posted on 2023-08-30, 15:45authored byMohammed A. Al-Amin
Radio Frequency Micro Electromechanical Systems (RF MEMS) technology is used
to help switch, filter or tune signals from Direct Current to RF. RF MEMS switches
are known to provide good isolation with low insertion loss and can be applied to a
wide range of frequencies with almost no power consumed to drive them, which
provides an advantage for integrated mobile wireless systems. Despite the benefits,
RF MEMS switches have not seen a rapid development for commercialisation in the
integrated mobile wireless systems market because of reliability issues and high
actuation voltage requirements, which makes additional voltage drive circuitry
necessary. This in turn makes the overall switch larger in size. Due to these shortfalls,
this research undertakes an investigation by optimising RF MEMS switches.
This thesis presents an RF MEMS switch for use in mobile systems, based on the
optimisation of a cantilever, ohmic type switch. The optimisation resulted in five
major iterations, each providing improvements over the cantilever. The final optimised
iteration researched is the ‘S’ Shaped, Split Pivot, Seesaw, Double-Pole Double-
Throw (DPDT) switch. This optimised design provides capabilities of high RF
isolation. It provides low actuation voltages (by using ‘Delta Plates’). The switch takes
advantage of an ‘S’ Shaped, Split Pivot, allowing the pivot to flex with less force,
which reduces actuation voltage. The optimised designs provide a selection of
switches, which take advantage of low voltages used by mobile systems (i.e. ≤ 5V).
The ‘S’ shaped pivot has a lower von mises stress (15MPa), which is below the yield
strength of copper (70 MPa), allowing the design to return to its original state without
deforming. This proved a 97.8% reduction in von mises stress over the cantilever and
a reduction of actuation voltage from 30V down to 1.13V. The functionality of the
switch is increased by 4 times to provide DPDT switching over the cantilever’s Single-
Pole Single-Throw (SPST) switching. Also, the ‘S’ Shaped, Split Pivot, Seesaw DPDT
switch, maintains a higher isolation over its predecessor (cantilever) with an average
isolation of -102.89 dB over a frequency range from 5GHz to 45GHz. This provides a
246% improvement to that of the cantilever’s isolation.
A Finite Element Analysis approach was used, with mathematical analysis to validate
the Intellisuite simulation tool. A secondary validation was conducted, with known
practical cantilever results against the Intellisuite Simulation tool for the
electromechanical characteristics of the switch. The electromagnetics (EM)
characteristics of the switch were also validated, with the Computer Simulation
Technology (CST) electromagnetic simulation tool, against the cantilever’s practical
results. The optimisation followed a linear approach, with each component of the
switch having incremental improvements, such as: Contacts, Beam, Electrostatic
Parallel Plates and Pivots. The research has discovered that RF MEMS switches (i.e.
cantilevers) are larger than the micro size, require high actuation voltages and have
increased von mises stress. The optimisations focused on four areas of improvements
to the characteristics of the switch and addressed them as follows: reducing actuation
voltage, decreasing von mises stress, increasing isolation of the contacts and
expanding functionality.
History
Institution
Anglia Ruskin University
File version
Accepted version
Language
eng
Thesis name
PhD
Thesis type
Doctoral
Legacy posted date
2018-10-29
Legacy creation date
2018-10-29
Legacy Faculty/School/Department
Theses from Anglia Ruskin University/Department of Engineering and Built Environment