Mohammad Rajabi

Amplitude and frequency analysis of multi-sine wireless power transfer

Transmitting multi-sine signals with high peak-to-average power ratio (PAPR) has emerged as an efficient solution to improve the power conversion efficiency (PCE) of wireless power transfer (WPT). This paper analyzes the radio frequency (RF) PCE as a function of the number of tones (Nt) and signal bandwidth (BW) in multi-sine based WPT networks. We show how the energy harvesting efficiency depends on the BW and the non-linear relationship between the instantaneous input amplitude and output voltage. As a result of these, the PCE first increases with increasing Nt and then decreases. We confirm this analysis using measurements. Depending on the circuit chosen for energy harvesting, we can improve PCE of the multi-sine WPT with 25.1% compared to a CW excitation WPT for -5 dBm input power.

Design of efficient rectifier for low-power wireless energy harvesting at 2.45 GHz

This paper reports an efficient rectifier operating at 2.45 GHz for wireless energy harvesting applications with low input power levels. Single diode shunt-mounted topology is adopted for operation with low input power level. The efficiency is measured as 27.7% at -20 dBm of input power, 39.2% at -15 dBm, and 51.2% at -10 dBm. The maximum efficiency of 61.7% is measured at -0.4 dBm input power.

Dual-mode wireless sensor network for real-time contactless in-door health monitoring

Due to the ageing population, real-time and autonomous health monitoring is an emerging priority in ambient assisted living. In this work, a wireless sensor network is proposed for home environments by which the sensors are dualmode radars, enabling concurrent remote localization of a person (i.e., without use of a tag) and fall detection. We elaborate on the network architecture, and in particular on the signaling as to enable real-time data processing (i.e., max. delay is 0.3 s) combined with radar-based wireless sensing. The approach is successfully demonstrated experimentally.

Large signal rectifier characterization for simultaneous data and Power Transfer

In this work we characterize the RF-to-baseband response of a diode used for a rectifier circuit. The measurement setup enables the synchronous acquisition of vector-calibrated baseband and RF time-domain waveforms. The behavior of a Schottky diode, widely employed for RF Energy Harvesting and Wireless Power Transfer applications, is first measured, then further optimized, in order to enable the level of accuracy needed for the correct decoding of a possible modulated input RF signal. Finally, the RF to baseband response is further validated with a single-stage rectifier, in a different measurement setup.

Design and analysis of a verification device for the nonlinear vector network analyzer

We propose a verification device to validate the calibration of a nonlinear vector measurement instruments such as Nonlinear Vector Network Analyzer (NVNA). The verification device is a two-port device that has two operating modes, namely linear and nonlinear. The designed circuits response is almost insensitive to small harmonic mismatches of the instrument ports (|Γ| <; 0.1). Since neither an amplifier nor a circulator is used, the traceability procedure of the device to Electro-Optical Sampling (EOS) is less complicated compared to earlier prototypes.

Multi-sine wireless power transfer with a realistic channel and rectifier model

This paper analyzes the multi-sine wireless power transfer (WPT) system efficiency under realistic channel conditions. A theoretical system model is established including the wireless channel and the rectifier to derive the output DC power based on the transmitted multi-sine signal. Multi-sine based WPT benefits from the transmission signals high peak-to-average-power-ratio (PAPR). Nevertheless, both simulation and measurement results show that the PAPR of the received signal is decreased when the channel becomes frequency-selective. In a static single-path channel, the rectifiers RF-to-DC power conversion efficiency (PCE) increases first and then saturates with increasing signal bandwidth (BW). This is because the signal PAPR only depends on the number of tones in a frequency-flat channel. The initial improvement is cause by the fact that a small enough envelope period is needed to enable efficient energy harvesting. However, in a static multi-path channel, the rectifier PCE increases first and then decreases with increasing BW of the signal, since the channel becomes more and more frequency-selective with the increasing signal BW. For a 10 MHz two-tone signal, the rectifier PCE difference between a frequency selective or frequency flat channel can be up to 10% for our simulation assumptions.

Hybrid rectifier-receiver node

Simultaneous Wireless Information and Power Transfer (SWIPT) studies the transmission of wireless energy and data in a single RF signal. It becomes interesting when a single receiver chain is able to both convert the RF power to DC power, while at the same time converting the RF signal to BaseBand (BB). A practical method to receive the RF signal and convert the signal to BB while simultaneously harvesting power is proposed. This purpose is possible by utilizing a two-tone signal with a suitable Hybrid Rectifier-Receiver (HRR). The efficiency of the rectifier with different symbols can vary from 39% to 43% considering the power of the first tone as −11 dBm. Therefore, all symbols provide a descent DC output power. The proposed decoding is able to grasp the non-linearity of the diode in order to have a precise estimation of the symbols with different power levels.

Measurement-based analysis of the throughput-power level trade-off with modulated multisine signals in a SWIPT system

Simultaneous wireless information and power transfer (SWIPT) has gained interest, especially due to its applicability in the world of Internet of Things. For pure wireless power transfer (WPT), multisine signals have already been shown to increase RF-to-DC power conversion efficiency (PCE) at the receiver which is key in WPT research. In a SWIPT system where the waveforms are modulated for information transfer, however, we expect the modulation scheme to impact both data transmission quality and WPT subsystem efficiency. This paper quantifies by means of an experimental study the impact of QAM and PSK modulated multisine signals, on the power and data transfer efficiency of a SWIPT system, taking into account the often neglected transmitter distortion. Error vector magnitude (EVM) is used as figure of merit for the impact of data transfer efficiency, output voltage ripple for the modulations impact on WPT.

A nonlinear verification device for nonlinear vector network analyzers

Verifying the calibration of a Nonlinear Vector Network Analyzer in a way that is not instrument specific requires a stable nonlinear device that is insensitive to port mismatch. We propose and explore the design of a nonlinear verification device to complement existing linear verification devices. We have evaluated a design operating at a fundamental frequency of 2 GHz and derived an improved figure of merit parameter that identifies sensitivity to load-pull.

Comparing LSNA Calibrations: Large-Signal Network Analyzer Round Robin

Large-signal network analyzers (LSNAs) provide direct measurements of the nonlinear behavior of active devices under realistic operating conditions. Large-signal measurements facilitate the extraction of more accurate transistor and power amplifier models. This is a key factor in the development of better communications systems by use of modern modulation schemes. However, the calibration of LSNAs is very challenging. In addition to a conventional linear scattering-parameter calibration, the calibration of an LSNA requires two extra standards: a phase reference (e.g., a comb generator) and a power meter.