- Email: [email protected]
Metamaterial inspired miniaturized SIW resonator for sensor applications
Accepted Manuscript Title: Metamaterial Inspired Miniaturized SIW Resonator for Sensor Applications Authors: Sen Yan, Juncheng Bao, Ilja Ocket, Bart Nauwelaers, Guy. A.E. Vandenbosch PII: DOI: Reference:
S0924-4247(18)30927-0 https://doi.org/10.1016/j.sna.2018.10.013 SNA 11059
To appear in:
Sensors and Actuators A
Received date: Revised date: Accepted date:
31-5-2018 9-9-2018 8-10-2018
Please cite this article as: Yan S, Bao J, Ocket I, Nauwelaers B, Vandenbosch GAE, Metamaterial Inspired Miniaturized SIW Resonator for Sensor Applications, Sensors and amp; Actuators: A. Physical (2018), https://doi.org/10.1016/j.sna.2018.10.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Metamaterial Inspired Miniaturized SIW Resonator for Sensor Applications Sen Yan,1,2,a),b) Juncheng Bao,2),b) Ilja Ocket,2,3) Bart Nauwelaers2), and Guy. A. E. Vandenbosch2)
School of Electronics and Information Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi, 710049, China
2
Deptartment of Electrical Engineering, KU Leuven, Kasteelpark Arenberg 10, Box 2444, 3001 Leuven, Belgium
3
Interuniversity Microelectronics Center (IMEC), Kapeldreef 75, 3001 Leuven, Belgium
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a) b)
Corresponding author: Sen Yan, Email: [email protected]. S. Yan and J. Bao contributed equally to this work.
Highlights
A miniaturized cavity with high quality factor is obtained.
A negative mode of a substrate integrated waveguide (SIW) resonator is obtained by loading metamaterials. The field distributions in the cavity are analyzed to study the operating mechanism.
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A planar substrate integrated waveguide (SIW) resonator is proposed in this letter. By loading a metamaterial inspired structure in a short section of an SIW, a miniaturized cavity (0.263×0.184×0.0063 λ03 at 2.39 GHz) with high quality factor (272.5) is obtained. The resonant modes of the cavity and their corresponding field distributions are analyzed. A resonator prototype has been fabricated and tested. The measured results agree well with the simulated ones. This cavity resonator has huge potential
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in sensor applications. A binary solvent water alcohol mixture is used to verify the sensor concept.
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1. Introduction
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Cavity resonators have huge application potential in the microwave and millimeter wave frequency range, e.g. for filters, oscillators, antennas, sensors, etc. To reduce the size of traditional metallic waveguide cavities and simplify the integration
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with other planar microwave circuits, recently substrate integrated waveguides (SIW) have been widely studied. These waveguides can be fabricated with standard printed circuit board (PCB) technology [1], [2], which will significantly reduce
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fabrication cost compared to the traditional metallic waveguides. Due to the relatively low radiation loss and high quality factor
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(Q factor) compared to other planar resonators, SIW cavities are prime candidates to be used in sensor applications [3]-[9]. Similar as for the traditional metallic waveguide cavity, the basic mode of a SIW cavity is also TE101. Its resonant frequency
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is determined by the permittivity of the loaded material (substrate) and the dimensions of the cavity. To reduce the size of SIW
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cavities, the epsilon-near-zero (ENZ) tunneling phenomenon [6], [7] can be used. The resonant frequency of ENZ tunneling is just as the cutoff frequency of the TE10 mode of the waveguide, which means that the related operating frequency is independent of the length of the waveguide. Thus, the resonance can be expressed as a TE 100 mode. However, this mode cannot be used to
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further reduce the width of the SIW cavity. Recently, the study of metamaterials has revealed that a waveguide can operate at negative modes if the loaded metamaterial simultaneously has a negative permittivity and negative permeability [10]-[12]. These negative modes can operate much lower than the cutoff frequency of the dominant (TE 10) mode. The negative permittivity can be automatically obtained by operating the waveguide below the cutoff frequency of the dominant TE mode. The negative permeability can be realized by inserting certain slots on the surface of the waveguide [10].
In this letter, a miniaturized SIW resonator is proposed. By loading two interdigital capacitors (meander slots) on the bottom layer of the SIW, a negative mode TE10(-1) mode is obtained. It shows a much lower resonant frequency than the normal positive modes. The field distributions in the cavity are analyzed to study the operating mechanism. A prototype is fabricated and measured. The results show that this resonator can be used as a sensor to measure the permittivity of a liquid.
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2. Topology The proposed SIW cavity is fabricated using the substrate Rogers RT5880 with thickness 0.787 mm. The dielectric constant and loss tangent are 2.2 and 0.0009, respectively. The diameter of the vias is 1.2 mm and the distance between the centers of neighboring vias is 2.5 mm, which guarantees that the leaky wave from the short slots can be neglected. [1]
The topology of the resonator is shown in Fig. 1. A section of SIW consists of two units, and each unit is loaded by an interdigital capacitor (meander slot) on the surface of the SIW. A cavity with size 33 × 23 mm2 is obtained by shorting the SIW
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at the two boundaries (left and right). This cavity is fed by two microstrip lines with characteristic impedance 50 Ω. The liquid
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sample is located in a center hole through the cavity. The bottom of the hole is sealed with silica gel. The top of the hole is
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open in order to be able to inject fluid. The detailed dimensions are labeled in Fig. 1 (a) and (b). The frequency domain solver
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in the commercial full-wave simulation software CST microwave Studio, which is based on the finite element method, is used in this letter [13].
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3. Operating Mechanism
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Firstly, a unit of SIW is calculated with and without the slot loading, respectively. The dispersion curve of this SIW is then retrieved from the S-parameters, see Fig. 2 (a). When there is no slot loaded on the SIW, the cutoff frequency of the dominant
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mode (TE10) is 5.05 GHz. For the proposed structure with slot, the SIW shows a left-handed transmission characteristic (phase advanced section) below the frequency 2.98 GHz, and a right-handed transmission characteristic (phase delayed section) above
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the frequency 3.75 GHz [10]. A stop band is observed between these two frequencies.
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Next, the cavity is Fig. 1 is analyzed. The resonant frequency of the cavity is determined by the length of the SIW, m p n
(1)
where βp is the phase delay of one unit cell, m is the number of unit cells (2 in our structure), n is the mode number (the number of standing wave periods inside the SIW), which means that n is an integer (0, ±1, ±2, …, ±(m-1)). Fig. 2 (b) shows the simulated S parameters of the cavity. When the cavity is without loading slots, its first resonance (TE101) is located at 6.544 GHz, which agrees well with the dispersion curve in Fig. 2 (a). The slight frequency shift is caused
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by the feeding line, which may perturb the original field distribution in the cavity. The loading of the slots may decrease the resonant frequency of the TE101 mode to 4.831 GHz, and more importantly, two additional lower modes are obtained. One is the negative mode TE10(-1) located at 2.39 GHz, and the other is the zero-order resonance (ZOR) mode at 3.072 GHz. The field distributions of these two modes are shown in Fig. 3. The mode TE 10(-1) has one standing wave in the SIW (see Fig. 3 (a) and (b)), similarly to the field distribution of mode TE101, while the magnetic field of the ZOR mode is almost constant in the cavity
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(see Fig. 3 (d)).
FIG. 1. Topology of the proposed SIW resonator. (a) top layer, (b) bottom layer, (c) photo of the fabricated prototype. The widths of the fingers and gaps are 0.6 mm and 0.4 mm, respectively.
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(a)
(b)
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FIG. 2. (a) Dispersion curve of the SIWs with and without slot loading, (b) S parameters of the cavity with and without slot loading. The analysis of the topology with slot is based on a single cell.
FIG. 3. Field distributions in the proposed resonator. The cavity is fed from the left port and the coordinate system is defined in Fig. 1.
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FIG. 5. Measured S parameters with liquid.
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FIG. 4. Simulated and measured S parameters without liquid.
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In this design, the TE10(-1) is chosen as the operating mode, not only because it operates at a lower resonant frequency than the ZOR mode, but more importantly, also because the electric field distribution is more concentrated around the center of the
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cavity. The relatively high field intensity results in the high sensitivity necessary in sensor applications. It should be noted that although the electric field is more concentrated in the meandering slot than at the center of the cavity, the latter location is
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chosen in our proposed design since it is easy to integrate with a vertical liquid tube. When a liquid sample is located in the center hole of the cavity, it will couple with the electric field, and thus perturb the
resonant frequencies. As for the normal TM101 mode in the waveguide cavity, the frequency shift of the TE10(-1) mode is also approximately proportional to the dielectric constant of the sample, since the perturbed electric field will be stronger when the dielectric constant of the sample is higher.
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4. Measurement and Results A prototype of the cavity resonator was fabricated, as shown in Fig. 1 (c). The measured S parameters agree quite well with the simulated ones, see Fig. 4. A sharp resonance is observed at ca. 2.39 GHz, with a Q factor of 272.5. The Q factor is calculated from the input impedance of the left port when the right port of the cavity is shorted [14].
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Next, a water alcohol mixture was tested with this resonator. Fig. 5 shows the measured S-parameters. Both the frequency shift of the resonance and the magnitude of the transmission (S12) show a good monotonicity with a growing alcohol concentration. A further analysis on parameter retrieval reveals that the figure-of merit (FOM) is ca.
FOM
f r '
0 .3 4 M H z
(2)
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where ∆f and ∆εr’ are the frequency shift and the permittivity shift corresponding with the water alcohol mixed sample [15],
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respectively. Other parameter retrieval methods for microfluidic sensors can be found in [16] and [17]. It should be mentioned that the Q factor decreases with increasing the alcohol concentration. The reason is that the high permittivity of the water
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prevents the electric field from the inner part of the sample and thus reduces the losses. Actually, when the sample is pure
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water, the electric field can only penetrate into a little thickness of the sample.
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The experiment was repeated 5 times for deionized water, and we found that the results are stable. The maximum shift of the resonant frequency was less than 1 MHz. It should be mentioned that the major limitation on the accuracy is the knowledge
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of the exact volume of the liquid. In this preliminary test, the volume of the liquid was controlled by using a pipette. This can
5. Conclusion
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be improved by using other methods, e.g., digital pumps.
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A compact SIW cavity resonator was proposed in this letter. By loading a metamaterial inspired structure in the cavity, the resonator can operate at its negative mode, which has a much lower resonant frequency than the traditional dominant mode.
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Field distributions were analyzed to study the operating mechanism of the cavity. A prototype was fabricated and measured, yielding a good agreement with simulated results. An initial test has shown that the cavity can be used as a permittivity sensor to characterize samples of liquid.
Acknowledgments: This work was partly supported by the Research Foundation-Flanders (FWO) Postdoctoral Fellowship (No. 12O1217N).
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REFERENCES [1] M. Bozzi, A. Georgiadis and K. Wu, "Review of substrate-integrated waveguide circuits and antennas," IET Microwaves, Antennas & Propagation, vol. 5, no. 8, pp. 909-920, June 6 2011. [2] K. Wu, Y. J. Cheng, T. Djerafi and W. Hong, "Substrate-Integrated Millimeter-Wave and Terahertz Antenna Technology,"
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Proceedings of the IEEE, vol. 100, no. 7, pp. 2219-2232, July 2012. [3] J. D. Barrera, and G. H. Huff, “Analysis of a variable SIW resonator enabled by dielectric material perturbations and applications,” IEEE Trans. Microw. Theory Techn., vol. 61, no. 1, pp.225-233, Jan. 2013.
[4] H. El Matbouly, N. Boubekeur and F. Domingue, "Passive Microwave Substrate Integrated Cavity Resonator for Humidity Sensing," IEEE Trans. Microw. Theory Techn., vol. 63, no. 12, pp. 4150-4156, Dec. 2015.
[5] C. Liu, and F. Tong, “An SIW Resonator Sensor for Liquid Permittivity Measurements at C Band,” IEEE Microw. Wireless
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Compon. Lett., vol. 25, no. 11, pp. 751-753, Nov. 2015.
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[6] H. Lobato-Morales, A. Corona-Chávez, J. L. Olvera-Cervantes, R. A. Chávez-Pérez, and J. L. Medina-Monroy, “Wireless
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Sensing of Complex Dielectric Permittivity of Liquids Based on the RFID,” IEEE Trans. Microw. Theory Techn., vol. 62,
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no. 9, pp. 2160-2167, Sep. 2014.
[7] A. K. Jha, and M. J. Akhtar, “Design of Multilayered Epsilon-Near-Zero Microwave Planar Sensor for Testing of Dispersive
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Materials,” IEEE Trans. Microw. Theory Techn., vol. 63, no. 8, pp. 2418-2426, Aug. 2015.
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[8] I.-J. Hyeon, W.-Y. Park, S. Lim , C.-W. Baek, “Ku-band bandpass filters using novel micromachined substrate integrated Waveguide structure with embedded silicon vias in benzocyclobutene dielectrics,” Sensors and Actuators A: Physical, vol.
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188, pp. 463-470, 2012.
[9] T. Yun, S. Lim, “High-Q and miniaturized complementary split ring resonator-loaded Substrate integrated waveguide
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microwave sensor for crack detection in metallic materials,” Sensors and Actuators A: Physical, vol. 214, pp. 25-30, 2014. [10] Y. Dong, and T. Itoh, “Promising future of metamaterials,” IEEE Microw. Mag., vol. 13, no. 2, pp.39-56, Mar. 2012.
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[11] S. Yan, P. J. Soh, G. A. E. Vandenbosch, “Wearable dual-band composite right/ left-handed waveguide textile antenna for WLAN applications,” Electron. Lett., vol. 50, no. 6, pp. 424-426, Mar. 2014.
[12] Y. Dong and T. Itoh, "Miniaturized Substrate Integrated Waveguide Slot Antennas Based on Negative Order Resonance," IEEE Transactions on Antennas and Propagation, vol. 58, no. 12, pp. 3856-3864, Dec. 2010. [13] Computer
Simulation
Technology
(CST).
(2016).
https://www.cst.com/Products/CSTMWS
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Microwave
Studio.
[Online].
Available:
[14] T. Ohira, "What in the World Is Q? [Distinguished Microwave Lecture]," IEEE Microwave Magazine, vol. 17, no. 6, pp. 42-49, June 2016. [15] A. Megriche, A. Belhadj, A. Mgaidi, “Microwave dielectric properties of binary solvent water-alcohol, alcohol-alcohol mixtures at temperatures between -35°C and +35°C and dielectric relaxation studies,” Mediterranean Journal of Chemistry, vol. 1, no. 4, pp. 200-209, 2012.
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[16] A. Ebrahimi, W. Withayachumnankul, S. Al-Sarawi and D. Abbott, "High-Sensitivity Metamaterial-Inspired Sensor for Microfluidic Dielectric Characterization," IEEE Sensors Journal, vol. 14, no. 5, pp. 1345-1351, May 2014. doi: 10.1109/JSEN.2013.2295312
[17] W. Withayachumnankul, K. Jaruwongrungsee, A. Tuantranont, C. Fumeaux, and D. Abbott, “Metamaterial-based
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microfluidic sensor for dielectric characterization,” Sens. Actuators A, Phys., vol. 189, pp. 233–237, Jan. 2013.
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Sen YAN received the bachelor’s and master’s degrees in information and telecommunication engineering from Xi’an Jiaotong University (XJTU), Xi’an, China, in 2007 and 2010, respectively, and the Ph.D. degree in electrical engineering from Katholieke Universiteit Leuven (KU Leuven), Leuven, Belgium, in 2015. From 2015 to 2017, he was a post-doctoral researcher with KU Leuven. In 2016, he joined EPFL, Lausanne, Switzerland, and the University of Texas at Austin, Austin, TX, U.S., as a Visiting Researcher. He has been a full professor with XJTU since 2017. Dr Yan’s current research interests include metamaterials and metasurfaces, wearable devices and textile antennas, reconfigurable antennas, antenna diversity and nano-antennas. He has authored or co-authored 33 international journal papers and 30 conference contributions. He was successful in achieving the post-doctoral fellowship from KU Leuven and FWO in 2015 and 2016, respectively. In 2017, He obtained the “Young Talent Support Plan” from XJTU. He currently serves as an active reviewer of more than 20 journals, including IEEE Access, IEEE Trans. Antennas propag., IEEE Trans. Microw. Theory Techn., IEEE Trans. Biomed. Circuits Syst., and etc. Juncheng Bao received the M.Sc. degree in electrical engineering from Katholieke Universiteit (KU) Leuven, Leuven, Belgium, in 2013. He had an internship with imec, Leuven, in 2013. He is currently working toward the Ph.D. degree in electrical engineering at KU Leuven. His current research interests include microwave biomedical applications, novel microwave-microfluidic devices design and fabrication, and microwave and millimeter wave metrology.
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Ilja Ocket received the M.Sc. and Ph.D. degrees in electrical engineering from Katholieke Universiteit (KU) Leuven, Leuven, Belgium, in 1998 and 2009, respectively. He has been with imec, Leuven, and KU Leuven, since 1999. With imec, he is currently involved in millimeter-wave antenna modules and packaging for 79- and 140-GHz radar. With KU Leuven, he leads the group working in the area of microwave and millimeter-wave applications for biology and medicine and is involved in integrated couplers for (sub) millimeter plastic waveguides.
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Bart Nauwelaers received the Ph.D. degree in electrical engineering from the Katholieke Universiteit (KU) Leuven, Leuven, Belgium, in 1988 and the Master’s degree in design of telecommunication systems from Telecom ParisTech, Paris, France. Since 1981, he has been with the Department of Electrical Engineering, KU Leuven, where he has been involved in research on microwave antennas, passive components, interconnects, microwave integrated circuits and MMICs, linear and nonlinear device modeling, MEMS,andwireless communications. He is the former Chair of IEEE AP/MTT-Benelux and past Chair of URSI-Benelux.
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Guy A. E. Vandenbosch received the M.S. and Ph.D. degrees in electrical engineering from Katholieke Universiteit Leuven (KU Leuven), Leuven, Belgium, in 1985 and 1991, respectively. From 1991 to 1993, he was a Post-Doctoral Researcher with KU Leuven, where he has been a Lecturer since 1993 and a Full Professor since 2005. In 2014, he joined Tsinghua University, Beijing, China, as a Visiting Professor. He has taught or teaches courses on Electromagnetic Waves, Antennas, Electromagnetic Compatibility, Electrical Engineering, Electronics, and Electrical Energy, and Digital Steer-and Measuring Techniques in Physics. He has authored or co-authored 230 papers in international journals and 330 papers at international conferences. His current research interests include electromagnetic theory, computational electromagnetics, planar antennas and circuits, nanoelectromagnetics, electromagnetic radiation, electromagnetic compatibility, and bio-electromagnetics. Dr. Vandenbosch has been a member of the “Management Committees” of the consecutive European COST actions on antennas since 1993. Within the ACE Network of Excellence of the EU during 2004–2007, he was a member of the Executive Board and coordinated the activity on the creation of a European antenna software platform. From 2008 to 2014, he was a member of the board of FITCE Belgium, Belgian branch of the Federation of Telecommunications Engineers of the European Union. From 2001 to 2007, he was the President of the SITEL, Belgian Society of Engineers in Telecommunication and Electronics. From 1999 to 2004, he was the Vice-Chairman, and he was the Secretary of the IEEE Benelux Chapter on Antennas and Propagation from 2005 to 2009. Currently, he holds the position of Chairman of this chapter. From 2002 to 2004, he was the Secretary of the IEEE Benelux Chapter on EMC. From 2012 to 2014, he was the Secretary of the Belgian National Committee for Radio-Electricity, where he is also in charge of the Commission E. He currently leads the EuRAAP Working Group on Software and represents this group within the EuRAAP Delegate Assembly.
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S0924-4247(18)30927-0 https://doi.org/10.1016/j.sna.2018.10.013 SNA 11059
To appear in:
Sensors and Actuators A
Received date: Revised date: Accepted date:
31-5-2018 9-9-2018 8-10-2018
Please cite this article as: Yan S, Bao J, Ocket I, Nauwelaers B, Vandenbosch GAE, Metamaterial Inspired Miniaturized SIW Resonator for Sensor Applications, Sensors and amp; Actuators: A. Physical (2018), https://doi.org/10.1016/j.sna.2018.10.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Metamaterial Inspired Miniaturized SIW Resonator for Sensor Applications Sen Yan,1,2,a),b) Juncheng Bao,2),b) Ilja Ocket,2,3) Bart Nauwelaers2), and Guy. A. E. Vandenbosch2)
School of Electronics and Information Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi, 710049, China
2
Deptartment of Electrical Engineering, KU Leuven, Kasteelpark Arenberg 10, Box 2444, 3001 Leuven, Belgium
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Interuniversity Microelectronics Center (IMEC), Kapeldreef 75, 3001 Leuven, Belgium
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a) b)
Corresponding author: Sen Yan, Email: [email protected]. S. Yan and J. Bao contributed equally to this work.
Highlights
A miniaturized cavity with high quality factor is obtained.
A negative mode of a substrate integrated waveguide (SIW) resonator is obtained by loading metamaterials. The field distributions in the cavity are analyzed to study the operating mechanism.
SC RI PT
A planar substrate integrated waveguide (SIW) resonator is proposed in this letter. By loading a metamaterial inspired structure in a short section of an SIW, a miniaturized cavity (0.263×0.184×0.0063 λ03 at 2.39 GHz) with high quality factor (272.5) is obtained. The resonant modes of the cavity and their corresponding field distributions are analyzed. A resonator prototype has been fabricated and tested. The measured results agree well with the simulated ones. This cavity resonator has huge potential
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in sensor applications. A binary solvent water alcohol mixture is used to verify the sensor concept.
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1. Introduction
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Cavity resonators have huge application potential in the microwave and millimeter wave frequency range, e.g. for filters, oscillators, antennas, sensors, etc. To reduce the size of traditional metallic waveguide cavities and simplify the integration
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with other planar microwave circuits, recently substrate integrated waveguides (SIW) have been widely studied. These waveguides can be fabricated with standard printed circuit board (PCB) technology [1], [2], which will significantly reduce
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fabrication cost compared to the traditional metallic waveguides. Due to the relatively low radiation loss and high quality factor
TE
(Q factor) compared to other planar resonators, SIW cavities are prime candidates to be used in sensor applications [3]-[9]. Similar as for the traditional metallic waveguide cavity, the basic mode of a SIW cavity is also TE101. Its resonant frequency
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is determined by the permittivity of the loaded material (substrate) and the dimensions of the cavity. To reduce the size of SIW
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cavities, the epsilon-near-zero (ENZ) tunneling phenomenon [6], [7] can be used. The resonant frequency of ENZ tunneling is just as the cutoff frequency of the TE10 mode of the waveguide, which means that the related operating frequency is independent of the length of the waveguide. Thus, the resonance can be expressed as a TE 100 mode. However, this mode cannot be used to
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further reduce the width of the SIW cavity. Recently, the study of metamaterials has revealed that a waveguide can operate at negative modes if the loaded metamaterial simultaneously has a negative permittivity and negative permeability [10]-[12]. These negative modes can operate much lower than the cutoff frequency of the dominant (TE 10) mode. The negative permittivity can be automatically obtained by operating the waveguide below the cutoff frequency of the dominant TE mode. The negative permeability can be realized by inserting certain slots on the surface of the waveguide [10].
In this letter, a miniaturized SIW resonator is proposed. By loading two interdigital capacitors (meander slots) on the bottom layer of the SIW, a negative mode TE10(-1) mode is obtained. It shows a much lower resonant frequency than the normal positive modes. The field distributions in the cavity are analyzed to study the operating mechanism. A prototype is fabricated and measured. The results show that this resonator can be used as a sensor to measure the permittivity of a liquid.
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2. Topology The proposed SIW cavity is fabricated using the substrate Rogers RT5880 with thickness 0.787 mm. The dielectric constant and loss tangent are 2.2 and 0.0009, respectively. The diameter of the vias is 1.2 mm and the distance between the centers of neighboring vias is 2.5 mm, which guarantees that the leaky wave from the short slots can be neglected. [1]
The topology of the resonator is shown in Fig. 1. A section of SIW consists of two units, and each unit is loaded by an interdigital capacitor (meander slot) on the surface of the SIW. A cavity with size 33 × 23 mm2 is obtained by shorting the SIW
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at the two boundaries (left and right). This cavity is fed by two microstrip lines with characteristic impedance 50 Ω. The liquid
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sample is located in a center hole through the cavity. The bottom of the hole is sealed with silica gel. The top of the hole is
A
open in order to be able to inject fluid. The detailed dimensions are labeled in Fig. 1 (a) and (b). The frequency domain solver
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in the commercial full-wave simulation software CST microwave Studio, which is based on the finite element method, is used in this letter [13].
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3. Operating Mechanism
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Firstly, a unit of SIW is calculated with and without the slot loading, respectively. The dispersion curve of this SIW is then retrieved from the S-parameters, see Fig. 2 (a). When there is no slot loaded on the SIW, the cutoff frequency of the dominant
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mode (TE10) is 5.05 GHz. For the proposed structure with slot, the SIW shows a left-handed transmission characteristic (phase advanced section) below the frequency 2.98 GHz, and a right-handed transmission characteristic (phase delayed section) above
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the frequency 3.75 GHz [10]. A stop band is observed between these two frequencies.
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Next, the cavity is Fig. 1 is analyzed. The resonant frequency of the cavity is determined by the length of the SIW, m p n
(1)
where βp is the phase delay of one unit cell, m is the number of unit cells (2 in our structure), n is the mode number (the number of standing wave periods inside the SIW), which means that n is an integer (0, ±1, ±2, …, ±(m-1)). Fig. 2 (b) shows the simulated S parameters of the cavity. When the cavity is without loading slots, its first resonance (TE101) is located at 6.544 GHz, which agrees well with the dispersion curve in Fig. 2 (a). The slight frequency shift is caused
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by the feeding line, which may perturb the original field distribution in the cavity. The loading of the slots may decrease the resonant frequency of the TE101 mode to 4.831 GHz, and more importantly, two additional lower modes are obtained. One is the negative mode TE10(-1) located at 2.39 GHz, and the other is the zero-order resonance (ZOR) mode at 3.072 GHz. The field distributions of these two modes are shown in Fig. 3. The mode TE 10(-1) has one standing wave in the SIW (see Fig. 3 (a) and (b)), similarly to the field distribution of mode TE101, while the magnetic field of the ZOR mode is almost constant in the cavity
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(see Fig. 3 (d)).
FIG. 1. Topology of the proposed SIW resonator. (a) top layer, (b) bottom layer, (c) photo of the fabricated prototype. The widths of the fingers and gaps are 0.6 mm and 0.4 mm, respectively.
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(a)
(b)
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FIG. 2. (a) Dispersion curve of the SIWs with and without slot loading, (b) S parameters of the cavity with and without slot loading. The analysis of the topology with slot is based on a single cell.
FIG. 3. Field distributions in the proposed resonator. The cavity is fed from the left port and the coordinate system is defined in Fig. 1.
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FIG. 5. Measured S parameters with liquid.
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FIG. 4. Simulated and measured S parameters without liquid.
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In this design, the TE10(-1) is chosen as the operating mode, not only because it operates at a lower resonant frequency than the ZOR mode, but more importantly, also because the electric field distribution is more concentrated around the center of the
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cavity. The relatively high field intensity results in the high sensitivity necessary in sensor applications. It should be noted that although the electric field is more concentrated in the meandering slot than at the center of the cavity, the latter location is
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chosen in our proposed design since it is easy to integrate with a vertical liquid tube. When a liquid sample is located in the center hole of the cavity, it will couple with the electric field, and thus perturb the
resonant frequencies. As for the normal TM101 mode in the waveguide cavity, the frequency shift of the TE10(-1) mode is also approximately proportional to the dielectric constant of the sample, since the perturbed electric field will be stronger when the dielectric constant of the sample is higher.
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4. Measurement and Results A prototype of the cavity resonator was fabricated, as shown in Fig. 1 (c). The measured S parameters agree quite well with the simulated ones, see Fig. 4. A sharp resonance is observed at ca. 2.39 GHz, with a Q factor of 272.5. The Q factor is calculated from the input impedance of the left port when the right port of the cavity is shorted [14].
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Next, a water alcohol mixture was tested with this resonator. Fig. 5 shows the measured S-parameters. Both the frequency shift of the resonance and the magnitude of the transmission (S12) show a good monotonicity with a growing alcohol concentration. A further analysis on parameter retrieval reveals that the figure-of merit (FOM) is ca.
FOM
f r '
0 .3 4 M H z
(2)
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where ∆f and ∆εr’ are the frequency shift and the permittivity shift corresponding with the water alcohol mixed sample [15],
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respectively. Other parameter retrieval methods for microfluidic sensors can be found in [16] and [17]. It should be mentioned that the Q factor decreases with increasing the alcohol concentration. The reason is that the high permittivity of the water
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prevents the electric field from the inner part of the sample and thus reduces the losses. Actually, when the sample is pure
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water, the electric field can only penetrate into a little thickness of the sample.
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The experiment was repeated 5 times for deionized water, and we found that the results are stable. The maximum shift of the resonant frequency was less than 1 MHz. It should be mentioned that the major limitation on the accuracy is the knowledge
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of the exact volume of the liquid. In this preliminary test, the volume of the liquid was controlled by using a pipette. This can
5. Conclusion
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be improved by using other methods, e.g., digital pumps.
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A compact SIW cavity resonator was proposed in this letter. By loading a metamaterial inspired structure in the cavity, the resonator can operate at its negative mode, which has a much lower resonant frequency than the traditional dominant mode.
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Field distributions were analyzed to study the operating mechanism of the cavity. A prototype was fabricated and measured, yielding a good agreement with simulated results. An initial test has shown that the cavity can be used as a permittivity sensor to characterize samples of liquid.
Acknowledgments: This work was partly supported by the Research Foundation-Flanders (FWO) Postdoctoral Fellowship (No. 12O1217N).
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REFERENCES [1] M. Bozzi, A. Georgiadis and K. Wu, "Review of substrate-integrated waveguide circuits and antennas," IET Microwaves, Antennas & Propagation, vol. 5, no. 8, pp. 909-920, June 6 2011. [2] K. Wu, Y. J. Cheng, T. Djerafi and W. Hong, "Substrate-Integrated Millimeter-Wave and Terahertz Antenna Technology,"
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Proceedings of the IEEE, vol. 100, no. 7, pp. 2219-2232, July 2012. [3] J. D. Barrera, and G. H. Huff, “Analysis of a variable SIW resonator enabled by dielectric material perturbations and applications,” IEEE Trans. Microw. Theory Techn., vol. 61, no. 1, pp.225-233, Jan. 2013.
[4] H. El Matbouly, N. Boubekeur and F. Domingue, "Passive Microwave Substrate Integrated Cavity Resonator for Humidity Sensing," IEEE Trans. Microw. Theory Techn., vol. 63, no. 12, pp. 4150-4156, Dec. 2015.
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[8] I.-J. Hyeon, W.-Y. Park, S. Lim , C.-W. Baek, “Ku-band bandpass filters using novel micromachined substrate integrated Waveguide structure with embedded silicon vias in benzocyclobutene dielectrics,” Sensors and Actuators A: Physical, vol.
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[9] T. Yun, S. Lim, “High-Q and miniaturized complementary split ring resonator-loaded Substrate integrated waveguide
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[11] S. Yan, P. J. Soh, G. A. E. Vandenbosch, “Wearable dual-band composite right/ left-handed waveguide textile antenna for WLAN applications,” Electron. Lett., vol. 50, no. 6, pp. 424-426, Mar. 2014.
[12] Y. Dong and T. Itoh, "Miniaturized Substrate Integrated Waveguide Slot Antennas Based on Negative Order Resonance," IEEE Transactions on Antennas and Propagation, vol. 58, no. 12, pp. 3856-3864, Dec. 2010. [13] Computer
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[14] T. Ohira, "What in the World Is Q? [Distinguished Microwave Lecture]," IEEE Microwave Magazine, vol. 17, no. 6, pp. 42-49, June 2016. [15] A. Megriche, A. Belhadj, A. Mgaidi, “Microwave dielectric properties of binary solvent water-alcohol, alcohol-alcohol mixtures at temperatures between -35°C and +35°C and dielectric relaxation studies,” Mediterranean Journal of Chemistry, vol. 1, no. 4, pp. 200-209, 2012.
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[16] A. Ebrahimi, W. Withayachumnankul, S. Al-Sarawi and D. Abbott, "High-Sensitivity Metamaterial-Inspired Sensor for Microfluidic Dielectric Characterization," IEEE Sensors Journal, vol. 14, no. 5, pp. 1345-1351, May 2014. doi: 10.1109/JSEN.2013.2295312
[17] W. Withayachumnankul, K. Jaruwongrungsee, A. Tuantranont, C. Fumeaux, and D. Abbott, “Metamaterial-based
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Sen YAN received the bachelor’s and master’s degrees in information and telecommunication engineering from Xi’an Jiaotong University (XJTU), Xi’an, China, in 2007 and 2010, respectively, and the Ph.D. degree in electrical engineering from Katholieke Universiteit Leuven (KU Leuven), Leuven, Belgium, in 2015. From 2015 to 2017, he was a post-doctoral researcher with KU Leuven. In 2016, he joined EPFL, Lausanne, Switzerland, and the University of Texas at Austin, Austin, TX, U.S., as a Visiting Researcher. He has been a full professor with XJTU since 2017. Dr Yan’s current research interests include metamaterials and metasurfaces, wearable devices and textile antennas, reconfigurable antennas, antenna diversity and nano-antennas. He has authored or co-authored 33 international journal papers and 30 conference contributions. He was successful in achieving the post-doctoral fellowship from KU Leuven and FWO in 2015 and 2016, respectively. In 2017, He obtained the “Young Talent Support Plan” from XJTU. He currently serves as an active reviewer of more than 20 journals, including IEEE Access, IEEE Trans. Antennas propag., IEEE Trans. Microw. Theory Techn., IEEE Trans. Biomed. Circuits Syst., and etc. Juncheng Bao received the M.Sc. degree in electrical engineering from Katholieke Universiteit (KU) Leuven, Leuven, Belgium, in 2013. He had an internship with imec, Leuven, in 2013. He is currently working toward the Ph.D. degree in electrical engineering at KU Leuven. His current research interests include microwave biomedical applications, novel microwave-microfluidic devices design and fabrication, and microwave and millimeter wave metrology.
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Ilja Ocket received the M.Sc. and Ph.D. degrees in electrical engineering from Katholieke Universiteit (KU) Leuven, Leuven, Belgium, in 1998 and 2009, respectively. He has been with imec, Leuven, and KU Leuven, since 1999. With imec, he is currently involved in millimeter-wave antenna modules and packaging for 79- and 140-GHz radar. With KU Leuven, he leads the group working in the area of microwave and millimeter-wave applications for biology and medicine and is involved in integrated couplers for (sub) millimeter plastic waveguides.
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Bart Nauwelaers received the Ph.D. degree in electrical engineering from the Katholieke Universiteit (KU) Leuven, Leuven, Belgium, in 1988 and the Master’s degree in design of telecommunication systems from Telecom ParisTech, Paris, France. Since 1981, he has been with the Department of Electrical Engineering, KU Leuven, where he has been involved in research on microwave antennas, passive components, interconnects, microwave integrated circuits and MMICs, linear and nonlinear device modeling, MEMS,andwireless communications. He is the former Chair of IEEE AP/MTT-Benelux and past Chair of URSI-Benelux.
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Guy A. E. Vandenbosch received the M.S. and Ph.D. degrees in electrical engineering from Katholieke Universiteit Leuven (KU Leuven), Leuven, Belgium, in 1985 and 1991, respectively. From 1991 to 1993, he was a Post-Doctoral Researcher with KU Leuven, where he has been a Lecturer since 1993 and a Full Professor since 2005. In 2014, he joined Tsinghua University, Beijing, China, as a Visiting Professor. He has taught or teaches courses on Electromagnetic Waves, Antennas, Electromagnetic Compatibility, Electrical Engineering, Electronics, and Electrical Energy, and Digital Steer-and Measuring Techniques in Physics. He has authored or co-authored 230 papers in international journals and 330 papers at international conferences. His current research interests include electromagnetic theory, computational electromagnetics, planar antennas and circuits, nanoelectromagnetics, electromagnetic radiation, electromagnetic compatibility, and bio-electromagnetics. Dr. Vandenbosch has been a member of the “Management Committees” of the consecutive European COST actions on antennas since 1993. Within the ACE Network of Excellence of the EU during 2004–2007, he was a member of the Executive Board and coordinated the activity on the creation of a European antenna software platform. From 2008 to 2014, he was a member of the board of FITCE Belgium, Belgian branch of the Federation of Telecommunications Engineers of the European Union. From 2001 to 2007, he was the President of the SITEL, Belgian Society of Engineers in Telecommunication and Electronics. From 1999 to 2004, he was the Vice-Chairman, and he was the Secretary of the IEEE Benelux Chapter on Antennas and Propagation from 2005 to 2009. Currently, he holds the position of Chairman of this chapter. From 2002 to 2004, he was the Secretary of the IEEE Benelux Chapter on EMC. From 2012 to 2014, he was the Secretary of the Belgian National Committee for Radio-Electricity, where he is also in charge of the Commission E. He currently leads the EuRAAP Working Group on Software and represents this group within the EuRAAP Delegate Assembly.
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