Produção Nacional
Revisado por pares
Planar sensor for powder grain characterisation
2018; Institution of Engineering and Technology; Volume: 12; Issue: 10 Linguagem: Inglês
10.1049/iet-map.2018.0138
ISSN1751-8733
AutoresM. S. Coutinho, Crislane Priscila N. Silva, M. R. T. de Oliveira, H. V. H. Silva Filho, Gabriel G. Machado, M. T. de Melo,
Tópico(s)Granular flow and fluidized beds
ResumoIET Microwaves, Antennas & PropagationVolume 12, Issue 10 p. 1666-1670 Research ArticleFree Access Planar sensor for powder grain characterisation Marcelo S. Coutinho, Corresponding Author msacou@gmail.com Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this authorCrislane Priscila N. Silva, Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this authorManuelle R. T. Oliveira, Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this authorHawson V. H. Silva Filho, Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this authorGabriel G. Machado, Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this authorMarcos T. de Melo, Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this author Marcelo S. Coutinho, Corresponding Author msacou@gmail.com Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this authorCrislane Priscila N. Silva, Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this authorManuelle R. T. Oliveira, Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this authorHawson V. H. Silva Filho, Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this authorGabriel G. Machado, Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this authorMarcos T. de Melo, Electronics and Systems Department, Federal University of Pernambuco, Recife, BrazilSearch for more papers by this author First published: 03 May 2018 https://doi.org/10.1049/iet-map.2018.0138Citations: 2AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat Abstract This study presents a microwave planar sensor for characterisation of powdered foods. The sensor is based on four coupled resonators designed to have four poles in the frequency range of 1.0–3 GHz. The pole with more sensitivity is used to measure the samples. The frequency characteristics of the sensor are obtained measuring several well-known samples. It is used to estimate the permittivity of six types of grains. The grains are two types of oatmeal, three types of corn and wheat flour. The experimental results have shown a sensitivity of 36 MHz/Fm−1. The estimated permittivity of materials can be used as the preliminary data for further investigation. 1 Introduction Microwave sensors for dielectric material characterisations have been widely used for different types of applications [[1]], such as biological liquid and chemical tests [[2], [3]], industrial materials [[4]–[6]], food and agricultural products [[7]–[12]] and medical applications [[13]]. The microstrip sensor projects emerged in the 1970s resulting in the first commercial sensor for fish meat processing [[14]]. Later, the same technique was used to measure the ripeness of the oil palm fruit [[7]] and the moisture content in green tea leaf. Microstrip structures are composed of a conductive strip, a dielectric and a ground plane. Sensors with this type of structure use transmission and reflection techniques for materials characterisation. In this paper, a microstrip resonator with rectangular open-loop rings is used as a microwave sensor [[15]–[19]]. The sensor was designed in order to obtain a high sensitivity in the 1–3 GHz frequency range and a suitable size to deposit a homogeneous sample. The sensor was developed for characterisation of powder grains, such as wheat flour, two types of oatmeal, corn meal, corn flour and corn bran. Samples of corn powder are important because there is a large agricultural production and consumption in the northeast of Brazil. 2 Theoretical background A microstrip resonator is a structure that contains at least one oscillating electromagnetic field. In general, resonators for filter design may be classified as lumped-element [[20]], quasi-lumped-element resonators, distributed line, patch resonators [[21]–[23]] and numerous forms of microstrip resonators. Coupled resonant circuits have great importance in the development of RF and microwave filters, mainly in narrowband filters, which are present in most applications. The techniques described in Chapter 8 of [[24]] are based on the coupling coefficients between resonators and the external quality factors. These techniques can be applied in micro-mechanical filter designs [[25]], superconducting filters [[26]], microstrip filters [[21], [27], [28]], interdigital ceramic filters [[29]], waveguide filters [[30]–[33]] and dielectrics filters [[31]]. 2.1 Coupled resonators design In order to facilitate the handling of samples and at the same time to have a device with satisfactory quality factor, the designed microstrip sensor is an open-loop resonator, composed of a set of four coupled rectangular rings as shown in Fig. 1. The design is based on coupled resonators with a single pair of transmission zeros described in [[24]] with minor modifications. Fig. 1Open in figure viewerPowerPoint Design of the four coupled resonators The used substrate was Rogers® 3010 (h = 1.27 mm, ɛr = 10.2, tan δ = 0.0023). The resonator was designed to have a central frequency at 2.12 GHz, whose wavelength λ is 54 mm. As can be seen in [[24]], the use of a λ/2 loop resonator is more convenient for the design because it is more flexible in projecting planar cross-coupling resonators. Such as devices that are made from square open-loop resonators [[17]]. The complete structure and the rectangular ring are shown in Fig. 1. Table 1 shows the dimensions of the sensor. The chosen length of 50 Ω feeding line is λ/2 with width w of 1.2 mm. The sum of the larger and the smaller sides of the loop resonator should be close to λ/2, so a variable a is defined as the larger side and b as the smaller side. The calculated gap is 0.3 mm. In addition, the length l of the lines connecting the rectangular rings is 27 mm. Table 1. Sensor dimensions Parameter Dimensions, mm l 27 a 16 b 11 g 0.3 w 1.2 2.2 Method to obtain the materials permittivity In this section, two methods that were used to estimate the permittivity of the grain samples are presented. Method 1 uses the full wave electromagnetic simulator CST Microwave Studio and Method 2 uses the measured data from the samples with known permittivity. Method 1 consists of measuring samples using a vector network analyser (VNA), in order to obtain the value of S21 or S11 with the corresponding resonant frequency f0. The results from the VNA can be used as a goal for the optimisation by CST Microwave Studio. The permittivity's sample is used as a parameter for the optimisation, and when the simulation result matches with the measured curve inserted on CST, the ɛr for the sample can be defined. Fig. 2 shows a flowchart of the procedure. Fig. 2Open in figure viewerPowerPoint Flowchart of a simulation proceeding to obtain the material permittivity In Method 2, substrates with well-known permittivity of materials are measured using the proposed sensor to validate it. The resonant frequency of the samples changes with the permittivity, thus it is possible to make a linear fit in the curve of the permittivity versus resonant frequency and predicate the permittivity. Table 2 shows the samples used with their respective characteristics. Table 2. Samples measured with the sensor Sample Height (h), mm ɛr Rogers® 6002 1.524 2.94 FR-4 1.6 4.5 RT/duroid® 5880 1.27 2.2 AD1000™ 3 10.2 3 Experimental demonstration 3.1 Experimental and simulated results for S11 A sensor with two pairs of poles was designed, consisting of four rectangular coupled open loops. The designed sensor is illustrated in Fig. 3a. The four poles of the simulated sensor are f1 = 1.10 GHz, f2 = 1.24 GHz, f3 = 2.13 GHz and f4 = 2.51 GHz as shown in Fig. 3b. For the four poles of the manufactured sensor are f1 = 1.04 GHz, f2 = 1.20 GHz, f3 = 2.14 GHz and f4 = 2.49 GHz and the comparison between the experimental and simulated results is shown in Fig. 3c. The shifts on the poles of the frequency response may be due to the fabrication tolerance. Fig. 3Open in figure viewerPowerPoint Sensor (a) Four coupled resonators design, (b) Frequency response for S11, (c) Comparison between simulated and experimental results The third pole is used to characterise the samples due to the higher sensitivity compared to the other poles. A single resonator is shown in Fig. 4a. The comparison between the sensibility of the single resonator and the four coupled resonators is shown in Fig. 4b. The sensitivity of a single resonator is 47.9 MHz/Fm−1, while the sensitivity of the third pole of the four coupled resonators is 48.8 MHz/Fm−1. The sensitivity is comparable, but the coupled resonators are more applicable in this case, because it contains a wider sensitive area of 32.3 mm × 22.3 mm compared to a single resonator of 9.2 mm × 6.3 mm. A wider sensitive area is suitable for measuring more homogeneously quantity of sample and the system becomes more robust for agricultural application. Fig. 4Open in figure viewerPowerPoint Sensitivity level (a) Single resonator, (b) Comparison between sensitivity level for a single resonator and the four coupled resonators 3.2 Experimental measurements The sensor was manufactured using an Everprecision EP2006H prototyping machine. Dimensions of the complete device are as small as 30 mm × 60 mm. Experimental results were obtained using an Agilent E5071B VNA. Fig. 5 shows the manufactured prototype. Fig. 5Open in figure viewerPowerPoint Sensor prototype Fig. 6 shows the measurement setup. Two blocks of acrylic and expanded polystyrene hold the sample under the test. Fig. 6Open in figure viewerPowerPoint Experimental configuration (a) Sensor connected to a VNA, (b) Sensor with sample Samples of wheat flour, oatmeal, corn meal, corn flour and corn bran are analysed. There are two types of oatmeal, one is less processed, with more whole grains, denominated as Oatmeal 1. The other oatmeal, named Oatmeal 2, has bigger grain size, compared to the Oatmeal 1. All samples were minimally processed, that is, free of industrial process and artificial preservatives which can change the chemistry of the grain structure. The objective is to make a real-time analysis in grains during harvesting. The minimum height of the sample which makes a stable result is 1.2 mm. Thus, the device sensitivity does not change above this height. The experiments were carried out at a temperature of 26°C and the relative humidity of 48%. Fig. 7 shows the measurement of the S11 of the samples. Fig. 8 shows the measured S21. In order to determine the sensitivity level of the device, the S11 parameter was used. The analysis frequency range is between 1.6 and 2.3 GHz, which is the third pole of S11 parameter. Fig. 7Open in figure viewerPowerPoint Reflection coefficient of the sensor with various types of grain (a) Group 1, (b) Group 2 Fig. 8Open in figure viewerPowerPoint Transmission coefficient of the sensor with various types of grain (a) Group 1, (b) Group 2 The following measurement results were divided into two groups to facilitate the analyses. Oatmeal 1, Oatmeal 2 and corn bran are in group 1 and wheat flour, corn meal and corn starch are in group 2. As shown in Figs. 7 and 8, the samples deposited on the sensor have different magnitudes of the reflection coefficient, |Γ|, and transmission coefficient, |T|. Comparing with the sensor without samples, the results in group 1 presented resonant frequency shifts of 50, 90 and 110 MHz for the Oatmeal 1, Oatmeal 2 and corn bran, respectively. For the group 2, wheat flour, corn meal and corn starch presented all the same shift of 110 MHz. As mentioned in Method 2, well-known samples were used to obtain the relation between the resonant frequency of the sensor and the permittivity of the deposited samples. This result is shown in Fig. 9. The experimental sensibility is 36 MHz/Fm−1. Fig. 9Open in figure viewerPowerPoint Sensitivity level for the device with the well-known samples With the resonance frequency of the sensor/sample, it is possible to obtain the permittivity checking out the expression of Fig. 9. Table 3 shows the estimated permittivity obtained using Methods 1 and 2. Method 1 uses predominantly simulations, in consequence, it ignores the influence of the fabrication tolerances in the frequency response. This may explain the difference in the results of the two methods. Table 3. Resonant frequency and permittivity of samples Material f, GHz ɛr (Method 2) ɛr (Method 1) corn bran 2.03 3.68 3.01 corn meal 2.03 3.62 2.97 corn flour 2.03 3.62 2.97 wheat flour 2.03 3.62 2.97 oatmeal 2 2.05 3.12 2.60 oatmeal 1 2.09 2.02 1.78 4 Conclusion The paper presented the design of a sensor as part of an initial process for characterisation of grains. The motivation is to bring agility and precision in grain measurement for the agricultural sector. Through the sensitivity curve of the sensor, it is possible to obtain the permittivity of other samples, without the aid of new software simulations. A sensor with four poles consisting of four rectangular coupled open loops was designed. The third pole was used to characterise the samples due to the higher sensitivity compared to the other poles. The shifts on the poles of the simulated and experimental frequency response may be due to the fabrication tolerance. 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