PIER Letters | PIER Journals

2026-05-15

PIER Letters

Vol. 130, 66-72, 2026

doi:10.2528/PIERL26040601

download: 76

Dielectric Measurements of High Dielectric Constant Materials at Microwave Frequency Using Five Well-Known Mixture Equations

Jyh Sheen and Yong-Lin Wang

The dielectric constant, which is the real part of the complex permittivity, of composite materials at microwave frequencies was investigated in this study. Ceramics of titanium dioxide, calcium titanate, and strontium titanate with high dielectric constants of 100, 170, and 300, respectively, were selected. Ceramic powders were spread in the polyethylene matrix to form composite samples. The dielectric constants of the composite samples were measured to determine their matching conditions with the mathematical curves of five well-known mixture equations. These five mixture rules were then applied to estimate the dielectric constants of the three selected ceramics from the measured dielectric properties of the composite samples with various volume percentages of ceramic fillers. The mathematical equations of the potential theory errors of the five mixture rules for the dielectric constant estimation were derived and discussed. One of the five rules was selected and modified to obtain a new empirical mixture equation. This proposed empirical equation can significantly improve the accuracy of dielectric constant measurements for the selected ceramic materials. An empirical mathematical relation of the new mixing rule with the dielectric constant of the ceramic is then concluded.

Dielectric Measurements of High Dielectric Constant Materials at Microwave Frequency Using Five Well-Known Mixture Equations

2026-05-14

PIER Letters

Vol. 130, 57-65, 2026

doi:10.2528/PIERL26020402

download: 101

Design of a DWDM Demultiplexer Using a 2D Photonic Crystal Hybrid Cavity

Vijayaraj Nivethitha and Arunagiri Sivasubramanian

A high-performance Two-Dimensional Photonic Crystal (2DPC) demultiplexer is proposed for application in Dense Wavelength Division Multiplexing (DWDM). Simultaneous high-field confinement and higher modal coupling are achieved using a new hybrid cavity geometry design, which consists of a square cavity with an inner rod radius (r = 110 nm) and a circular cavity with an outer rod radius (r = 100 nm). It is an operating silicon platform featuring a square lattice, bus waveguide, and four drop ports. Plane Wave Expansion (PWE) and Finite Difference Time Domain (FDTD) simulation methods reveal a large photonic bandgap (0.27-0.37a/λ) and excellent spectral performance, including a 98.75% average transmission efficiency, a high Q-factor of 7281, and precise 0.8 nm channel separation. System-level verification, Lumerical INTERCONNECT, and eye diagram and BER analyses were used to test signal integrity. The hybrid geometry also has a smaller footprint and improved integration, making it a suitable design for next-generation optical communication systems.

Design of a DWDM Demultiplexer Using a 2D Photonic Crystal Hybrid Cavity

2026-05-08

PIER Letters

Vol. 130, 52-56, 2026

doi:10.2528/PIERL26032401

download: 130

Approximating Processing Delays in High Energy Laser Directed Energy System Performance Prediction

Graham V. Weinberg

This study addresses an issue with high-energy laser directed energy weapon performance assessment when applied to the problem of countering swarms of uncrewed aerial systems (UAS). Queueing theory provides a suitable modelling framework for the performance assessment of such systems, as a single server queue can process only one threat at a time, based on the order in which threats arrive at the theatre of operation. Consequently, this introduces delays into the processing of sequences of threats. Delays in such queues typically have time-dependent service times, due to the target's movement. This results in considerable complexity in terms of producing performance predictions through stochastic models. In recent applications of queueing theory to directed energy systems an ad hoc approximation has been used to estimate the delays that threats experience while waiting for service. This approach involves approximating the processing delay of a given threat by a constant value. In particular, it has been estimated by measuring the delay as a product of the expected service time and the number of threats present less one. Such an approximation can result in severely reduced and inaccurate performance predictions. In the current study, the mean delay will be used instead, and improvement on the aforementioned approximation will be demonstrated through explicit examples of swarm UAS defeat.

Approximating Processing Delays in High Energy Laser Directed Energy System Performance Prediction

2026-04-30

PIER Letters

Vol. 130, 44-51, 2026

doi:10.2528/PIERL26030411

download: 231

Design of a Single Layer Substrate and via-Free Transmit-Reflect Array Antenna Based on Metasurface

Xinwei Chen, Xinmiao Zhao, Jinrong Su, Guorui Han, Runbo Ma and Li Li

In this study, a single-layer substrate and via-free transmit-reflect-array antenna based on a metasurface is proposed. The array antenna comprises transmissive and reflective unit cells arranged alternately in sequence. To achieve a 360° phase coverage, two sets of antisymmetric U-shaped lines are etched on the top and bottom layers of the substrate to form the transmissive unit cells, and multi-layer stacking and vias are avoided. Moreover, by adjusting the lengths of a split-ring structure with phase delay lines for reflective unit cells, a 360° phase coverage is achieved. The measurement results demonstrate that the antenna simultaneously generates a reflective focused beam with a peak gain of 20.8 dBi and a transmissive +1-mode OAM vortex beam with a peak gain of 20 dBi and a mode purity of 90% at 17 GHz.

Design of a Single Layer Substrate and Via-Free Transmit-Reflect Array Antenna Based on Metasurface

2026-04-29

PIER Letters

Vol. 130, 36-43, 2026

doi:10.2528/PIERL26011604

download: 146

Modulation Technique of Conformal Metasurface for 3D Spiral Shaped Near-Field with High SNR and Efficiency

Hui-Fen Huang and Ke-Chun Niu

The curvature effects of curved metasurface (MTS) lead to oblique incidence and different unit radiation normal vectors (DURNVs). Oblique incidence causes a reduction in scattering amplitude and degrades focusing efficiency (FE), and DURNV distorts the radiation pattern of curved MTSs. To the knowledge of the authors, for the first time, this paper proposes a phase amplitude modulation and phase modulation (PAM-PM) combined modulation technique for cylindrical MTS to generate a high signal-to-noise ratio (SNR) and high FE three-dimensional (3D) shaped near field with a spiral cross-sectional shape. In addition, a near field with controllable spatial positions is a practical application requirement, and this paper provides a method to establish a 3D-shaped near field with controlled spatial positions. The proposed cylindrical MTS with PAM-PM modulation technique outperforms the PM technique significantly, achieving an SNR above 13 dB and an FE of 38.1%. For cylindrical MTS with only PM, there exists some noise, and the FE is 33.2%. This proposed modulation technique can be applied to 3D near-field systems based on conformal MTS, including wireless power transfer, radiometric temperature sensors for hyperthermia, and medical imaging systems.

Modulation Technique of Conformal Metasurface for 3D Spiral Shaped Near-Field with High SNR and Efficiency

2026-04-25

PIER Letters

Vol. 130, 28-35, 2026

doi:10.2528/PIERL26030406

download: 355

Compact 13.56 MHz Wireless Power Transfer Architecture Using Self-Resonant Coils with Inherent Source Power Limiting

Zixuan Yi, Ziheng Li, Xiaojun Tao and Meiling Li

Megahertz wireless power transfer (MHz-WPT) enables compact resonant components; yet the matching, compensation, and filtering stages used in conventional systems can dominate loss and standby dissipation at MHz operation. To address this issue, this work proposes a compact 13.56 MHz WPT architecture in which impedance transformation is integrated into the resonant hardware. A self-resonant transmitting coil is co-designed with a Class-E power amplifier to shape the reflected load toward the optimum operating condition, thereby removing the external compensation network, the additional matching stage, and the lumped-element LC output filter. The analysis shows that, when the receiver is removed, the effective load becomes dominated by the transmitter resistance, inherently suppressing delivered power without sensing or closed-loop control. A prototype delivers 9 W over 30 mm with 81.5% end-to-end DC–DC efficiency, while under receiver absence, the DC input power decreases from 11 W to 1.15 W. These results demonstrate a simplified and robust MHz-WPT architecture with reduced component count and inherently low standby dissipation.

Compact 13.56 MHz Wireless Power Transfer Architecture Using Self-Resonant Coils with Inherent Source Power Limiting

2026-04-06

PIER Letters

Vol. 130, 23-27, 2026

doi:10.2528/PIERL26012201

download: 248

Integrated Slotted SIW Oscillator-Antenna Based on the TE210 Mode with High Spectral Purity

Abdelmounim Sellidj, Tarek Djerafi, Said Gaoua and Mustapha Yagoub

In this work, a Substrate-Integrated Waveguide (SIW) cavity-based positive-feedback oscillator integrated with a slot antenna on a single substrate was designed. The proposed design incorporates a radiating element, an oscillator tank, and a coupling structure within the same cavity, thereby eliminating external interconnections and significantly enhancing overall efficiency. By employing the TE₂₁₀ mode instead of the TE₁₁₀, the design exploits a field node to minimize the parasitic loading effects of the oscillator coupling probe on the antenna radiation. This approach simultaneously enhances the cavity's quality factor Q and preserves the spectral purity of the integrated SIW antenna-oscillator, all this without affecting the antenna radiation. The SIW cavity achieves a measured quality factor (Q) of 250, ensuring high spectral selectivity at the 10 GHz resonant frequency. The oscillator exhibits low phase noise of -131 dBc/Hz at a 1 MHz offset, along with exceptional suppression of harmonics, including the total suppression of the third harmonic, while the slot antenna achieves a gain of 6 dBi. This fully integrated architecture delivers performance equivalent to discrete implementations while offering a compact footprint and eliminating insertion losses between the antenna and the oscillator.

Integrated Slotted SIW Oscillator-Antenna Based on the TE210 Mode with High Spectral Purity

2026-04-03

PIER Letters

Vol. 130, 15-22, 2026

doi:10.2528/PIERL26021202

download: 212

A High-Selectivity 3-D Dual-Polarized Frequency Selective Rasorber with Wide Absorption Bands Based on Multiple Strip-Type Resonators

Hao Shen, Borui Bian and Dan Zhang

This letter presents a high-selectivity three-dimensional (3-D) dual-polarized frequency-selective rasorber (FSR). The proposed design comprises a 3-D array of multiple lossy strip-type resonators integrated with a planar bandpass frequency-selective surface (FSS). While the multiple resonances of the strips provide wideband absorption, a parallel LC structure is loaded within each resonator to achieve a low-loss transmission band. Numerical and experimental results demonstrate an ultra-wide low-reflection band with a fractional bandwidth (FBW) of 162.2% from 2.0 to 19.2 GHz. This includes a transmission band at 10 GHz with an insertion loss of 0.47 dB, alongside a lower frequency absorption band (2.0-9.5 GHz, FBW 130.4%) and an upper frequency absorption band (10.5-19.2 GHz, FBW 58.6%). The operating mechanism is further validated by an equivalent circuit model and measurement of a fabricated prototype, showing good agreement between theory and experiment.

A High-selectivity 3-D Dual-polarized Frequency Selective Rasorber with Wide Absorption Bands Based on Multiple Strip-type Resonators

2026-03-24

PIER Letters

Vol. 130, 9-14, 2026

doi:10.2528/PIERL25072504

download: 337

Design of a Tunable Wide-Stopband Plasmonic Filter Based on a Metal-Insulator-Metal (MIM) Waveguide for Mid-Infrared Applications

Ahmed Lounis, Imane Zegaar, Hocine Bensalah and Abdesselam Hocini

Wide-stopband plasmonic filters are essential components in compact mid-infrared (MIR) photonic systems. This work proposes a geometrically tunable wide-stopband plasmonic filter based on a metal-insulator-metal (MIM) waveguide with dual resonator cavities. The optical response is numerically investigated using the two-dimensional finite-difference time-domain (2D FDTD) method. The influence of the resonator height H₂ and the inter-cavity distance D on the stopband characteristics is analyzed. The symmetric dual-cavity configuration enables effective control of the stopband bandwidth and central wavelength. The design achieves a significantly broadened stopband while maintaining compactness and high transmission selectivity, making it a promising candidate for integration into mid-infrared photonic and sensing systems.

Design of a Tunable Wide-stopband Plasmonic Filter Based on a Metal-Insulator-Metal (MIM) Waveguide for Mid-infrared Applications

2026-03-18

PIER Letters

Vol. 130, 1-8, 2026

doi:10.2528/PIERL26010302

download: 429

Design and Experimental Validation of Linear to Circular Polarization Converter for Point to Point THz Communication

Murtaza Waheed, Javid Ahmad Ganie, Mingyan Zhong, Qusay Raghib Al-Taai, Kushmanda Saurav and Chong Li

This letter presents a compact, low profile singe substrate transmissive linear-to-circular polarization (LCP) converter designed and experimentally validated for point-to-point THz communication bands. The proposed LCP converter consists of an H-shaped gold metallic pattern deposited on both sides of a 100 μm-thick fused silica substrate. The LCP converter operates within the 0.225-0.307 THz frequency band, achieving a simulated 3-dB axial ratio bandwidth of 30.8% in simulation. Owing to its wide axial ratio bandwidth, the proposed design is a promising candidate for point-to-point THz communication applications. The performance of the proposed converter is verified through surface current distribution, which explains the occurrence of Huygens response and equivalent circuit model. The proposed converter exhibits a measured 3-dB axial-ratio bandwidth of 27.8% in the frequency band 0.229-0.303 THz. The simple geometry and single-substrate implementation, with a thin profile and wide 3-dB axial ratio bandwidth, make the proposed design suitable for practical deployment scenarios.