Mechanical structures for smart-phone enabled sensing

The paper presents a new strategy for sensor design that is made possible by the usage of ubiquitous mobile devices for signal capture, digitization, and data processing. The approach taken is to design simple mechanical sensor elements such that they produce a sensor output that is easily acquired by a mobile smart device such as a phone or tablet computer. To illustrate this concept, two mechanical displacement transducers have been designed and tested. These sensors make use of displacement amplification structures, Moiré pattern gratings and a double-ended-tuning-fork (DETF) resonant structure. The sensors produced either an acoustic or optical signal in response to an input load or displacement, which can then be acquired using the camera or microphone of a mobile device. The computing power and connectivity of mobile devices makes a wide range of processing, visualisation and storage techniques possible at low cost. Using this technique an optical displacement transducer with a range of 150 µm, and a resolution of <5 µm; and an acoustic displacement transducer with a range of 20 µm and a standard error of 0.14 µm, are demonstrated.