transport and presumably reflect passive conductance mechanisms which therefore must be presumed different for the electrogenic and nonelectrogenic states.