Alexis Boegli

Power supply energy optimization for ultra low-power wireless sensor nodes

The wireless sensor nodes are most energy-efficient when they operate at the minimal operating voltage. The nominal voltage of the batteries used is often significantly higher. This paper analyzes DC-DC power conversion from the point of view of ultra low-power wireless sensor nodes. Using a modified circuit of a suitable commercial DC-DC converter and a supercapacitor, this paper shows that it is possible to extend battery lifetime of a wireless sensor node for certain spectrum of applications. The efficiency of the DC-DC conversion as well as supercapacitor charge-discharge efficiency have been analyzed and measured. The influence of battery discharge currents and leakage currents is also presented. Furthermore, in this paper, we outline the specifications of a module needed between the battery and the sensor node that will be controlled by the nodes MCU and will keep the node operating at minimal operational voltage while at the same time maximizing the energy delivered from the battery to the node. Thus, this paper also aims at setting foundations for future development of an energy-optimization module for ultra low power wireless sensor nodes.

Robust ultra low power Wireless Sensor platform with embedded over-molded antenna

In this paper a new wireless sensor node intended for use in ultra-low power Wireless Sensor Networks (WSN) is presented. The node uses commercial of-the-shelf radio, microcontroller and a custom developed antenna embedded in the housing. Over-molding with food-compatible material is used to improve the mechanical robustness of the node. The present work is targeted at commercial food cold chain management and temperature monitoring applications. The node presented operates in the license-free European and US sub-GHz Industrial, Scientific and Medical (ISM) band. The paper provides an insight into the platforms hardware giving the results of the test measurements. Results obtained from a demo network are also shown including the first results from long-term battery lifetime measurements.

Firmware for ensuring realtime radio regulations compliance in WSN

All wireless devices must comply with the local radio regulations which are set by international and national regulatory bodies such as the European Telecommunication Standardization Institute (ETSI) for Europe and the Federal Commission for Communication (FCC) for US. In this paper a new firmware module is proposed, that will ensure that devices, in all circumstances will comply with the ETSI regulations for single channel emissions in the 868MHz ISM band. Namely, assuring compliance with the duty-cycle limit, the maximum Tx time and minimum Tx-off time limit. Such a solution has not been researched mostly due to the popularity of the virtually world-wide 2.4 GHz ISM band which at present does not impose duty-cycle limitations. The wireless sensor networks (WSNs) operating in the 868MHz band have their own niche applications that benefit from the increased signal range. The development and the acceptance of such applications will benefit from the existence of the proposed module implemented in firmware/software. We propose such a solution and demonstrate its implementation on a custom developed node and protocol. Implementation with IEEE 802.15.4 standard is discussed as well. We also analyze the memory, time and energy overheads caused by including the module in the firmware.

Design of an integrated thermoelectric generator power converter for ultra-low power and low voltage body energy harvesters aimed at ExG active electrodes

This paper describes a detailed design procedure for an efficient thermal body energy harvesting integrated power converter. The procedure is based on the examination of power loss and power transfer in a converter for a self-powered medical device. The efficiency limit for the system is derived and the converter is optimized for the worst case scenario. All optimum system parameters are calculated respecting the transducer constraints and the application form factor. Circuit blocks including pulse generators are implemented based on the system specifications and optimized converter working frequency. At this working condition, it has been demonstrated that the wide area capacitor of the voltage doubler, which provides high voltage switch gating, can be eliminated at the expense of wider switches. With this method, measurements show that 54% efficiency is achieved for just a 20 mV transducer output voltage and 30% of the chip area is saved. The entire electronic board can fit in one EEG or ECG electrode, and the electronic system can convert the electrode to an active electrode.

Phase and frequency self-configurable efficient low voltage harvester for zero power wearable devices

This paper describes a converter which configures itself to increase power transfer and decrease losses. The system controls its three timing variables by three loops in a stable manner. A time domain state-space averaging model is used to design the system. This reduces the necessary components, and therefore the power consumption. The system is implemented in 0.18 μm CMOS technology with ultra-low power circuits. The converter has a 52% efficiency with just a 15 mV input voltage. It follows changes in electrical specifications of a harvester, in order to increase the systems output power.

Design of an Integrated Thermoelectric Generator Power Converter for Ultra-Low Power and Low Voltage Body Energy Harvesters aimed at EEG/ECG Active Electrodes

This paper describes a design procedure for an efficient body thermal energy harvesting integrated power converter. This procedure is based on loss examination for a self-powered medical device. All optimum system parameters are calculated respecting the transducer constraints and the application form factor. It is found that it is possible to optimize converters working frequency with proper design of its pulse generator circuit. At selected frequency, it has been demonstrated that wide area voltage doubler can be eliminated at the expense of wider switches. With this method, more than 60% efficiency is achieved in simulation for just 20mV transducer output voltage and 30% of entire chip area is saved.