How a new switching system could make phones and power cables more durable
A new switching system could make mobile phones and power cables more durable, as Ellis Davies reports.
A new type of microelectromechanical system (MEMs) has been developed by researchers at Binghamton University, USA. MEMs is a switch comprising two electrodes of which one is moveable and pulled toward the static electrode using electrostatic force, commonly found in wireless devices such as mobile phones. It uses a new opening mechanism that enables the system to become more durable by employing electrostatic levitation – a force that permits charged electrodes to push apart rather than pull together. Researchers believe it has applications in wireless communications, to avoid common failures such as wear on the electrodes after frequent contact with each other. The study, A reliable MEMS switch using electrostatic levitation, is published in Applied Physics Letters.
Opening it up
The team began the study with the aim to explore possibilities beyond the conventional MEMs switches that suffer from instability caused by frequent contact. MEMs designers often try to mitigate this problem by adding dimples or landing pads to the electrodes to reduce impact when they collide. But it can’t be avoided, and ultimately results in failure and a breakdown in the electrode material. The new mechanism prevents the problem to result in more reliable switches that last longer and save money.
The issue is avoided by adding more electrodes – three electrodes on the bottom and one electrode parallel to the others. Binghamton University Assistant Professor, Shahrzad Towfighian, told Materials World, ‘Current switches consist of two electrodes that pull together when charged. Thus, the force between them is always in one direction and toward each other. We added two more electrodes in a creative configuration that enables a force in the opposite direction. This provides easier release of the switch, which was not possible in conventional switches. The result is a bi-directional and robust switch that can last longer.’ The switch is now closed to be opened, rather than open and closed as was the case previously.
The use of four electrodes is made possible by electrostatic levitation. The electrodes are pushed apart rather than together, which allows the side electrodes, using voltage pulses of over 100V, to push strongly upward overcoming the forces of the middle electrode, at ground voltage, to open the switch.
Electrostatic levitation does, however, use very high voltage potential because of the weak fringe fields. To generate an electrostatic levitation force the voltage must be more than an order of magnitude larger than the corresponding voltage – the other electrodes. Previously, researchers have used voltages of over 150V. The high voltage will be an issue that will need to be addressed in the future.
Longer life electronics
The team says that switching over to this kind of switch could extend the lifetime of wireless communication devices and limit component replacements. Other applications for the mechanism could be in MEMs filters used for signal processing, which bolster sound performance in devices such as radio or TV.
These switches also have potential use in powerlines, when voltage goes beyond a limit and a switch needs to be opened. Towfighian in a university statement, ‘The design allows us to have more reliable switches to monitor unusual spikes in voltage, like those caused by an earthquake, which can cause danger to public safety.
‘We plan to operate these switches autonomously from mechanical shock or impact. This can be possible using triboelectric transducers that convert mechanical impact to electric voltages. This concept opens up possibilities for many safety switches, such as those in air bag deployment devices. When they experience shock beyond a limit, the switch can trigger the air bag without a power source.’