RF-powered Sensor Research Articles

Design and Measurement of Near-Zero Thermopile RF Power Sensors for GaAs MMIC Applications

Design and Measurement of Near-Zero Thermopile RF Power Sensors for GaAs MMIC Applications

A Near-Zero Thermoelectric RF Power Sensor for High Dynamic Range Applications

A Near-Zero Thermoelectric RF Power Sensor for High Dynamic Range Applications

Determination of measurement uncertainty by a Monte Carlo method for an RF power sensor calibration system using a VNA

This work proposes a systematic assessment of measuring type A uncertainty (caused by random errors) used in RF power sensor calibration. To reduce A type uncertainty, several successive measurements are repeated. The uncertainty arises from repeatability errors in connectors caused by changes in their electrical properties during repeated mating. The suitability of the METAS UncLib software was analysed and we concluded that software should be developed to take into account the shape of probability density function (PDF) using a Monte Carlo method (MCM), which was lacking in METAS UncLib. The self-developed software was then tested on an example taken from the literature and the superiority of the MCM over the analytical method (GUM) was confirmed. During the calibration of the RF sensor using a vector network analyzer (VNA), a series of repeated measurements were performed and, after applying our MCM software, it was found that the measurement uncertainties calculated by the MCM method were several times larger than those by the GUM. The reason for this was that the correlation between the measured input quantities was not taken into account. When this was done using a covariance matrix and assuming a normal PDF of the input quantities, the results obtained with the GUM and the MCM converged. Our main objective was to investigate the influence of the PDF shape of the input measurement samples on the measurement uncertainty. Taking more than a dozen measurements is too costly, on the other hand, the small sample size prevents a reliable determination of the PDF shape. Finally, to overcome this inconvenience, we have developed a special method that uses the histograms of standardized input data taken at all measurement frequencies under fixed conditions without disconnecting the connectors, to increasing the total number of results which were needed to create the PDF histograms of input quantities.

Development of RF Power Sensor Measurement System Using VNA Method and Heating Block

Development of RF Power Sensor Measurement System Using VNA Method and Heating Block

Developing RF Power Sensor Calibration Station in Direct Comparison Transfer System using Vector Network Analyzer

Calibration of RF power sensors is crucial issue in RF power measurements. Many calibration laboratories use the direct comparison transfer system with a signal generator and a power splitter. Increasing performance of modern vector network analyzers makes it possible to perform a power sensor calibration with acceptable uncertainties. The main advantage when using a VNA is a simple measurement setup with a wide frequency range (up to 50 GHz, limited only by the VNA and the standard power sensor), where all of required components, i.e. signal generator, a directional coupler and a reference power indicator are built in the VNA technology. This paper reports performing a VNA-based RF power sensors calibration for 10 MHz – 18 GHz band, carried out in the Laboratory of Electric, Electronic and Optoelectronic Metrology at the National Institute of Telecommunications in Warsaw, Poland. In order to validate the proposed solution two of power sensors were calibrated at a reference laboratory. The validation consisted of two steps. At first, one of those characterized power sensors was calibrated at our laboratory in direct comparison transfer system. Finally, the results obtained from the VNA-based system were compared with the previously obtained ones.

A Novel Thermistor-Based RF Power Sensor With Wheatstone Bridge Fabricating on MEMS Membrane

A novel thermistor-based RF power sensor with Wheatstone full-bridge structure is proposed using MEMS technology combined with monolithic microwave integrated circuit (MMIC) process in this paper. A MEMS substrate membrane is carefully designed beneath the hot area by back etching technology. Such a design can effectively suppress the longitudinal heat loss, which facilitates the improvement of sensitivity. In addition, in this design, low TCR (temperature coefficient of resistance) TaN (tantalum nitride) resistors are adopted to achieve the stability of impedance matching. Measurement results show that the output response of this device has excellent linearity with the power from 1 to 200mV. Considering the effect of the distance between the hot and cold areas, three sensor configurations with different arrangements of thermistors were investigated experimentally. And their corresponding sensitivities are 0.16 mV/mW, 0.19 mV/mW and 0.22 mV/mW at 10GHz, respectively. Meanwhile, the measured response times of these three configuration sensors are 20.7 ms, 22.3 ms and 27.2 ms, respectively. Therefore, there is a trade-off consideration between high sensitivity and fast response time. Moreover, the measured return losses are less than −20 dB in the frequency range from 10 MHz to 20GHz. This indicates that these devices have good matching characteristics. The proposed thermistor-based RF MEMS power sensor demonstrates a good performance, especially high sensitivity and stable impedance match, providing great application potential. [2020-0260]

Online Optimal Control for Wireless Cooperative Transmission by Ambient RF Powered Sensors

Ambient radio frequency (RF) energy harvesting technology provides a hopeful solution to power the low-power electronic system. Nevertheless, the extremely low power density and randomness of ambient RF energy pose a significant obstacle to the application of ambient RF energy harvesting technology. Aiming at wireless transmission by ambient RF-powered sensors, this paper presents a cooperative communication technology by combining ambient backscattering and energy beamforming to significantly decrease the transmission energy consumption of each sensor. For wireless transmission via this cooperative communication technology, a novel optimization problem is formulated to maximize the long-term time-averaged sensed data size, which jointly takes into account sensing scheduling, transmission power allocation and the control of sensed data size. Moreover, we employ techniques of Lyapunov drift and Lyapunov optimization to propose an online optimal control algorithm, which achieves the optimal solution to the proposed problem without requiring a-priori knowledge of harvested energy and wireless channels. By exploiting mixed integer programming (MIP) and signomial geometric programming (SGP) that cause the proposed problem difficult to solve, a novel Sequential Convex Approximation algorithm is further introduced into the online optimal control algorithm. Simulation results indicate the proposed online algorithm offers a dramatic performance gain over alternative online algorithms.

Deep Learning-Based Food Quality Estimation Using Radio Frequency-Powered Sensor Mote

In the past decades, the emerging concern about food safety has led to the increasing demand for monitoring food quality across the world. Aiming towards a novel solution for monitoring food, this study proposes a non-destructive method with self-powering capability for online food monitoring, which can be extendable to IoT applications. Furthermore, the study introduces a novel deep neural network model to predict different states of food quality based on the monitoring results. To monitor the variation in food quality, the paper proposes the detection of total volatile organic compounds (TVOCs) inside the food packages, which have been released during food deterioration. A low-power sensor mote comprised of a capacity humidity sensor and a metal-oxide (MOX) gas sensor was manufactured for this purpose. The self-powering capability of the mote is provided through an energy harvester module, which benefits from the far-field Radio Frequency Energy Harvesting (RFEH) technology. The operating frequency of the module was chosen at the 915-MHz ISM band. The analysis of the harvester performance showed that the harvester could generate 3.3-V dc with an RF input power of as low as -8 dBm, which was sufficient for the mote operation. To verify the proposed solutions, a demonstration to monitor the deterioration of packaged pork and fish was conducted in eight days under ambient and refrigerated storage conditions, using the self-developed RF-powered sensor mote. The raw variations in TVOCs were analyzed to evaluate the reliability of the proposed TVOC-based method. A one-dimensional (1-D) convolutional neural network (CNN) model was trained on the TVOCs dataset to predict different states of food quality. To investigate the applicability of the proposed 1-D CNN to multi-class determination of food quality, two other supervised machine learning algorithms using 2-D inputs, including Multilayer Perceptron (MLP), and Support Vector Machine (SVM), are studied. Their classification accuracies based on the confusion matrix are identified and compared.

Comparison on calibration factor measurement of power sensor

This comparison covers the measurement of calibration factors (CF) of power sensors and was carried out where SASO NMCC and TUBITAK UME participated, on the frame of GULFMET.Calibration factors are used for characterization of RF power sensors. RF power sensors are used to measure RF power, and is an important mean to achieve traceability of RF power measurements. This bilateral comparison was performed by measuring a power sensor at frequencies of 10 MHz, 50 MHz, 1 GHz, 4 GHz, 8 GHz, 12 GHz, 15 GHz, and 18 GHz, at a power level of 0 dBm.TÜBİTAK UME was acting as the pilot laboratory. The travelling standard was provided by SASO NMCC. TUBITAK UME was responsible for monitoring standard performance during the circulation and the evaluation and reporting of the comparison results.The comparison was carried out in accordance with the CCEM Guidelines for Planning, Organizing, Conducting and Reporting Key, Supplementary and Pilot Comparisons.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Integrated cmos rectifier for rf-powered wireless sensor network nodes

This article presents a review of the CMOS rectifier for radio frequency energy harvesting application. The on-chip rectifier converts the ambient low-power radio frequency signal coming to antenna to useable DC voltage that recharges energy to wireless sensor network (WSN) nodes and radiofrequency identification (RFID) tags, therefore the rectifier is the most important part of the radio frequency energy harvesting system. The impedance matching network maximizes power transfer from antenna to rectifier. The design and comparison between the simulation results of one- and multi-stage differential drive cross connected rectifier (DDCCR) at the operating frequencies of 2.44GHz, and 28GHz show the output voltage of the multi-stage rectifier doubles at each added stage and power conversion efficiency (PCE) of rectifier at 2.44GHz was higher than 28GHz. The (DDCCR) rectifier is the most efficient rectifier topology to date and is used widely for passive WSN nodes and RFID tags.

Simultaneous Sensor Placement and Scheduling for Fusion-Based Detection in RF-Powered Sensor Networks

When deploying radio frequency (RF)-powered sensor networks for mission-critical applications such as security surveillance, it is often required to maximize or guarantee the quality of surveillance. Both placing and scheduling the charging/working modes of sensors are of key importance in order to continuously ensure a satisfying quality of surveillance. Traditionally, sensor placement and scheduling have been considered separately. The first decision regards where to place the sensors, and then when to activate them. In this paper, we study simultaneous sensor placement and charging/working scheduling problem for fusion-based detection in RF-powered sensor networks. The problem is formulated as a constrained optimization problem and proved to be NP-complete. Two greedy heuristic algorithms, joint optimization greedy algorithm with fixed fusion radius (JOGA-FFR) and joint optimization greedy algorithm with dynamic fusion radius (JOGA-DFR) based on fixed and dynamic fusion radiuses, respectively, are presented to solve the problem. We validate our approaches through extensive numerical simulations as well as simulations based on real data traces collected from a vehicle detection experiment. The results show that, our proposed algorithms always outperform two-stage greedy algorithm (TSGA), an algorithm that optimizes sensor placement and scheduling separately, in all the simulation scenarios, and are near optimal in small-scale networks. Besides, JOGA-DFR outperforms JOGA-FFR under certain specific sensing model settings, but more often has a comparable performance with JOGA-FFR. JOGA-FFR is thus more recommended for its lower complexity.

A Long-Distance RF-Powered Sensor Node with Adaptive Power Management for IoT Applications

We present a self-sustained battery-less multi-sensor platform with RF harvesting capability down to −17 dBm and implementing a standard DASH7 wireless communication interface. The node operates at distances up to 17 m from a 2 W UHF carrier. RF power transfer allows operation when common energy scavenging sources (e.g., sun, heat, etc.) are not available, while the DASH7 communication protocol makes it fully compatible with a standard IoT infrastructure. An optimized energy-harvesting module has been designed, including a rectifying antenna (rectenna) and an integrated nano-power DC/DC converter performing maximum-power-point-tracking (MPPT). A nonlinear/electromagnetic co-design procedure is adopted to design the rectenna, which is optimized to operate at ultra-low power levels. An ultra-low power microcontroller controls on-board sensors and wireless protocol, to adapt the power consumption to the available detected power by changing wake-up policies. As a result, adaptive behavior can be observed in the designed platform, to the extent that the transmission data rate is dynamically determined by RF power. Among the novel features of the system, we highlight the use of nano-power energy harvesting, the implementation of specific hardware/software wake-up policies, optimized algorithms for best sampling rate implementation, and adaptive behavior by the node based on the power received.

An Inline RF Power Sensor Based on Fixed Capacitive Coupling for GaAs MMIC Applications

This letter proposes an inline RF power sensor based on fixed capacitive coupling for GaAs MMIC applications. In the design, a certain percentage of the input power coupled by a beam and sensed in a thermopile sensor, where the beam is not required to release to obtain a fixed capacitance for high-power levels and increase the dynamic range. This sensor offers the compatible capability with the GaAs MMIC technology. Measured reflection and insertion losses are <;-24.2 and 0.73 dB at X-band, respectively. Experiments demonstrate that this inline sensor exhibits good linearity of the output response from 1 to 200 mW, and results in the average sensitivity of ~29.5 μV/mW at 10 GHz. The sensitivity increases with the increase of the X-band frequency, with small measurement errors.

Millimeter-Wave Power Sensor Based on Silicon Rod Waveguide

This paper presents a novel type of RF power sensor, based on a metallic structure integrated into an mm-wave range dielectric rod waveguide made of Si. The metallic structure is employed as a bolometer. Numerical simulations of temperature distribution are shown. A prototype was tested at frequencies of 45 GHz-1 THz and a power levels from 0.1 to 500 mW. The power sensor showed the sensitivity of 0.51 Ω/mW resistance change.

A 90-nm CMOS Threshold-Compensated RF Energy Harvester

This paper presents an efficient energy harvester for RF-powered sensor networks. The circuit is based on an improved multi-stage rectifier, which exploits a fully passive threshold self-compensation scheme to overcome the limitation due to the input dead zone. A CAD-oriented design methodology is also proposed, which is aimed at maximizing the overall power conversion efficiency of the harvester through an optimum trade-off among matching losses, power reflection and rectifier efficiency. According to the proposed methodology, a 915-MHz harvester comprising an integrated input matching network and a 17-stage self-compensated rectifier has been designed and fabricated in a 90-nm CMOS technology. The rectifier exhibits a remarkably low input power threshold, as it is able to deliver a 1-V dc output voltage to a capacitive load with a very small input power of -24 dBm (4 μW). When driving a 1-MΩ load, the device can supply a 1.2-V output with an input power of -18.8 dBm (13.1 μW). The achieved results exceed the performance of previously reported RF multi-stage rectifiers in standard analog CMOS technology.

New Thermocouple-Based Microwave/Millimeter-Wave Power Sensor MMIC Techniques in GaAs

We describe a new RF and microwave power sensor monolithic microwave integrated circuit design. The circuit incorporates a number of advances over existing designs. These include a III-V epitaxial structure optimized for sensitivity, the figure-of-merit applicable to the optimization, a mechanism for in-built detection of load ageing and damage to extend calibration intervals, and a novel symmetrical structure to linearize the high-power end of the scale.

Final report on EUROMET.EM.RF-K10.CL (EUROMET comparison 525 (GT-RF/99-2)): Power in the coaxial PC 3.5 mm line system

The results and the measurement methods of the EUROMET comparison 525 are summarized in this report. The task of the comparison was to determine the calibration factor for frequencies up to 26 GHz of two identical RF power sensors with PC 3.5 mm connector in the coaxial 3.5 mm line system. Eight European national metrology institutes (NMIs) participated in this comparison, which was organized as a successor to the CCEM key comparison CCEM.RF-K10.CL on the same subject. Two RF power travelling standards with male PC 3.5 mm connectors were measured at: EIM (Greece), AREPA (Denmark), BNM-LCIE (France), NPL (United Kingdom), NMI-VSL (Netherlands), SP (Sweden), UME (Turkey), with PTB (Germany) as the pilot laboratory.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

A capacitive RF power sensor based on MEMS technology

Wideband 100 kHz–4 GHz power sensors are presented, which are based on sensing the electrostatic force between an RF signal line and a suspended membrane. The electrostatic force, which is proportional to the square of the rms signal voltage and thus to the signal power, results in a displacement of the suspended membrane. This displacement is detected capacitively, allowing the sensing of the signal power with extremely low dissipative losses; therefore the sensor can be placed in a transmission line with negligible disturbance of the signal. Devices have been designed and fabricated successfully by aluminum surface micromachining using photoresist as the sacrificial layer. Optimization of the design with SONNET has resulted in measured return and insertion losses (S11 and S21) better than −30 dB and −0.15 dB, respectively, up to 4 GHz, and a sensitivity of 90 aF mW−1.

Final report on CCEM key comparison CCEM.RF-K10.CL (GT-RF/99-2) 'Power in 50 Ω coaxial lines, frequency: 50 MHz to 26 GHz' – measurement techniques and results

This report summarizes the results and the measuring methods of an international key comparison between twelve national metrology institutes (NMIs) and is concerning the calibration factor of RF power sensors in the coaxial 3.5 mm line for frequencies up to 26 GHz. Two RF power travelling standards fitted with male PC 3.5 mm connectors were measured at seven frequencies. The following NMIs participated: NMIJ (Japan), NRC (Canada), NIST (USA), METAS (Switzerland), CSIR-NML (South Africa), NMIA (Australia), NPL (UK), SiQ (Slovenia), IEN (Italy), VNIIFTRI (Russian Federation), SPRING (Singapore) and PTB (Germany), as the pilot laboratory.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Scanning near field thermal microscopy on a micromachined thin membrane

A resistive probe based scanning thermal microscope (SThM) has been used to perform complementary near field thermal measurements on the surface of a thin semiconductor membrane. This thin structure is part of a micromachined thermal rf power sensor and includes an integrated resistive heater used as an absorbing element for the input power. The resulting 2D surface temperature distribution and the 2D thermal wave propagation characteristic were determined. Considering the thermal wave behaviour at near field conditions, the local thermal conductivity of the thin membrane and the surrounding bulk material was investigated by usage of the 3 ω -method.