3D Metamorphic Stretchable Microphone Arrays

Abstract

and form factor. To the best of our knowledge, a metamorphic microphone array has not been reported. Within the field of metamorphic electronics, two fabrication strategies are commonly used. The first uses electronic devices in combination with a bendable carrier and bendable interconnects. Here origami- [2] and kirigami [3] like methods are used to fold the structure into a desired shape. The topological complexity dictates the number of folds that are required and certain topologies, for example, a sphere, and are difficult to fabricate. The microphone arrays discussed in this communication morph from a (i) concave to a (ii) planar to a (iii) convex and a (iv) cone-like topology, which would be very difficult to achieve using the origami/kirigami approach.An alternative to the origami-inspired method is to build on recent advancements in the field of stretchable electronics. Stretchable electronics incorporates electronic functions (in our case, microphones and other active and passive devices) inside or on top of a stretchable elastomeric membrane. One essential element is the requirement of stretchable electrical interconnects between the device elements. Different interconnect solutions are known today. Most of the solutions go back to the original work by Lacour, [4] Chen, [5] and Whitesides [6] and their respective co-workers who reported (i) metallization layers with topological wrinkles, [4] (ii) meander or horse-shoe designs, [5] and (iii) liquid metals, [6] as the stretchable interconnecting metal layers, respectively. A large set of applications have been demonstrated, which include smart clothing, [7] conformable photo voltaics, [8] optoelectronics, [9] digital cameras, [10] artificial electronic skins, [11] stretchable batteries, [12] robotics, [13] and mechanically soft and conformable health-monitoring devices [14] to give a few recent examples. However, considering the current state of the art, the number of interconnects to the isolated device elements has been small (2-4 connections per device), and the total number of devices continues to be limited (5-22 devices). [15] This points to scaling and robustness challenges.As a result, the desired microphone array has been difficult to fabricate using the reported methods. The array has a total number of 60 interconnects, contains 5 different device types, and a total of 25 commercially available surface mount devices (SMDs). This goes beyond the metrics previously reported in the field of stretchable electronics.This article describes the realization of a metamorphic microphone array. The array morphs from a concave to a planar and then to a convex shape. The morphing array enables a better (12×) sound source localization when compared to existing static and planar arrangements. To enable the realization, a novel stretchable (elongated up to 320% of the original length) printed circuit board fabrication process is reported. The fabrication process enables high-temperature processing, alignment, and registration. Moreover, conventional and otherw...

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