Proposed Energy Harvesting System Research Articles

Energy Harvesting System

Abstract: This paper presents a novel energy harvesting system designed to harness ambient mechanical energy using piezoelectric sensors, with the Arduino Uno microcontroller serving as the central processing unit. The system's primary objective is to convert mechanical vibrations into electrical energy, storing it for potential use in powering low-energy electronic devices. The proposed setup incorporates piezoelectric materials strategically positioned to capture mechanical vibrations from various sources. The core of the system is an Arduino Uno microcontroller, programmed to efficiently manage the energy harvesting process. The harvested energy is stored in a rechargeable battery, ensuring a consistent power supply for applications with intermittent energy demands. To validate the effectiveness of the system, a light bulb is employed as a demonstrative load, allowing for real-time observation of the energy harvesting capabilities. The paper details the experimental setup, including the placement and configuration of piezoelectric sensors, the Arduino Uno programming logic, and the integration of a light bulb for visual confirmation of the generated current. Performance metrics such as voltage output, current production, and power generation efficiency are thoroughly analyzed under varying environmental conditions and mechanical vibrations. Results demonstrate the feasibility of the proposed energy harvesting system, showcasing its potential as a sustainable power source for low-power electronic devices. The combination of piezoelectric materials, Arduino Uno control, and a practical load application illustrates a promising approach to energy harvesting, paving the way for advancements in self-sufficient and ecofriendly power solutions

Sustainable Sea of Internet of Things: Wind Energy Harvesting System for Unmanned Surface Vehicles.

Harvesting wind energy from the environment and integrating it with the internet of things and artificial intelligence to enable intelligent ocean environment monitoring are effective approach. There are some challenges that limit the performance of wind energy harvesters, such as the larger start-up torque and the narrow operational wind speed range. To address these issues, this paper proposes a wind energy harvesting system with a self-regulation strategy based on piezoelectric and electromagnetic effects to achieve state monitoring for unmanned surface vehicles (USVs). The proposed energy harvesting system comprises eight rotation units with centrifugal adaptation and four piezoelectric units with a magnetic coupling mechanism, which can further reduce the start-up torque and expand the wind speed range. The dynamic model of the energy harvester with the centrifugal effect is explored, and the corresponding structural parameters are analyzed. The simulation and experimental results show that it can obtain a maximum average power of 23.25 mW at a wind speed of 8 m/s. Furthermore, three different magnet configurations are investigated, and the optimal configuration can effectively decrease the resistance torque by 91.25% compared with the traditional mode. A prototype is manufactured, and the test result shows that it can charge a 2200 μF supercapacitor to 6.2 V within 120 s, which indicates that it has a great potential to achieve the self-powered low-power sensors. Finally, a deep learning algorithm is applied to detect the stability of the operation, and the average accuracy reached 95.33%, which validates the feasibility of the state monitoring of USVs.

Energy Harvester Based on a Rotational Pendulum Supported with FEM

The proposed energy harvesting system is based on a rotational pendulum-like electromagnetic device. Pendulum energy harvesting systems can be used to generate power for wearable devices such as smart watches and fitness trackers, by harnessing the energy from the human body motion. These systems can also be used to power low-energy-consuming sensors and monitoring devices in industrial settings where consistent ambient vibrations are present, enabling continuous operation without any need for frequent battery replacements. The pendulum-based energy harvester presented in this work was equipped with additional adjustable permanent magnets placed inside the induction coils, governing the movement of the pendulum. This research pioneers a novel electromagnetic energy harvester design that offers customizable potential configurations. Such a design was realized using the 3D printing method for enhanced precision, and analyzed using the finite element method (FEM). The reduced dynamic model was derived for a real-size device and FEM-based simulations were carried out to estimate the distribution and interaction of the magnetic field. Dynamic simulations were performed for the selected magnet configurations of the system. Power output analyses are presented for systems with and without the additional magnets inside the coils. The primary outcome of this research demonstrates the importance of optimization of geometric configuration. Such an optimization was exercised here by strategically choosing the size and positioning of the magnets, which significantly enhanced energy harvesting performance by facilitating easier passage of the pendulum through magnetic barriers.

A High-Performance Circularly Polarized and Harmonic Rejection Rectenna for Electromagnetic Energy Harvesting.

This paper presents a novel circularly polarized rectenna designed for efficient electromagnetic energy harvesting at the 2.45 GHz ISM band. A compact antenna structure is designed to achieve high performance in terms of radiation efficiency, axial ratio, directivity, effective area, and harmonic rejection over the entire bandwidth of the ISM frequency band. The optimized rectifier circuit enhances the RF harvested energy efficiency, with an AC-to-DC conversion efficiency ranging from 36% to 70% for low-level input power ranging from -10 dBm to 0 dBm. The stable output of DC power confirms the suitability of this design for various practical applications, including wireless sensor networks, energy harvesting power supplies, medical implants, and environmental monitoring systems. Experimental validation, which includes both the reflection coefficient and radiation patterns of the designed antenna, confirms the accuracy of the simulation. The study found that the proposed energy harvesting system has a high total efficiency ranging from 53% to 63% and is well-suited for low-power energy harvesting (0 dBm) from ambient electromagnetic radiation. The proposed circularly polarized rectenna is a competitive option for efficient electromagnetic energy harvesting, both as a standalone unit and in an array, due to its high performance, feasibility, and versatility in meeting various energy harvesting requirements. This makes it a promising and cost-effective solution for various wireless communication applications, offering great potential for efficient energy harvesting from ambient electromagnetic radiation.

Bidirectional Thermoelectric Assisted Synchronous Charge Extraction Circuit Based on Buck Structure for Piezoelectric Energy Harvesting

Energy harvesting technology is currently a research hotspot, which can effectively solve energy supply problems in fields such as wireless sensor networks, wearable devices, and smart homes. An energy harvesting system using a thermoelectric generator (TEG) for energy assistance of a piezoelectric transducer (PZT) is proposed. It employs a synchronous charge extraction circuit based on a buck structure (BUCK-SECE), which uses thermoelectric energy to inject energy into the piezoelectric element in both directions to boost the initial voltage of the BUCK-SECE, increasing its output power. The experimental results demonstrate that the utilization of thermoelectric energy can increase the output power of BUCK-SECE by a factor of 3.3 under low-vibration conditions and by a factor of 0.8 under high-vibration conditions. Therefore, the proposed energy harvesting system in this article can effectively enhance the output power of piezoelectric energy transducers and yield desirable performance in real-world applications.

3-D-Printed Dual-Band Rectenna System for Green IoT Application

This paper describes the novel fully 3D-printed dual-band RF energy harvester suitable for wireless sensor network green IoT applications. The proposed energy harvesting system is composed of a dual-band circular omnidirectional monopole antenna array with a T-junction power divider, RF rectifier, and an impedance matching network. The circular monopole antenna array is conformed to a cylindrical substrate to achieve the compact system. The Villard multiplier-based rectifier has been used for the conversion of RF signal to DC voltage. The presented rectenna is fabricated using a 3D printable, biodegradable, conformal and an economical substrate. The test is performed in an RF ambient environment. The manufactured configuration obtained conversion efficiencies of 67.29% with output voltage of 1.39 V and 42.16% with output voltage of 1.1 V at 0 dBm RF input power in 2.4 GHz and 5.2 GHz frequency bands respectively. The proposed configuration’s simulated and measured results are in concordance with each other. The study emphasizes the potential of 3D-printed rectenna in terms of cost-effective prototyping.

Development of renewable energy system for low power underwater devices

Underwater sensor networks (UWSNs) are an emerging field in the research area as they have potential applications starting from pollution monitoring to defense and ocean exploration. Ocean monitoring is of great importance in marine scientific research. However, battery-operated devices utilized in such systems have limited power and maintenance is difficult. So, devices used underwater suffer from many research challenges and energy issues. Apart from all the problems, harvesting energy underwater is the main limiting factor. Nonrenewable energies come from sources that may not be replenished in our lifetime. Hence, it is very much essential to use renewable energy sources. Ocean has an unlimited amount of energy like wind energy, solar power, and tidal energy. Obtaining sufficient energy is sort of difficult since devices are underwater. Researchers are continuously working on it. Water energy is quite environmentally friendly, and it is a sustainable solution for a secure energy system. This paper implements a renewable energy system using piezoelectric (PZT) sensor, which generates sufficient power for lowpower underwater devices by employing two stage amplifier circuits. Experimental outcome shows the proposed energy harvesting system can generate a maximum voltage of 10.6 V and current of 10.1 mA which is sufficient to run low power underwater device.

Analysis and Experiment of Self‐Powered, Pulse‐Based Energy Harvester Using 400 V FEP‐Based Segmented Triboelectric Nanogenerators and 98.2% Tracking Efficient Power Management IC for Multi‐Functional IoT Applications

AbstractA self‐powered system for the Internet of Things (IoT) is demonstrated for efficient energy harvesting of naturally available mechanical energy. In this system, new contact‐separation mode triboelectric nanogenerators (TENGs), based on fluorinated ethylene propylene, are investigated using the segmented multi‐TENG configuration to reduce the effect of parasitic capacitance. The TENG extraction is optimized using a unit step excitation involved with the Dawson function to achieve a high voltage (400 V) and a high current (26.6 µA). To fully extract the power of the TENGs, the power management integrated circuit (PMIC) specially designed for adaptively controlled, high‐voltage (HV) maximum power point tracking (MPPT) is proposed. The PMIC implemented in a bipolar CMOS‐DMOS 180 nm process can handle a wide input range (5–70 V) by consuming 420 nW. The MPPT control allows a wide range of impedance matching from 10 to 300 MΩ, achieving a tracking efficiency of up to 98.2%. The end‐to‐end efficiency of 88% demonstrates state‐of‐the‐art performance. To supply a higher instantaneous power than that available from the TENGs, a duty‐cycling technique is successfully demonstrated. The proposed energy harvesting system provides a promising approach to realizing sustainable and autonomous energy sources for various IoT applications.

Environmental Noise Harvester Using a Helmholtz Resonator and Piezoelectric Transducer

This work represents a guideline for designing, analyzing, and implementing a compact, low-cost, lightweight, and portable system that harvests energy from environmental noise at different locations. Considering that the proposed energy harvesting system (EHS) is based on a piezoelectric transducer (PZT) embedded in a Helmholtz resonator (HR), we first characterize the noise at four different locations selecting the most suitable ones for energy harvesting. Then, we electrically analyze and describe the PZT determining its resonance frequency. Subsequently, by using this frequency, we perform the sizing of the HR. Thus, we analyze the behavior of the implemented EHS under controlled and actual conditions. In controlled conditions, we determine the gain of the implemented EHS using a pure sinusoidal signal at 500 Hz and a pink noise signal. In actual conditions, we measured its gain considering two different locations. We observed that under controlled conditions, the implemented EHS achieved a gain between 168.3% and 200.3%, and under actual conditions, its gain was 159.5% in the traffic zone and 597.7% in the music zone. In addition, for the HR modeling and design, we show that its theoretical gain corresponds to its simulation gain but differs from its experimental gain due to the used material and manufacturing. Finally, we show that the implemented EHS performs similarly or better than other more sophisticated systems or systems with more piezoelectric elements.

Self-powered sensing of power transmission lines galloping based on piezoelectric energy harvesting

Online monitoring sensors are a feasible solution for conductor galloping that greatly harms the stable operation of power transmission systems. However, power supply that drives sensors has become one of the bottlenecks restricting the development of distributed sensing systems. This work initially proposes harvesting the energy of conductor galloping and joint utilization to assess conductor galloping degree. A swinging piezoelectric energy harvester based on frequency boost conversion is also proposed. The output characteristics of harvester and the physical validation of the scale model of power transmission line galloping are further explored. Experiment results showed a maximum output voltage and current of 29.6 V and 29 µA, respectively, under the characteristic conditions of conductor galloping. The corresponding load capacity of the harvester reached a maximum power output of 155.58 µW under minimum resistance of 70 kΩ at 35 cm vibration amplitude and 1.3 Hz frequency. The conductor galloping testing platform indicated that the frequency boost conversion effect was weakened due to the occurrence of torsion movement during conductor galloping, and the output presented a nonlinear variation with the vibration amplitude and frequency. The degree and direction of conductor galloping can be preliminarily judged according to the output trend, and the maximum output power of load capacity of the harvester reached 101.5 μW under 107 MΩ resistance at 1.3 Hz vibration frequency, validating that the proposed energy harvesting system is promising for self-powered sensing applications in low-power monitoring sensors for conductor galloping.© 2017 Elsevier Inc. All rights reserved.

Cooperative compliant traction mechanism for human-friendly biomechanical energy harvesting

In this study, a human-friendly biomechanical energy harvester (HF-BEH) utilizing cooperative compliant traction mechanism is proposed. The knee joint is used to drive the harvester through a compliant medium without wearing any mechanical components. The driving force is large, and there is no added weight and restraint on the knee joint. The work of the harvester can naturally collaborate with the walking/running of the user due to the mechanical adaptability of the compliant medium and reasonable settings, that is, the harvester collects energy when the user does negative work. Frequency up-conversion and mechanical rectification are used to improve electromechanical conversion efficiency. A man wearing the HF-BEH prototype can generate an average power of 0.22 W while walking (4 Km/h) and 0.30 W when running (10 Km/h), with little impact on his mobility. The possibility of self-powered emergency call, positioning and tracking, health monitoring and physical therapy based on HF-BEH has been verified by powering commercial smart electronics with these functions. Human-vehicle interaction through self powered wireless sensing based on HF-BEH is demonstrated to improve the safety of people with limited responsiveness and mobility in the traffic environment. The proposed energy harvesting system can be integrated with functional modules as a self-powered human-assisted system.

Design and Development of a Lead-Freepiezoelectric Energy Harvester for Wideband, Low Frequency, and Low Amplitude Vibrations

In recent years, energy harvesting from ambient vibrations using piezoelectric materials has become the center of attention due to the fact that it has the potential to replace batteries, providing an easy way to power wireless and low power sensors and electronic devices. Piezoelectric material has been extensively used in energy harvesting technologies. However, the most commercially available and widely used piezoelectric materials are lead-based, Pb (PZT), which contains more than 60 weight percent lead (Pb). Due to its extremely hazardous effects on lead elements, there is a strong need to substitute PZT with new lead-free materials that have comparable properties to those of PZT. Lead-free lithium niobate (LiNbO3) piezoelectric material can be considered as a substitute for lead-based piezoelectric materials for vibrational energy scavenging applications. LiNbO3 crystal has a lower dielectric constant comparison to the conventional piezoceramics (for instance, PZT); however, at the same time, LiNbO3 (LN) single crystal presents a figure of merits similar to that of PZT, which makes it the most suitable choice for a vibrational energy harvester based on lead-free materials. The implementation was carried out using a global optimization approach including a thick single-crystal film on a metal substrate with optimized clamped capacitance for better impedance matching conditions. A lot of research shows that standard designs such as linear piezoelectric energy harvesters are not a prominent solution as they can only operate in a narrow bandwidth because of their single high resonant peak in their frequency spectrum. In this paper, we propose, and experimentally validate, a novel lead-free piezoelectric energy harvester to harness electrical energy from wideband, low-frequency, and low-amplitude ambient vibration. To reach this target, the harvester is designed to combine multi-frequency and nonlinear techniques. The proposed energy harvesting system consists of six piezoelectric cantilevers of different sizes and different resonant frequencies. Each is based on lead-free lithium niobate piezoelectric material coupled with a shape memory alloy (nitinol) substrate. The design is in the form of a circular ring to which the cantilevers are embedded to create nonlinear behavior when excited with ambient vibrations. The finite element simulation and the experimental results confirm that the proposed lead-free harvester design is efficient at low frequencies, particularly different frequencies below 250 Hz.

Performance of a Piezoelectric Energy Harvesting System for an Energy-Autonomous Instrumented Total Hip Replacement: Experimental and Numerical Evaluation.

Instrumented implants can improve the clinical outcome of total hip replacements (THRs). To overcome the drawbacks of external energy supply and batteries, energy harvesting is a promising approach to power energy-autonomous implants. Therefore, we recently presented a new piezoelectric-based energy harvesting concept for THRs. In this study, the performance of the proposed energy harvesting system was numerically and experimentally investigated. First, we numerically reproduced our previous results for the physiologically based loading situation in a simplified setup. Thereafter, this configuration was experimentally realised by the implantation of a functional model of the energy harvesting concept into an artificial bone segment. Additionally, the piezoelectric element alone was investigated to analyse the predictive power of the numerical model. We measured the generated voltage for a load profile for walking and calculated the power output. The maximum power for the directly loaded piezoelectric element and the functional model were 28.6 and 10.2 µW, respectively. Numerically, 72.7 µW was calculated. The curve progressions were qualitatively in good accordance with the numerical data. The deviations were explained by sensitivity analysis and model simplifications, e.g., material data or lower acting force levels by malalignment and differences between virtual and experimental implantation. The findings verify the feasibility of the proposed energy harvesting concept and form the basis for design optimisations with increased power output.

Topological cavities in phononic plates for robust energy harvesting

Piezoelectric energy harvesting has attracted tremendous interest for designing sustainable self-powered devices/systems targeted to special environment such as wireless or wearable applications. The traditional cavity (e.g., phononic cavity mode) excitation is highly applicable in terms of sufficient power generation, nevertheless, has to endure the drawback of extremely poor robustness intrinsic to the trivial cavity modes. We propose to use phononic thin plate systems for robust energy harvesting application relying on zero-dimensional cavities confined by the Kekulé distorted topological vortices. The harvesting power induced by topological cavities is about 30 times that of the bare plate. Further studies on the effects of deliberately introduced defects on the output power show that the proposed energy harvesting system is highly robust against symmetry-preserving defects, and is less influenced even for symmetry-breaking defects at moderate perturbation level. Beyond the reported energy harvesting application, we foresee that our work may open avenues for robust operations in the realm of wireless sensing and structural health monitoring.

Modeling and analysis of novel coupled magneto-electro-aeroelastic continuous system for flutter-based energy harvesting system

This paper presents a novel continuous model for improving energy harvesting from the aeroelastic flutter induced vibrations based on the use of magneto-electro-elastic (MEE) materials. The proposed model includes a rigid airfoil attached to an elastic beam. The elastic beam is covered with one or two layers of MEE material, and two electrodes are connected to the MEE layers to harvest the electric potential from the electric field. Besides, an external coil is utilized to induce the electric energy resulting from the MEE layer's magnetic field. The equations governing the proposed energy harvesting system are derived considering the continuous beam model using the constitutive equations of MEE materials and the Gauss and Faraday's laws based on Hamilton's principle. The derived governing equations are then modified based on the method of assumed modes. Assuming that the flow is subsonic, the flow is modeled with Peter's unsteady aerodynamic theory. Moreover, the effects of system parameters such as electric and magnetic resistance on the voltage, generated current, and power are realized to determine the best design parameters in terms of generated power. The ascending trend of generated power up to a specific resistance was observed by examining the electric resistance effect, followed by a descending trend with a further increase in the electric resistance. Besides, it was found that the generated power increases with the increase of magnetic resistance. Finally, the comparison between the MEE and piezo-aeroelastic harvesting efficiencies was performed, which revealed the prior one's superiority from the generated power perspective.

Magnetically coupled piezoelectric galloping-based energy harvester using a tandem configuration

Herein, we propose a piezoelectric galloping-based energy harvester that uses a magnetic coupling effect to improve its energetic performance. This proposed structure includes two elastic structures with bluff bodies arranged in a tandem configuration and a pair of repulsive magnets installed between the two bluff bodies to enable the use of their mutual interaction. A nonlinear coupled aero-electro-mechanical model is established using the extended Hamilton principle to gain a comprehensive understanding of the nonlinear dynamic behaviors of the proposed system. The mechanism of the magnetic interaction between the outer and inner bluff bodies was thoroughly investigated through time histories, phase portrait, and frequency spectrum analysis. The experimental results exhibited good agreement with the analytic results, highlighting that the present model is considerably accurate and reliable. Compared with the conventional system without the engagement of the magnetic coupling effect, a maximum overall average output power of 8.09 mW and power improvement rate of 65% could be obtained for the proposed energy harvesting system with the optimal magnetic gap distance. The proposed energy harvesting system is expected to be a promising alternative for the convenient and practical development of efficient wind energy harvesters.

Broadband spring-connected bi-stable piezoelectric vibration energy harvester with variable potential barrier

To improve the harvesting performance of bi-stable energy harvesters, this paper proposes a novel bi-stable piezoelectric energy harvester which consists of a piezoelectric cantilever beam with a tip magnet and a movable magnet. The movable magnet connects to the base through a spring and is allowed to move along the spring compression direction. The nonlinear distributed parameters dimensionless mathematic model of the harvester is derived based on Hamilton’s principle. The effects of excitation amplitude, excitation frequency, spring stiffness and Gaussian white noise on harvesting performance are analyzed by applying bifurcation diagram, phase trajectory, Poincare map and power output. The numerical simulations show that the proposed energy harvesting system reduces the potential barrier and makes the snap-through motion easier. It is demonstrated that the proposed energy harvester provides wider bandwidth and higher efficiency than the typical bi-stable energy harvester when subjected to low excitation amplitudes or low excitation frequencies.

Wind energy harvesting using piezoelectric macro fiber composites based on flutter mode

Mechanical energy such as the wind flow widely exists in nature as renewable and sustainable energy source. It could be converted into electrical energy throughout piezoelectricity which has capability for converting mechanical energy into electrical energy. In this paper, an innovation piezoelectric energy harvesting (PEH) system is proposed by using the piezoelectric macro fiber composites (MFC) based on flutter mode. It is demonstrated that this PEH-MFC system exhibits the excellent characteristic of flexibility on large deformation and reliability in energy harvesters and effectively captures power from wind energy. The PEH-MFC system is composed of a soft substrate linked with a polymer triangular leaf by a copper hinge. The active MFC is attached at the bottom of the soft substrate as the core component of system. A series of experiments on energy harvesting systems for various substrate materials and various types of MFC are performed in wind tunnel. The flutter mode is obtained under the critical flutter wind speed in order to acquire the excellent behavior of extracting power through this innovation PEH-MFC system. The experimental results show that the thickness and stiffness of PEH substrate have significant effects on the performance of energy harvesting. The maximum peak-to-peak open circuit voltage of 82 V is obtained using the MFC-2807 with Al substrate at the wind speed of 7.5 m/s. The resulting direct voltage and electric power are 25.8 V and 0.54 mW with a load resistance of 680 kΩ, respectively. It is concluded that the proposed energy harvesting system using MFC based on flutter mode can generate a power efficiency of 9.18 mW/cm3 which can meet the requirement of conventional MEMS.

Investigation of Thermoelectric Generator with Power Converter for Energy Harvesting Applications

This research work investigates the analytical modelling of thermocouple, thermoelectric module (TEM) and TEM with a single switch power converter. The TEM with a power converter is used to boost the output voltage to meet the load requirement. The P-I and V-I curve of a TEM for a temperature difference (ΔT) of 95°C and 135°C is compared with the experimental results. The prototype model of the proposed energy harvesting system has been developed and tested in the laboratory to validate its feasibility. A large voltage conversion ratio of 19.57 with an efficiency of 91.5% is obtained from the power converter. Hence, the proposed system can employ to power DC micro-grid applications, when TEMs are connected in series and/or parallel configuration.

A Triple-Band High-Gain Multibeam Ambient RF Energy Harvesting System Utilizing Hybrid Combining

Overcoming the challenge of battery recharging and replacement in industry Internet-of-Things (IoT) applications is considered by proposing the design of a triple-band high-gain multibeam ambient radio frequency (RF) energy harvesting system utilizing hybrid combining. The novelty of the design is that it simultaneously exploits frequency, space, and polarization to maximize the harvested RF energy. Wideband hybrid combining is proposed, which enables the harvesting of energy at low RF power densities while maintaining the wide frequency and space coverage necessary for ambient RF energy harvesting. The antenna design consisting of 16-ports has an average area per port of 0.3λ × 0.3λ (where λ is the freespace wavelength at 1.8 GHz) and is demonstrated to achieve a wide relative bandwidth of 38.5% covering the GSM-1800, UMTS-2100, and WiFi frequency bands. Hybrid combining of the 16-port antenna provides multiple antenna beams each with up to 11 dBi antenna gain and these provide broad beam coverage. The design for the rectifiers, using multistub impedance matching, is also provided and these are shown to be efficient over the frequency bands of interest. Measurements in an anechoic chamber demonstrate that the proposed energy harvesting system can provide an output dc voltage of more than 755 mV, an output dc power of more than -6.4 dBm and RF-to-dc efficiencies greater than 40% when the power density is more than 1400 μW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . It is also shown that the proposed system can provide output dc power of 80 μW and 7.3 μW in real outdoor and indoor ambient environments, respectively.