## 5 Conclusions  
The tunability of two microfluidic inductor structures were investigated; wire-wound inductor and wire bond inductor. Oil-based ferrofluids as high permeable liquids were used as microfluid. The liquid is being injected through microchannel created for bot inductor structure to alter its permeability property, thus giving a tunable inductance. For the wire-wound structure, the highest tuning range was achieved with EMG901 ferrofluid equal to 90.6% at 300 MHz, while the best quality factor was maintained. The wire-bonded structure, which has a high potential to use in the MEMS process, achieved a tuning ratio of 81% at 310 MHz with EMG901 ferrofluid. As for a conclusion, a tunable inductor with high quality factor can be realized using microfluidic techniques.  
Several authors were involved in this project. [PERSON] was former PhD student in this project. She involved from conceptualization, methodology and data curation including original draft writing. [PERSON], [PERSON] and [PERSON] were research officer in this project. They involved to assist [PERSON] in validation method, formal analysis and data curation. [PERSON] is co-supervisor PhD to [PERSON]. He involved on validation the measurement method, review and editing. The corresponding author is main supervisor to [PERSON]. He involved in conceptualization, visualization, investigation, formalism analysis, original draft writing and project administration. S.K.K.M.: Formal analysis, Writing-review & editing. A.A.M.: Conceptualization, Supervision, Writing-original draft, Writing-review & editing. All authors have read and agreed to the published version of the manuscript.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Wire-bonded** & **Sim. L** & **Sim.** & **Meas. L** & **Meas.** & **Sim.** & **Meas.** \\
**@150 MHz** & **(nH)** & **Q** & **(nH)** & **Q** & **TR\%** & **TR\%** \\ \hline Vacuum & 46.5 & 21.52 & 42.6 & 39.1 & - & - \\ EMG901 & 160.79 & 49.594 & 66.6 & 17.2 & 245.7\% & 56.2\% \\ EMG905 & 100.77 & 44.177 & 54.2 & 22.3 & 116.7\% & 27.2\% \\ EMG909 & 81.19 & 36.067 & 49.8 & 26.2 & 74.6\% & 16.9\% \\ EMG911 & 59.36 & 26.498 & 46.2 & 33.2 & 27.6\% & 8.45\% \\ \hline \hline \end{tabular}
\end{table}
Table 4: Characterization of wire-bonded structure tunable inductor.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameters** & **Wire Bond** & **Wire Wound** & **([PERSON] et al. 2004) [27]** & **([PERSON] et al. 2006) [28]** \\ \hline
**Type** & Solenoid & Solenoid & Solenoid & Solenoid \\
**Technique** & Liquid-based core & Liquid-based core & Magnetic core tuned by & thin-film ferromagnetic \\
**Maximum tuning ratio** & 81\% & 90.6\% & 18\% & 85\% \\
**Quality factor** & 12.7 & 31.3 & 5 & <2 \\
**Peak quality factor** & 18.4 & 69 & & \\  & 6108 MHz & @30 MHz & 18 & 2 \\  & EMG901 & EMG901 & & \\
**Frequency** & 310 MHz & 300 MHz & 5 MHz & 100 MHz \\ \hline \hline \end{tabular}
\end{table}
Table 5: Characterization of wire-bonded structure tunable inductor.  
**Funding:** This research was funded by research university (RU) grant (Universiti Sains Malaysia) with grant number 1001/PELECT/8014010 and Universiti Sains Malaysia (USM) bridging grant with grant number 304/PCDEC/6316088.  
**Acknowledgments:** The author would like to thank the Universiti Sains Malaysia and Collaborative Microelectronic Design Excellence Center (CEDEC) for all the research facilities provided for this project.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection; analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.