Experiments on the Use of Fiber-Optic Strain Sensors in Active Structural Acoustic Control

Among the sensors available for active control of noise, strain sensors are of great interest as they can eliminate the need for far-field acoustic sensors, such as microphones. Fiber-optic strain sensors are especially of interest because they are easily embeddable into composite materials. This paper aims at a validation of the use of Fabry-Perot fiber-optic strain sensors in active structural control strategies. Two control approaches based on the direct use of discrete strain sensing are herein employed for the minimization of the acoustic radiation from a vibrating beam. The first approach involves the direct minimization of the strain levels at discrete points on the beam. The second cost function is defined as the radiated acoustic power; it involves the beam's displacement reconstruction from the strain field and is expressed in the wavenumber domain. Proper concentration of the control effort is expected with the cost function defined in the wavenumber domain but experimental constraints do not allow to demonstrate this clearly. The use of fiber-optic sensors is first validated for both control approaches with respect to an optimal solution and the impact of both approaches on radiated acoustic power is presented. It is shown that optimal and controller solutions agree well on a wide frequency band with the exception of some discrepancies arising from real-time approximations and fiber-optic reading unit limitations. The control mechanism of both approaches is then highlighted through experimental results combining acoustic and vibration measurements. Finally, the control performance obtained using the fiber-optic sensors is compared with the control performance obtained using PVDF strain sensors and it is shown that fiber-optic sensors offer a comparable performance.