Microwave Power Measurement Research Articles

Dual‐Function Microwave Devices Based on Metamaterials

AbstractMicrowave detectors play a crucial role in modern technological applications, but traditional detectors suffer from limited functionality, limited detection accuracy, and difficulties in large‐scale deployment. This study proposes a dual‐function microwave detector based on metamaterials, capable of simultaneously measuring microwave power and polarization angle. The detector consists of a metal disc with 12 concave grooves, a dielectric layer, a metal reflector, and a resistive network. The designed detector achieves efficient absorption of 93.54% of microwave energy, with 75.4% dissipated in the resistive component and converted into heat. By detecting the temperature using a thermocouple thermometer, the incoming wave power can be determined, and by discriminating between different resistive temperatures, the polarization angle of the incoming wave can be identified. Simulation and experimental results demonstrate the outstanding detection efficiency and stability of this detector. It exhibits a linear response to different incident power densities and polarization angles, showing potential application value in the field of microwave wireless power transmission.

Microwave emissions from the cold atmospheric helium plasma jet

One of the recently observed effects of plasma in medical applications is the physical effect, suggesting that the electromagnetic (EM) emission of cold atmospheric plasmas can lead to cell membrane oscillations and sensitization to the chemical active ingredient of treatments such as cancer drugs. This is a new aspect that must be considered along with the plasma chemical effects for the future dose definition which is the most urgent research topic of plasma medicine. However, unlike the reactive oxygen and nitrogen species generated from plasma chemistry which is well-known as playing a key role in apoptosis cancer cells, the EM emission power spectrum and emission mechanism are still unquantified. This makes the uncertainty of the physical dosage of the therapy and thus impedes the further understanding and optimization of the plasma therapy. In this paper, we compute the 3D spatial distribution of the power density spectrum of EM emission from a cold atmospheric helium plasma jet. The simulations indicate that the plasma oscillations following the plasma streamer propagation are the main source of EM emission, while the emissions of the bulk current caused by net charge movements and the bremsstrahlung due to charge collisions are negligible. The results are also verified by a microwave power measurement using a heterodyne frequency sweep. These findings will thus fill out the last missing piece of the jigsaw before the plasma medicine community can define the dose in the future.

Microwave Passive Direction-Finding Method Based on NV Color Center in Diamond

In this study, we established a passive direction-finding scheme based on microwave power measurement: Microwave intensity was detected using microwave-frequency proportion integration differentiation control and coherent population oscillation effect converting the change in microwave resonance peak intensity into a shift of the microwave frequency spectrum, for which the minimum microwave intensity resolution was −20 dBm. The direction angle of the microwave source was calculated using the weighted global least squares method of microwave field distribution. This lay in the 12~26 dBm microwave emission intensity range, and the measurement position was in the range of (−15°~15°). The average angle error of the angle measurement was 0.24°, and the maximum angle error was 0.48°. In this study, we established a microwave passive direction-finding scheme based on quantum precision sensing, which measures the microwave frequency, intensity, and angle in a small space and has a simple system structure, small equipment size, and low system power consumption. In this study, we provide a basis for the future application of quantum sensors in microwave direction measurements.

High-Resolution Detection of Microwave Fields on Chip Surfaces Based on Scanning Microwave Microscopy

With the development of microwave chips toward high integration, new challenges have been posed to high-precision microwave field test techniques. In this article, we propose a chip surface microwave field characterization method and design a corresponding microwave power measurement system based on a scanning probe imaging system and microwave test technology. The minimum detected microwave power of the system is better than 1 nW by experimental verification. The proposed method can be applied to image the distribution of the microwave field of the chip and it is helpful to optimize chip design and performance in the future.

Determining Electron Density of Atmospheric Microwave Air Plasma Torch by Microwave Power Measurement

Determining Electron Density of Atmospheric Microwave Air Plasma Torch by Microwave Power Measurement

Plasma-based microwave power limitation in a printed transmission line: a self-consistent model compared with experimental data

Plasma-based microwave power limitation in a suspended microstrip transmission line integrating a micro hollow cathode discharge (MHCD) in its centre is experimentally and numerically studied. Transient and steady state microwave power measurements exhibit a limitation threshold of 28 dBm and time responses of 25 microseconds. Intensified charge-coupled device imaging shows that microwave breakdown occurs at the top of the MHCD. The plasma then extends towards the microwave source within the suspended microstrip transmission line. Besides, a self-consistent model is proposed to simulate the non-linear interaction between microwave and plasma. It gives numerical results in agreement with the measurements, and show that the plasma expansion during the transient response is related to a shift between the ionization source term and the electron density maximum. The propagation speed, under the tested conditions, depends mainly on the stepwise ionization from the excited states.

Optimized microwave sensing in broad frequency range by a fiber diamond probe

Diamond based quantum sensing is a fast-emerging field with both scientific and technological importance. The nitrogen-vacancy (NV) center, a crystal defect in diamond, is a unique model system for microwave sensing application due to its excellent photo-stability, long spin coherence time in ambient conditions. In this work, we systematically optimized the measurement parameters for microwave sensing. The system noise is analyzed, and 1/f noise is suppressed by introducing a differential algorithm. The gain of avalanche photodiode and the gating window of the pulsed fluorescence is optimized to further suppress the noise floor. The decoherence of spin is characterized by varying the duration of the laser and microwave. The minimal detectable power on a standard microstrip is characterized with sampling time down to 1 ms, showing flat frequency dependence. The results have important implications toward fast measurement of broadband microwave power, especially in the field of IC testing and radar signal processing under intense electromagnetic interference.

Power Sensor Characterization From 110 to 170 GHz Using a Waveguide Calorimeter

This article proposes a new calorimetry-based measurement method to measure absolute microwave power obtained through dc substituted power from 110 to 170 GHz (WG 29, WR 6/7, or D-band) using a custom-designed thin-film microwave power sensor. This method complements traditional microcalorimetry techniques used to provide traceability for microwave power in this band while diversifying the potential applications and accessibility to such traceability. The thermopile of the measurement system was characterized using a known dc power with the microwave sensor and the thermopile coefficient obtained. Absolute microwave power on the microwave sensor was calculated using the thermopile coefficient and was used to remove the effect of a thermal isolation section (TIS) and calorimeter unbalance effect. To transfer the power traceability from the calorimeter to microwave power measurement applications, the effective efficiency of a device under test (DUT), consisting of a power sensor/meter combination, was defined using the calorimeter’s absolute microwave power and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters of the measurement system and the DUT. The effective efficiency (EE) of the DUT was obtained between 0.9386 and 0.9815 for the whole frequency band.

Detection of electron paramagnetic resonance in La0.6Ca0.4MnO3 using a copper stripcoil

Recently, we had reported the detection of electron paramagnetic resonance (EPR) from magnetoimpedance (MI) measurements in bulk La0.60Ca0.40MnO3 (LCMO) samples using radio frequency (rf) currents [U. Chaudhuri and R. Mahendiran, Appl. Phys. Lett. 115, 092405 (2019)]. Here, we report an alternative method which involves measuring the effective MI changes of a copper stripcoil that encloses the LCMO sample. Magnetoresistance (∆R/R0) and magnetoreactance (∆X/X0) of the sample were measured indirectly via the stripcoil for frequencies of current from f = 0.5 to 2.5 GHz. During the field sweep, ∆R/R0 shows an abrupt increase that is accompanied by a dip in ΔX/X0 at a critical value of dc magnetic field (Hc) when f ≥ 0.9 GHz. Hc increased linearly with frequency (f) of the current in the stripcoil, satisfying the EPR relation fr = (γ/2π)Hdc, where γ is the gyromagnetic ratio and fr is the resonance frequency. The same stripcoil and the sample were also used to measure microwave power absorption using a vector network analyzer. The features observed in both these techniques were strikingly similar to the results obtained from the direct MI measurement in LCMO, which confirms the electrical detection of EPR.

Measurements of Microwave Power Absorbed during ECR Plasma Heating at the L-2M Stellarator

The results are presented from measurements of the power absorbed in plasma of the L-2M stellarator in experiments on the electron cyclotron resonance (ECR) plasma heating at the second harmonic of the gyrofrequency. Hydrogen plasma was created and heated in the stellarator vacuum chamber as a result of the resonance absorption of microwave power supplied by the gyrotrons in the pulse-periodic operation regime. The total energy of the toroidal plasma column and the absorbed power were measured using the diamagnetic diagnostics. The shielding effect of the metal vacuum chamber on the diamagnetic signal measurements was taken into account. It was ascertained that, during the axial ECR heating, up to 90% of the inputted gyrotron power is absorbed in the plasma that is consistent with the theoretical estimates.

Research on Measurement Accuracy of the Double‐Channel Microwave Power Sensors Based on an MEMS Cantilever Beam

A thermopile-based microwave power sensor and a double-channel microwave power sensor are compared in order to research the measurement accuracy of microwave power. The relationship of the displacement of MEMS cantilever beam with the measured microwave power is researched, and the reason that the microwave power consumed by the MEMS cantilever cannot be ignored at low power level is explained. The ratio of microwave power consumed by the MEMS cantilever with the microwave frequency is obtained, and the measured results show that the percentage is 51.96%@8GHz, 52.31%@10GHz and 55.11%@12GHz on the average, respectively. There is an important reference value to achieve the accurate microwave power measurement of the double-channel microwave power sensors.

NIST-Traceable Microwave Power Measurement in a Waveguide Calorimeter With Correlated Uncertainties

To realize microwave power traceability, we apply a newly developed calibration technique for measuring the correction factor of a calorimeter with a vector network analyzer in the WR-15 frequency band. The wave-parameter approach is used to formulate analytic expressions for the correction factor and effective efficiency. This allows us to systematically track the uncertainty with correlation along an unbroken path. Measurement results are consistent with what was previously obtained by use of the conventional method.

Design of LTE-Band Microwave Power Detection System Based on Schottky Diode

In this paper, a novel microwave power detection system based on Schottky diode is constructed in order to measure microwave power in the LTE-band (1.8~2.7 GHz). The proposed detection system is consisted of three modules: a collecting module, a measuring module, and a processing module. Among them, a microwave power detection circuit based on Schottky diode is developed to realize the high-quality conversion of microwave power signal to voltage signal. The experimental results reveal that the presented system has good linearity. In the range of 1.8~2.7 GHz, the incident microwave power is increased from 1 uW to 50 mW, and the sensitivity of the detection system is 1.86 mV/uW at 2.0 GHz, 1.61 mV/uW at 2.3 GHz, and 1.2 mV/uW at 2.6 GHz, which is much better than other microwave power sensors. Therefore, the microwave power detection system based on Schottky diode provides an effective solution for microwave power detection in the LTE-band.

DC-25 GHz and Low-Loss MEMS Thermoelectric Power Sensors with Floating Thermal Slug and Reliable Back Cavity Based on GaAs MMIC Technology.

Wideband and low-loss microwave power measurements are becoming increasingly important for microwave communication and radar systems. To achieve such a power measurement, this paper presents the design and measurement of wideband DC-25 GHz and low-loss MEMS thermoelectric power sensors with a floating thermal slug and a reliable back cavity. In the sensors, the microwave power is converted to thermovoltages via heat. The collaborative design of the thermal slug and the back cavity, i.e., two thermal flow paths, is utilized to improve the efficiency of heat transfer and to ensure reliable applications. These sensors are required to operate up to 25 GHz. In order to achieve low microwave losses at the bandwidth, the floating thermal slug is designed instead of the grounded one. The effects of the floating slug on the reflection losses are analyzed by the simulation. The fabrication of these sensors is completed by GaAs monolithic microwave integrated circuits (MMIC) and micro-electro-mechanical systems (MEMS) technology. Measured reflection losses are less than −25.6 dB up to 12 GHz and −18.6 dB up to 25 GHz. The design of the floating thermal slug reduces the losses, which is equivalent to improving the sensitivity. At 10 and 25 GHz, experiments exhibit that the sensors result in sensitivities of about 51.13 and 35.28 μV/mW for the floating slug and 81.68 and 55.20 μV/mW for the floating slug and the cavity.

Photonic Microwave Frequency Measurement Based on Frequency-Configurable Pilot Tones

A photonic technique for microwave frequency measurement with flexible range and high resolution is proposed based on frequency-configurable pilot tones. The method extracts the remote unknown microwave frequency by measuring electrical power at two known pilot frequencies, avoiding dual-channel photodetection and broadband microwave power measurement over the whole interested frequency range. Moreover, it enables flexible measurement range by configuring two pilot frequencies. A proof-of-concept experiment is successfully demonstrated with the frequency range of 6–18.9 GHz and the resolution of 0.1 GHz.

Wideband Resistive Sensors for Double-Ridged Waveguides

Two types of resistive sensors with flat frequency response for WRD840 and WRD250 double-ridged waveguides were developed. The first type of sensors is optimized for microwave power measurements inside the waveguide. The second type of sensors is connected to the particular horn antenna and optimized for microwave pulse power density (or electric field strength) measurements in free space. The flat frequency response of the sensors was designed by changing the parameters of the sensing element. Proposed sensors can measure high-power microwave pulses covering frequency ranges 0.84-2.0 GHz and 2.6-7.8 GHz.

Non-Resonant Microwave Absorption in SmFeAsO 0.80 F 0.20: Line Shape and Structure Evolution with Temperature

‘Non-resonant Microwave Absorption’ (NRMA) or the ‘Low field microwave absorption’ (LFMA) measurements on high-quality polycrystalline SmFeAsO0.80F0.20 superconducting sample were carried as functions of temperature and microwave power. The LFMA line shape is complex with two peaks namely; broad peak 1 and narrow peak 2 akin to one reported in SmFeAsO0.88F0.12 as reported by Onyancha et al (Supercond. Nov. Magn. 28, 2927–2934, 2015). This unquestionably illustrates that these peaks are a common feature in F-doped SmFeAsO. The LFMA signal as a function of temperature reveals that T c − T ∗ = 1K in SmFeAsO0.80F0.20 compared to 4 K in SmFeAsO0.88F0.12 (T ∗ is the characteristic temperature at which the narrow peak appears as we cool down the sample below T c); hence inferring that the narrow peak is fluorine doping dependent. Furthermore, LFMA signal evolution with microwave power does not show phase reversal (anomalous absorption) at 2.227 mW which is a stark contrast to what was observed in SmFeAsO0.88F0.12 as reported by Onyancha et al (Physica C: Supercond. Appl. 533:49–52, 2017). The absence of phase reversal within measured microwave power indicates presence of hysteretic Josephson junction. These findings establish few non-superconducting inclusions in SmFeAsO0.80F0.20 system.

Hyperbolic-cosine waveguide tapers and oversize rectangular waveguide for reduced broadband insertion loss in W-band electron paramagnetic resonance spectroscopy. II. Broadband characterization.

Experimental results have been reported on an oversize rectangular waveguide assembly operating nominally at 94 GHz. It was formed using commercially available WR28 waveguide as well as a pair of specially designed tapers with a hyperbolic-cosine shape from WR28 to WR10 waveguide [R. R. Mett et al., Rev. Sci. Instrum. 82, 074704 (2011)]. The oversize section reduces broadband insertion loss for an Electron Paramagnetic Resonance (EPR) probe placed in a 3.36 T magnet. Hyperbolic-cosine tapers minimize reflection of the main mode and the excitation of unwanted propagating waveguide modes. Oversize waveguide is distinguished from corrugated waveguide, overmoded waveguide, or quasi-optic techniques by minimal coupling to higher-order modes. Only the TE10 mode of the parent WR10 waveguide is propagated. In the present work, a new oversize assembly with a gradual 90° twist was implemented. Microwave power measurements show that the twisted oversize waveguide assembly reduces the power loss in the observe and pump arms of a W-band bridge by an average of 2.35 dB and 2.41 dB, respectively, over a measured 1.25 GHz bandwidth relative to a straight length of WR10 waveguide. Network analyzer measurements confirm a decrease in insertion loss of 2.37 dB over a 4 GHz bandwidth and show minimal amplitude distortion of approximately 0.15 dB. Continuous wave EPR experiments confirm these results. The measured phase variations of the twisted oversize waveguide assembly, relative to an ideal distortionless transmission line, are reduced by a factor of two compared to a straight length of WR10 waveguide. Oversize waveguide with proper transitions is demonstrated as an effective way to increase incident power and the return signal for broadband EPR experiments. Detailed performance characteristics, including continuous wave experiment using 1 μM 2,2,6,6-tetramethylpiperidine-1-oxyl in aqueous solution, provided here serve as a benchmark for other broadband low-loss probes in millimeter-wave EPR bridges.

A Microwave Transmission Instrument for Rapid Dry Rubber Content Determination in Natural Rubber Latex

We report the design, implementation and testing of an instrument for rapid dry rubber content (DRC) determination in rubber latex. It is composed of rectangular waveguide antennae, microwave generator, power detector, and microcontroller. According to the theory of microwave transmission, the power loss of microwaves passing through latex is related to the DRC. This attenuation is determined by measuring the transmitted microwave intensity with a power detector. The appropriate frequency that gives the best correlation between DRC and attenuation was found to be about 2.36 GHz. The microwave power measurement is processed by the microcontroller using the empirical calibration equation to estimate DRC in rubber latex. The instrument was tested using new latex samples with various DRC, sampled locally in Songkhla province, Thailand, and the DRC estimates by the instrument were compared to the slow but accurate standard oven-drying results. The estimates had an 0.21 % mean error and R2 = 0.9983, indicating good practical performance.

An Integrated Microwave Power and Frequency Sensor For 1–10 GHz Application

In this paper, an integrated sensor for microwave power and frequency measurement is proposed for 1–10 GHz application. The novelty is that this device cannot only measure microwave power but also can realize microwave frequency measurement at the same time. The incident power is dissipated and converted heat by two loaded resistors, and then detected indirectly by output voltage based on Seebeck effect. A microelectromechanical system (MEMS) coupler is designed over the coplanar waveguide transmission line and the coupled power varies with the frequency of the signal. Therefore, by measuring the coupled power, the frequency of the signal can be deduced. This integrated power and frequency sensor is fabricated by GaAs monolithic microwave integrated circuit process and MEMS technology. The measured return loss is about −26 dB at 1 GHz and −22 dB at 10 GHz. The power measurement indicates that the sensitivity is close to 0.116 mV/mW at 1 GHz and 0.110 mV/mW at 10 GHz. The frequency measurement is performed and the sensitivity is close to 0.035 mV/GHz under the incident power of 60 mW.