Ultra-low Power Wireless Sensor Research Articles

Dynamic Voltage and Frequency Scaling and Duty-Cycling for Ultra Low-Power Wireless Sensor Nodes

Energy efficiency presents a significant challenge to the reliability of Internet of Things (IoT) services. Wireless Sensor Networks (WSNs) present as an elementary technology of IoT, which has limited resources. Appropriate energy management techniques can perform increasing energy efficiency under variable workload conditions. Therefore, this paper aims to experimentally implement a hybrid energy management solution, combining Dynamic Voltage and Frequency Scaling (DVFS) and Duty-Cycling. The DVFS technique is implemented as an effective power management scheme to optimize the operating conditions during data processing. Moreover, the duty-cycling method is applied to reduce the energy consumption of the transceiver. Hardware optimization is performed by selecting the low-power microcontroller, MSP430, using experimental estimation and characterization. Another contribution is evaluating the energy-saving design by defining the normalized power as a metric to measure the consumed power of the proposed model per throughput. Extensive simulations and real-world implementations indicate that normalized power can be significantly reduced while sustaining performance levels in high-data IoT use cases.

Vortex-induced piezoelectric cantilever beam vibration for ocean wave energy harvesting via airflow from the orifice of oscillation water column chamber

Micro piezoelectric generators have attracted immense interest to convert mechanical vibrations into electric energy for ultralow power wireless sensors. Herein, an ocean wave vortex-induced vibration piezoelectric energy harvester(Wavee-VIVPEH) is proposed to extract wave energy. The renewable and sustainable ocean environment energy harvesting device consists of an oscillating water column(OWC) air chamber, wind tunnel, and piezoelectric energy converter. A fixed bluff body in the vent tunnel induces airflow vortexes and excites the piezoelectric cantilever vibration converting up the ultralow frequency of ocean waves. The novel Wave-VIVPEH is a complex multi-physics system requiring feasible methodologies to enhance its performance. The theoretical models are derived to systematically investigate and optimize the operation. The flume and wind tunnel experiments and the related fluid-solid electric coupling simulations are carried out to verify the concept's feasibility. The aerodynamic kinetic performance in the OWC chamber is characterized by the models. The instantaneous maximum exhalation airspeed reaches 16.55 m/s with the air pressure of 349.97 Pa and the wave period of T = 2.5 s. In this wave condition, the results are well agreed with the simulation values of wind speed of 17.96 m/s, and air pressure of 382.55 Pa. The output power characteristics of the piezoelectric energy harvester are analyzed for the distance of the vortex wake between the piezoelectric cantilever beam and the bluff body. With the bluff body diameter of 25 mm and distance of d/dD= 4, the theoretical results on the maximum peak voltage and output power are 10.46 V, 3.26 mW agree with the simulation optimized values of the maximum peak voltage of 10.85 V and the output power of 3.55 mW. When the wind speed is 15 m/s, the theoretical voltage of 8.62 V approaches the experimental result of 8.47 V. Especially, the comparisons of the theoretical power and voltage to experimental and simulational results indicate that the ingenious Wave-VIVPEH has great potential in ocean wave energy harvesting applications to supply power for intelligent buoys.

Ultra-Low Power Wireless Sensor Networks Based on Time Slotted Channel Hopping with Probabilistic Blacklisting

Devices in wireless sensor networks are typically powered by batteries, which must last as long as possible to reduce both the total cost of ownership and potentially pollutant wastes when disposed of. By lowering the duty cycle to the bare minimum, time slotted channel hopping manages to achieve very low power consumption, which makes it a very interesting option for saving energy, e.g., at the perception layer of the Internet of Things. In this paper, a mechanism based on probabilistic blacklisting is proposed for such networks, which permits to lower power consumption further. In particular, channels suffering from non-negligible disturbance may be skipped based on the perceived quality of communication so as to increase reliability and decrease the likelihood that retransmissions have to be performed. The only downside of this approach is that the transmission latency may grow, but this is mostly irrelevant for systems where the sampling rates are low enough.

Physically Flexible Ultralow-Power Wireless Sensor

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 is transmitted by embedding it into Bluetooth advertising packets, contributing to ultra-low-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 bytes information packet varied between 19.83 μW and 105.93 μW 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.

A Fully Integrated Programmable 6.0–8.5-GHz UWB IR Transmitter Front-End for Energy-Harvesting Devices

Ultra-wideband impulse radio transceivers are becoming a key building block for establishing ultralow power wireless sensor networks. However, impulse radio transmitters commonly suffer from a low spectral quality and a coarse frequency tuning resolution, which limits their global applicability. In this article, we present a fully integrated ultralow power impulse radio transmitter front-end (TFE) whose pulse shaping capabilities and integrated output matching network make it globally applicable up to a 4-MHz pulse repetition rate. We demonstrate a digital carrier frequency-tuning method that achieves a 28-MHz resolution over the frequency band of 6.0–8.5 GHz. In addition, we show that the temperature dependence of the TFE’s carrier frequency can be compensated digitally over the industrial temperature range from −40°C to 85 °C. The proposed TFE supports energy-harvesting applications particularly well due to its low leakage power level of 380 nW and a high tolerance to power supply transients during pulse generation. It is demonstrated to operate robustly with low-drive regulators powered by low-quality sources. The TFE is fabricated in a 65-nm CMOS process. It generates 1.8-pJ pulses at a 7.5-GHz carrier frequency while consuming 63 pJ per pulse, corresponding to 2.3% efficiency.

Simulation and experiment on bridge-shaped nonlinear piezoelectric vibration energy harvester

There is abundant of vibration energy in environment. Using piezoelectric energy harvesters to power ultra-low power wireless sensors has become a hot topic in recent years. Most piezoelectric energy harvesters have satisfactory output only at one resonant frequency, while once the external excitation frequency deviates from the resonant frequency, the voltage output will drop significantly. Therefore, this paper proposes a bridge-shaped piezoelectric energy harvester to broaden the frequency band for energy harvesting, and the harvester can adaptively adjust the natural frequency of the system to match the external excitation. Based on the two-dimensional nonlinear Euler–Bernoulli beam hypothesis and the Hamilton principle, the distributed-parameter dynamic model of the nonlinear energy harvesting system is set up. By use of variation operator and nondimensionalization, we derive the dimensionless electromechanical coupling equations. With the harmonic balance method, the approximate equations for calculating voltage amplitude and average power are derived. And then the model is numerically solved and analyzed by considering the influence of excitation frequency, excitation amplitude, mass position and load on the output performance of the bridge-type piezoelectric energy harvester. Finally, various comprehensive experiments are performed to verify the results of simulation, and the dynamic effects of the moving mass on the output characteristics are studied. It can be noted that the moving mass can improve the voltage output of the bridge type energy harvester by changing the resonant frequency of the bridge-type piezoelectric energy harvester and impacting the piezoelectric beam. The proposed vibration energy collection device can adaptively tune the resonant frequency and has practical value in engineering.

Predictive Maintenance of Induction Motors Using Ultra-Low Power Wireless Sensors and Compressed Recurrent Neural Networks

In real-world applications - to minimize the impact of failures - machinery is often monitored by various sensors. Their role comes down to acquiring data and sending it to a more powerful entity, such as an embedded computer or cloud server. There have been attempts to reduce the computational effort related to data processing in order to use edge computing for predictive maintenance. The aim of this paper is to push the boundaries even further by proposing a novel architecture, in which processing is moved to the sensors themselves thanks to decrease of computational complexity given by the usage of compressed recurrent neural networks. A sensor processes data locally, and then wirelessly sends only a single packet with the probability that the machine is working incorrectly. We show that local processing of the data on ultra-low power wireless sensors gives comparable outcomes in terms of accuracy but much better results in terms of energy consumption that transferring of the raw data. The proposed ultra-low power hardware and firmware architecture makes it possible to use sensors powered by harvested energy while maintaining high confidentiality levels of the failure prediction previously offered by more powerful mains-powered computational platforms.

BATS: Adaptive Ultra Low Power Sensor Network for Animal Tracking.

In this paper, the BATS project is presented, which aims to track the behavior of bats via an ultra-low power wireless sensor network. An overview about the whole project and its parts like sensor node design, tracking grid and software infrastructure is given and the evaluation of the project is shown. The BATS project includes a lightweight sensor node that is attached to bats and combines multiple features. Communication among sensor nodes allows tracking of bat encounters. Flight trajectories of individual tagged bats can be recorded at high spatial and temporal resolution by a ground node grid. To increase the communication range, the BATS project implemented a long-range telemetry system to still receive sensor data outside the standard ground node network. The whole system is designed with the common goal of ultra-low energy consumption while still maintaining optimal measurement results. To this end, the system is designed in a flexible way and is able to adapt its functionality according to the current situation. In this way, it uses the energy available on the sensor node as efficient as possible.

An experimental study of ultra-low power wireless sensor-based autonomous energy harvesting system

Technological advances for low power consumption and flexible electronics have spurred research on energy harvesting. In this paper, an innovative methodology is proposed to power an ultra-low power wireless sensor node (milliwatt level) autonomously by using a piezoceramic patch which is bonded to a low-frequency vibrating beam. An LTC3588 based energy harvesting module was developed to transfer and collect the energy efficiently. Through a switching interface between the energy harvesting module and the wireless sensor, a 0.33F supercapacitor was charged for 12 h by the harvested vibrational energy to allow the wireless sensor node to join the network and transmit data packets. It was experimentally demonstrated that this applied switching interface could effectively provide on-off control to the power of the wireless sensor node. In order to allow this function, the supercapacitor worked alternatively in the charging mode and the discharging mode. When the supercapacitor stored enough harvested energy, the wireless sensor node initiated the effort to join the wireless network automatically and then sent data packets to the network manager which was connected to a monitoring computer. In addition, wireless sensors which were powered by the energy harvesting system could also send or receive data packets in the network. The developed piezoceramic based energy harvesting method has the potential to be used in structural health monitoring systems by harvesting the ambient mechanical energy.

A Power Processing Circuit for Indoor Wi-Fi Energy Harvesting for Ultra-Low Power Wireless Sensors

This article proposes a complete power processing circuit for an indoor 2.45 GHz Wi-Fi energy harvesting system. The proposed power processing circuit works by using power harvested from indoor Wi-Fi transmitters. The overall system of this work is simplified as an equivalent circuit and analyzed mathematically. A two-port network is analyzed in formulating the relevant equations of the equivalent circuit. The importance of matching the impedance of a harvesting antenna to the rectifier circuit is highlighted by using simulation analysis, and it is shown that the impedance matching for both components has satisfied the conditions for a high sensitivity circuit and radio frequency-to-direct current (RF-to-DC) power conversion. Actual experiments showed that the proposed power processing circuit could operate with an incident power as low as −50 dBm. It has been found that the proposed harvesting system stored 0.11 J in a 200 mF supercapacitor as the storage device in 20 hours of the experimentation periods. Moreover, actual results for the overall energy harvesting system is compared with previous research, and it has been found that the proposed system has advantages over the listed works.

A 2.4 GHz Interferer-Resilient Wake-Up Receiver Using A Dual-IF Multi-Stage N-Path Architecture

A 2.4 GHz interferer-resilient wake-up receiver for ultra-low power wireless sensor nodes uses an uncertain-IF dual-conversion topology, combining a distributed multi-stage N-path filtering technique with an unlocked low-Q resonator-referred local oscillator. This structure provides narrow-band selectivity and strong immunity against interferers, while avoiding expensive external resonant components such as BAW resonators or crystals. The 65 nm CMOS receiver prototype provides a sensitivity of −97 dBm and a carrier-to-interferer ratio better than −27 dB at 5 MHz offset, for a data rate of 10 kb/s at a 10−3 bit error rate, while consuming 99 $\mu \text{W}$ from a 0.5 V voltage supply under continuous operation.

Enerji verimli ve düşük maliyetli sensör ağlarının ISM bandı FSK alıcı vericiyle tasarlanması

Safe wireless link and long battery life are indispensable feature for a portable and outdoor used device with build-in sensors. For this purpose, duty cycling, ultra-low power electronics design, dynamic power management, wireless network architecture and medium access control concepts in the design are explained in detailed. In this work, an ultra-low power wireless sensor network is designed with 4cmx4cm size and light weight nodes sending once every three minutes 115.2 kbps 5 byte package that have up to 131.25 year battery life time in theory with 3V (2x1.5V) 1000mAh battery. 868 and 915 MHz programmable 115.2 kbps ISM band FSK RF transceiver with a low power wake-up scheme is utilized for low cost unlicensed-used wireless sensor networks designed with Back Inverted F Antennas with 100m communication range for outdoor applications and 25m for indoor applications. Sensor node requires 0.5 uA, 2.5 mA, 0.8 uA, 14.6 mA and 25mA during sleep, measurement, sniff, receive and transmit mode respectively @ 868 MHz with 3V battery. The sensors has temperature compensation feature with -40-85 °C working range.

Unifying energy harvesting, sensing, and communication for ultra-low power structure health monitoring

A new ultra-low power (ULP) wireless sensor network (WSN) is proposed to monitor the vibration properties of critical structures such as buildings, bridges, and the wings and bodies of aircrafts. The new scheme integrates energy harvesting, data sensing, and wireless communication into a unified process, and it is fundamentally different from all the existing WSNs. In the new WSN, self-powered sensors are employed to harvest vibration energy and measure vibration intensity simultaneously, by utilizing the fact that the harvested energy accumulated through time is proportional to the vibration amplitude and frequency. Once the harvested energy reaches a threshold, it is released as an impulse with a wireless transmitter. An estimate of the structure vibration intensity can then be obtained by measuring the number of binary impulses in a unit time. Such an approach does not require complicated analog-to-digital conversion or signal processing, and it can achieve an ULP performance unrivaled by existing technologies. Optimum and sub-optimum impulse density estimation algorithms are proposed to take advantage of the spatial correlation among signals from the sensors. Analytical and simulation results demonstrate that the proposed scheme can efficiently operate at a low signal-to-noise ratio (SNR).

A Sub-nW Multi-stage Temperature Compensated Timer for Ultra-Low-Power Sensor Nodes

Accurate measurement of synchronization cycle time is required for ultra-low power wireless sensor nodes with stringent power budgets. A multi-stage gate-leakage-based timer with boosted charging is proposed to address the high jitter of prior-art gate-leakage-based timers. The key approaches are faster load capacitor charging, wider voltage swing, and an improved gain sensing inverter. The proposed timer reduces RMS jitter by 8.1× and synchronization uncertainty by 4.1×, which allows hourly tracking with 200 ms uncertainty while consuming 660 pW. A novel closed-loop temperature compensation scheme with dynamic leakage adjustment is also proposed to achieve temperature sensitivity of 31 ppm/°C.

Unique Activity-Meter with Piezoelectric Poly(vinylidene difluoride) Films and Self Weight of the Sensor Nodes

We have developed piezoelectric switches for application in ultra low-power wireless sensor nodes to monitor the health condition of chickens. Using Pb(Zr0.52,Ti0.48)O3 (PZT) thin films, we have developed S-shaped PZT cantilevers with proof masses. Since the resonant frequency of PZT devices is approximately 24 Hz, we have utilized their superharmonic resonance to detect chicken movements with frequencies as low as 5–15 Hz. By attaching sensor nodes to chickens, we successfully measured the activity of chickens. However, the PZT devices of other sensor nodes broke down. S-shaped PZT devices are adequate for low vibrations, but are beset by the structural problems of fragmentation upon impact. To address these problems, we examine a method of utilizing poly(vinylidene difluoride) (PVDF) films, which are tough and generate high piezoelectric output voltages under a large stress, as piezoelectric switches. We suggest that the self-weight of sensor nodes be used as the mass of the cantilevers of the PVDF films. One end of a PVDF film is fixed to the case of a sensor node, and the other end is attached to the sensor node. Since PVDF films are subjected to force generated by the self-weight of sensor nodes, high output voltages are expected. A result of measuring output voltages, we confirm the output voltages to be approximately the same as those of PZT devices below 15 Hz at 0.5 m/s2 vibration, which is close to chicken movements. Thus, we consider that we have successfully fabricated a tough wireless sensor node for chickens, utilizing the features of PVDF films.

Piezoelectric MEMS switch to activate event-driven wireless sensor nodes

We have developed piezoelectric microelectromechanical systems (MEMS) switches and applied them to ultra-low power wireless sensor nodes, to monitor the health condition of chickens. The piezoelectric switches have ‘S’-shaped piezoelectric cantilevers with a proof mass. Since the resonant frequency of the piezoelectric switches is around 24 Hz, we have utilized their superharmonic resonance to detect chicken movements as low as 5–15 Hz. When the vibration frequency is 4, 6 and 12 Hz, the piezoelectric switches vibrate at 0.5 m s−2 and generate 3–5 mV output voltages with superharmonic resonance. In order to detect such small piezoelectric output voltages, we employ comparator circuits that can be driven at low voltages, which can set the threshold voltage (Vth) from 1 to 31 mV with a 1 mV increment. When we set Vth at 4 mV, the output voltages of the piezoelectric MEMS switches vibrate below 15 Hz with amplitudes above 0.3 m s−2 and turn on the comparator circuits. Similarly, by setting Vth at 5 mV, the output voltages turn on the comparator circuits with vibrations above 0.4 m s−2. Furthermore, setting Vth at 10 mV causes vibrations above 0.5 m s−2 that turn on the comparator circuits. These results suggest that we can select small or fast chicken movements to utilize piezoelectric MEMS switches with comparator circuits.

RoSe: A Subgigahertz Wireless Sensor Platform With Housing-Integrated Overmolded Antenna

A wireless sensor platform for use in ultralow-power wireless sensor networks (WSNs) is presented. The proposed round sensor (RoSe) node is physically robust, is resistant to humidity, and has a housing that can be in direct contact with food. These characteristics are achieved via injection molding technology which is investigated at both the component and the system levels. The results of injection molding tests on the node's electronic components are reported, while a housing-integrated overmolded antenna is conceived and realized. The radiator, operating in the subgigahertz industrial, scientific, and medical (ISM) band (ISM 868 or 915 MHz), has been characterized, and a good correspondence with theoretical predictions is observed. The proposed system enables industrialized mass production and results in a generic platform for wireless monitoring applications. In this paper, we present the RoSe node with a temperature sensor for use in food cold chain management, i.e., for use at temperatures down to -30 °C and in frequent contact with water due to condensation or cleaning. Its ultralow-power characteristics are demonstrated by the analysis of the charge consumption when the node performs specific tasks both in a test case and operating in a WSN. Long-term battery lifetime results while running a demo WSN are also presented.

A Variable RF Carrier Modulation Scheme for Ultralow Power Wireless Body-Area Network

In this paper, a modulation technique, viz., differential frequency shift keying (DFSK), has been proposed for ultralow power wireless sensor node applications, which has been shown to be the most energy-efficient transmission technique for short-distance wireless communication systems, such as wireless body area network. The proposed technique is a variant of the binary frequency shift keying and is based on the principle that even though the frequency values of a radio frequency (RF) tone-pair of an oscillator may vary under various environmental conditions, the difference between the frequencies remains largely invariant. The proposed DFSK technique significantly relaxes the frequency stability requirement in the transmitter RF front-end at the cost of a little increased transmission power, which, in turn, significantly simplifies the circuit complexity as well as reduces the overall circuit power consumption within the transmitter. Theoretical analyses of the bit error rate, phase noise, interferer effects, and energy consumption for DFSK have been provided, supplemented by the simulation results using detailed MATLAB modeling for the medical implant communications service frequency band.

A review of piezoelectric energy harvesting based on vibration

This paper reviews energy harvesting technology from mechanical vibration. Recent advances on ultralow power portable electronic devices and wireless sensor network require limitless battery life for better performance. People searched for permanent portable power sources for advanced electronic devices. Energy is everywhere around us and the most important part in energy harvesting is energy transducer. Piezoelectric materials have high energy conversion ability from mechanical vibration. A great amount of researches have been conducted to develop simple and efficient energy harvesting devices from vibration by using piezoelectric materials. Representative piezoelectric materials can be categorized into piezoceramics and piezopolymers. This paper reviews key ideas and performances of the reported piezoelectric energy harvesting from vibration. Various types of vibration devices, piezoelectric materials and mathematical modeling of vibrational energy harvestings are reviewed.

Positioning in Synchronized Ultra Low-Power Wireless Sensor Networks

Wireless Sensor Networks (WSNs) consist of densely deployed, independent, and collaborating low cost sensor nodes. The nodes are highly resource-constrained in terms of energy, processing, and data storage capacity. Thus, the protocols used in WSNs must be highly energy-efficient. WSN communication protocols achieving the lowest power consumption minimize radio usage by accurately synchronizing transmissions and receptions with their neighbors. In this paper, we show how network signaling frames of state-of-the-art synchronized communication protocols for low-power WSNs supporting mobile nodes can be used for positioning. We derive mathematical models for node power consumption analysis. Both centralized and distributed positioning architectures are modeled. The models provide a tool for estimating what kind of network lifetimes can be expected when average positioned node speed, the amount of anchor nodes required by the location estimation algorithm, and the location refresh rate required by the application are known. The presented analysis results are based on two kinds of node hardware: with and without Received Signal Strength Indicator (RSSI). The results show that the positioning parameters and used hardware have significant impact on node power consumption and network lifetime. In the presented results, the network lifetime ranges from over 10 years to 2 months with different positioning requirements and hardware. keywords: Wireless, Low-Power, Sensor Networks c ⃝[2010] IEEE. Portions reprinted, with permission, from [Ville Kaseva, Timo D. Hamalainen, and Marko Hannikainen, Positioning in Resource-Constrained Ultra Low-Power Wireless Sensor Networks, Ubiquitous Positioning Indoor Navigation and Location Based Service (UPINLBS), October/2010]