Design of planar electrodes for multifunctional piezoelectric sensors

Acoustic ultrasound methods are at the core of many modern structural health monitoring methods and piezoelectric transducers are favored for this purpose due to their simplicity and functionality as both actuators and sensors. However, ongoing efforts to reduce impact on host structures while increasing resolution requires increasing the number of sensors and decreasing their size and weight. This compels us to re-evaluate the design of the transducers, to reduce their size and facilitate their integration into more complex functional systems like those typically used in the semiconductor industry. Numerous electrode designs have been developed over the years; however none are satisfactory for the task at hand. The piezoelectric transducers most commonly used in SHM simply have electrodes that fully cover the top and bottom surfaces; this requires wiring of two electrodes in two different planes which significantly complicates the fabrication process, design and realization, especially when using nanofabrication techniques. Other designs introduce significant signal directionality that may not be desirable in large networks or require excessive wiring which adds complexity and weight to the system. Creating new electrode patterns for the piezoelectric transducers that are planar, omni-directional, and scalable has become necessary. A feasibility study was conducted to develop a new nanofabrication compatible, multifunctional piezoelectric transducer design based on radially alternating, planar electrodes. Efficient integration of temperature sensors is complementary to the system and enables compensation of temperature effects in ultrasonic signals without additional sensors. Planar, radially alternating electrodes provide major advantages of: 1) significantly simplifying fabrication by reducing the number of layers; 2) eliminating out of plane features which eases manufacture using nanofabrication techniques and eliminates failure points; 3) allowing the overall networking and wiring to be thinner and thus less intrusive in a host structure; 4) reduced directionality compared to other designs; and 5) functional similarity to current designs allows for implementation with current SHM hardware and algorithms with minimal modification.