Inkjet fabrication of spiral frequency-steerable acoustic transducers (FSATs)

Abstract

The frequency-based beam steering concept effectively supports Guided-Wave-based Structural Health Monitoring (SHM) by enabling directional waveguide inspection. This is implemented by acoustic transducers whose peculiar shapes provide different wavelength tuning in different directions. When these devices are used for guided wave (GW) sensing, spatial filtering of the propagating wavefield results in a prominent frequency component within the recorded signal spectrum, which can be uniquely associated with the direction of an incoming wave. A sensor geometry whose 2D spatial Fourier Transform produces a spiral-like distribution of maxima in the wavenumber domain allows for one-to-one frequency-angle correspondence in the [0 • , 180 • ] range. Prototypes of this wavenumber spiral frequency steerable acoustic transducer (WS-FSAT) have been fabricated by patterning the electrodes' shape on a metallized polyvinylidene fluoride (PVDF) substrate through inkjet printing. Prototype testing in various pitch-catch configurations demonstrates accurate 2D localization of acoustic sources and scattering events by processing a single output signal. Extremely easy, quick and inexpensive fabrication approach, along with very low hardware and computational requirements make the proposed FSAT an ideal candidate for a wide range of in-situ, low-cost and wireless SHM applications.

An Optimal Shaped Sensor Array Derivation

“…Although the experimental validation is beyond the scope of this paper, it is worth mentioning that the proposed cluster of shaped sensors can be realized by relying on different piezoelectric materials and manufacturing techniques, e.g., metallized PVDF (polyvinylidene fluoride) sheets can be used by shaping the electrodes on the upper surface with a laser cut as in [ 42 ]. Alternatively, the shaping strategy can be based on printing metallic electrodes on PVDF films to obtain the desired shape sensors as proposed in [ 43 ] or by using litographic procedures as in [ 44 ]. Screen printing was used also to realize shaped PZT transducers [ 45 ].…”

Predictive simulation of guide-wave structural health monitoring

“…We call these transducers piezoelectric wafer active sensors (PWAS) [10]. This approach has been successful in emulating the guided-wave NDE methods (pitch-catch, pulse-echo, phased array [10] [11] [12] [13] [14] [15] [16]) as well as in developing new techniques such as the electromechanical (E/M) impedance spectroscopy (EMIS) [17] [18] [19] [20].…”

Frequency Steerable Transducers for Ultrasonic Structural Health Monitoring

“…These devices, called Frequency steerable transducers (FSATs), will be reviewed in this paper and it will be shown how the electrode shapes design methodology could be adapted to remove the 180°degrees ambiguity which characterizes the first realizations of the frequency steering concepts [6], and how the concept could be extended to transmit and sense wide band signals.…”