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The key challenges of local sensor networks are in supporting high sensor density, information security, physical size, and especially energy efficiency at a level that could eliminate the need for batteries or external power supplies. This article presents a novel scheme that answers all issues at the cost of minor information losses in low data rate applications that tolerate latency. Experimental verification is made using a sensor node implemented on a flexible electronics platform. Lightly encrypted data are transmitted by embedding it into Bluetooth advertising packets, contributing to ultralow-energy wireless power consumption, and theoretically enabling an unlimited number of nodes in the local network. In the experiments, the energy dissipation per transmitted 14-B information packet varied between 19.83 and 105.93 mu text{W} depending on the system configuration, while the data loss rates ranged from 7.4% to 0.004%, respectively. As the flexible substrate can be attached to various surfaces, the applications extend from wearable to industrial condition monitoring devices.

This paper presents an introduction and overview of wireless sensors in IoT applications. A typical sensor architecture is described from sensor to the cloud. Four distinct methods of achieving power autonomy are developed. These are battery powered short lifetime devices, energy harvester powered devices for indefinite operation, inductively coupled wireless powered devices for short distances and devices based on passive radio back scattering. Four concrete technical examples of whole system solutions, each exploiting one of the mentioned powering strategies are presented.

Industrial internet will improve process control and increase efficiency to maximize industrial output. Key enabling technologies include low-power wireless communication, energy harvesting power autonomous devices along with the latest in sensing devices. This paper presents a wireless sensing system developed for the key industrial application of condition monitoring, specifically; valve leakage detection. The system integrates advances in all of the three aforementioned topics. A novel MEMS-based acoustic emission sensor is described to detect valve leakage manifested as vibrations in certain frequency bands. An in-house developed ultra-low power wake up radio technology, which enables the deployment of this sensor, will be presented. Two energy-harvesting systems: thermal harvesting in the sensor node and an industrial current loop harvester for the base station are developed. Integration and piloting of this system is described and evaluation results presented. The system presented offers a repeatable and adaptable sensor system deployed for valve leakage detection in an ATEX industrial environment.

The zero power sensor network represents a platform that enables fully passive wireless sensing based on the third order intermodulation principle. This work describes the development and evaluation of a zero power reader device. Results from the initial characterization are presented for the evaluation of the reader's performance in sensor readout at a distance of 5 m. The limitations affecting the readout range are investigated and highlighted to be based on the reader's self-intermodulation.