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Continuous advances in ultralow-power electronics are a fundamental driving force of developing far-field wireless power harvesting techniques, which generally harnesses low/ambient energy in free space or dedicated wireless power from a power base station. This article reviews recent developments and technology trends in far-field (radiative) wireless power harvesting, including modeling of rectification process inside nonlinear devices, insights into rectenna system design, and demonstrations of emerging applications. The rectification process inside nonlinear devices will be explored, upon which a device selection guideline is provided to help quickly identify suitable devices. Then, the optimization of rectenna design is discussed to realize efficiency enhancement at a limited input power level. Since far-field wireless power harvesting has become a critical enabling technology for battery-free Internet of Things, a series of promising applications is demonstrated in this article to highlight the challenges and opportunities in the field.

It all started with a spark. Let us rewind back to 1887, in Germany. The days were getting cooler in the garden of the Technische Hochschule in Karlsruhe as Heinrich Rudolf Hertz was setting up the first-ever far-field wireless power transmission with increasingly more power [1]. He was striving to demonstrate the wireless nature of electromagnetic waves and propagation. Moreover, as no high-frequency (nearly 100 MHz) voltmeter was available at that time for his experiment, he had to transmit enough power to generate a spark-hundreds of volts!-at the receiver to validate the famous theory of James Clerk Maxwell.

This work summarizes an outdoor dynamic measurement of ambient radiofrequency (RF) power density in the core areas of Montreal city, which can eventually be exploited for possible battery-free Internet of Things (IoT) sensor network planning. The measurement covers a frequency range of 400–2700 MHz. The power density along major streets, roads, and highways is captured and analyzed, which differs from previous stationary measurements. Results indicate that cellular communication bands (GSM/LTE850 and LTE700) are the best choice for RF energy recycling in downtown (populated) areas. The largest average power levels of GSM/LTE850 and LTE700 bands are −35.50 and −36.95 dBm, respectively. In contrast, in suburban areas where cellular communication signals are generally weak, the digital television band with a peak level of −47.68 dBm presents the largest among all frequency bands. Moreover, one separate measurement at a fixed location is conducted on a typical workday to study the effects of foot traffic on ambient RF power density. Results illustrate that no obvious fluctuations are detected during this daytime measurement. For example, both average power levels of GSM/LTE850 and LTE700 remain at a relatively stable level of −25 dBm throughout the measurement. With the advance of far-field wireless power transfer and backscattering techniques, ambient RF power-enabled battery-free IoT sensors are feasible and will contribute to the planning and implementation of a smarter and greener city.

This work proposes to enlarge the maximum readout distance of battery-free harmonic transponders through a careful Schottky diode selection and a consideration of low-temperature operations. Diode SMS7621 is identified to deliver lower conversion loss (CL) of harmonic transponders based on a diode selection guide. Moreover, an analytical method for studying temperature effects on the transponder CL performance is introduced and derived with satisfactory accuracy. A diplexer inserted in the harmonic transponder design can help reduce the antenna number. To mitigate matching difficulties at both fundamental and second-harmonic frequencies, a third-order diplexer is developed to enhance its bandwidth performance. Experimental verification has shown that low-temperature operations can effectively reduce the CL of the SMS7630-based harmonic transponder, thus increasing its readout distance. Specifically, its maximum readout distance at −40 °C has increased by more than 10%, from 6.4 to 7.1 m, compared with that at +40 °C. A complete harmonic transponder based on SMS7621, with dimensions of 85 mm $\times45$ mm has reached a maximum readout distance of 8 m when the fundamental frequency is 3.5 GHz.

Ambient power rectifiers are pivotal for batteryless or self-powered internet of things architectures and self-sustained communication/sensor platforms. The core of rectifiers, a nonlinear device, has been subject to significant research and improvements recently, especially at a low-power level, where rectifying efficiency is so limited. Current responsivity (the key rectification parameter describing the nonlinearity) is known to be impacted by the operating temperature, as predicted by William Shockley's law. However, no work has been carried out to quantify the impact of temperature in the RF rectification process, nor to relate existing diodes with their optimum operating temperature range. To address those missing links, this article first develops an analytical method to predict power conversion efficiency (PCE) of rectifiers from approximate milli-watt down to nano-watt level. Next, it identifies the optimum operating temperature of rectifiers corresponding to peak PCE. It also reports that the previous PCE ceiling of 15% (at an input power level below -30 dBm) can be broken when rectifiers operate at their optimum temperatures. Enhanced PCE results are then validated experimentally on SMS7630 and HSMS-2850-based rectifiers when operating at their optimum temperatures. Noticeably, the SMS7630-based rectifier delivers efficiency of 17.5% at -30 dBm and 41.7% at -20 dBm, showing respectively comparable and better PCE than that of tunnel diode-based counterparts at similar power levels. This article also indicates that rectifier design should consider the operating temperature when selecting diodes to maximize rectifying potential.

In this paper, an ambient power harvester with a single-diode device is proposed for simultaneously scavenging both radiofrequency (RF) and thermal energy in a mixed and cooperative manner. This cooperative harvesting process is theoretically examined through a proposed model of the diode and then validated by simulation and measurement. In the proposed cooperative power harvester, the harvested dc voltage from a thermal source is used to bias the diode for improving the diode's RF-to-dc power conversion efficiency (PCE). An accurate analytical model of the Schottky diode is developed for specifying the constraining parameters of RF-to-dc PCE and accurately predicting diode's performances in a low RF power range $({ \leq - \text{25}\;{\text{dBm}}})$ , respectively. The calculated results are found to be in a good agreement with the simulated ones obtained by the harmonic balance simulator in the advanced design system. For demonstration and validation, the proposed mixed cooperative power harvester is designed and prototyped on the basis of diode SMS7630. A total measured output dc power around 0.8 μ W is obtained with an RF-to-dc PCE around 33.4%, when the two injecting power sources at the diode are both −30 dBm. In addition, rectennas with and without a matching network are both fabricated and tested. By eliminating the L matching network, the rectenna is found to offer a higher dc output power. The proposed mixed cooperative power harvester is hoped to find potential real-world applications in an ambient atmosphere with RF coverage and temperature gradient. It not only helps to produce a higher power but also provides a reliable way of improving the resilience of dc power production.

A novel diplexer-based fully passive transponder is presented in this paper, which targets sub-6-GHz 5G-compatible internet-of-things applications. To alleviate the antenna design restrictions of traditional transponder with two separate antennas, a new architecture has been proposed with the introduction of a diplexer, which allows transponder to simply employ a dual-band antenna. In this paper, a dual-band circularly polarized omnidirectional spiral slot antenna, with enhanced bandwidth and gain performance, is designed as the transponder Tx/Rx antenna. Besides the new architecture, a diode selection criterion is proposed as well. Analytical models are derived, showing relationships between the diode’s SPICE parameters and the conversion efficiency or conversion loss (CL) of such diode-based transponders. With help of the analysis, transponder designers can easily identify diodes to implement transponders with better performance. Under the guidance of the criterion, low-barrier diode SMS7630 is chosen for verification. Measured CL results of the transponder circuitry part show a noticeable improvement over the state-of-the-art works. The complete prototype was tested with radar’s transmitting power of 25 dBm, and it presents a maximum read-out distance up to 7 m when the operating fundamental frequency is 3.5 GHz.

Ambient electromagnetic and RF energy is an ubiquitous energy resource that is found everywhere but difficult to harvest because of the time-varying orientation of incoming radiations and the low efficiency of RF rectifiers resulting from a low input power density operation. In response to these two challenges that come with the design of rectennas for ambient energy harvesting, this paper discusses a figure of merit to evaluate the rectenna performance that combines the rectification efficiency, the radiation efficiency, and the spherical coverage of the antenna. To illustrate this proposed figure of merit, a rectenna with a strengthen RF-to-dc efficiency and also a full spatial coverage is designed using beam-forming networks. The resulting system is demonstrated for a wireless sensor mounted on a pole. To maintain a reasonable size of the prototype, a miniaturization technique of a $4 \times 4$ Butler matrix (BM) is investigated, which allows for the reduction of the footprint of the BM by 2 compared to its classical microstrip design counterpart at 2.4 GHz. The overall rectification efficiency and dc power patterns are reported for the elevation plane of one multidirectional rectenna at 2.4 GHz for an incident power density of $0.45\,\,\mu \text {W}\cdot \text {cm}^{-2}$ . It is shown that the system can triple the dc output power compared to a three-dipole counterpart occupying the same area. Furthermore, while the maximum harvesting capability at $1 \,\,\mu \text {W}\cdot \text {cm}-^{2}$ does not exceed $28\pi $ %.steradian in the literature, it reaches $43.6\pi $ %.steradian with the proposed demonstrator.

Wireless Power Transfer (WPT) technology has paved the way to energize numerous sensor nodes for the Internet of Things (IoT) applications. This work theoretically and experimentally shows how a commercial multi-function sensor board can be energized by an ultra-high-frequency (UHF) multi-stage rectifier at low RF input power levels. Firstly, an analytical model characterizing multi-stage rectifiers is derived. Good accuracy of modeling results is observed in the low input power range of interest, compared with results obtained from the ADS Harmonic Balance simulator. Then, a 5-stage rectifier is employed to power the multi-function sensor board that can acquire the information of temperature, humidity, and light. This sensor board further transmits packets to an access point connected to a laptop for data visualization, making the power consumption of the sensor board relatively large. Hence, a 50-mF supercapacitor is required to drive such a power-hungry sensor board. The final demonstration shows that the multi-function sensor board works adequately in a low-duty cycle powered by a 5-stage rectifier with an input power of-10 dBm.

This work presents a battery-free temperature sensor based on a reconfigurable sensing antenna (RSA). Temperature-dependent varactors are loaded on RSA to detect temperature differences. Thus, temperature variations are first converted into capacitance changes of varactors and further into resonant frequency shifts of RSA. A harmonic radar interrogates this sensor by sending a fundamental signal, and then the sensor backscatters a second-harmonic signal with certain frequency shifts. Finally, the radar could decode temperature information based on the frequency shifts remotely with a doubled resolution through harmonic generation. Such an entirely passive temperature sensor is believed to find many potential Internet of Things (IoT) applications.

This work summarizes an outdoor dynamic radiofrequency (RF) power density measurement on the island of Montreal, QC, Canada. Different from previous stationary measurements, our scheme captures ambient power density along major streets, roads, and highways, through a moving vehicle carrying equipment. This work focuses on the populated downtown area in the city of Montreal. Results show that GSM/LTE-850 band reserved for mobile communications has the highest power density in general within the spectrum of interest (400 MHz to 2700 MHz). Whereas, despite lower density, digital TV signals are distributed more evenly in this area. Based on this observation, this work then gives several suggestions on far-field wireless power harvesting (WPH) for smart city, IoT, and other metropolitan wireless applications.

Backscattering communication is a key feature that will enable the true IoT/5G revolution towards massive use. However, the specification pressure it puts on the reader/gateway is a major drag on their deployment. In fact, self-jamming resulting from backscattering operation is highly problematic. Harmonic Backscattering Communication comes as a great solution to improve the dynamic range of the backscattered signal that can be received/analysed, thus increasing communication distance. We propose here a harmonic backscattering front-end based on nonlinear negative resistance device that also operates like usual backscatter tag with legacy reader. The circuit provides above +20dB conversion gain and reflection gain, and operates with a supply voltage below 200mV, which is a critical improvement over transistor technology.

International audience; Enzymatic reactions involving glucose hold the potential for building implantable biosensors and embedded power generators for various medical applications. While Biofuel cells (BFCs) such as enzymatic glucose/O2 are ensured to benefit from abundant chemical resources that can be harvested in the immediate environment of the human body, the highly critical in vivo kinetics of biofuel cell is not yet fully understood. Unfortunately, existing solutions for real-time monitoring of the reaction on rodents are not possible today, or too bulky, which has a biasing impact on the animal behavior. This work presents a light, battery-less, and wireless strategy to continuously monitor a BFC implanted in a laboratory rat using a Frequency Identification (RFID) link. An extremely lightweight and flexible tag antenna of footprint lower than 10 cm² is presented with communication capability above 60 cm in field environment. The operational capabilities are demonstrated with a 24-hour continuous monitoring of an enzymatic glucose/O2 reaction, both in vitro and in vivo.

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The highly power-efficient backscattering communication scheme holds solid potentials to lead the Internet of Things technologies. However, the asymmetric radio frontend architectures that ensure cheap and pervasive communicating things and tags at one end of the link, overburden the other end of the link (“reader”) with complicated and expensive hardware. This turns out to prevent the integration of the technology in the wide spectrum of consumer electronic devices (e.g. RF smartphone platforms). By separating TX and RX frequency bands, the harmonic backscattering scheme drastically loosens the technological constraints toward integration. We propose here the use of a single tunnel diode to build a harmonic reflection amplifier (HRA), using the nonlinear behavior of the negative differential resistance region to both generate harmonics and amplify the signals. The circuit also behaves like a common backscatter, with the same-frequency backscattering modulation for operation with legacy readers. Operating below 150 mV, the HRA drains 144- $\mu \text{W}$ dc power with a measured positive conversion gain of 18 dB.

An integrated cooperative harvester capable of collecting both electromagnetic [(principally radio frequency (RF)] and kinetic energy simultaneously is proposed and studied in this paper. One single substrate board is demonstrated to accommodate and integrate an electromagnetic kinetic generator, an F-shaped antenna, and a rectifying circuit, having a compact credit-card size. Cooperative harvesting mode enables a significant enhancement of the diode’s power conversion efficiency (PCE) and also greatly strengthening the resilience of harvester at the same time. Measured results suggest that SMS7630 and HSMS-2850-based cooperative harvesters can increase dc output power by 50% to around 100% when both injecting power sources exhibit below −37 dBm with reference to the total added amount of dc power harvested directly from separate RF and kinetic excitation modes. A closed-form method is proposed and used to predict the enhanced efficiency performance of the cooperative harvester within a low power range of interest (from −50 to −30 dBm). Our analysis highlights the roles of the diode’s nonlinear junction resistance and capacitance. Good agreements are observed when comparing the analysis results with harmonic balance simulations by ADS. Furthermore, this method is carefully verified by measured results of two different diode-based harvesters. Measured dc output power rectified from cooperative harvesting mode is reported to be 1.16 and 1.97 times larger with SMS7630 and HSMS-2850, respectively, when both power sources are −40 dBm, compared to the conventional single RF harvesting mode. The proposed cooperative harvester with its strong resilience is highly suitable for ambient power harvesting in an ever-changing environment.

An integrated ambient kinetic and microwave energy scavenger is presented in connection with its strategy of two-level hybridization, namely structural and functional integration of the two dissimilar energy harvesting techniques. Specifically, they are related to two-resonator/transducer integration and simultaneous/collaborative rectification. An F-shaped radiofrequency antenna serves as the microwave energy collector and a Michael Faraday’s generator mounted on a mechanical beam cut out of the printed circuit board acts as the electrical current producer. Both microwave and mechanical resonators are optimally designed and accommodated on the same substrate with a compact size comparable to that of a credit card ( $80\,\,\text {mm} \times 50\,\,\text {mm}$ ). The demonstrated hybrid power harvester has a capacity to operate properly with either microwave or mechanical excitation. When both power sources are accessible, it can provide a notable efficiency enhancement compared with the separate harvesting of two single sources. The measurements show that at a typical injecting AC power of −38 dBm, the rectified DC output power could be increased by at least 50% compared with a direct summation of DC output power through two separate modes. An efficiency enhancement of 85% can be achieved when diode’s injecting power sources are −45 dBm. With a strong resilience, such a hybrid power harvester is able to potentially find its wide practical applications.

Benefiting from advantageous features of fast tuning, small size, and easy integration, the electronic impedance synthesizer (EIS) has been developed for on-wafer load–pull characterization systems, tunable matching networks, reconfigurable devices and systems, and so on. The previous designs of the EIS were mostly based on the empirical data instead of a closed-form design. Moreover, incomplete figures of merit (FOM) were chosen to optimize and evaluate the EIS. In this paper, we propose and present, first of all, a semiclosed-form design procedure for the distributed EIS. Then, a particle swarm optimization method is introduced to optimize the proposed nonuniformly distributed EIS, which comprises an adjusting circuit and a nonuniformly distributed circuit. Experimental results demonstrate that the proposed nonuniformly distributed structure can not only improve the Smith chart coverage but also reduce the size, compared to the uniform counterpart. The fabricated nonuniform EIS operating from 0.8 to 2.5 GHz, exhibits a good agreement between theory and measurement. Furthermore, the most comprehensive FOM are presented to evaluate the fabricated EIS.

Deployment of 5G network infrastructure is a timely opportunity for millimeter-sized battery-free sensors. However, millimeter-wave (mmW) devices often suffer from high conversion loss and path loss that are heavily limiting their communication/detection distance, especially for the case of harmonic transponders based on Schottky diodes. A deep and comprehensive parametric understanding of the second-harmonic generation mechanism of Schottky diodes in the mmW 5G bands can help us to identify suitable diodes or guide diode fabrication to reduce transponder conversion loss. This work reveals that both diode nonlinear junction resistance and capacitance contribute to the second-harmonic generation across the mid-band (sub-7 GHz) and high-band (mmW) 5G frequency bands. However, the nonlinear junction capacitance dominates the second-harmonic generation in the mmW bands. Without Joule heating during the conversion process, the capacitive nonlinearity is more efficient than the resistive nonlinearity, which means that a Schottky diode with a lower junction capacitance will efficiently reduce its associated conversion loss. The VDI GaAs zero bias diode with a low zero bias nonlinear junction capacitance (19.19 fF) shows superior conversion loss performance, which indicates that it can be employed to enhance the detection distance of battery-free harmonic transponders in the mmW 5G bands.

finalist, Best paper award; International audience; This paper presents a modular and reconfigurable rectenna unitcell (RU) made up of an antenna, a rectifier and radiofrequency (RF) power combiners intended to form a scalable and adaptative beam-forming network, for autonomous passive tracking or RFID monitoring applications. The reconfigurable rectenna unitcell allows a dual mode operation thanks to both RF and DC possible combinations of multiple rectenna unitcells. On the one hand, the passive beam-forming operation, coming from the RF combination of multiple rectenna unitcells provides oriented communication or localization capabilities. On the other hand, the series DC connection of RF isolated rectenna unitcells delivers DC power to the system with high output voltage under low RF power densities. Prototypes of 4-edges rectenna unitcells are designed in the 2.4 GHz band. The operation of one individual RU is demonstrated, and it is shown that multiple RUs are suitable for RF energy harvesting, multiple-tag communication and tag localization.

Scarcity of accessible energy compels battery-less micro-energy wireless devices to embed energy harvesting, backscattering modulation, and even harmonic operation to avoid self-jamming. However, since those Internet of Things (IoT) devices are meant to be ubiquitous, keeping a low level of complexity of the nonlinear operation. Also, a small footprint circuit is becoming an ever-challenging task. This paper presents a hybrid IoT frontend architecture capable of rectification, second-harmonic generation and modulation using a single diode controlled by harmonic terminations. The proposed solutions of reconfigurability are validated by measurements.

International audience; This paper presents a miniaturized microstrip antenna on an air-filled paper substrate. The presence of air in the substrate accounts for low dielectric losses and a high dielectric thickness, resulting in a high radiation efficiency and a large bandwidth. In addition, the edge of the antenna is exploited to feed the antenna with a coplanar line that can be connected to a 50 coaxial probe. This original feeding technique permits the reduction of the frequency of resonance as the air gap increases. The antenna is further miniaturized with the insertion of a slot in the ground plane. As a result, a high degree of miniaturization can be obtained along with a high efficiency. The influence of the air gap and of the slot on the antenna's performances is investigated. Two prototypes with dimensions of 0.29 x 0.29 x 0.065 radiating at 2.45 GHz are fabricated with copper tape and silver ink and the antennas' performances are experimentally validated: a gain of 4.5 dBi and a front-to-back ratio of 9.5 dB are measured, corresponding to a radiation efficiency of 70%. Index Terms-Paper substrate, microstrip antenna, air gap, air-filled, miniaturization, light weight antenna, low cost.

International audience; As an answer to the self-interference problem inherent to RFID systems, this work proposes a dual-band backscat-tering architecture. A dual-band RFID system architecture can bring several advantages to the RFID technology. In fact, a dual-band reader could operate without any self-interference cancellation circuit that currently limits its sensitivity; moreover, its dual-band architecture would be compatible with software defined radio-based cellphones. Dual-band readers will need to talk with low-powered dual-band tags that up-convert, modulate, and backscatter the impinging signal from the fundamental frequency to the 2 nd harmonic without weakening the communication link. This article reports on the UHF dual-band Harmonic Tun-neling Tag capable of backscattering and amplifying a 900 MHz signal when receiving an input carrier at 450 MHz. The Harmonic Tunneling Tag provides positive conversion gains (+7 dB) that improve the communication link by a factor of 2 and operates under a very low bias voltage of 0.16 V.

Conversion loss performance of fully passive harmonic transponders, which is drastically affected by low power mixing operation, determines their detection ranges directly. This work presents both theoretical and experimental studies of thermal effects on the performance of fully passive harmonic transponders. For the zero bias Schottky diode-based harmonic transponder, it is found that a lower temperature can lead to a larger detection range of the transponder in the power range of interest (≤-30 dBm). The conversion loss decreases by around 3.25 dB when the temperature goes down to -20°C compared to the loss performance at +30 °C. In other words, the theoretical figure-of- merit maximum detection range has been enlarged by about 19.3 %. This work also highlights the opportunity of operating the Internet of Things transponders in winter, as thermal conditions play an important role in the design of nonlinear component-based devices to achieve higher reliability and better performance.

Estimating the amount of harvestable ambient RF and microwave power from the omnipresent electromagnetic sources is of vital importance when designing a wireless device that makes use of ambient microwave power harvesting (AMPH) as a power source. This paper studies and looks into the underlying RF and microwave rectification mechanism at low input ambient power levels, specifically −30 dBm and below. A fundamental theory is formulated and developed, which is able to correctly predict the efficiency of a rectifier including the effects of matching network insertion losses through an easy-to-understand analytical model. The suggested model provides a direct design guideline in determining and choosing the optimal diode for a predetermined application. Based on the developed theoretical framework, the diode characteristics that have a direct impact on the microwave power conversion efficiency are discussed in detail. Three different Schottky diode rectifiers were designed on the basis of the tools described in this paper, thereby validating the proposed model and highlighting the influence of critical diode parameters on its performances. The measured results are then compared with those predicted by the proposed model and state-of-the-art microwave power rectifiers, showing a good model accuracy and also a 10% improvement in the rectifying efficiency for the low input power levels of interest.

International audience; Harvesting low-density ambient microwave power as an alternative power source for small ubiquitous wireless nodes has been proposed in recent papers discussing emerging technologies like the Internet of Things and Smart Cities. However, a literature review of the state-of-the-art Schottky diode based microwave rectifiers shows that a maximum efficiency has been reached for such devices operating in the low-power regime, as is the case for ambient microwave power-harvesters. This work examines the underlying physical mechanisms responsible for this RF-to-dc power conversion efficiency limitation, and explores a high I-V curvature backward tunnel diode to overcome this efficiency limitation. Measurements of the 2.4 GHz RF-to-dc power conversion efficiency at -40 dBm input power demonstrates that the backward tunnel diode outperforms the HSMS-285B Schottky diode by a factor of 10.5 and the Skyworks SMS7630 by a factor of 5.5 in a lossless matching network scenario. A prototype built using a new GSG probe embedded with a matching circuit showed a total power conversion efficiency of 3.8% for -40 dBm input power and 18.2% for -30 dBm input power at 2.35 GHz.

International audience; Unlike near-field wireless power transfer based on the non-radiative inductive and magnetic resonant coupling which has already had a number of successful commercial applications, far-field radiofrequency (RF) ambient energy harvesting still trades its operation distance for a limited power density and low rectifying efficiency. Particularly, its low rectifying efficiency has been proved to be directly associated with rectifier's input power. Thus, by gathering more out of the available surrounding energy in the direct environment, the total dc output level can be efficiently enhanced. This paper reviews recent related works and provides a comprehensive picture of this idea through analytical modelling and experimental validation. It can be shown that a collaborative harvesting of multi-physical sources can be an effective solution to enable battery-free applications.

session: Antenna and Propagation; International audience; The design of antennas on cellulosic flexible materials such as paper can be very challenging because of the limited thickness and the high losses in the Radio Frequency (RF) domain. In this paper, a novel patch antenna with an origami structure is proposed to address the null radiation efficiency obtained with the conventional paper-based structure. As the electromagnetic waves mostly travel in the air, ideal conditions such as no loss and a low dielectric constant allow for the asymptotic value of directivity of microstrip antennas to be reached with a 63 % experimental radiation efficiency. This flexible antenna can be used for RF energy harvesting or sensing applications due to the sensitivity of paper on atmospheric conditions.

An analytical model for the conversion loss (CL) calculation of diode-based fully passive harmonic transponders is proposed in this work. Given diode’s SPICE parameters, the proposed model can accurately predict second-harmonic output based on RF input power. Thus, CL can be easily obtained. Such an accurate analytical model can be applied to evaluating potential CL performance of each diode candidate. Then, a novel diplexer-based fully passive harmonic transponder is designed, prototyped and measured. Through the introduction of the diplexer, traditional stringent antenna design restrictions can be alleviated. For an input power level of −30 dBm, measured CL of the proposed harmonic transponder is around 20.2 dB, which is more than 10 dB lower than the state-of-the-art counterpart.

International audience; The Magnetically Coupled Resonant Wireless Power Transmission (MCR-WPT) is a promising technique to deliver milliwatts of power to mm-size implanted devices at centimeter distances. Such a resonant link is primary dependent on the Q factor of the implanted receiving magnetic resonator, since the transmitting bears much less design constraints. This work uses a high Q topology to propose a 3 mm implantable resonator built with state of the art quality factor of 61.4 when measured in saline water emulating the worst-case dielectric characteristics of the human tissues.

Monitoring small animal to collect telemetry during their movement is a challenging task, as the body displacement tend to impact greatly the field distribution. A power transfer scheme based on complementary split ring resonator is demonstrated here for UHF RFID reader-tag link rodent telemetry application. It is shown that the operation of the tag is maintained in all the region of the cage where the animal can move. Thanks to an adequate ground plane, the wearable tag antenna is minimally effected by the presence of the biological tissues. The map of the efficiency along the cage surface was derived from multiple simulations and measurements. It results a minimum efficiency of an order of magnitude higher than required, and a maximum of 1.8% while the tag is worn by the animal.

session Rectifier and Rectennas; International audience; This paper introduces a novel rectenna with a double-sided ground plane microstiip antenna that has a bidirectional radiation pattern for ambient RadioFrequency (RF) energy harvesting. The microstrip antenna has a supplementary slot that enhances the aperture efficiency of a conventional rectangular patch antenna from 50% to 72% in simulation and allows for a high gain bi-directional pattern. With a maximum experimental gain of 7 dBi, the proposed rectenna can capture as much ambient RF power as a patch antenna and rectify it with an efficiency of 25.8% for a 0.15 nW/cm 2 power density, while being less sensitive to the energy source location. By duplicating the rectenna, two complementary radiation patterns can be obtained allowing incoming RF radiations with four different orientations to be collected.

A novel diplexer-based passive harmonic transponder for 5G-compatible IoT applications is presented in this work. Tx/Rx isolation is obtained through the generation of the 2nd harmonic signal. The proposed architecture design is based on a high isolation diplexer with a single (dual band) antenna as opposed to a traditional design using two-antenna isolation. Such an architecture relaxes the stringent design requirements of antennas in traditional architectures. Subsequently, antennas with enhanced performance can be utilized without resorting to compromise. Measured results of the proposed transponder circuit have shown improved performance over the state of the art counterparts. The conversion loss is about 20.2 dB at -30 dBm input power, which shows more than 10 dB better than previous work.

An accurate analytical model for the efficiency prediction of a hybrid ambient thermal and RF energy harvester is proposed in this paper. The DC power provided by the Thermoelectric Generator (TEG) is directly influencing the operation of the RF rectification. The proposed analytical model can provide an accurately predicted efficiency performance within a low-power range « −30 dBm)., thanks to a precise separation of each harmonic and DC component generated by diode. This has been verified by comparing with results obtained by both ADS simulation and experiments. Moreover., such a hybrid ambient thermal and RF energy harvester shows an advantage over its hybrid mechanical and RF energy harvesting counterpart in terms of rectified DC output power in the low-power range of interest. This is mainly due to the instinct of DC output converted from thermal energy and its huge contribution.

This paper proposes a varactor-based or reactive device-based frequency downconverter for low power harvesting applications. Theoretical formulation is derived to estimate the conversion efficiency. For demonstration purpose, a frequency downconverter with output frequency of 800 MHz is developed using two input frequencies of 2.4 GHz and 1.6 GHz. Considering practical situations, the two input signals are set to have an equal power level. A reasonable agreement is obtained between the simulated and calculated results. It was found that the varactor can achieve a high conversion efficiency above 90% in the case of no harmonic and matching losses. The prototype was fabricated and measured. When the two input powers are around −20 dBm, the measured output power is around −37 dBm. This preliminary result can be improved using a more accurate varactor model in future measurements.

With advantages of small size, light weight, and fast tuning capability, electronic impedance synthesizer (EIS) presents game-changing opportunities for industry. However, their widely acceptance is still restrained by the understanding of power-handling capacity and linearity issues. This work addresses both issues through the development of a voltage distribution theory which enables simulating voltage at the position of every PIN diode in the distributed EIS. It provides a way of understanding and predicting the power-handling capacity and nonlinearity of EIS from its linear region. As an example of validation for this theory, a 12-bit EIS along with an automatic measurement setup is presented. Experimental results show a good match among measurement, simulation, and analytical model. The 1 dB compression point (P1dB) of the EIS is larger than 35 dBm, and the third-order input intercept point is larger than 57 dBm. Since the proposed theory is validated, it is possible to be used as a criterion in the optimization process to enhance the power-handling capacity and linearity. Potential applications of such high-linearity EIS can be found in Load-Pull systems, noise measurements, variable impedance loads, tunable matching networks, reconfigurable components, and so on.