This paper presents a 220-320-GHz hemispherical lens antenna fabricated using photopolymer-based additive manufacture and directly fed by the standard WR-3 rectangular waveguide without any additional waveguide extension. The microfabrication process is based on digital light processing rapid prototyping using the Monocure 3DR3582C resin-based photocurable polymer. This gives various key advantages, including ease of antenna fabrication, manufacturing speed, and cost-effectiveness due to its rapid fabrication capability. Even though the photopolymer is found to have a loss tangent of 0.034 at 320 GHz, the all-polymer lens antennas still achieve a fractional bandwidth of 37%, covering the whole 220-320-GHz WR-3 waveguide band with a measured gain of approximately 16 dBi at 0 • over the whole band. A measured return loss of better than 14 dB is achieved from 220 to 320 GHz with a half-power beamwidth of approximately 12 • , which is relatively constant over the whole WR-3 band. INDEX TERMS Lens antenna, digital light processing, terahertz antennas.
In this paper, resin-based photocurable polymer materials for stereolithography, digitallight-processing (DLP), and polymer-jetting additive manufacturing techniques were characterized from 0.2 to 1.4 terahertz (THz) for their comprehensive dielectric properties, e.g., refractive index, absorption coefficient, dielectric constant, and loss tangent, by using laser-based THz time-domain spectroscopy. A total of 14 photocurable 3D-printing polymers were chosen, owing to their suitability, in terms of printing resolution, material characteristics, and so on, for millimeter-wave (mm-wave) and THz applications. The measurement results from 0.2 to 1.4THz, the dielectric constants of all photopolymer samples under test are between 2.00-3.10, while the loss tangents are from 0.008 to 0.102, which are quite useful for many applications, e.g., 3D printed antennas and THz transmission lines, which were demonstrated by an asymptotically quasi-single-mode Bragg fiber microfabricated by DLP micromanufacturing technique using HTM140-V2 photopolymer, which is previously reported at the nominal frequencies from 0.246 to 0.276 THz.
This work presents, for the first time, an in-situ self-aligned fluidic-integrated microwave sensor for characterizing NaCl contents in NaCl-aqueous solution based on a 16-GHz bandpass combline cavity resonator. The discrimination of the NaCl concentration is achievable by determining amplitude differences and resonant frequency translations between the incident and reflected microwave signals at the input terminal of the cavity resonator based on the capacitive loading effects of the comb structure inside the cavity introduced by the NaCl solution under test. Twelve NaCl-aqueous liquid mixture samples with different NaCl concentrations ranging from 0% to 20% (0-200 mg/mL), which are generally exploited in most industrial and biomedical applications, were prepared and encapsulated inside a Teflon tube performing as a fluidic channel. The Teflon tube is subsequently inserted into the cavity resonator through two small holes, fabricated through the sidewalls of the cavity, which can be used to automatically align the fluidic subsystem inside the combline resonator considerably easing the sensor setup. Based on at least five repeated measurements, the NaCl sensor can discriminate the NaCl content of as low as 1% with the measurement accuracy of higher than 96% and the maximum standard deviation of only 0.0578. There are several significant advantages achieved by the novel NaCl sensors, e.g. high accuracy, traceability and repeatability; ease of sensor setup and integration to actual industrial and biomedical systems enabling insitu and real-time measurements; noninvasive and noncontaminative liquid solution characterization as well as superior sensor reusability due to a complete physical separation between the fluidic and microwave subsystems.
This article presents, for the first time, new design and fabrication techniques for Hollow Substrate Integrated Waveguides (HSIWs), demonstrated in the nominal frequency from 21 to 31 GHz, for use in wireless communication applications such as 5G, IoT and robotics. The design and fabrication techniques introduced in this paper feature: 1) the use of low-cost rapid prototyping additive manufacturing based on polymer jetting (PJ), and 2) the use of commercially available through-substrate copper via transitions. In contrast to the conventional SIW designs and fabrications, this new approach does not rely on through-substrate via fabrication, hence avoiding some difficult manufacturing steps, such as through-substrate etching, via formation and via metallization, which are considered complex and expensive to implement. The 3D printed HSIWs in this article can achieve a propagation loss of lower than 1.56 Np/m (13.55 dB/m), which is considered one of the results with the lowest propagation loss achieved to date, when compared to the state-of-the-art.
This paper presents a comprehensive study of the optical and electrical dielectric material properties of six commonly-used silicon and glass substrates at terahertz (THz) frequencies, including refractive index, absorption coefficient, dielectric constant and loss factor. The material characterization techniques used in this paper feature THz time-domain transmission and reflection spectroscopy with the measurement frequencies from 0.5 THz up to a maximum of 6.5 THz. Of the six selected dielectric and semiconductor substrates, two are silicon wafers with resistivities ranging from 0.001 to 0.02 Ω-cm. From the measurement results, loss tangents of the selected silicon wafers range from 0.680 to 5.455 and the dielectric constants are from 1.079 to 17.735. The four other wafers are all glass-based substrates: D263 glass, Borofloat 33 glass, fused silica and Sapphire. From the measurements, it is found that the THz dielectric properties vary considerably between the substrate samples e.g. dielectric constants range from 1.925 to 3.207 while loss tangents are from 0.042 × 10−3 to 0.127. Most of the selected silicon and glass-based substrates are quite useful for many THz applications, e.g., THz integrated circuits (THz ICs), THz microsystem technologies (THz MSTs) and THz system-on-a-chip (THz SoC) and system-on-substrate (SiP).
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