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Low-power wireless sensor nodes for ubiquitous long-term biomedical signal monitoring

In the past few years, the use of wireless sensor nodes for remote health care monitoring has been advocated as an attractive alternative to the traditional hospital-centric health care system from both the economic perspective and the patient comfort viewpoint. The semiconductor industry plays a crucial role in making the changes in the health care system a reality. User acceptance of remote health monitoring systems depends on their comfort level, among other factors. The comfort level directly translates to the form factor, which is ultimately defined by the battery size and system power consumption. This article introduces low-power wireless sensor nodes for biomedical applications that are capable of operating autonomously or on very small batteries. In particular, we take a closer look at component-level power optimizations for the radio and the digital signal processing core as well as the trade-off between radio power consumption and on-node processing. We also provide a system-level model for WSNs that helps in guiding the power optimization process with respect to various trade-offs.

Vacuum-packaged piezoelectric vibration energy harvesters: Damping contributions and autonomy for a wireless sensor system

This paper describes the characterization of thin-film MEMS vibration energy harvesters based on aluminum nitride as piezoelectric material. A record output power of 85 μW is measured. The parasitic-damping and the energy-harvesting performances of unpackaged and packaged devices are investigated. Vacuum and atmospheric pressure levels are considered for the packaged devices. When dealing with packaged devices, it is found that vacuum packaging is essential for maximizing the output power. Therefore, a wafer-scale vacuum package process is developed. The energy harvesters are used to power a small prototype (1 cm\3 volume) of a wireless autonomous sensor system. The average power consumption of the whole system is less than 10 μW, and it is continuously provided by the vibration energy harvester.

Shock induced energy harvesting with a MEMS harvester for automotive applications

In this work we report shock induced measurement and simulations on AlN based piezoelectric vibration energy harvesters. We compare the result with sinusoidal input vibrations, where we obtain a record power of 489 µW. The vacuum packaged harvesters have high quality factors and high sensitivity. We validate the potential of piezoelectric vibration harvesters for car tire applications by measurements and simulations.

Ultra low power wireless and energy harvesting technologies — An ideal combination

Rapid developments of energy harvesting in the past decade have significantly increased the efficiency of devices in converting ambient free energy into usable electrical energy, thus offering opportunities to design energy autonomous systems nowadays. To achieve such energy autonomous systems, a good understanding of the harvesting capability from the source side strongly motivates the design of ultra low power (ULP) systems. In this paper, we focus on wireless body area networks (WBAN) applications and show that ULP wireless is the key technology to enable wireless autonomous transducer solutions (WATS). We first show that the current energy harvesters cannot provide sufficient power for a typical wireless sensor node based on off-the-shelf components. We then point out that the wireless module is the main component whose power consumption needs to be significantly reduced. To address this problem, we present a ULP wireless module that could satisfy the typical performance requirement of WBAN. Using this ULP wireless module, we demonstrate the feasibility of energy autonomous sensor nodes (i.e. WATS) with the current energy harvesting technology. Moreover, with this ULP module, we point out some new research trends on the miniaturization and cost reduction of energy harvesters. Therefore, we conclude that ultra low power wireless system is an ideal application for energy harvesting.

First autonomous wireless sensor node powered by a vacuum-packaged piezoelectric MEMS energy harvester

This paper describes the experimental characterization of piezoelectric harvesters with different dimensions. We present a record level of generated power of 85 µW obtained from an unpacked device. We have developed a wafer-scale vacuum package which shows a 100–200 fold increase in power output compared with packaged devices under atmospheric pressure. A wireless sensor node was fully powered by a piezoelectric harvester. The average power consumption was less than 10 µW while it was operating at 15 seconds duty cycle.

Human++: wireless autonomous sensor technology for body area networks

Recent advances in ultra-low-power circuits and energy harvesters are making self-powered body wireless autonomous transducer solutions (WATS) a reality. Power optimization at the system and application level is crucial in achieving ultra-low-power consumption for the entire system. This paper deals with innovative WATS modeling techniques, and illustrates their impact on the case of autonomous wireless ElectroCardioGram monitoring. The results show the effectiveness of our power optimization approach for improving the WATS autonomy.

A MEMS vibration energy harvester for automotive applications

The objective of this work is to develop MEMS vibration energy harvesters for tire pressure monitoring systems (TPMS), they can be located on the rim or on the inner-liner of the car tire. Nowadays TPMS modules are powered by batteries with a limited lifetime. A large effort is ongoing to replace batteries with small and long lasting power sources like energy harvesters [1]. The operation principle of vibration harvesters is mechanical resonance of a seismic mass, where mechanical energy is converted into electrical energy. In general, vibration energy harvesters are of specific interest for machine environments where random noise or repetitive shock vibrations are present. In this work we present the results for MEMS based vibration energy harvesting for applying on the rim or inner-liner. The vibrations on the rim correspond to random noise. A vibration energy harvester can be described as an under damped mass-spring system acting like a mechanical band-pass filter, and will resonate at its natural frequency [2]. At 0.01 g2/Hz noise amplitude the average power can reach the level that is required to power a simple wireless sensor node, approximately 10 μW [3]. The dominant vibrations on the inner-liner consist mainly of repetitive high amplitude shocks. With a shock, the seismic mass is displaced, after which the mass will “ring-down” at its natural resonance frequency. During the ring-down period, part of the mechanical energy is harvested. On the inner-liner of the tire repetitive (one per rotation) high amplitude (few hundred g) shocks occur. The harvester enables an average power of a few tens of μW [4], sufficient to power a more sophisticated wireless sensor node that can measure additional tire-parameters besides pressure. In this work we characterized MEMS vibration energy harvesters for noise and shock excitation. We validated their potential for TPMS modules by measurements and simulation.

Improving energy-efficiency in building automation with event-driven radio

Sensor, actuator, and radio constitute the three basic components in a building automation system. Among all the three, radio consumes a significant part of the total power. In this paper, an ultra-low power event-driven radio is proposed as a solution to minimize the power consumption of a building automation system. Generic system architecture is formalized according to the application scenario. Event-driven radio is compared against other commercial low power radios. Our analysis shows that significant energy efficiency enhancement is achieved by an event-driven radio. Based on the state of the art micro power technology, possibility of implementing autonomous radio is also investigated in the building automation scenario.

Human++: Key Challenges and Trade-offs in Embedded System Design for Personal Health Care (Abstract)

The cost of health care in first-world countries is increasing dramatically as a result of advances in medicine, a population that is becoming older and an increasingly unhealthy lifestyle. Personal health care concepts where sensors within and around the body monitor and measure all kind of physiological signals can be an addition to medicare with high benefits. This concept allows patients to stay in their home environment and hence have a better quality of life with lower costs involved. For these reasons research and development is ongoing on many body worn and implantable sensor nodes. In this paper it is shown that application knowledge and understanding the contribution of different components to the system power consumption is the best starting point to make optimal trade-offs in the system design. This will minimize the overall power consumption of a sensor node without losing track of the major functionality needed. Besides the importance of system optimization, it is also shown that new components and circuit techniques need to be developed to achieve orders of magnitude increase in energy efficiency. This is a must to realize ultra-thin electrocardiogram patches as well as more demanding nodes with a small form factor like real-time Electro Encephalogram processing for brain computer interaction or neuro-implants.

Ultra Low-Power Wireless Body-Area Sensor Networks

In wireless body area network (WBAN) applications, wireless sensors are used to collect, monitor and transmit vital signs and other medical information. In such scenarios, it is critical to maximize the autonomy, while satisfying application performance. A unique platform for introduction of such ultra-low power technology components is an electrocardiography (ECG) patch for BAN applications, and is taken in this work as an example to illustrate the development of an ultra low-power transceiver.