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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The detection of single binding has been a recent trend in sensor research introducing various sensor designs where the active sensing elements are nanoscopic in size. Currently, transport and collection of airborne analytes for gas sensors is either diffusion based or non-localized and it becomes increasingly unlikely for analytes to interact with sensing structures where the active area is shrunk, trading an increased sensitivity with a slow response time. This report introduces a corona discharge based analyte charging method and an electrodynamic nanolens based analyte concentration concept to effectively transport airborne analytes to sensing points to improve the response time of existing gas sensor designs. Localized collection of analytes over a wide range, including microscopic particles, nanoparticles, and small molecules, is demonstrated. In all cases, the collection rate is several orders of magnitudes higher than in the case where the collection is driven by diffusion. The collection scheme is integrated on an existing SERS (surfaceenhanced Raman spectroscopy) based sensor. In terms of response time, the process is able to detect analytes at 9 ppm (parts per million) within 1 s. As a comparison, 1 h is required to reach the same signal level when diffusion-only-transport is used.

To match the properties of a semiconductor to a desired application, it is crucial to control its crystal structure. Here, we show that, by implementing a corona discharge in a chemical vapor deposition process, the growth morphology of gallium oxide can be adjusted to produce nanowires and layerlike and columnar crystal structures. The three morphologies can be explained by the transition from a classic chemical vapor process to a corona-assisted chemical vapor process with directed transport. Specifically, the excitation of the carrier gas by the corona discharge is exploited as a switch to transition from a vapor–liquid–solid nanowire growth mechanism to a layer by layer growth mechanism. The second switching parameter is the substrate bias which affects the directed precursor transport and enhances the growth rate. While the switching of the morphology has no effect on the crystal phase, the photoluminescence properties of the three morphologies are different. The grown structures are used as optical gas sensors at room temperature. Tin-doped gallium oxide is shown to be capable of detecting trace amounts (200 ppm) of alcohols such as acetone, ethanol, and isopropanol. The layerlike morphology provides the highest response.