José Luis Olvera-Cervantes

Complex permittivity measurements using cavity perturbation technique with substrate integrated waveguide cavities

Cavity perturbation technique is widely used in the measurements of complex dielectric permittivity of materials due to its accuracy and ease of configuration. This paper presents the theoretical formulas for the evaluation of complex permittivity of materials using cavity perturbation technique with substrate integrated cavity resonators. With the proposed formulas, the use of various planar cavities is possible by taking into account the dielectric characteristics of the substrate in which the cavity is implemented. Simulations and measurements are performed on various dielectric samples to validate the proposed theory. The maximum deviation in the measured dielectric permittivity values is below 6% compared to the literature values. The implemented substrate integrated cavity is then analyzed in terms of sensitivity, showing a good performance.

Permittivity Measurements at Microwave Frequencies Using Epsilon-Near-Zero (ENZ) Tunnel Structure

A planar epsilon-near-zero (ENZ) tunnel structure implemented on substrate integrated waveguide (SIW) technology is used to evaluate the complex dielectric permittivity of various materials. Design, optimization, and fabrication of the ENZ tunnel structure are explained. Simulations and measurements on various dielectric samples using the cavity perturbation technique of the proposed structure are presented. Measured values of the permittivity are in good agreement with standard values. Sensitivity analyses are performed on the ENZ structure and the conventional SIW cavity techniques. The proposed structure has very high sensitivity, which yields more accurate results when compared to other techniques, such as perturbation of conventional cavities.

Dielectric Properties of Beans at Different Temperatures and Moisture Content in the Microwave Range

Dielectric properties of common Mexican beans (Phaseolus vulgaris L.) were determined and analyzed at microwave frequencies (800–2500 MHz). The free-space transmission technique was employed for the measurements of three varieties (“Flor de mayo,” “Bayo,” and “Negro”) with different moisture content (8.8–12.3%, w.b.) at 20, 30, 40, 50, and 60°C. The dielectric constant and loss factor of beans decreased with increasing frequency for a fixed temperature, and increased with increasing temperature at a fixed frequency. The dielectric constant increased with increasing moisture content, while the loss factor remained nearly constant. With these results, disinfestation or quality control measurements can be proposed for beans using microwaves.

Wireless Sensing of Complex Dielectric Permittivity of Liquids Based on the RFID

A wireless sensing system for the evaluation of the complex dielectric permittivity of solvent liquids is presented. Two sensing tags are proposed for testing of the samples. The first tag is based on a cavity resonator and the second makes use of the epsilon-near-zero effect. Both circuits are designed over the planar substrate-integrated-waveguide (SIW) technology, and operate at 4 GHz. A quartz capillary tube is used for the liquid measurements where only a small amount of sample volume is required. With the addition of planar antennas at the input and output of the sensors, the complete system is implemented for wireless sensing of the materials following the RF identification scheme. The cavity perturbation technique for SIW structures is applied for the dielectric liquid characterization. The proposed sensing tags and system have high potentials for low-cost wireless measurements and real-time monitoring applications.

Dual-Band Multi-Pole Directional Filter for Microwave Multiplexing Applications

A novel microstrip directional filter for multiplexing applications is presented. This device uses composite right-left-handed transmission lines and resonators to achieve dual-band frequency response. In addition, by cascading two or more stages using dual frequency immitance inverters, multi-pole configurations can be obtained. Simulation and experimental results are presented with good agreement.

Dielectric properties of guava, mamey sapote, prickly pears, and Nopal in the microwave range

ABSTRACT Dielectric properties (DPs) of selected fruits: guava (Psidium guajava), mamey sapote (Pouteria sapota), red prickly pear (fruit from Opuntia streptacantha), and white prickly pear (fruit from Opuntia ficus-indica), as well as nopal (young cactus pads or cladodes from Opuntia ficus-indica) were studied. DPs were determined using the open-ended coaxial probe method at microwave frequencies (500 MHz–2 GHz) and temperatures of 20, 40, and 60ºC. At 20ºC and 915 MHz for unripe fruits, dielectric constant values ranged from 65.7 to 70.9, while the loss factor had values between 8.4 and 20.7. Both dielectric constant and dielectric loss factor were affected by temperature and frequency (p < 0.05). For example, loss factor for red prickly pear at 2450 MHz decreased from 13.88 at 20ºC to 12.8 at 40ºC and 11.7 at 60ºC. DPs of fruits were also affected by their ripening (quantified through the maturity index). In addition, penetration depth decreased with increasing frequency, ranging from 1.98 to 4.80 cm at 915 MHz and from 0.25 to 0.41 cm at 5800 MHz. Results are valuable to develop further applications with microwave technology for these foods, such as microwave-assisted disinfestation treatments or microwave drying.

Dielectric properties of tequila in the microwave frequency range (0.5–20 GHz) using coaxial probe

ABSTRACT In this work, an open-ended coaxial probe was used to characterize the dielectric properties of different tequilas and agave-distilled spirits in the range from 500 MHz to 20 GHz. The alcohol content of these beverages was clearly identified at these frequencies. From a Cole–Cole plot, the relaxation time (τ) was extracted and it was observed that there was a linear correlation between alcohol content and τ, where lower τ corresponds to lower ethanol content. In addition, dielectric differences were also found between silver, aged, and extra-aged tequilas. As aging increased, the real and imaginary parts of the permittivity increased (p < 0.05). These findings offered a new method for detecting alcohol content in tequila as well as for identifying tequila aging.

Planar sensors for RFID wireless complex-dielectric-permittivity sensing of liquids

Two planar sensors for wireless RFID dielectric permittivity sensing of liquids are presented. The first sensor consists of a Substrate-Integrated-Waveguide (SIW) resonant cavity while the second one is composed by an SIW Epsilon-Near-Zero (ENZ) tunnel sensor. Both structures produce a notch resonance response at 4 GHz which is used for the characterization of the liquids using the Cavity-Perturbation-Technique. The proposed sensors present good sensitivity using a small amount of sample volume.

Novel microstrip diplexer for ultra-wide-band (UWB) and wireless LAN (WLAN) bands

A new microstrip diplexer for ultra-wide-band (UWB) and wireless LAN (WLAN) bands is presented in this paper. The proposed structure integrates a multipole directional filter operating at WLAN band coupled to a UWB filter. The prototype is capable of processing the whole UWB region (from 3.1 to 10.6 GHz) with the WLAN band notch in one channel, and the passband WLAN band in other channel with a good selectivity due to the presence of transmission zeros at both sides of the WLAN band. The proposed diplexer is simple to fabricate, as it is designed using planar microstrip technology, and presents compact dimensions, making use of a low number of elements. Moreover, it presents the capacity of processing a narrow band (WLAN with 8% bandwidth) with a wide band (UWB). Simulated and measured results are presented with good agreement and the diplexer presents a good performance up to 15 GHz.

Dielectric Properties of Beans at Ultra- Wide Band Frequencies

Abstract Dielectric properties of three varieties of common beans (Phaseolus vulgaris L.) were determined at Ultra-Wideband (UWB) frequencies (3–10.6 GHz) using a free space transmission method. Beans were conditioned to get different moisture contents; the bulk density of beans (ρ) increased at higher moisture contents. Permittivity and conductivity of beans also increased with moisture content. The dielectric constant (ε’) remained practically constant in the studied frequency range, while loss factor (ε’) decreased in frequency. The ε’/ρ vs ε’/ρ complex-plane plot (Argand diagram) was built and a linear trend was observed, with positive slope. However, this slope value decreased at higher frequencies.