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- ItemPractical design of variable fractional-order capacitors with a single tuning feature using field effect transistors and variable capacitance diodes(Springer Nature, 2025-07-01) Šotner, Roman; Black, Chloe; Jeřábek, Jan; Freeborn, Todd; Colburn, Simon; Svoboda, MarekThis paper presents two discrete circuit solutions for realizing passive, electronically adjustable constant-phase elements, specifically half-order capacitors with a -45 degrees phase shift. Fractional-order capacitors with electronically adjustable pseudocapacitance are especially useful for designing tunable filters and oscillators. The ability to adjust pseudocapacitance electronically and continuously is a major improvement over traditional passive solutions. Their pseudocapacitance can be controlled by a DC voltage, allowing key parameters like the cut-off or oscillation frequency to be tuned. Two presented design approaches differ in accuracy, tuning range, and signal-handling capability. Both solutions maintain a constant phase over one frequency decade, with a phase ripple within +/- 2 degrees. The tuning range spans from hundreds of Hz to several MHz. Presented solutions allow pseudocapacitance tuning in range of hundreds of nano F/sec0.5 (with varicaps) and tens of micro F/sec0.5 (with MOSFETs). The MOS-based circuit offers a tuning ratio of 7 but shows a 19% deviation between simulation and measurement. It also suffers from notable nonlinearity, with undistorted operation limited to signal levels up to 20 mV peak-to-peak. The varicap-based solution achieves a tuning ratio of 5, with high accuracy (up to 6% error), and handles input signals in the hundreds of mV with acceptable distortion. PSpice simulations and laboratory measurements confirm the performance of both designs.
- ItemPulsed Electromagnetic Excitation of a Thin Wire-An Approximate Numerical Model Based on the Cagniard-DeHoop Method of Moments(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2024-02-01) Štumpf, Martin; Antonini, Giulio; Ekman, JonasAn approximate computational model of an electromagnetic pulse-excited thin-wire antenna is developed. The presented solution methodology is based on the Cagniard-DeHoop method of moments and Hallen's approximation of the thin-wire model. It is shown that the proposed time-domain solution leads to an inversion-free and efficient updating procedure that mitigates the marching-on-in-time accumulation error. An illustrative numerical example demonstrates the validity of the proposed model.
- ItemA wireless W-band 3D-printed temperature sensor based on a three-dimensional photonic crystal operating beyond 1000C(Springer Nature, 2024-09-23) Sánchez-Pastor, Jesús; Kaděra, Petr; Sakaki, Masoud; Jakoby, Rolf; Láčík, Jaroslav; Benson, Niels; Jiménez-Sáez, AlejandroIn addressing sensing in harsh and dynamic environments, there are no available millimeter-wave chipless and wireless sensors capable of continuous operation at extremely high temperatures. Here we present a fully dielectric wireless temperature sensor capable of operating beyond 1000°C. The sensor uses high-Q cavities embedded within a three-dimensional photonic crystal resonating at 83.5GHz and 85.5GHz, and a flattened Luneburg lens enhances its readout range. The sensor is additively manufactured using Lithography-based Ceramic Manufacturing in Alumina (Al2O3). Despite the clutter, its frequency-coded response remains detectable from outside the furnace at 50cm and at temperatures up to 1200°C. It is observed that the resonance frequencies shift with temperature. This shift is linked to a change in the dielectric properties of Al2O3, which are estimated up to 1200°C and show good agreement with literature values. The sensor is thus highly suitable for millimeter-wave applications in dynamic, cluttered, and high-temperature environments.
- ItemNovel Second-Order Transfer Section for Frequency-Selective Response Generation in Comb Filters(IEEE, 2025-03-07) Šotner, Roman; Semenov, Dmitrii; Andriukaitis, Darius; Svoboda, Marek; Polák, LadislavThis article introduces a novel unified second-order filtering topology for standard band-reject (sBR) and inverting band-reject filter, enabling selective response generation. It is applied in the design of special comb filters that allow attenuation as well as amplification of specific bands. The presented solution offers several advantageous features in topology, enhanced cascadability, better parameter-setting performance, and the use of readily available off-the-shelf components, all while reducing overall costs. This is a significant improvement compared to the previous solutions in this field, which relied on a very expensive CMOS process. The topology employs a combination of an operational transconductance amplifier (OTA) and a current feedback amplifier. The intended center frequencies and transfer values of the comb filter are set to 50 Hz (-20 dB), 1 kHz (+26 dB), 10 kHz (+17 dB), and 100 kHz (-30 dB). The comb filter was experimentally verified via simulations as well as laboratory measurements utilizing LT1228 devices in a fabricated prototype.
- ItemComments on "Transient Magnetic Shielding of a Planar Conductive ThinScreen via Exact Image Theory"(IEEE, 2024-05-14) Štumpf, MartinThe main result of Lovat et al. (2023) is put into context of previously published papers on the subject. Its correction is described.