This paper presents the design, manufacturing, and electrical characterization of a dielectric triple-mode bandpass filter. The filter utilizes a triple-mode resonator based on the combination of a ring-shaped TE single-mode and a Y-shaped dual-mode dielectric resonator. For the realization of the resonator consisting of zircona, the cost-efficient Direct Ink Wrinting (DIW) approach is used. Simulations and practical measurements validate the design, showcasing the suitability of the approach to combine different basic resonator types for the realization of multi-mode structures.

This paper presents a novel broadband directional resistive coupler. A simple, low-cost coupler is designed for a project to measure moisture content with a fast network analyzer. A novel approach to directional coupler design is presented, which eliminates the need for ferrites and enables a nearly frequency-independent coupling of -16 dB. The innovative design, which works on the Wheatstone Bridge principle, uses crossed ohmic resistors on a Roger 4003C substrate and has a high bandwidth from 1 to 12.6 GHz with a directivity over 20 dB. The study combines simulations and practical implementations to validate the performance of the proposed directional coupler. A circuit board has been developed that uses two high bandwidth directional couplers to demonstrate its potential for microwave applications.

This letter presents the design and electrical measurement results of a novel compact diplexer design in Ku-band. The proposed diplexer is based on TM01 delta mode dielectric resonators (DRs). A fourth-order filter with one triplet section for each channel is used. An additively manufactured inset is used for each filter, which contains the resonators and the required support structure and is printed from two materials in one piece. The chosen arrangement enables a compact design and simple assembly. To validate the concept, the design, fabrication, and measurement of the fourth-order dielectric diplexer are presented.

The pursuit for advanced magnetoelectric field sensors has gained momentum, driven by applications in various fields, ranging from biomedical applications to soft robotics and the automotive sector. In this context, a capacitive read-out based magnetostrictive polymer composite (MPC) sensor element is introduced, offering a new perspective on magnetic field detection. The sensor element’s unique feature is the possibility to independently tailor its mechanical and magnetic properties. When compared to other composite-based magnetic field sensors, the limit of detection (LoD) is three orders of magnitude lower (95.6 nT/√Hz at a resonance frequency of 160.5 Hz). In contrast to other electret-based ME sensors, the LoD is reduced by a factor of 20. To the best of the authors’ knowledge, this work marks the first comprehensive attempt to characterize a sensor magnetically, aligning with the thorough assessment standards of ME sensors. This study aims to narrow the disparity between established magnetic field sensors, featuring consistent characterization protocols, and the novel MPC sensors, which often undergo limited magnetic characterization as part of their evaluation. The presented sensor, built from readily available materials, offers a versatile and tuneable platform for magnetic field detection, and ongoing research aims to unlock its full potential in diverse applications.

This paper compares the performance of two eighth-order waveguide filters in D-band. Both filters have a complex pair of transmission zeros, which is used for phase equalization, as well as an imaginary transmission zero pair for blocking improvement in the near passband region. The filters are designed in order to be manufactured in E-plane cut, which reduces the insertion loss compared to H-plane-cut manufacturing. Both filters are designed in a way that a quadruplet section implements the complex transmission zero pair. However, they distinguish each other by the realization of the imaginary transmission zeros. While one filter consists of a second quadruplet section, the other filter has two stub-loaded cavities. The flexibility of both approaches is discussed and a performance comparison of manufactured prototypes takes place.

Refractory concrete materials require a time and energy intensive drying and dehydration process at temperatures up to approximately 600 degrees C before safe use in industrial applications is possible. To monitor the dehydration process of hydrate phases, a measurement setup based on a high-temperature resistant microwave resonator is presented. The resonator is constructed with conventional, commercially widely available materials and measurements are conducted with inexpensive measurement hardware while allowing for real-time data acquisition during the heating cycle. The resonance frequency f(r) and the 3 dB-bandwidth are extracted from measurement data and related to the dehydration process. The measurement results correspond to the loss of evaporated water from the refractory castable material. Ultimately, the temperature stability and reliability of the measurement setup are confirmed.

Clinical motion analysis plays an important role in the diagnosis and treatment of mobility-limiting diseases. Within this assessment, relative (point-to-point) tracking of extremities could benefit from increased accuracy. Given the limitations of current wearable sensor technology, supplementary spatial data such as distance estimates could provide added value. Therefore, we propose a distributed magnetic tracking system based on early-stage demonstrators of novel magnetoelectric (ME) sensors. The system consists of two body-worn magnetic actuators and four ME sensor arrays (body-worn and fixed). It is enabled by a comprehensive signal processing framework with sensor-specific signal enhancement and a gradient descent-based system calibration. As a pilot study, we evaluated the technical feasibility of the described system for motion tracking in general (Scenario A) and for operation during treadmill walking (Scenario B). At distances of up to 60 cm, we achieved a mean absolute distance error of 0.4 cm during gait experiments. Our results show that the modular system is capable of centimeter-level motion tracking of the lower extremities during treadmill walking and should therefore be investigated for clinical gait parameter assessment.

This paper describes the realization of a fourth order waveguide filter, which is designed in the WR-3 frequency band (220 GHz - 330 GHz). The filter implements a classical quadruplet topology. A cross-coupling between the first and fourth resonator realizes a pair of transmission zeros (TZs) to improve the near passband rejection properties. A source to load (SL) cross-coupling is added to the topology for the realization of further TZs. In comparison to former investigations, the SL cross-coupling proposed here consists of two individual coupling slots. An SL cross-coupling in waveguide technique can be designed to show a dispersive behaviour, wherefore additional TZs can be introduced to the filter response. A double slot coupling aperture increases the degrees of freedom with respect to placing these additional TZs. As a result, in total seven TZs in the WR-3 frequency band are generated. Six of these TZs can be placed nearly symmetrically above and below the passband. An adapted coupling matrix description as well as a discrete equivalent circuit are proposed as well. Furthermore, parameter studies are carried out and measurement results are compared to simulation.

This work demonstrates the use of structured-glass waveguide (SGW) technology in a stackable multi-layer configuration in order to exhibit the versatile nature of structured-glass in high-frequency and high-performance applications. A novel multi-layer corrugated elliptic horn antenna composed of nine wafer layers is designed for operation in the D-band frequency range and exhibits the use of a circular waveguide feed line. In this manner, the structured-glass waveguide antenna design is introduced to the literature for the first time and demonstrated with the highest operating frequency to date for structured-glass based waveguide components. Detailed build profiles are provided with reference to the structured-glass fabrication method. Two of the proposed antenna components are fabricated in order to validate the gain measurement. The measured results are shown to achieve highly accurate S-parameter results and beam patterns throughout the selected frequency range.

This work presents an in-depth analysis of the four most basic waveguide inverter types; E-plane irises, E-plane stubs, H-plane irises and H-plane stubs. A thorough investigation and tolerance analysis of fourth-order filters, which are comprised of each of the inverter types, is undertaken in order to identify and communicate sensitivity, fabrication practicality and special considerations for the mass production of waveguide filters operating in the sub-terahertz region, while in addition, aims to resolve open questions with regards to the direct comparison of performance between each of the filter profiles. A total of 40 filters are fabricated and measured for operation at 267.5 GHz with a 5.6% fractional bandwidth. The results are detailed and a yield summary is presented for an 80% bandwidth criteria with return loss operating conditions at 18 dB and 20 dB. The highest product yield is found to be of the stub filter types, that being 90% each when a 20 dB criteria is applied, while the lowest yield is of the H-plane iris filter type, that being 50% when a 20 dB criteria is applied. The measured results indicate that both of the stub-type filter profiles also result in a lower insertion loss when compared to the iris-type designs. An additional evaluation is provided at the end of the article with the production of another 6 H-plane iris-type filter prototypes with per-contra cutting planes in order to discuss and contrast the measured results of E- and H-plane cutting profiles and their respective relationship to the milling depth and attainable aspect ratio in sub-terahertz applications.

A novel wideband multiplexer is introduced as a communications equipment solution in order to provide simultaneous operation of satellite and terrestrial services in the dedicated $K$ / $Ka$ frequency bands (passbands ranging from 19.5 GHz to 30.5 GHz). Advanced RF filtering techniques are applied in order to accommodate a compact multiplexer design while maintaining low insertion loss and high rejection demands up to 33 GHz. Due to the overall wide bandwidth and the demanding requirements for the assigned three operational bands, different filter types have been employed. Thus, the multiplexer considers the combination of filters with rectangular, evanescent combline, and conductor-loaded resonator types. The multiplexer relies on the direct branching approach, i.e., all filters are connected to a central (star-junction) waveguide branching region. This region exhibits a reduced waveguide size to suppress interference by higher order modes. For a verification of the approach, WR34 waveguide interfaces have been considered at all ports for prototype design, however, the design can be well adapted for integrated equipment solutions with associated direct interfaces. Accurate coincidence of analyzed and measured performance of the prototype demonstrates the validity of the special approach. Moreover, additional simulations are provided as an outline for terminals with specific industry demands.

In this letter, the design and additive manufacturing (AM) of a groove gap waveguide (GGW) filter in the $D$ -band is presented. For this kind of filter, the manufacturing of very small periodic pin structures is necessary. The conventional manufacturing of these structures by CNC milling is time-consuming, and high-precision milling machines are extremely expensive. Other manufacturing processes such as screen printing are, therefore, required for the cost-effective and efficient production of large quantities. The screen printing process is presented, and its suitability for the production of GGW components in the millimeter-wave area is validated by a third-order bandpass filter prototype in $D$ -band, which was manufactured and electrically characterized.

AbstractConverse magnetoelectric sensors enable the detection of low‐frequency and low‐amplitude magnetic fields over a bandwidth of several kilohertz by combining the electrical excitation of a magnetoelectric resonator via a piezoelectric layer with an inductive readout. Here, a comprehensive sensor model is presented to further foster the development of this promising sensor concept. The model relates the output signal to the device characteristics, taking into account the magnetoelastic and electromechanical properties, the resonator geometry, and operating conditions. The sensor system is thoroughly experimentally analyzed to validate the model. Based on the analysis, the sensor concept is explained in detail, including the origin of its loss and bandwidth and their connection with the magneto‐mechanical loss in the magnetostrictive layer. Significant advances have been made in the comprehensive understanding of converse magnetoelectric sensors, providing a solid basis for future improvements in magnetoelectric sensor systems.

Within this paper, a corrugated horn antenna in the sub-terahertz regime is manufactured using a novel printing technique and the results are presented. The antenna aperture utilizes an elliptical shape which leads to symmetric radiation. Furthermore, the implemented antenna design leads to low side lobes, also the overall length and weight is comparably small. In addition to the antenna characteristics, the surface of the printed antenna is examined to investigate the roughness and accuracy. A symmetric radiation pattern as well as low losses are reached, which indicates a smooth surface and high accuracy.

This paper presents the measurement procedure as well as the calculations and theoretical background for the estimation of particle sizes with the help of a dual-frequency measurement setup. For the measurement, two fully integrated radar sensors are implemented which offer advantages over typically used technologies at high frequencies. The first sensor has a constant transmitting frequency of 90 GHz while the second sensor offers a possibility to vary the transmitting frequency over the entire D-band with frequencies between 110 and 180 GHz. With these frequencies, different sizes can be determined. The presented approach makes use of the different transitions between the linear increasing Rayleigh scattering regime and the Mie regime. With a fitting indoor measurement setup that resembles an industrial duct, the approach is verified for spheroid glass particles with a diameter of 0.875 mm. The results show a slight deviation from the expected value of particle sizes overall

This work introduces a novel metamaterial-based design concept where the combination of metasurface unitcells and dielectric-substrate stencils is applied to create various passive microwave components by controlling the slow-wave (SW) and electromagnetic-bandgap (EBG) properties of the unitcells. In this manner, the SW and EBG conditions are synonymous to on-state or off-state, respectively, and various components can be created by adopting stencil patterns that effectively control the propagation of electromagnetic waves. The underlying principle for the concept is first described and then applied to create various passive components using patterned substrate stencils. To validate the concept, a multipurpose four-port testbed is developed for implementing different passive components, which include a transmission line, an H -plane bend, a power divider/combiner, and a two-pole filter. Moreover, for the purpose of exploring other practical applications, an additional two-port testbed is designed and demonstrated for various surface-mount filter scenarios.

In this paper, a lithography based additive manufacturing (AM) technique is used for the realization of a ceramic X-shaped dual-mode filter. The fourth order filter consists of two identical ceramics which are mounted in a copper housing and which are coupled by an aperture. Due to the arrangement of the ceramics and the associated coupling scheme, a negative cross-coupling between the first and fourth resonance is realized, leading to two transmission zeros (TZs), one above and one below the passband. The digital light processing process used for fabrication of the ceramics is described and compared to the stereolithography approach. Subsequently, the filter design process is addressed. The measurement results are compared to the simulation and reveal good agreement.

Detection of magnetic fields generated by deep brain stimulation (DBS) using optically pumped magnetometers (OPMs) operating in the spin-exchange relaxation-free (SERF) regime holds significant promise. High bandwidth DBS signals are particularly valuable for understanding current OPM limitations and developing predictive strategies to overcome them. This primary study investigates the response of commercially available SERF-OPMs (QZFM Gen-2, QuSpin Inc.) with their limited 135 Hz bandwidth and open-loop operation when exposed to magnetic DBS signals emitted by a commercially available DBS lead and generated by a DBS implantable pulse generator (IPG), which are characterized by short-duration rectangular pulses. Such magnetic fields emitted from a real DBS lead were measured using OPMs across a range of DBS pulse repetition frequencies from 2 to 255 Hz. A versatile 304-channel superconducting quantum interference device (SQUID) vector magnetometer system was employed in the Berlin Magnetically Shielded Room-2.1 for reference measurements. Our findings identified peaks at several spectral frequencies in addition to those relevant to the DBS signal, including the known DBS repetition frequency and its spectral harmonics peaks. These additional peaks are attributed to the interaction between the lock-in detection-based OPM's 923 Hz modulating field, supplied by the OPM's on-sensor coils, and the DBS repetition frequency. These peaks were successfully reconstructed by developing an OPM lock-in model and applying this model to signal characteristics provided by SQUID reference measurements. This letter identifies and clarifies the origin of various spectral peaks observed when using bandlimited OPMs for high bandwidth signal detection. This understanding allows magnetometer users of this particular sensor technology to differentiate between artificially introduced signal components and the DBS signal components. These findings are essential for improving the application utility of OPM-based detection for DBS and contribute to the advancement and understanding of OPM technology and address its current limitations.

When using high-sensitivity sensors in arrays, it is essential to divide the sensor system into individual, robust and separable components. This is the most effective way to achieve a sufficient sensor density and to make efficient use of techniques such as multiplexing. This paper presents a compact surface acoustic wave (SAW) oscillator ring composed of discrete components for magnetic field measurement. The output signal of the oscillator is the frequency modulated (FM) sensor signal and can be directly demodulated or down-converted for demodulation, depending on the operating frequency of the sensitive element.

This work presents a novel implementation of metasurface filters with high performance and compact size for future space applications. A $K$ -band fourth-order metasurface filter is proposed with a center frequency of 18.5 GHz and bandwidth of 400 MHz with an out-of-band rejection that is better than 30 dB over the range of 20–50 GHz. The proposed filter has a measured insertion loss of 1.47 dB and a quality factor of 670. The resonators implemented in this filter exhibit a miniaturization of 63% when compared to a conventional rectangular waveguide (RWG) resonator. The compact size and high-performance capabilities make the proposed filter an ideal solution for space applications.