High-voltage direct-current (HVdc) transmission lines are gaining more attention as an integral part of modern power system networks. Monitoring the dc current is important for metering and the development of dynamic line rating control schemes. However, this has been a challenging task, and there is a need for wireless sensing methods with high accuracy and a dynamic range. Conventional methods require direct contact with the high-voltage conductors and utilize bulky and complex equipment. In this paper, an ultra-high-frequency (UHF) radio frequency identification (RFID)-based sensor is introduced for the monitoring of the dc current of an HVdc transmission line. The sensor is composed of a passive RFID tag with a custom-designed antenna, integrated with a Hall effect magnetic field device and an RF power harvesting unit. The dc current is measured by monitoring the dc magnetic field around the conductor using the Hall effect device. The internal memory of the RFID tag is encoded with the magnetic field data. The entire RFID sensor can be wirelessly powered and interrogated using a conventional RFID reader. The advantage of this approach is that the sensor does not require batteries and does not need additional maintenance during its lifetime. This is an important feature in a high-voltage environment where any maintenance requires either an outage or special equipment. In this paper, the detailed design of the RFID sensor is presented, including the antenna design and measurements for both the RFID tag and the RF harvesting section, the microcontroller interfacing design and testing, the magnetic field sensor calibration, and the RF power harvesting section. The UHF RFID-based magnetic field sensor was fabricated and tested using a laboratory experimental setup. In the experiment, a 40 mm-diameter-aluminum conductor, typically used in 500 kV HVdc transmission lines carrying a dc current of up to 1200 A, was used to conduct dc current tests for the fabricated sensor. The sensor was placed near the conductor such that the Hall effect device was close to the surface of the conductor, and readings were acquired by the RFID reader. The sensitivity of the entire RFID sensor was 30 mV/mT, with linear behavior over a magnetic flux density range from 0 mT to 4.5 mT.

In this article, a compact wireless electric field sensor based on a chipless, contactless air-filled substrateintegrated waveguide (CLAF-SIW) resonator integrated with an aperture-coupled microstrip patch antenna is presented. CLAF-SIW technology provides a high Q-factor, enabling wireless far-field interrogation with increased distance. The integrated aperture-coupled antenna provides a compact, thin planar structure. The time variation of the external electric field results in variation of the resonance frequency of the CLAF-SIW sensor which is detected by analyzing the backscattered ringback signals from the sensor. An experimental setup is developed to perform wireless measurement of a time-varying external electric field. The experiments show that the sensor can measure an external time-varying electric field up to 7 kV/m in the frequency range of 3 Hz to 1 kHz. The measured sensitivity of the CLAF-SIW sensor and the interrogation distance are 342 (Hz)/(V/m) and 55 cm, respectively.

We demonstrate nonreciprocal control of the speed of light by sending a microwave pulse through a cavity magnonics device. In contrast to reciprocal group velocity controlled by conventional electromagnetically induced transparency (EIT) effects, incorporating a dissipative magnon-photon coupling establishes a nonreciprocal EIT effect, allowing slow and fast light propagation in opposite directions at the same frequency with comparable amplitude. Remarkably, reversing the magnetic field enables a directional switch between nonreciprocal fast and slow light. This discovery may offer new possibilities for pulse time regulation in microwave signal communications, neuromorphic computing, and quantum signal processing.

This paper presents a lens-free imaging approach utilizing an array of light sources, capable of measuring the dielectric properties of many particles simultaneously. This method employs coplanar electrodes to induce velocity changes in flowing particles through dielectrophoretic forces, allowing the inference of individual particle properties from differential velocity changes. Both positive and negative forces are detectable. The light source utilized in this system is composed of LEDs with a wavelength of 470 nm, while detection is performed using a 256-element optical array detector. Measurements with 10 μm polystyrene beads demonstrate this method can resolve changes equivalent to a Clausius–Mossotti factor of 0.18. Simulations in this work, using values from the literature, predict that Clausius–Mossotti factor differences of 0.18 are sufficient to differentiate viable from nonviable cells and cancerous from multidrug-resistant cancerous cells. We demonstrate that for Chinese hamster ovary (CHO) cells, the method can collect a dielectric response spectrum for a large number of cells in several minutes. We demonstrate that for CHO cells, Clausius–Mossotti factor differences of 0.18 can be discriminated. Due to its simple detection apparatus and the utilization of high-throughput, wide, clog-resistant channels, this method holds promise for a wide range of applications.

In this work, we use a microfluidic flow cytometer for the simultaneous imaging and dielectric characterization of individual biological cells within a flow. Knowledge of cell size in conjunction with dielectric properties enhance the ability to characterize individual cells. A high-speed camera is used to capture and track multiple cells in real-time as they traverse a microfluidic channel. This channel incorporates a coplanar electrode array, which produces a non-uniform electric field, thereby introducing dielectrophoretic forces, and translating to higher or lower velocity. Multiphysics electrostatic-fluid dynamics simulation is employed to establish the relationship between cell velocity, differential velocity and size and the Clausius-Mossotti factor (CMF), which is a function of the cell's dielectric properties. The system is evaluated using polystyrene microspheres (PSS) and demonstrated using Chinese hamster ovary (CHO) cells.

On stator windings, it is typical to perform online partial discharge (PD) measurements in the VHF range using high voltage capacitors to couple high frequency currents, and in the UHF range using near-field sensors placed adjacent to stator slot wedges to couple induced PD currents. The installation of conventional stator winding PD measurement systems can be challenging to utilities because it requires the generator to be out of service, and it also requires specialized labour to carefully install the sensors and associated wiring without damaging the asset. It would be advantageous to use antennas for online PD measurements since an outage may not be required and installation would be simple. This paper investigates antenna-based UHF techniques for online PD measurement, using rectangular microstrip patch antennas designed and fabricated with resonant frequencies of 900, 1500, and 2450 MHz. These antennas are used to detect and quantify PD on single Roebel bars in a laboratory and on the stator winding of an operating hydrogenerator. This is done by placing each antenna near the specimen under test, acquiring pulses with a digital oscilloscope, and generating PRPD patterns and time-frequency plots. Agreement with test results obtained with a commercial instrument shows that PD can be successfully measured with UHF antennas for every specimen tested.

The performance of electrical power systems relies on a healthy and properly functioning grounding network. Buried vertical electrodes are the pillars of a grounding system. This paper presents a Time Domain Reflectometry (TDR) technique based on surface wave propagation along a single wire to detect a fault. In SW-TDR, a fast rise-time pulse is injected onto the single conductor grounding electrode primarily exciting transverse magnetic (TM) mode surface wave propagation. The surface wave propagates along the electrode and is reflected at any impedance mismatch such as a fault in the electrode. The mismatch location and severity of the fault can be identified using the reflected signal waveform. Expressions for the fields of the surface wave supported by a single electrode in a lossy media is presented. Full wave electromagnetic simulation is used to evaluate the wide-band input impedance and then FFT is applied to determine the TDR response. Simulation results show that SW-TDR can identify a break-point or even partial corrosion of a grounding electrode for a wide range of soil conductivity for a system bandwidth of 200 MHz. A surface wave launcher design is also presented which enables the SW-TDR to be implemented without disconnecting the electrode from the grounding grid. A scale model experiment demonstrates the feasibility of the SW-TDR approach. Measurements show detection capabilities are similar to those obtained by simulation.

In this paper, we present a microfluidic flow cytometer for simultaneous imaging and dielectric characterization of individual biological cells within a flow. Utilizing a combination of dielectrophoresis (DEP) and high-speed imaging, this system offers a dual-modality approach to analyze both cell morphology and dielectric properties, enhancing the ability to analyze, characterize, and discriminate cells in a heterogeneous population. A high-speed camera is used to capture images of and track multiple cells in real-time as they flow through a microfluidic channel. A wide channel is used, enabling analysis of many cells in parallel. A coplanar electrode array perpendicular to cell flow is incorporated at the bottom of the channel to perform dielectrophoresis-based dielectric characterization. A frequency-dependent voltage applied to the array produces a non-uniform electric field, translating cells to higher or lower velocity depending on their dielectric polarizability. In this paper, we demonstrate how cell size, obtained by optical imaging, and DEP response, obtained by particle tracking, can be used to discriminate viable and non-viable Chinese hamster ovary cells in a heterogeneous cell culture. Multiphysics electrostatic-fluid dynamics simulation is used to develop a relationship between cell incoming velocity, differential velocity, size, and the cell's polarizability, which can subsequently be used to evaluate its physiological state. Measurement of a mixture of polystyrene microspheres is used to evaluate the accuracy of the cytometer.

This paper presents a wireless chipless resonator-based sensor for measuring the absolute value of an external time-varying electric field. The sensor is developed using contactless air-filled substrate-integrated waveguide (CLAF-SIW) technology. The sensor employs a low-impedance electromagnetic band gap structure to confine the electric field within the sensor’s air cavity. The air cavity is loaded with varactor diodes whose reverse bias voltage is modified by the to-be-measured external electric field. Variation in the external electric field results in a variation of the sensor’s resonant frequency. The CLAF-SIW sensor offers a high unloaded quality factor, which is required for a long-distance ringback-based interrogation system. A prototype of the proposed sensor is fabricated and tested. It can measure a time-varying external electric field up to 6.9 kV/m, has a sensitivity of 1.86 (kHz)/(V/m), and can be interrogated from a distance of 80 cm. The feasible maximum bandwidth of the external electric field is 25 kHz. The proposed sensor offers a compact planar multilayer structure that can easily be incorporated with a planar antenna and its size can be reduced by selecting a higher operating frequency without an increase in dielectric loss.

High-voltage direct current (HVdc) transmission lines are gaining more attention as an integral part of modern power system networks. Monitoring the dc current is important for metering and development of dynamic line rating control schemes. However, this has been a challenging task and there is a need for remote sensing methods with high accuracy and dynamic range. Conventional methods require direct contact with the high-voltage conductors and utilize bulky and complex equipment. In this paper, we introduce a UHF radio frequency identification (RFID)-based sensor to monitor the dc current of an HVdc transmission line. The sensor is comprised of a passive RFID tag, with a custom design antenna, integrated with a Hall effect magnetic field device. The dc current is measured by monitoring the dc magnetic field around the conductor using the Hall effect device. The internal memory of the RFID tag is encoded with the magnetic field data. The RFID tag enables remote wireless interrogation using a conventional RFID reader. The unique advantage of this approach is that the sensor does not require batteries and does not need additional maintenance during its lifetime. This is an important feature in a high voltage environment where any maintenance requires either an outage or special equipment. The UHF RFID-based magnetic field was fabricated and tested in a laboratory experimental setup, which consists of a 34 mm diameter aluminum conductor typically used in a 500 kV HVdc system carrying a dc current of up to 1200 A. The sensor was attached to the conductor such that the Hall effect device was 30 mm from its surface. A dc current in the range of 100–1200 A was measured with an accuracy of 5% for a reader-to-sensor distance of 3 m.

Bulk electrical impedance spectroscopy (bio-capacitance) probes, hold significant promise for real-time cell monitoring in bioprocesses. Focusing on Chinese hamster ovary (CHO) cells, we present a sensitivity analysis framework to assess the impact of cell and culture properties on the complex permittivity spectrum, εmix, and its associated parameters, permittivity increment, Δε, critical frequency, fc, and Cole-Cole parameter, α, measured by bio-capacitance probes. Our sensitivity analysis showed that Δε is highly sensitive to cell size and concentration, making it suitable for estimating biovolume during the exponential growth phase, whereas fc provides information about cumulative changes in cell size, membrane permittivity, and cytoplasm conductivity during the transition to death phase. The analysis indicated that specific information about cell membrane permittivity or internal conductivity cannot be extracted from εmix spectrum. Based on the sensitivity analysis, we proposed two alternative parameters for monitoring cells in bioprocesses: Δε1 MHz and Δε1 MHz/Δε0.3 MHz, using measurements at 300 kHz, 1 MHz, and 10 MHz. Δε1 MHz is suitable for estimating viable cell density during the exponential growth phase due to its lower sensitivity to cell size. Δε1 MHz/Δε0.3 MHz can replace fc due to similar sensitivities to cell size and dielectric properties. These frequencies are within most bio-capacitance probes' optimal operation range, eliminating the need for low-frequency electrode polarization and high-frequency stray capacitances corrections. Experimental measurements on CHO cells confirmed the results of sensitivity analysis.

Faults in a grounding network pose a serious threat to power system equipment protection and worker safety. A large number of vertical electrodes is used in a grounding network and break-points in these due to soil induced corrosion is one of the prime reasons for faults. We present a rod insertion time domain reflectometry (TDR) technique for vertical grounding electrode break-point detection. A secondary bare rod is inserted adjacent to the grounding electrode while a fast risetime pulse is continuously applied to excite a transverse electromagnetic (TEM) wave that propagates along the rods and reflects back from the break-point. The reflected signals for different depths of the secondary rod are analyzed to identify the location and severity of the break-point. We show that fault detection is possible without prior knowledge of soil electrical parameters. To show the feasibility of the proposed technique, a full wave simulation approach is used to evaluate the wideband input impedance of the grounding and inserted rod system and then FFT is applied to obtain TDR responses. The results show the method is capable of detecting faults for a wide range of soil conductivity for a system bandwidth of 300 MHz.

A grounding network is an integral part of an electrical power substation. It protects expensive equipment and provides safety to workers. This paper presents a Surface Wave (SW) Time Domain Reflectometry (TDR) technique for grounding network health integrity monitoring by detecting faults in vertical grounding electrodes. In SW-TDR, a fast rise-time pulse is applied using a horn launcher into the grounding electrode. The injected pulse travels along the electrode in the form of a transverse magnetic (TM) propagating mode and is reflected at any impedance mismatch, such as a break-point in the electrode. By investigating the reflected signal waveform, the mismatch location and severity can be identified. Theoretical expressions and simulation of the fields of the surface wave guided by a single electrode in a lossy media is presented. A single electrode system with a conical horn launcher is designed and analyzed using full wave electromagnetic simulation to evaluate the wide-band input impedance and then TDR response as obtained by applying FFT. The results show that the SW-TDR is capable of detecting break-points in a grounding electrode for a system bandwidth of 300 MHz.

The cooperation of coherent and dissipative coupling produces nonreciprocity in cavity magnonic devices, in which the isolation ratio can theoretically be infinite at a matching condition (zero-damping condition). In this article, we report the design of such a prototype, where a yttrium–iron–garnet sphere is strongly coupled to a planar microwave cavity resonator. Three different microwave isolator design schemes have been constructed according to the latest developed theory, resulting in considerable isolation, design flexibility, and device size reduction. Fabricated devices achieved the isolation of 65.8, 40.5, and 31.0 dB and the corresponding insertion loss of 23.6, 0.7, and 0.7 dB, respectively. These devices promise to be useful in microwave range applications that demand miniature, low cost, and narrowband. Furthermore, our magnonic device may open a promising way for signal processing through the manipulation of coherent and dissipative coupling.

Sensing of volatile acidic/basic gases plays a significant role in the early detection of food spoilage. This letter presents a compact low-cost quasi-chipless sensor for monitoring of such gases. The sensor utilizes a dual-band annular ring antenna to receive, modulate, and retransmit an incoming interrogation signal at double the frequency and with an orthogonal polarization. The application of the sensor for monitoring ammonia is presented. The resonant frequency of the receiving mode of the antenna is sensitized to ammonia using a varactor-based transduction scheme utilizing a hydrogel-coated pH electrode pair. The sensor provides a linear response to the logarithm of the concentration of ammonia, a sensitivity of 2.3 MHz per unit log concentration and greater than 1-m range for a signal to noise of better than 30 dB.