Tunable millimeter-wave phase shifter based on dielectric elastomer actuation

P. Romano, O. Araromi, S. Rosset, H. Shea, J. Perruisseau-Carrier
2014 Applied Physics Letters  
A very low-loss tunable millimeter-wave phase shifter driven by dielectric elastomer actuators (DEAs) is presented. The device consists of a fixed coplanar waveguide (CPW) and two metallic loading strips suspended on an elastomer membrane. The horizontal offset between the CPW and the strips is dynamically controlled by integrated DEAs. The variable interaction between the CPW and the loading strips results in a change in the effective permittivity, thereby providing analogcontrolled
more » ... elay. The design, fabrication, and measurements of this phase shifter based on DEAs are presented, demonstrating state-of-the-art phase shift to loss performance, achieving 235 /dB at 35 GHz. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4862272] Reconfigurable phase shifters are key components in phased array antennas for microwave (MW) and millimeterwave (MMW) communications, radars, and remote sensing systems. Dynamic reconfiguration of MW and MMW devices is in fact becoming a prime need, notably for updating in real time antenna characteristics (e.g., coverage, polarization, frequency of operation), as needed both in earth terminals and satellite antennas. 1,2 In this context, low-loss reconfigurability, complexity, and cost are driving factors in the choice of a given technology. Reconfigurable phase shifters are currently implemented using several technologies, including monolithic microwave integrated circuit (MMIC), ferromagnetic, and RF-MEMS. 2 All these technologies present peculiar advantages and disadvantages, which can often result in increased cost, loss, and complexity when high-performance reconfiguration capabilities are needed at MW and MMW. MMIC performs well in terms of reliability, switching speed, and power handling, but the main drawback of this technology is related to the high RF losses (>5 dB). Ferrite phase shifters are suitable to high power applications and can achieve high performance in terms of reliability and radiation tolerance; however, they are bulky, expensive, and have significant DC power consumption. Metal MEMS-based phase shifters exhibit very low insertion loss, high linearity, and low power consumption, but their use is still limited by their reliability issues and low switching speed. They also rely on advanced cleanroom fabrication processes. Here, we propose the use of dielectric elastomer actuators (DEAs) to implement mechanical reconfiguration. DEAs are stretchable actuators capable of very large strains (over 200%). 3 They consist of thin elastomer membranes sandwiched between two compliant electrodes. 4,5 Applying a voltage bias across the electrodes results in thickness compression and in-plane expansion of the membrane as a result of electrostatic interactions and the material incompressibility. In our design, we utilize the in-plane expansion to displace loading elements in the electromagnetic (EM) active area, thus achieving a phase shifter reconfiguration. Such an approach allows for isolation of the actuator parts from the EM-active area, resulting in reconfigurable devices with losses comparable to their fixed counterparts. DEAs possess appealing properties for mechanical reconfiguration, 3-5 including inexpensive materials and fabrication, high power densities, relatively large (analog) strain outputs, and very low DC power consumption. DEAs currently typically require a voltage in the kilovolt range to achieve large strain actuation. This high voltage is considered an acceptable drawback given the advantages brought by the DEA technology, including their extremely low DC power consumption. The required actuation voltages can be readily obtained using commercial DC-DC converters, with volumes of less than 2 cm 3 . Moreover, these voltages can be significantly reduced by the use of ultra-thin elastomer films (e.g., <5 lm thick). For instance, replacing a 40 lm thick membrane by a stack of ten 4 lm thick membranes decreases the actuation voltage by a factor of ten with no reduction in device performance. Lower driving voltages would greatly reduce the cost of the control electronics. The use of DEAs has seldom been investigated thus far for the development of RF concepts, and the presented device is the only available reconfigurable phase shifter based on this technology. Only basic antenna concepts using DEA reconfiguration have been demonstrated at L-band. 6,7 Nevertheless, these works do not exploit the analogue, very low-loss and large tuning range offered by DEAs, which can be very favorable at high frequency where other technologies can result in increased losses and complexity. In addition, a soft elastomeric membrane has been used as a flexible substrate in a reconfigurable phase shifter. 8 However, the elastomeric membrane is passive (i.e., does not provide any type of actuation), and actuation must be provided by external and off-the-shelf, electromagnetic actuators. a)
doi:10.1063/1.4862272 fatcat:c6tzbfb5ffclffvw4joljdykn4