5. Simple in-field detection circuit

The phase-shift method, as it was stated above, is the simple method that can be used for the determination of the complex permittivity. Therefore, the expensive instrument for the determination of permittivity can be replaced with a simple detection circuit. The block diagram, and detailed electrical scheme for measurement of the phase shift at single operating frequency, is presented in Figure 18 together with the fabricated prototype realized in LTCC (low-temperature cofired ceramics) technology.

Detection circuit consists of a microwave oscillator, a quadrature hybrid, a sensor element, and a phase detector functional blocks. The operating principle can be described in the following way: sinusoidal signal generated by source, that is, microwave oscillator, is divided by quadrature hybrid on measurement and referent signal. The measurement signal propagates along sensor element where phase shift occurs according to the dielectric properties of the surrounding medium. The signal from the sensor element is fed into the input of the phase detector which compares the phase of the measurement and the referent signal. The output of the phase detector is the voltage proportional to the phase shift of the input signals which can be related to the measured dielectric constant. Referent signal propagates through the phase-shifter module which has a purpose to provide the calibration of the sensor and to overcome deviations of the nominal properties of the materials and

components used for sensor fabrication. In this way the repeatability of measure-

Phase-shift measurement device: (a) block diagram, (b) fabricated circuit, and (c) detail electronic circuit of

Phase-Shift Transmission Line Method for Permittivity Measurement and Its Potential in Sensor…

DOI: http://dx.doi.org/10.5772/intechopen.81790

The phase-shift measurement electrical circuit is detailly presented in Figure 18c, indicating abovementioned functional blocks of the circuit, Figure 18a. The oscillator is realized by the voltage-controlled oscillator MAX2751 (8), which is

ment of the different sensors will be secured.

the phase-shift measurement device [13].

Figure 18.

85

Phase-Shift Transmission Line Method for Permittivity Measurement and Its Potential in Sensor… DOI: http://dx.doi.org/10.5772/intechopen.81790

#### Figure 18.

5. Simple in-field detection circuit

Blok diagram and layout of the CRLH sensor.

Electromagnetic Materials and Devices

ceramics) technology.

84

Figure 16.

Figure 17.

The phase-shift method, as it was stated above, is the simple method that can be used for the determination of the complex permittivity. Therefore, the expensive instrument for the determination of permittivity can be replaced with a simple detection circuit. The block diagram, and detailed electrical scheme for measurement of the phase shift at single operating frequency, is presented in Figure 18 together with the fabricated prototype realized in LTCC (low-temperature cofired

Response of the CLRH sensor: (a) transmission characteristic and (b) phase characteristic.

Detection circuit consists of a microwave oscillator, a quadrature hybrid, a sensor element, and a phase detector functional blocks. The operating principle can be described in the following way: sinusoidal signal generated by source, that is, microwave oscillator, is divided by quadrature hybrid on measurement and referent signal. The measurement signal propagates along sensor element where phase shift occurs according to the dielectric properties of the surrounding medium. The signal from the sensor element is fed into the input of the phase detector which compares the phase of the measurement and the referent signal. The output of the phase detector is the voltage proportional to the phase shift of the input signals which can be related to the measured dielectric constant. Referent signal propagates through the phase-shifter module which has a purpose to provide the calibration of the sensor and to overcome deviations of the nominal properties of the materials and

Phase-shift measurement device: (a) block diagram, (b) fabricated circuit, and (c) detail electronic circuit of the phase-shift measurement device [13].

components used for sensor fabrication. In this way the repeatability of measurement of the different sensors will be secured.

The phase-shift measurement electrical circuit is detailly presented in Figure 18c, indicating abovementioned functional blocks of the circuit, Figure 18a. The oscillator is realized by the voltage-controlled oscillator MAX2751 (8), which is adjusted by the referent voltage (9) and the voltage divider (10) to operating frequency of 2.2 GHz. The signal from the oscillator is divided into measurement and referent signals using commercially available quadrature coupler circuit HY22-73 (2). The phase-shifter module allows control of the phase shift and enables fine-tuning of the difference in the phase between the measurement and referent signals. The phase shift can be achieved by varying the control voltage (11) that affects the capacitance of the varactor diodes (12 and 13). The change in capacitance affects the signals (14) and (15) which superimpose with the input referent signal (3) through the quadrature coupler (16) and in this way changes the phase of the resultant signal at the output of the module (17). The measurement of the phase shift between the measurement and referent signal is done using a phase detector module implemented with the integrated circuit AD8302 Analogue Devices (18). The phase detector circuit is set to the phase difference measurement mode according to the manufacturer's recommendation. Integrated circuit AD8302 on its output (21) gives a voltage signal that is proportional to the phase difference of the signal on its inputs (19) and (20).

The accuracy of the designed phase-shift measurement device was experimentally verified by comparing the results of the measurement of the phase shift of the signal, induced by phase-shift circuit (functional block (7), Figure 18c), in the range from 0 to 90° with the results of the measurement obtained using vector network analyzer (VNA). The results of the comparison are shown in Figure 19. It can be seen that the results agree well and the relative error in respect of the full-scale output is 5.56% which confirms performance of the designed phase-shift circuit.

Additional module for different sensor topologies can be designed to provide a conversion of the measured voltage to the corresponding value of the dielectric constant.

Acknowledgements

ment No. 664387.

Figure 19.

Author details

87

This result is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under the grant agree-

Phase-Shift Transmission Line Method for Permittivity Measurement and Its Potential in Sensor…

Vasa Radonic\*, Norbert Cselyuszka, Vesna Crnojevic-Bengin and Goran Kitic University of Novi Sad, BioSense Institute–Research and Development Institute for

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Information Technologies in Biosystems, Novi Sad, Serbia

Comparisons between VNA and designed phase-shift measurement circuit.

DOI: http://dx.doi.org/10.5772/intechopen.81790

\*Address all correspondence to: vasarad@uns.ac.rs

provided the original work is properly cited.
