In this paper, the feasibility of an active vibration control scheme using Fiber Bragg Grating (FBG) sensors and
piezoelectric (PZT) actuators for vibration suppression of an aluminum plate is investigated. Four FBGs have been
bonded to the structure below the same number of PZT actuators in co-located configuration. A Proportional-Derivative
controller has been used to generate the command signals required to drive the actuators. Preliminary results from
"closed loop" configuration tests are reported showing up to 17 dB of noise reduction at 80 Hz.
Magnetoelastic materials used as sensors are obtaining an increasing interest in the last few years. The magnetoelastic wave resonance frequency is the sensitive parameter generally measured to obtain key information on the magnetoelastic material; nevertheless, it was shown that also the amplitude of the magnetoelastic wave, stimulated at a frequency close to the sensor core resonance frequency (pseudo-resonance), is very sensitive to measure magnetic fields. By basing on that characteristic, both parameters, "pseudo-resonance" amplitude and resonance frequency, could be used as the "sensitive parameter" in no-contact vibration sensors or stress, flux and magnetic field sensors.
In a previous paper the authors proposed a signal condition technique for magnetoelastic elements, and used it for no-contact vibration and displacement measurements. The measurements, even though had a good linearity and low distortion, comparable to that of traditional devices (LVDT or accelerometer), had a too poor repeatability, due to a time-varying behavior of the sensor magnetoelastic core.
This paper proposes an On-Line self-Calibration technique for magnetoelastic sensors, OLC, that solves the repeatability problem by improving the sensor accuracy of about one order of magnitude. No external reference sensor is used, but just an easy to obtain reference stimulus. A tuning procedure is then shown, able to put the sensor into a repeatable, time-invariant status, by acting on a static polarization magnetic field. Finally, the proposed technique is applied for no-contact vibration measurements. Results are presented, comparing them with the case of no OLC applied.
Magnetoelastic materials are obtaining an increasing interest in the last few years. Magnetoelastic wave resonant frequency is the sensory parameter generally used to reliably obtain critical information, nevertheless, it was shown that wave amplitude also is very sensitive to measure displacements or magnetic fields. Both parameters, amplitude and resonance frequency could be used as the 'sensitive parameter' in no- contact vibration sensors or stress, flux or magnetic field sensors. To make them advantageous to be used, some problems should be solved: the excitation problem (to induce resonance) and the conversion problem (to transduce frequency or amplitude information into a convenient electric signal); in other words, the signal conditioning problem. The paper describes a signal conditioning technique for magnetoelastic sensors developed by using metallic glass materials. Analysis and synthesis phases of design for the signal-conditioning prototype are presented. From the frequency response analysis of a magnetoelastic metallic glass ribbon, a very low damping factor is pointed out. This means that a stationary oscillation could be easily induced into the ribbon and it was seen that the oscillation frequency changed when the boundary conditions (mechanical stress or magnetic field) changed. So, the ribbon can be used as a sensor. The proposed device (PLG 3) for the sensor signal conditioning is described in detail. Finally, PLG 3 plus a magnetoelastic sensor is used for a no contact vibration measurement and compared to the results from traditional tools.
Sound radiation is not only matter of comfort, but also of people's exposure noise limits. Public demand about the life quality is leading to produce laws and standards able to preserve people's health. The authors have been working for a long time in the field of Smart Structures, with the development of different hardware systems devoted to the characterization of implemented active devices and to their guidance. On the basis of what developed in the phase 1 of the research, a feed-forward controller has been developed, aimed at reducing the vibration field of, or the sound radiated by, generic elastic structures. Piezo-ceramic patches are used as actuators and accelerometers as sensors, so avoiding the use of microphones. In the specific case, a thin-walled beam has been referred to as representative of complex elements in general architectures and single tone excitations have been investigated. Key features of the controller: its capability in identifying the disturbance and following its frequency and amplitude variations; the frequency independence of the 90° phase shifter analog section. The application here presented deals with the band around 100 Hz, specifically interesting for human annoyance problems, a range where passive noise reduction systems are ineffective.