## 4 Conclusions  
Water adulteration in honey is the simplest and most popular adulteration method because the physical properties of honey adulterated with water (color, smell, taste, viscosity and crystallization) are very similar to natural pure honey. A modified SMA-connector sensor is successfully fabricated and is accurately validated with the methanol for the frequency range of 0.5-4.0 GHz at the constant temperature of 25 \({}^{\circ}\)C. The modified SMA-connector sensor has been proposed to measure the complex relative permittivity, the electrical conductivity, and the phase constant of honey adulterated with water at 0-30\(\%w/w\) in the frequency range of 0.5-4.0 GHz at the constant temperature of 25 \({}^{\circ}\)C. There is little difference in the imaginary part of the complex relative permittivity of honey samples adulterated with water at 5-30\(\%w/w\) throughout the frequency range of 0.5-4.0 GHz at 25 \({}^{\circ}\)C. The real part of the complex relative permittivity of the honey sample adulterated with water is significantly different throughout the frequency range of 0.5-4.0 GHz at 25 \({}^{\circ}\)C. The frequency of 0.6 GHz is the most suitable to detect water adulteration in honey using the real part of complex relative permittivity since the FOM1 is the highest at 1.108 (\(\%w/w\))\({}^{-1}\). The electrical conductivity of the honey sample is directly proportional to the frequency. The electrical conductivity of the honey sample increases when the water adulteration increases. To use the electrical conductivity as an indicator to detect water adulteration in honey, the frequency of 3.74 GHz is the most appropriate frequency since the FOM2 is the highest at this frequency at 0.069 S/m * (\(\%w/w\))\({}^{-1}\). The phase constant of the honey sample is directly proportional to the frequency. For the phase constant as an indicator to detect water adulteration in honey, the frequency of 4.0 GHz is the most appropriate frequency because the maximum FOM3 is at this frequency at 0.007 rad/mm * (\(\%w/w\))\({}^{-1}\). From this concept, the proposed sensor could have many other potential applications for determination of relative permittivity, such as alcohol content determination in some solutions, dry rubber content determination in fresh latex, and etc. Further study is performed in the natural latex. Normally, DRC is inversely proportional to the water content of the natural latex sample. The proposed method can be used to determine the complex relative permittivity of natural latex samples. The real part is in the range of 34-37 and the imaginary part is in the range of 7-14. In the experiments for the natural latex samples with DRC in the range of 29.28-35.27\(\%w/w\), the real part of the complex relative permittivity increases when the DRC decreases. The maximum FOM is equal to 1.4462 (\(\%w/w\))\({}^{-1}\) at the frequency of 0.5 GHz. The imaginary part of the complex relative permittivity increases when the DRC decreases. The maximum FOM is equal to 0.2759 (\(\%w/w\))\({}^{-1}\) at the frequency of 4.0 GHz. The electrical conductivity and the phase constant  
Figure 22: Phase constant of natural latex samples with different DRCs over the frequency range of 0.5–4.0 GHz at the temperature of 25 \({}^{\circ}\)C.  
increase when the DRC decreases. The maximum FOMs for the electrical conductivity and the phase constant are 0.0612 S/m * \((\%\omega t/w)^{-1}\) and 0.0093 rad/mm * \((\%\omega t/w)^{-1}\) at the frequency of 4.0 GHz, respectively. The results demonstrate that it is possible to apply this technique to determine the DRC in the natural latex. Conceptualization, A.N.-O. and N.A. ; methodology, A.N.-O. and N.A. ; software, A.N.-O. and N.P. ; validation, A.N.-O. and N.A. ; formal analysis, A.N.-O. and N.A. ; investigation, A.N.-O. and N.A. ; resources, A.N.-O. and C.S. ; data curation, A.N.-O. and N.P. ; writing--original draft preparation, A.N.-O. and N.A. ; writing--review and editing, N.A. ; visualization, A.N.-O. and C.S. ; supervision, N.A. ; project administration, N.A.