A Novel Actuator Phasing Method for Ultrasonic De-icing of Aircraft Structures

Open Access
Borigo, Cody J
Graduate Program:
Engineering Science and Mechanics
Doctor of Philosophy
Document Type:
Date of Defense:
October 13, 2014
Committee Members:
  • Joseph Lawrence Rose, Dissertation Advisor
  • Joseph Lawrence Rose, Committee Chair
  • Clifford Jesse Lissenden Iii, Committee Member
  • Bernhard R Tittmann, Committee Member
  • Edward C Smith, Committee Member
  • de-icing
  • aircraft
  • ultrasound
  • ultrasonic
  • vibration
  • ice protection
  • anti-icing
  • phasing
  • piezoelectric
Aircraft icing is a critical concern for commercial and military rotorcraft and fixed-wing aircraft. In-flight icing can lead to dramatic decreases in lift and increases in drag that have caused more than a thousand deaths and hundreds of accidents over the past three decades alone. Current ice protection technologies have substantial drawbacks due to weight, power consumption, environmental concerns, or incompatibility with certain structures. In this research, an actuator phasing method for ultrasonic de-icing of aircraft structures was developed and tested using a series of finite element models, 3D scanning laser Doppler vibrometer measurements, and experimental de-icing tests on metallic and composite structures including plates and airfoils. An independent actuator analysis method was developed to allow for practical evaluation of many actuator phasing scenarios using a limited number of finite element models by properly calculating the phased stress fields and electromechanical impedance curves using a complex coupled impedance model. A genetic algorithm was utilized in conjunction with a series of finite element models to demonstrate that phase inversion, in which only in-phase and anti-phase signal components are applied to actuators, can be utilized with a small number of phasing combinations to achieve substantial improvements in de-icing system coverage. Finite element models of a 48”-long airfoil predicted that phase inversion with frequency sweeping can provide an improvement in the shear stress coverage levels of up to 90% compared to frequency sweeping alone. Experimental evaluation of the phasing approach on an icing grid showed a 189% improvement in de-icing coverage compared to frequency sweeping alone at comparable power levels. 3D scanning laser Doppler vibrometer measurements confirmed the increased variation in the surface vibration field induced by actuator phasing compared to unphased frequency sweeping. Additional contributions were made to facilitate actuator phasing and to advance the state-of-the-art in ultrasonic de-icing technology. These contributions include the development of improved frequency optimization, reduction in the size of the system hardware, and improvements in actuator bonding techniques. It was demonstrated that a dynamic frequency selection method is critical to effectively implementing the actuator phasing method. A miniaturized relay system was also designed and implemented to facilitate actuator phasing in conjunction with a phase splitter circuit and a single amplifier. An improved frequency tuning method was adopted and implemented in the de-icing system to eliminate the need for an impedance analyzer and to provide more accurate frequency selection by directly measuring the forward and reflected power between the amplifier and the de-icing actuators. Overall, it was demonstrated that this novel method can greatly improve the efficiency and effectiveness of the ultrasonic de-icing system by effectively redistributing the shear stress fields at the ice-structure interface, and that this method can be practically implemented in the de-icing system with an overall reduction in size and weight compared to previous versions of the technology.