Wireless Sensor Node Applications Research Articles

A compact self-powered inductor-less piezoelectric energy harvesting circuit using gyrator

In traditional low-frequency energy harvesting circuits, a large matched inductor with a large size is unavoidable. To reduce the size of the circuit, this paper proposes a compact self-powered inductor-less high-efficiency piezoelectric energy harvesting circuit using a low-power-consumption gyrator. A self-powered floating gyrator inductor is used in place of an inductor in the proposed circuit, and the required phasor response is acquired by using its voltage–current (V–I) relationship. The proposed circuit offers easy adjustability and performance benefits in small integrated circuits packages. The proposed circuit can be cost-effective and provide reduced area advantages in autonomous self-powered Internet-of-Things and wireless sensor nodes applications. Regarding harvested energy, the proposed circuit with a storage capacitor of 0.24 F can obtain 320% improved performance than standard energy harvesting along with the lowest power consumption of 0.25 µW in self-powered operation. The proposed technique can also be applied to similar piezoelectric energy harvesting strategies with large inductors.

Optimizing Visual Sensor Node Image Compression for Resource-Constrained Environments

Abstract: An Approximate hybrid multiplier design is proposed to reduce the data-path width of lifting 2-D discrete wavelet transform (DWT) especially for wireless visual sensor node applications. The proposed multiplier design takes multiplier operand of size less by 3 bit and calculates full-width outputs with marginal loss of accuracy, which is significant. The proposed approximate 2-D DWT structure uses data-path DWT levels and produces reconstructed color images higher than the 70-dB peak-signal-to-noise ratio (PSNR). Compared with the existing fractional wavelet transform (FrWT)-based 2D DWT structures, the proposed structure has a smaller data-path width and free from overhead. Compared with the existing parallel structure

A Rail-To-Rail and Low Offset Novel Strongarm Comparator Circuit for Low Power Data Converter Architectures

With the rapid improvements in the design of advanced high performance communication receivers, hand-held electronic devices are in widespread usage for some time. These devices facilitate high speed and secured access to internet data. The demand for realizing a smart and better usage experience puts forth strict requirements on the design aspects of next-generation high speed low power complementary metal oxide semiconductor (CMOS) receiver design. One of the major modules in the implementation of high speed low power CMOS receiver device is the analog to digital converter (ADC) architecture. In the process of conversion from analog to digital signals, Quantization and sampling operations are vital and are realized using comparator circuits. The comparator design has a significant role in the design of data converter architecture. Several comparator architectures exist, but StrongARM topology is discussed and implemented in this work due to its negligible static power dissipation and rail to rail output voltages. The proposed novel comparator architecture is designed and simulated in 90nm CMOS process using Cadence Virtuoso tool and operated at supply voltage of VDD=1.5V, a clock frequency of 250MHz. Compared to the previous designs, the energy delay product was reduced by 8% which is an important observation to be observed for use in wireless sensor node applications.

Approximate Lifting 2-D DWT Hardware Design for Image Encoder of Wireless Visual Sensors

In this paper, a novel approximate hybrid multiplier design is proposed to reduce the data-path width of lifting two-dimensional (2-D) discrete wavelet transform (DWT) especially for wireless visual sensor node applications. The proposed multiplier design takes multiplier operand of size less by 3-bit and calculates full-width outputs with marginal loss of accuracy which is significant. A parallel approximate lifting 2-D DWT structure is derived using the proposed multiplier design. The proposed approximate 2-D DWT structure uses data-path width 9 and 11 for first and second DWT levels and produces reconstructed colour images higher than 70dB peak-signal-to-noise ratio (PSNR). Compared with the existing fractional wavelet transform (FrWT)-based 2-D DWT structures, the proposed structure has a smaller data-path width and free from overhead. The proposed structure has equal or marginally higher on-chip memory requirement than the existing FrWT based 2-D DWT structures, but involves a substantially less area-delay product (ADP) and energy per image (EPI). The ADP and EPI reduction is O(10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ×). Compared with the existing parallel structure based on hybrid approximate radix-4 and radix-8 encoded Booth multiplier, the proposed approximate structure involves nearly 23% less ADP and 22% less EPI and calculates output images with nearly (4 ~ 7)dB higher PSNR.

Hybrid acoustic, vibration, and wind energy harvester using piezoelectric transduction for self-powered wireless sensor node applications

Energy harvesters are considered to be a promising solution for long lasting operation of wireless sensor nodes, moreover, make these power-sustainable in hazardous, implantable, remote, harsh, embedded, and abandoned environments where frequent battery replacement is a challenge. Existing energy harvesters utilize only one or two ambient energy sources, however, in this paper, we developed a novel piezoelectric-based energy harvester that converts three ambient energies (acoustic, vibration, and wind) simultaneously into electrical energy. The developed harvester comprises a Helmholtz resonator, a unimorph piezoelectric composite plate, and a cambered aerofoil connected with a piezoelectric plate using a base support. Acoustic, vibration, and wind induced deformation in the harvester’s piezoelectric plate and intrun electrical energy is produced based on piezoelectric phenomena. The harvester showed two peaks (at 802 and 1417 Hz frequencies) when subjected to a forward frequency sweep (FFS) which corresponds to its resonant frequencies. Under resonance, in the acoustic and vibrations environment, the harvester produced a maximum power of 210.6 µW, and 1.38 mW on excitation at 130 dB sound pressure level (SPL) and 0.8 g base acceleration, respectively. Furthermore, the harvester produced maximum power of about 285 µW when exposed to 8 m/s wind speed. The developed harvester can be a potential power source for self-powered wireless sensors used for the structural health monitoring of bridges, tall buildings, and railway tracks.

A nanowatt noise-shaping SAR ADC for passive wireless sensor node application

A nanowatt noise-shaping SAR ADC for passive wireless sensor node application

An energy-efficient single-cycle RV32I microprocessor for edge computing applications

With the advancement in the Internet of Things (IoT) and Wireless Sensor Node (WSN) applications computation on edge is preferred over computation on the cloud. However, due to limited resource availability in the edge environment, energy efficiency can be seen as the primary barrier in the growth of edge computing devices. In edge computing applications like wearable devices, forest monitoring systems, and other such applications, power is of utmost importance. The use of a complex, pipelined, general-purpose processor is redundant for such low-end applications and it leads to high power consumption. Hence, edge computing systems require low-power solutions while still maintaining a minimum performance level. In this work, an energy-efficient single-cycle RISC-V instruction set architecture (ISA) based RV32I processor is designed for low-end edge computing applications. The design incorporates base integer implementation of RISC-V ISA. The proposed computing system is designed using Verilog HDL and synthesized on Semi-conductor Laboratory (SCL) 180 nm CMOS process technology node. The synthesis tool reports power consumption of 14.7 mW at 50 MHz frequency with an area of 0.24 mm2. Though synthesis of this design reports area of 0.24 mm2, the design is taped out as a part of an available shuttle project where die size is fixed to 5 mm × 5 mm. The PNR (Place and Route) tool reports power consumption of 11.8 mW at an operating frequency of 40 MHz. A basic functional testing of proposed fabricated RV32I chip is carried out in laboratory experimental setup and results are presented. The comparison result shows that the proposed RV32I processor consumes 0.29 mW/MHz power which is less than state-of-the-art low-end processors. Hence, the proposed design is suitable for low-end edge computing applications.

Enhanced Performance of Monolithic Chalcogenide Thermoelectric Modules for Energy Harvesting via Co-optimization of Experiment and Simulation.

With the development of application of wireless sensor nodes (WSNs), the need for energy harvesting is rapidly increasing. In this study, we designed and fabricated a robust monolithic thermoelectric generator (TEG) using a simple, low-energy, and low-cost device fabrication process. Our monolithic device consists of Ag2S0.2Se0.8 and Bi0.5Sb1.5Te3 as n-type and p-type legs, respectively, while the empty space between the legs was filled with highly dense, flexible, and thin Ag2S that serves as both an insulating spacer and a shock absorber, which potentially augments the robustness of preventing from damage from an external mechanical force. From the optimization of the device structure via finite element method (FEM) simulations, a three-pair device with dimensions of 12 mm × 10 mm × 10 mm was found to have a theoretical maximum power density of 8.2 mW cm-2 at a ΔT of 50 K. For considering this inevitable contact resistance, experimental measurement and FEM simulation were combined for quantifying the junction resistance; a power density of 2.1 mW cm-2 was established with the consideration of the contact resistance at the p-n junctions. Using these optimized structural parameters, a device was fabricated and was found to have a maximum power density of 2.02 mW cm-2 at a ΔT of 50 K, which is in good agreement with our simulations. The results from our monolithic TEG show that despite the simple, low-energy, and low-cost device fabrication process, the power generation is still comparable to other reported TEGs. It is worth mentioning that our design could be extended to other chalcogenide materials of appropriate temperature regions and/or better zT. Besides, the quantification of contact resistance also exhibited reference value for the enhancement of thermoelectric conversion application. These results provide a convenient, economic, and efficient strategy for waste energy harvesting close to room temperature, which can broaden the applications of waste heat harvesting.

Challenges, Applications, and Future of Wireless Sensors in Internet of Things: A Review

The addition of massive machine type communication (mMTC) as a category of Fifth Generation (5G) of mobile communication, have increased the popularity of Internet of Things (IoT). The sensors are one of the critical component of any IoT device. Although the sensors posses a well-known historical existence, but their integration in wireless technologies and increased demand in IoT applications have increased their importance and the challenges in terms of design, integration, etc. This survey presents a holistic (historical as well as architectural) overview of wireless sensor (WS) nodes, providing a classical definition, in-depth analysis of different modules involved in the design of a WS node, and the ways in which they can be used to measure a system performance. Using the definition and analysis of a WS node, a more comprehensive classification of WS nodes is provided. Moreover, the need to form a wireless sensor network (WSN), their deployment, and communication protocols is explained. The applications of WS nodes in various use cases have been discussed. Additionally, an overlook of challenges and constraints that these WS nodes face in various environments and during the manufacturing process, are discussed. Their main existing developments which are expected to augment the WS nodes, to meet the requirements of the emerging systems, are also presented.

A Novel Dual-band Ambient RF Energy Harvesting System for Autonomous Wireless Sensor Node Application

This paper presents a novel dual-band ambient Wi-Fi energy harvesting system for an autonomous wireless sensor node (AWSN) which operates independently without other external power source. While conventional wireless sensor nodes employing batteries with limited lifespans, an AWSN is supplied by harvested energy and does not require frequent battery replacement. Due to that reason, research on the energy harvesting aspect of AWSNs has been carried out intensively in recent years. By optimizing the matching network, the proposed ambient Wi-Fi energy harvesting system achieves a relatively good efficiency in dual-band at 2.45 GHz and 5.8 GHz. The efficiency reaches a peak at 47.45 % and 42 % at 2.45 GHz and 5.8 GHz, respectively. The proposed idea is numerically and experimentally demonstrated with the Wi-Fi source in building.

PERFORMANCE EVALUATION OF VOLTAGE RECTIFIERS FOR ENERGY HARVESTING APPLICATIONS

Voltage multipliers are used to convert the low AC voltage output of energy harvesters into relatively high DC voltage for portable devices and wireless sensor nodes (WSNs) applications. DC voltage conversion is required to operate an electronic device or recharge battery. In order, to convert the low AC voltage output of the energy harvester into relatively high DC voltage, a voltage multiplier circuit need to be integrated with the energy harvester. In this study, a Prototype-1 (two-stages) and Prototype-2 (three-stage) Dickson voltage multipliers and Prototype-3 (seven-stage) Cockcroft-Walton voltage multiplier circuits are developed. The device is capable of converting a low voltage of 50 mV into 350 mV. The research focuses on the development and characterization of Prototype-1, Prototype-2 and Prototype-3 circuits. Results indicate that the determination of load resistance is important for better output power. The maximum power of 11.97 μW was obtained by prototype-3 elucidating better power compared to prototype-1 and prototype-2 and the power was obtained at an optimum load of 560 kΩ. Furthermore, a rectenna tested at different distances from the source, revealed that a prototype-2 produced a maximum power of 3.01 × 10 -6 μW, at an optimum load of 560 kΩ.

CPW-Fed Super-Wideband Antenna With Modified Vertical Bow-Tie-Shaped Patch for Wireless Sensor Networks

In this paper a coplanar waveguide-fed super-wideband antenna is presented for wireless sensor networks. The studied low-profile design is comprised of a modified bow-tie-shaped vertical patch and two asymmetrical ground planes and has been prototyped on a single-sided FR4 microwave substrate. The anticipated antenna has an overall size of $0.25\lambda \times 0.20\lambda $ at 3.035 GHz, the lowest frequency of the operating band. The vertical radiator coupled well with the two coplanar ground planes which enabled the studied antenna to achieve an operating band of 3.035–17.39 GHz (140.56%). The presented antenna demonstrates almost omnidirectional radiation patterns over the entire operating with an average gain of 4.56 dBi and average efficiency of 76.62%. The antenna also features with high fidelity factor, flat group delay, small phase distortion, and good response of transfer function. All these characteristics of the studied antenna make it a robust contender for wireless sensor node applications.

MEMS based antenna of energy harvester for wireless sensor node

This paper deals with glass surface micromachined antenna of RF energy harvesting for wireless sensor node applications. The research aims to provide a system based on a new integrated RF energy harvester circuitry using a transparent receiving antenna by micromachining process. The energy harvester system is studied using CST-MWS software by Pyrex glass as the antenna substrate having dielectric constant ɛr = 4.6. Besides, PSpice and Cadence analyze the DC output solutions. The fabrication of the micromachined antenna based on metal patterning of the radiator patch and metal sputtering on the top and bottom of the glass surface, respectively. The analysis of the wave propagation of the antenna shows good agreement between the simulation solutions and experimental validations. It is present that the antenna achieved a maximum gain of > 4 dB, reflection coefficient (S11) 100 MHz, omnidirectional radiation pattern and VSWR ratio < 2. From DC analysis, with an ultra-low input power of − 20 dBm incoming from this optimal antenna, the MOSFET rectifier reaches an efficiency of 46.23% and DC output voltage of 2.15 V at 1 MΩ load. Further, the developed antenna integrated into the RF energy harvester on the same circuit platform that yield a highly efficient operating system at 5 GHz ISM band.

Three-fold improved set-voltage variability of a Cu atom switch with a split electrode for very-large-scale integration

We propose a self-selected smallest set-voltage cell (4S-cell) to realize three-fold improvement of the set-voltage (Vset) variability of Cu atom switches. In the cell, switches are connected in parallel and the switch with the smallest Vset is automatically selected, resulting in smaller Vset variability. For practical application, a split-electrode structure is introduced. The 4S-cells of 2-in-1 by using a split electrode without any increase in cell area reduced the 6σ of Vset with an equivalent σVset of 28 mV. The developed 4S-cell enables very-large-scale integration of atom switches for embedded memory and routing switch applications used in ultra-low-power systems-on-chips for wireless sensor node applications.

Battery’s Life-Time Estimation of Industrial WirelessHART Sensor Actuator Node

In industrial applications of wireless technologies, very common, wireless sensor and actuator nodes are installed at fields. Therefore, it is critical to extend battery’s lifetime for ensuring continuous servicing period of field instruments over years. Apart from periodic battery status update during operations of the nodes, at planning stage, plant management team can estimate batteries’ lifetime at field wireless instruments for operational budget estimation and preventive maintenance planning. This work proposes a framework to estimate the battery’s lifetime taken into consideration of periodic update periods and devices’ operational frequencies. The framework is based on the knowledge of wireless node, microcontroller’s power consumption, and battery specifications. Based on the analysis, at particular operational conditions (i.e., update period of 512 s, low-power mode with voltage of 1.8 V), the estimated battery’s lifetime of a wireless node can reach up to 9 years.

Balun LNA Thermal Noise Analysis and Balancing With Common-Source Degeneration Resistor

The Balun low noise amplifier (LNA) is an LNA that exploits a combination of a common-source (CS) and a common-gate (CG) transistors, which cancels the noise and distortion of the CG stage. And since the CG is known to be linear, only the CS needs to be carefully designed and optimized. The Balun LNA also cancels the distortion and noise of the CG. In this paper, the CS section will be fully analyzed, and shown how the condition set in the literature review still satisfy the balancing output and cancel the CS stage thermal noise as well as the CG thermal noise. Also, forward body biasing (FBB) is used to reduce the threshold voltage and an addition of CS degeneration resistor to balance the output while still canceling the thermal noise of the transistors is tested using UMC180nm on Cadence. The LNA achieves a gain of 19-16dB, NF < 3.6 over the bandwidth 200M-1.9GHz without a CS degeneration. A 17.8-14.8dB gain, a NF < 3.8 over the bandwidth 200MHz-2.1GHz and power consumption of 12mW in both cases. Although outside the bandwidth, at ISM 2.4GHz a gain of 14.5dB and a NF of 3.8 is achieved, making it suitable for wireless sensor node (WSN) applications. According to the author’s knowledge, this is the first time the degeneration resistor noise analysis on a Balun LNA is derived and analyzed.

A Low-Power Relaxation Oscillator With Switched-Capacitor Frequency-Locked Loop for Wireless Sensor Node Applications

This letter presents a 600-kHz relaxation oscillator with 2.2- $\mu \text{W}$ power consumption. A low-power frequency-locked loop (FLL) structure is proposed to increase the frequency immunity against process, voltage, and temperature variations. A front regulator is proposed to further enhance the voltage stability and widen the voltage range. A current-injection scheme is proposed to compensate the frequency shift due to the temperature shift of the on-chip resistor. Fabricated with 180-nm technology, this oscillator can operate at an unregulated supply from 1.1 to 3.3 V with 0.046%/V voltage stability. The measured temperature stability is 48.69 ppm/°C from −45 °C to 125 °C and the measured jitterrms is 1.56 ns with 120-k hits.

A P&amp;O MPPT With a Novel Analog Power-Detector for WSNs Applications

This brief presents a perturb and observe (P&O) maximum power point tracking (MPPT) with a novel analog power detector for wireless sensor nodes (WSNs) applications. The proposed analog power detector can judge the output power variation only by the voltage measurements, which eliminates the use of current measurements or microcontroller unit (MCU), so that its complexity and power consumption are greatly reduced. The proposed P&O MPPT circuit with the analog power detector has the advantages of simple structure, low power consumption, and high power efficiency. The proposed MPPT is used in a discontinuous conduction mode (DCM) buck-boost converter with fixed duty cycle to improve the efficiency performance. This design has been implemented in a $0.18\mu \text{m}$ CMOS process occupying an active area of $0.98\times 0.9$ mm2. The input voltage range can be from 2V to 7.2V. The peak conversion efficiency and peak tracking efficiency are 86% and 98% respectively, with power consumption about $9\mu \text{W}$ .

Miniaturised Triangular Microstrip Antenna with Metamaterial for Wireless Sensor Node Applications

This paper presents a simple, low cost and compact triangular microstrip antenna with metamaterial, designed for wireless sensor node applications. The proposed microstrip antenna consists of a triangular patch and circular shaped split ring resonator (SRR) as a ground plane. The metamaterial-based triangular microstrip patch antenna is designed at 2.4 GHz with a return loss of S11 < 10 dB and acceptable gain. The proposed antenna is of small size (0.065 λ0 × 0.065 λ0) and uses a FR-4 substrate of dielectric constant 4.3. The simulated and measured normalised radiation patterns are in concurrence with each other. The antenna covers 2.4 GHz ISM band making it appropriate for WSN applications.

High-performance self-powered wireless sensor node driven by a flexible thermoelectric generator

As industrial environments expand and become more automated, wireless sensor networks are attracting attention as an essential technology for efficient operation and safety. A wireless sensor node (WSN), self-powered by an energy harvester, can significantly reduce maintenance costs as well as the manpower costs associated with the replacement of batteries. Among the many studies on energy harvesting technologies for self-powered WSNs, however, the harvested power has been too low to be practically used in industrial environments. In this work, we demonstrate a self-powered WSN driven by a flexible thermoelectric generator (f-TEG) with a significantly improved degree of practicality. We developed a large-area f-TEG which can be wrapped around heat pipes with various diameters, improving their usability and scalability. A study was conducted to optimize the performance of the f-TEG for a particular WSN application, and an f-TEG fabricated with an area of 140 × 113 mm2 harvested 272 mW of energy from a heat pipe at a temperature of 70 °C. We also tested a complete self-powered WSN system capable of the remote monitoring of the heat pipe temperature, ambient temperature, humidity, CO2 and volatile organic compound concentrations via LoRa communication. The fabricated self-powered WSN system can wirelessly transmit the data at distances as long as 500 m.