Multipurpose Software Defined Measurement System for Dielectric Characterization Sandra Costanzo, Giuseppe Di Massa, David Moreno, Francesco Spadafora DIMES, University of Calabria, 87036 Rende (CS) – Italy email:
[email protected]
Abstract—A low cost Software Defined Measurement system is proposed in this work to implement a multipurpose dielectric characterization procedure able to work under various materials conditions. Two different retrieving algorithms are discussed as application examples in the presence of single and multilayer dielectric structures, and the relative permittivity reconstructions versus frequency are reported.
algorithms, thus enabling the multipurpose feature in terms of adaptability to a large variety of dielectric materials characterization.
Index Terms—dielectric characterization, software defined radio.
I.
INTRODUCTION
The dielectric properties of materials are strongly influenced by several different factors, such as frequency, temperature, homogeneity. As a consequence of this, no single technique can be assumed to perform an accurate dielectric characterization at all frequency bands and loss conditions. A special challenge occurs in the presence of thin materials, such as dielectric substrates, usually adopted in microstrip structures, where the accuracy uncertainty of the retrieving procedure significantly increases [1]. Existing methods for the dielectric characterization, based on cavity resonators, coaxial probes, striplines [2] or open resonators [3], usually adopt expensive vector network analyzers to perform the scattering parameters measurement. Furthermore, depending on the specific material and application, the retrieving procedures require dedicated hardware and software, thus increasing the overall cost of the test setup. In this communication, the adoption of a Software Defined Radio (SDR) transceiver is proposed to implement a Software Defined Measurement (SDM) system with multipurpose feature [4], able to perform a dielectric material characterization under different conditions, with low costs and high flexibility in terms of retrieving software implementation. The details of the proposed software-based platform are outlined in the next section. II.
SOFTWARE DEFINED MEASUREMENT PLATFORM: APPLICATION EXAMPLES
The block diagram of the proposed SDM platform is shown in Fig. 1. A custom SDR transceiver is adopted as lowcost measurement instrument, which is equipped with transmitting (TX) and receiving (RX) antennas. It is directly connected to a PC hosting the necessary data processing
Fig. 1. Block diagram of Software Defined Measurement system
Two application examples are described in this communication to validate the proposed SDM approach. In the first case, the measurement setup illustrated in Fig. 2 is assumed to retrieve the unknown dielectric permittivity of the test material.
Fig. 2. First example of SDM setup
The analysis is performed by making an amplitude comparison between two signals, the first acquired by the system without the dielectric slab, and the second one measured in the presence of the material. It is easy to show that the real part ε’ of the dielectric permittivity can be retrieved by the following expression: (1) where A1, A2 are the amplitudes of the received signals with and without the dielectric slab, respectively.
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A successful reconstruction examplee for a standard dielectric substrate usually adopted in miccrostrip circuits is illustrated in Fig. 3, where the variation veersus frequency of the relative permittivity is reported.
Fig. 5. Range profile relative to test structure s in Fig. 4 Fig. 3. Dielectric permittivity reconstruction examplle with SDM setup of Fig. 2
In the second application example, the problem p relative to the dielectric characterization of a mulltilayer dispersive material is considered. A multiband analysiss is required in this case, thus leading to the adoption of an Orthhogonal FrequencyDivision Multiplexing (OFDM) signal, a combination of modulation and multiplexing technique abble to transmit M different waves associated to M different carrier c frequencies [5].
where the term Δd representts the range shift measured at various frequencies. As validation example of thhe OFDM-based SDM approach, a two-layers material with εr1 = 27 and εr2 = 76 at 2.3 GHz is considered. The algorithm is applied to reconstruct first the layers thicknesses d1 = 39 cm m and d2 = 44 cm, and then to retrieve, by a M = 3 OFDM signal, s the permittivity variation versus frequency reported in Taable I. TABLE I.
PERMITTIVITY VARIIATION FOR TEST STRUCTURE OF FIG. 4
Frequency [GHz]
εr1
εr2
2.3
26.8855
72.165
3.3
27.9177
73.215
4.3
27.9333
73.237
The theoretical details and the relative discussion concerning ill-posedness and accuracy a aspects of the proposed reconstruction algorithms will be given during the conference presentation. REFER RENCES
Fig. 4. Multilayer test structure for OFDM-based SDM M approach
Referring to the multilayer test structure of Fig. 4, where the layers thicknesses d1, d2 are also assumed as unknowns, a single band OFDM signal is first considerred to retrieve the relative permittivity εr1, εr2 from the knowledge k of the measured reflection coefficient. The distaances di are then reconstructed from the range profile of Fig. 5, 5 by the following relationship:
[1]
[2]
[3]
(2) [4]
Finally, a multiband OFDM signal is adopted a to retrieve the frequency variation of dielectric permittivvity on the basis of the following equation: ∆
∆
[5]
(3)
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S. Costanzo, I. Venneri, G. Di Massa, M A. Borgia, “Benzocyclobutene as substrate material for planar millimeter-wave structures: dielectric characterization and applicationn,” Journal of Infrared, Millimeter and Terahz Waves, vol. 31, pp. 66-777, 2010. J. Baker-Davis, R. G. Geyer, J. H. Jr. Grosvenor, M. D. Janezic, “Dielectric characterization of low-loss materials – a comparison of techniques,” IEEE Trans. Dieleectrics Electric. Insul., vol. 5, pp. 571577, 2002. H Moreno, “Accurate circuit model of G. Di Massa, S. Costanzo, O. H. open resonator system for dielecctric material characterization,” Journal of Electrom. Waves Applicat., vool. 5-6, pp. 783-794, 2012. S. Costanzo, F. Spadafora, A. Borgia, B O. H. Moreno, A. Costanzo, G. Di Massa, “High resolution software defined radar system for target detection,” Advances in Intelliggent Systems and Computing, vol. 206, pp. 997-1005, 2013. S. Costanzo, F. Spadafora, O. H. H Moreno, F. Scarcella, G. Di Massa, “Multiband software defined raadar for soil discontinuities detection,” Journal of Electrical and Compputer Engineering, , article ID 379836, 2013.
