A highly miniaturized wireless inertial sensor using a novel 3D flexible circuit

Abstract

PurposeTo develop a highly miniaturized wireless inertial sensor system based on a novel 3D packaging technique using a flexible printed circuit. The device is very suitable for wearable applications in which small size and light weight are required such as body area networks for medical, sports and entertainment applications. Design/methodology/approachModern wireless inertial measurement units are typically implemented on a rigid 2D printed circuit board (PCB). The design concept presented here is based around the use of a novel planar, 6-faceted, crucifix or cross-shaped flexible printed circuit (FPC) instead of a rigid PCB. A number of specific functional blocks (such as MEMs gyroscope and accelerometer sensors, microcontroller (MCU), radio transceiver, antenna etc) are first assigned to each of the 6 faces which are each 1cm squared in area. The FPC cross is then developed into a 1cm cubed, 3D configuration by folding the cross at each of 5 bend planes. The result is a low-volume and lightweight, 1.5 cm cubed wireless inertial sensor that can sense and send motion sensed data wirelessly to a base station. The wireless sensor device has been designed for low power operation both at the hardware and software levels. At the base station side, a radio receiver is connected to another MCU unit, which sends received data to a PC and 2 graphical user interface (GUI). The Industrial, Scientific and Medical (ISM) band (2.45GHz) was used to achieve half duplex communication between the two sides. FindingsA complete wireless sensor system has been realized in a 3D cube form factor using a flexible printed circuit. The packaging technique employed during the work was shown to be efficient in fabricating the final cubic system and resulted in a significant saving in the final size and weight of the system. A number of design issues were identified regarding the use of flexible printed circuit for implementing the 3D structure and the chosen solutions were shown to be successful in dealing with these issues. Research limitations/implicationsCurrently, a limitation of the system is the need for an external battery to power the sensor system. A second phase of development would be required to investigate the possibility of the integration of a battery and charging system within the cube structure. In addition, the use of flexible substrate imposes a number of restrictions in terms of the ease of manufacturability of the final system due to the requirement of the required folding step. Practical implicationsThe small size and weight of the developed system was found to be extremely useful in different deployments. It would be useful to further explore the system performance in different application scenarios such as wearable motion tracking applications. In terms of manufacturability, component placement needs to be carefully considered, ensuring that there is sufficient distance between the 3 components, bend planes and board edges and this leads to a slightly reduced usable area on the printed circuit. Originalit...

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“…Recently, wireless sensor networks (WSNs) have been attracting more and more attention for application to medicine, security and safety, logistics, energy management, structure monitoring, agriculture, and more [1][2][3][4][5][6][7][8]. A novel circuit technology has also been developed for WSNs [9,10]. In a WSN, a reasonably large number of wireless sensor nodes are deployed and environmental data such as temperature, humidity, acceleration, pressure and power are collected.…”