In this letter, we design and fabricate a three-dimensional printed all-dielectric planar metalens for microwave focusing into a receiving antenna. The structure allows the antenna gain to be increased by 7.5 dB at 32.5 GHz with a bandwidth of 2.4 GHz. The metalens has a focus full-width at half-maximum of ∼0.85λ with a 3 dB depth-of-focus of approximately 5 cm. We show that the antenna half-power beamwidth can be reduced from 36° to 3° in the azimuthal plane and from 4.5° to 3° in the elevation plane with the help of the metalens. In addition, we demonstrate that the metalens performs equally well at oblique incidence, with a 50° and 40° span in the azimuthal and elevation planes, respectively.

In this paper, a microwave biosensor with unprecedented sensitivity based on encoded pulse propagation and microfluidics is theoretically investigated and experimentally demonstrated. The structure consists of a double-spiral transmission line on FR4 substrate electromagnetically coupled to a copper coiled capillary tube above it. The working principle for improved sensitivity consists of propagating an encoded sequence of short pulses (Walsh-Hadamard spreading code with variable temporal length) in a recirculating manner so that the pulses are deformed both due to dispersive and time-delay effects. Once the recirculation is finished, the energy of the code at the sensor output is calculated, providing an indicator directly related with the analyte concentration. The experimental results demonstrate the improved sensitivity of this sensor approach for the case of glucose with 2.9 mg/ml resolution. Furthermore, we demonstrate the potential of this technology as a sensor platform by investigating other chemical compounds such as isopropyl alcohol (IPA) and acetone with a sensitivity of 20% of the volume. Finally, the outstanding performance, both in terms of accuracy and sensitivity, situates the present multi-purpose approach within the state-of-the-art of microwave (bio)chemical sensors.

In 2021, approximately 537 million people were diagnosed with diabetes mellitus. With rates expected to rise, health expenditures are projected to reach one trillion USD by 2030. Thus, measuring glucose levels is essential for rationalizing the costs of public health systems. In this context, this paper presents two major contributions. First, it demonstrates that using deionized water (DI-water) as a reference for glucose sensing is not a reliable approach for representing human blood plasma (BP), as it lacks ions and suppresses essential effects such as losses. As an alternative, we investigate the use of an artificial blood plasma solution (ABPS) that closely resembles real human BP. Characterized over a range from 500 MHz to 10 GHz, ABPS shows marginal differences in real permittivity but significant differences in imaginary permittivity compared to DI-water. The second contribution is the design of a highly sensitive microwave sensor based on double concentric circular split ring resonator (DCCSRR) on a 49 mm × 45 mm ROGERS 5880 TM substrate. This sensor can differentiate glucose concentrations from 0 to 400 mg/dL, exceeding the relevant range for diabetic individuals (50-300 mg/dL). The DCCSRR operates at 2.48 GHz and can detect minimal concentration variations of 25 mg/dL in low concentrations, representing a significant advancement in the field. Differently from most sensitive approaches available to date, this structure operates in a non-licensed band and in a fully passive form, offering flexibility for implementation and low cost. These characteristics position it as a state-of-the-art solution in microwave glucose sensors.

This letter presents the design, fabrication, and characterization of an ultra-wideband (UWB) microstrip patch antenna engineered for the early detection of breast tumors. The proposed design offers a nearly constant radiation pattern, high gain, and compact size through the utilization of an inhomogeneous artificial magnetic conductor (I-AMC) structure comprising four different unit cells. This design feature ensures uniform coverage and reception across breast tissue, critical for early-stage tumor detection. Operating in the 2.9 GHz to 7.0 GHz frequency band, the antenna integrates a back-plane reflector that helps increasing the gain by 3 dB while enhancing bandwidth at low frequencies, thereby improving directivity and front-to-back ratio. The proposed antenna achieves a peak gain of ∼8.1 dBi with the I-AMC. Furthermore, our antenna presents a radiation efficiency of over 86% and exhibits a nearly constant radiation pattern across 93% of its operating bandwidth. These characteristics highlight the antenna suitability for applications such as diagnosis of breast carcinoma and microwave imaging.

In this work, we combine microwave dielectric spectroscopy and machine learning techniques to assess the authenticity of extra virgin olive oil (EVOO). We investigate four common adulterants of EVOO, namely soybean oil, corn oil, sunflower oil, and canola oil. We use a low-cost spiral shaped microwave resonator-based sensor operating at 546.8 MHz to detect changes in the complex permittivity of oil samples. A vector network analyzer (VNA) is used to extract complex scattering parameters S11 and S21 that serves as inputs for two different feedforward artificial neural network classifiers. The first model, using only the real and imaginary parts of S21, achieves an overall accuracy of 91.4% in predicting the applied adulterant in test samples. In contrast, the second model, incorporating the real and imaginary parts of both S11 and S21, attains a 99.2% accuracy for test samples. Additionally, we investigate the relationship between the measured |S21| (in dB) and the adulteration level, expressed as the percentile value of the volume of adulterant per volume of the sample (mL/mL). For each adulterant, a calibration equation is developed using partial least squares regression (PLSR) to predict adulteration levels up to 50%. The maximum root mean square error (RMSE) is 2.1% for canola oil adulteration prediction. PLSR yields RMSE values of 0.9% for soybean oil, 1.1% for corn oil, and 1.0% for sunflower oil adulteration. This methodology offers both qualitative and quantitative analyses of EVOO, capable of identifying adulterations as low as 5% with a simple, portable, and practical system.

A fully passive terahertz (THz) pulse amplification device is proposed based on leveraging the temporal Talbot effect (TTE) on a highly dispersive silicon-based metamaterial Bragg fiber. To maximize the TTE passive gain, we introduce and explore three different strategies, denoted as coherent pulse addition (CPA), forward Talbot illuminator (FTAI), and backward Talbot illuminator (BTAI). The BTAI strategy allows additional degrees of freedom for controlling the output pulse shape. Moreover, by using a continuous phase profile, we overcome the hurdle of implementing discrete phase gratings in limited time response phase modulators. We explore different pulse shapes and chirped pulses with CPA, and different gain factors with both BTAI and FTAI. Numerical simulation results show a 5.8 dB gain for a 9.8 cm long fiber with the CPA method, a 9.9 dB gain with FTAI (1.37 cm long), and a 8.8 dB gain with BTAI (1.25 cm long). These results indicate the potential of the approaches presented here, which can be used as a springboard for further developments toward high gain passive amplification THz devices.