Slot-Loaded Microstrip Patch Sensor Antenna for High-Sensitivity Permittivity Characterization

Abstract

A slot-loaded microstrip patch sensor antenna is proposed to enhance sensitivity in measuring the permittivity of planar materials. A thin rectangular slot was etched along the radiating edge of a rectangular patch antenna fed by a microstrip transmission line. Two resonant frequencies were created at a lower frequency compared to the single resonant frequency of a conventional ordinary patch antenna. The sensitivity of the proposed slot-loaded patch antenna was measured by the shift in the resonant frequency of the input reflection coefficient when the planar dielectric superstrate was placed above the patch, and was compared with that of a conventional patch antenna without the slot. The two antennas were designed and fabricated on a 0.76 mm-thick RF-35 substrate for the first resonant frequency to resonate at 2.5 GHz under unloaded conditions. Five different standard dielectric samples with dielectric constants ranging from 2.17 to 10.2 were tested for sensitivity comparison. The experiment results showed that the measured sensitivity of the proposed patch antenna were 3.54 to 4.53 times higher, compared to a conventional patch antenna, for the five samples.

CSRR-Based Microwave Sensor for Dielectric Materials Characterization Applied to Soil Water Content Determination

“…The performance of the sensor proposed in this work was validated by measuring the dielectric constant of three materials commonly used in literature-which are FR-4, Roger RO4003C, and glass-confirming the effectiveness of the proposed model. The proposed sensor is compared with another sensor presented in the literature [21] and the comparison results are in good agreement.…”

“…The sensitivity evaluation of the proposed sensor ( Figure 2b) was performed for each MUT by analyzing the variation observed in resonant frequency (∆fr), the percentage change in resonance frequency (PRFS), the enhancement of the percentage change in resonance frequency (PRFSE), sensitivity (S), and sensitivity enhancement (SE). Then, the results obtained were compared with those of another work carried out using a dual-band antenna sensor to characterize the relative permittivity of solid materials [21], according to Equations (5)- (9). Figure 3a,b show, respectively, that the resonance frequencies f r 1 and f r 2 of the proposed sensor have their values decreased as the relative permittivity value of the container-confined MUT sample is increased, as the total capacitance of the patch element also increases.…”

“…where f ru is the resonant frequency of the proposed antenna (or of the reference antenna shown in [21]) without MUT samples and f rl is the resonant frequency of the proposed antenna (or of the reference antenna) with MUT samples, ε ru is the relative permittivity of the medium when the antennas are without MUT samples, and ε rl is the relative permittivity of the medium when the antennas are without MUT samples. The parameter values shown in Figure 3a,b are summarized in Table 2 along with results presented in [21]. Then, the simulated f r results shown in Table 2 were used in Equations (4)-(8) to determine the proposed sensor sensitivity parameters dependencies on the relative permittivity, as shown in Figure 4.…”

“…Then, the simulated f r results shown in Table 2 were used in Equations (4)-(8) to determine the proposed sensor sensitivity parameters dependencies on the relative permittivity, as shown in Figure 4. In addition, the results of the dual-band sensor presented in [21] were included for comparison purpose. The shift in resonant frequency (∆f r ) at f r 1 and f r 2 are presented in Figure 4a-c exhibit, respectively, the PRFS and PRFSE results at the sensor's two resonance bands.…”

“…Results of the sensors sensitivity (S) and sensitivity enhancement (SE) are shown in Figure 4d,e. In this case, only the sensitivity results at resonant frequency f r2 are presented because the f r1 value of the proposed sensor is different from that of the sensor developed in [21], not allowing a direct comparison.…”