Leaf Motion Research Articles

Charge generation by passive plant leaf motion at low wind speeds: design and collective behavior of plant-hybrid energy harvesters

Energy harvesting techniques can exploit even subtle passive motion like that of plant leaves in wind as a consequence of contact electrification of the leaf surface. The effect is strongly enhanced by artificial materials installed as ‘artificial leaves’ on the natural leaves creating a recurring mechanical contact and separation. However, this requires a controlled mechanical interaction between the biological and the artificial component during the complex wind motion. Here, we build and test four artificial leaf designs with varying flexibility and degrees of freedom across the blade operating on Nerium oleander plants. We evaluate the apparent contact area (up to 10 cm2 per leaf), the leaves’ motion, together with the generated voltage, current and charge in low wind speeds of up to 3.3 m s−1 and less. Single artificial leaves produced over 75 V and 1 µA current peaks. Softer artificial leaves increase the contact area accessible for energy conversion, but a balance between softer and stiffer elements in the artificial blade is optimal to increase the frequency of contact-separation motion (here up to 10 Hz) for energy conversion also below 3.3 m s−1. Moreover, we tested how multiple leaves operating collectively during continuous wind energy harvesting over several days achieve a root mean square power of ∼6 µW and are capable to transfer ∼80 µC every 30–40 min to power a wireless temperature and humidity sensor autonomously and recurrently. The results experimentally reveal design strategies for energy harvesters providing autonomous micro power sources in plant ecosystems for example for sensing in precision agriculture and remote environmental monitoring.

A novel EPID-based MLC QA method with log files achieving submillimeter accuracy.

The purpose of this study is to develop an electronic portal imaging device-based multi-leaf collimator calibration procedure using log files. Picket fence fields with 2-14mm nominal strip widths were performed and normalized by open field. Normalized pixel intensity profiles along the direction of leaf motion for each leaf pair were taken. Three independent algorithms and an integration method derived from them were developed according to the valley value, valley area, full-width half-maximum (FWHM) of the profile, and the abutment width of the leaf pairs obtained from the log files. Three data processing schemes (Scheme A, Scheme B, and Scheme C) were performed based on different data processing methods. To test the usefulness and robustness of the algorithm, the known leaf position errors along the direction of perpendicular leaf motion via the treatment planning system were introduced in the picket fence field with nominal 5, 8, and 11mm. Algorithm tests were performed every 2weeks over 4 months. According to the log files, about 17.628% and 1.060% of the leaves had position errors beyond ±0.1 and ±0.2mm, respectively. The absolute position errors of the algorithm tests for different data schemes were 0.062±0.067 (Scheme A), 0.041±0.045 (Scheme B), and 0.037±0.043 (Scheme C). The absolute position errors of the algorithms developed by Scheme C were 0.054±0.063 (valley depth method), 0.040±0.038 (valley area method), 0.031±0.031 (FWHM method), and 0.021±0.024 (integrated method). For the efficiency and robustness test of the algorithm, the absolute position errors of the integration method of Scheme C were 0.020±0.024 (5mm), 0.024±0.026 (8mm), and 0.018±0.024 (11mm). Different data processing schemes could affect the accuracy of the developed algorithms. The integration method could integrate the benefits of each algorithm, which improved the level of robustness and accuracy of the algorithm. The integration method can perform multi-leaf collimator (MLC) quality assurance with an accuracy of 0.1mm. This method is simple, effective, robust, quantitative, and can detect a wide range of MLC leaf position errors.

Assessing quality assurance of multi-leaf collimator using the structural similarity index.

This study aims to evaluate the viability of utilizing the Structural Similarity Index (SSI*) as an innovative imaging metric for quality assurance (QA) of the multi-leaf collimator (MLC). Additionally, we compared the results obtained through SSI* with those derived from a conventional Gamma index test for three types of Varian machines (Trilogy, Truebeam, and Edge) over a 12-week period of MLC QA in our clinic. To assess sensitivity to MLC positioning errors, we designed a 1cm slit on the reference MLC, subsequently shifted by 0.5-5mm on the target MLC. For evaluating sensitivity to output error, we irradiated five 25cm×25cm open fields on the portal image with varying Monitor Units (MUs) of 96-100. We compared SSI* and Gamma index tests using three linear accelerator (LINAC) machines: Varian Trilogy, Truebeam, and Edge, with MLC leaf widths of 1, 0.5, and 0.25mm. Weekly QA included VMAT and static field modes, with Picket fence test images acquired. Mechanical uncertainties related to the LINAC head, electronic portal imaging device (EPID), and MLC during gantry rotation and leaf motion were monitored. The Gamma index test started detecting the MLC shift at a threshold of 4mm, whereas the SSI* metric showed sensitivity to shifts as small as 2mm. Moreover, the Gamma index test identified dose changes at 95MUs, indicating a 5% dose difference based on the distance to agreement (DTA)/dose difference (DD) criteria of 1mm/3%. In contrast, the SSI* metric alerted to dose differences starting from 97MUs, corresponding to a 3% dose difference. The Gamma index test passed all measurements conducted on each machine. However, the SSI* metric rejected all measurements from the Edge and Trilogy machines and two from the Truebeam. Our findings demonstrate that the SSI* exhibits greater sensitivity than the Gamma index test in detecting MLC positioning errors and dose changes between static and VMAT modes. The SSI* metric outperformed the Gamma index test regarding sensitivity across these parameters.

A novel lung SBRT treatment planning: Inverse VMAT plan with leaf motion limitation to ensure the irradiation reproducibility of a moving target

This study exposed the implementation of a novel technique (VMATLSL) for the planning of moving targets in lung stereotactic body radiation therapy (SBRT). This new technique has been compared to static conformal radiotherapy (3D-CRT), volumetric-modulated arc therapy (VMAT), and dynamic conformal arc (DCA). The rationale of this study was to lower geometric complexity (54.9% lower than full VMAT) and hence ensure the reproducibility of the treatment delivery by reducing the risk for interplay errors induced by respiratory motion. Dosimetry metrics were studied with a cohort of 30 patients. Our results showed that leaf speed limitation provided conformal number (CN) close to the VMAT (median CN of VMATLSL is 0.78 vs 0.82 for full VMAT) and was a significant improvement on 3D-CRT and DCA with segment-weight optimized (respectively 0.55 and 0.57). This novel technique is an alternative to VMAT or DCA for lung SBRT treatments, combining independence from the patient's breathing pattern, from the size and amplitude of the lesion, free from interplay effect, and with dosimetry metrics close to the best that could be achieved with full VMAT.

The Potential Ability of Plan Complexity Metrics on the Dose Calculation and Plans Delivery in Intensity Modulated Radiotherapy.

The excessive modulation of treatment plan during radiotherapy (RT) increases the complexity. Evaluation of the multidimensional relationship between program complexity metrics, computation-based patient-specific quality assurance (PSQA), and conventional measurement-based PSQA could assist in enhancing the robustness of treatment planning, guide the allocation of clinical QA resources, and ultimately lessen QA workload. The fifty-five metrics affecting RT planning and delivery accuracy were calculated by a house-built program to describe the complexity of 404 dynamic IMRT plans, with sensitivity to the small field, aperture position, MLC edge, low MUs, MLC leaf motion, leaf speed/acceleration, etc. The calculation-based PSQA was performed using Monte Carlo (MC) method and Collapsed Cone Convolution (CCC) algorithm, implemented in SciMoCa and Mobius 3D, respectively. The measurement-based PSQA was performed using 3D diode arrays with different geometries covering "O", "+" and " × " shapes which exist in ArcCheck, Delta4 phantom+ (Delta4) and Delta4PT phantom (Delta4PT), respectively. Gamma passing rates (GPRs) were recorded to measure the results of each QA system. This multidimensional relationship was evaluated using correlation analysis and principal component linear regression (PCR) analysis. A total of 4448 GPRs for various QA systems corresponding to two Linacs were counted. The modulation index for speed (MIs) and modulation index for acceleration (MIa) were consistently located at the high points of the radarplots of the Spearman correlation coefficient |rs| between metrics and GPRs of the four QA systems, just except Delta4. Besides, the rs between SciMoCa and ArcCheck were 0.275-0.531 (P ≤ 0.001), SciMoCa and Delta4 were 0.32-0.418 (P ≤ 0.001), and Mobius 3Dand Delta4PT were 0.124-0.226 (P ≤ 0.05). The PCR model's coefficients determination (R2) for SciMoCa were 0.461-0.756 (P ≤ 0.001), ArcCheck were 0.243-0.440 (P ≤ 0.001), Delta4 were 0.268-0.402 (P ≤ 0.001), Mobius 3D were 0.299-0.407 (P ≤ 0.001), and Delta4PT were 0.087-0.141 (P ≤ 0.05). This study is the first overall assessment of the impact of various complexity metrics on the accuracy of TPS calculation and Linac delivery. Of the metrics studied, MIs and MIa metrics have a standout impact on the ability of the TPS calculation and delivery system, extra attention should be paid during the planning process. It is inappropriate to utilize calculation-based QA to predict the results of measurement-based QA since there is a poor correlation between the two. Furthermore, calculation-based QA outperforms measurement-based QA in identifying highly complex plans, which can further guide clinical QA process optimization and save limited clinical resources.

PO-2042 Plan quality & deliverability of IMRT plans for lung cancer using various leaf motion calculators

PO-2042 Plan quality & deliverability of IMRT plans for lung cancer using various leaf motion calculators

Monte Carlo based continuous aperture optimization for VMAT on conventional and MR-linacs: A proof of concept.

Currently, the commercial treatment planning systems for magnetic-resonance guided linear accelerators (MR-linacs) only support step-and-shoot intensity-modulated radiation therapy (IMRT). However, recent studies have shown the feasibility of delivering arc therapy on MR-linacs, which is expected to improve dose distributions and delivery speed. By accurately accounting for the electron return effect in the presence of a magnetic field, a Monte Carlo (MC) algorithm is ideally suited for the inverse treatment planning of thistechnique. We propose a novel MC-based continuous aperture optimization (MCCAO) algorithm for volumetric modulated arc therapy (VMAT), including applications to VMAT on MR-linacs and trajectory-based VMAT. A unique feature of MCCAO is that the continuous character of gantry rotation and multileaf collimator (MLC) motion is accounted for at every stage of theoptimization. The optimization process uses a multistage simulation of 4D dose distribution. A phase space is scored at the top surface of the MLC and the energy deposition of each particle history is mapped to its position in this phase space. A progressive sampling method is used, where both MLC leaf positions and monitor unit (MU) weights are randomly changed, while respecting the linac mechanical limits. Due to the continuous nature of the leaf motion, such changes affect not only a single control point, but propagate to the adjacent ones as well, and the corresponding dose distribution changes are accounted for. A dose-volume cost function is used, which includes the MC statisticaluncertainty. We applied our optimization technique to various treatment sites, using standard and flattening-filter-free (FFF) 6 MV beam models, with and without a 1.5 T magnetic field. MCCAO generates deliverable plans, whose dose distributions are in good agreement with measurements on ArcCHECK and stereotactic radiosurgery End-To-EndPhantom. We show that the novel MCCAO method generates VMAT plans that meet clinical objectives for both conventional andMR-linacs.

Beneath the tree: The sounds of a trembling giant

The Pando aspen grove (Populus tremuloides) consists of more than 40000 genetically identical aspen stems spread across 106 acres in south-central Utah. While Pando resembles a forest, it is a single organism connected at the roots, making it the world's largest tree and one of the largest living things on the planet. First identified in 1976, Pando has not been studied as a bioacoustic subject. Focusing on recordings captured simultaneously above and below ground on July 12, 2022 during a thunderstorm, our presentation reveals a unique acoustic portrait of this botanical wonder. We compare audible sounds of Pando’s leaves with hydrophone recordings made in connection with the tree's root system. This dual soundscape shows that leaf motion causes vibrations that pass throughout the organism, from its branches to its base. The recordings suggest that the grove’s massive, interconnected root system is highly resonant with potential for future recordings and research.

Early Detection of Ginger Rhizome Rot Using Leaf Motion

Early Detection of Ginger Rhizome Rot Using Leaf Motion

A Simulation Study of Tolerance of Breathing Amplitude Variations in Radiotherapy of Lung Cancer Using 4DCT and Time-Resolved 4DMRI.

As patient breathing irregularities can introduce a large uncertainty in targeting the internal tumor volume (ITV) of lung cancer patients, and thereby affect treatment quality, this study evaluates dose tolerance of tumor motion amplitude variations in ITV-based volumetric modulated arc therapy (VMAT). A motion-incorporated planning technique was employed to simulate treatment delivery of 10 lung cancer patients' clinical VMAT plans using original and three scaling-up (by 0.5, 1.0, and 2.0 cm) motion waveforms from single-breath four-dimensional computed tomography (4DCT) and multi-breath time-resolved 4D magnetic resonance imaging (TR-4DMRI). The planning tumor volume (PTV = ITV + 5 mm margin) dose coverage (PTV D95%) was evaluated. The repeated waveforms were used to move the isocenter in sync with the clinical leaf motion and gantry rotation. The continuous VMAT arcs were broken down into many static beam fields at the control points (2°-interval) and the composite plan represented the motion-incorporated VMAT plan. Eight motion-incorporated plans per patient were simulated and the plan with the native 4DCT waveform was used as a control. The first (D95% ≤ 95%) and second (D95% ≤ 90%) plan breaching points due to motion amplitude increase were identified and analyzed. The PTV D95% in the motion-incorporated plans was 99.4 ± 1.0% using 4DCT, closely agreeing with the corresponding ITV-based VMAT plan (PTV D95% = 100%). Tumor motion irregularities were observed in TR-4DMRI and triggered D95% ≤ 95% in one case. For small tumors, 4 mm extra motion triggered D95% ≤ 95%, and 6-8 mm triggered D95% ≤ 90%. For large tumors, 14 mm and 21 mm extra motions triggered the first and second breaching points, respectively. This study has demonstrated that PTV D95% breaching points may occur for small tumors during treatment delivery. Clinically, it is important to monitor and avoid systematic motion increase, including baseline drift, and large random motion spikes through threshold-based beam gating.

Measuring Triboelectric Energy Conversion in Leaves of Living Plants

Contact electrification or triboelectric charging is a long-known ubiquitous phenomenon which occurs on almost all material surfaces. It comprises the generation of longer- or shorter-lived static charges on the surface of a material upon contact with another material. The classical example is the charging of hairs with a rubber balloon. The effect is receiving increased attention as a possible mechanism to convert mechanical energy into electricity for energy harvesting. It is required that an electrode is installed near the charged surface (often a dielectric polymer) into which the generated charges can be electrostatically induced. Multiple artificial energy harvesters have been developed in the last decade to exploit this mechanism. Interestingly, also in nature, configurations exist that allow structures to convert mechanical energy into electricity by the triboelectric effect. These are especially the leaves of all living plants. Indeed, living plants have recently been used as triboelectric energy converters and for harvesting energy from leaf motion in the wind [1]–[5]. Here, we describe in detail how to measure triboelectric charges in the tissue of living plants, the particularities of measuring such signals in the organisms, and what is essential when using them for energy harvesting.

Wind dynamics and leaf motion: Approaching the design of high-tech devices for energy harvesting for operation on plant leaves.

High-tech sensors, energy harvesters, and robots are increasingly being developed for operation on plant leaves. This introduces an extra load which the leaf must withstand, often under further dynamic forces like wind. Here, we took the example of mechanical energy harvesters that consist of flat artificial "leaves" fixed on the petioles of N. oleander, converting wind energy into electricity. We developed a combined experimental and computational approach to describe the static and dynamic mechanics of the natural and artificial leaves individually and join them together in the typical energy harvesting configuration. The model, in which the leaves are torsional springs with flexible petioles and rigid lamina deforming under the effect of gravity and wind, enables us to design the artificial device in terms of weight, flexibility, and dimensions based on the mechanical properties of the plant leaf. Moreover, it predicts the dynamic motions of the leaf-artificial leaf combination, causing the mechanical-to-electrical energy conversion at a given wind speed. The computational results were validated in dynamic experiments measuring the electrical output of the plant-hybrid energy harvester. Our approach enables us to design the artificial structure for damage-safe operation on leaves (avoiding overloading caused by the interaction between leaves and/or by the wind) and suggests how to improve the combined leaf oscillations affecting the energy harvesting performance. We furthermore discuss how the mathematical model could be extended in future works. In summary, this is a first approach to improve the adaptation of artificial devices to plants, advance their performance, and to counteract damage by mathematical modelling in the device design phase.

Insensitivity of machine log files to MLC leaf backlash and effect of MLC backlash on clinical dynamic MLC motion: An experimental investigation.

PurposeMulti‐leaf‐collimator (MLC) leaf position accuracy is important for accurate dynamic radiotherapy treatment plan delivery. Machine log files have become widely utilized for quality assurance (QA) of such dynamic treatments. The primary aim is to test the sensitivity of machine log files in comparison to electronic portal imaging device (EPID)‐based measurements to MLC position errors caused by leaf backlash. The secondary aim is to investigate the effect of MLC leaf backlash on MLC leaf motion during clinical dynamic plan delivery.MethodsThe sensitivity of machine log files and two EPID‐based measurements were assessed via a controlled experiment, whereby the length of the “T” section of a series of 12 MLC leaf T‐nuts in a Varian Millennium MLC for a Trilogy C‐series type linac was reduced by sandpapering the top of the “T” to introduce backlash. The built‐in machine MLC leaf backlash test as well as measurements for two EPID‐based dynamic MLC positional tests along with log files were recorded pre‐ and post‐T‐nut modification. All methods were investigated for sensitivity to the T‐nut change by assessing the effect on measured MLC leaf positions. A reduced version of the experiment was repeated on a TrueBeam type linac with Millennium MLC.ResultsNo significant differences before and after T‐nut modification were detected in any of the log file data. Both EPID methods demonstrated sensitivity to the introduced change at approximately the expected magnitude with a strong dependence observed with gantry angle. EPID‐based data showed MLC positional error in agreement with the micrometer measured T‐nut length change to 0.07 ± 0.05 mm (1 SD) using the departmental routine QA test. Backlash results were consistent between linac types.ConclusionMachine log files appear insensitive to MLC position errors caused by MLC leaf backlash introduced via the T‐nut. The effect of backlash on clinical MLC motions is heavily gantry angle dependent.

Automated conversion of Millennium-120 VMAT plans to HDMLC geometry: Software development and treatment of first patients.

PurposeTo provide plan backup resiliency for patients treated on a solitary high definition multileaf collimator (HDMLC) linac by developing a fully integrated Eclipse script, which converts patient plans initially optimized on Millennium‐120 (M120) MLC to dosimetrically equivalent leaf motions for delivery on HDMLC. In the event of HDMLC machine downtime, affected patients can be transferred to Millennium‐120 units, and their backup plan delivered without delay.MethodsWrite‐enabled Eclipse scripting is leveraged to generate HDMLC treatment fields with control points parameterized to mimic apertures of an existing Millennium‐120 VMAT plan. Non‐parity between intermediate control point gantry angles of script generated arcs relative to VMAT is reconciled through an interpolation subroutine to correct for the apertures and monitor units that would have existed at intermediate angles. Differences in dosimetric leaf gap are corrected by displacing the subset of leaves undergoing dynamic motion. A nominal change to plan normalization corrects for remaining discrepancies between beam models.Results Over 220 non‐SABR VMAT patients were treated on a solitary HDMLC linac with plans converted using the developed script. All have undergone streamlined RO review and physics quality assurance (QA), where the converted plan replicates the original leaf patterns, representing a minor dosimetric perturbation. Analyzing a subset of converted plans delivered at four anatomical sites, on average 99.3% of points pass the 1%/1 mm gamma criterion. Dose‐volume histograms between the original and converted plans are in excellent agreement. ArcCheck measurements comparing delivery of the converted HDMLC plan to the calculated M120 dose distribution averaged a gamma pass rate of 99.4% (95.2%) at a 3%/3 mm (2%/2 mm) criterion. The conversion process takes 30 s to run, avoids errors in exporting/re‐importing, and generates leaf motions deliverable within machine limits.ConclusionThe methodology developed for automated plan conversion helped maximize the utilization of a solitary HDMLC linac, while preserving backup interoperability with minimal overhead.

Optimization of sliding windows IMRT treatment planning

Intensity-modulated radiation therapy (IMRT) with sliding windows is a form of radiation therapy that delivers precise radiation dose to a tumor/target region. It uses a multi-leaf collimator (MLC) to move pairs of unidirectional tungsten leaves across a radiation emitting region to conform the shape of the radiation beam to the target regions. This is a dynamic treatment approach which aims to deliver adequate radiation dose to target regions while minimizing radiation delivery to healthy tissues. This paper proposes a linear optimization model for IMRT with sliding windows. This model directly incorporates a number of deliverability constraints to conform to physical limitations of the LINAC, including the required distance between leaves through the treatment process and restrictions on leaf interdigitation. We demonstrate the viability of this model using patient data and discuss the leaf motion proposed by our model. Such a model can be embedded in treatment planning systems to improve both the quality of the treatment and the efficiency of the treatment planning process.

A digital sensor to measure real-time leaf movements and detect abiotic stress in plants.

Plant and plant organ movements are the result of a complex integration of endogenous growth and developmental responses, partially controlled by the circadian clock, and external environmental cues. Monitoring of plant motion is typically done by image-based phenotyping techniques with the aid of computer vision algorithms. Here we present a method to measure leaf movements using a digital inertial measurement unit (IMU) sensor. The lightweight sensor is easily attachable to a leaf or plant organ and records angular traits in real-time for two dimensions (pitch and roll) with high resolution (measured sensor oscillations of 0.36 ± 0.53° for pitch and 0.50 ± 0.65° for roll). We were able to record simple movements such as petiole bending, as well as complex lamina motions, in several crops, ranging from tomato to banana. We also assessed growth responses in terms of lettuce rosette expansion and maize seedling stem movements. The IMU sensors are capable of detecting small changes of nutations (i.e. bending movements) in leaves of different ages and in different plant species. In addition, the sensor system can also monitor stress-induced leaf movements. We observed that unfavorable environmental conditions evoke certain leaf movements, such as drastic epinastic responses, as well as subtle fading of the amplitude of nutations. In summary, the presented digital sensor system enables continuous detection of a variety of leaf motions with high precision, and is a low-cost tool in the field of plant phenotyping, with potential applications in early stress detection.

Effective Organs-at-Risk Dose Sparing in Volumetric Modulated Arc Therapy Using a Half-Beam Technique in Whole Pelvic Irradiation.

BackgroundAlthough there are some controversies regarding whole pelvic radiation therapy (WPRT) due to its gastrointestinal and hematologic toxicities, it is considered for patients with gynecological, rectal, and prostate cancer. To effectively spare organs-at-risk (OAR) doses using multi-leaf collimator (MLC)’s optimal segments, potential dosimetric benefits in volumetric modulated arc therapy (VMAT) using a half-beam technique (HF) were investigated for WPRT.MethodsWhile the size of a fully opened field (FF) was decided to entirely include a planning target volume in all beam’s eye view across arc angles, the HF was designed to use half the FF from the isocenter for dose optimization. The left or the right half of the FF was alternatively opened in VMAT-HF using a pair of arcs rotating clockwise and counterclockwise. Dosimetric benefits of VMAT-HF, presented with dose conformity, homogeneity, and dose–volume parameters in terms of modulation complex score, were compared to VMAT optimized using the FF (VMAT-FF). Consequent normal tissue complication probability (NTCP) by reducing the irradiated volumes was evaluated as well as dose–volume parameters with statistical analysis for OAR. Moreover, beam-on time and MLC position precision were analyzed with log files to assess plan deliverability and clinical applicability of VMAT-HF as compared to VMAT-FF.ResultsWhile VMAT-HF used 60%–70% less intensity modulation complexity than VMAT-FF, it showed superior dose conformity. The small intestine and colon in VMAT-HF showed a noticeable reduction in the irradiated volumes of up to 35% and 15%, respectively, at an intermediate dose of 20–45 Gy. The small intestine showed statistically significant dose sparing at the volumes that received a dose from 15 to 45 Gy. Such a dose reduction for the small intestine and colon in VMAT-HF presented a significant NTCP reduction from that in VMAT-FF. Without sacrificing the beam delivery efficiency, VMAT-HF achieved effective OAR dose reduction in dose–volume histograms.ConclusionsVMAT-HF led to deliver conformal doses with effective gastrointestinal-OAR dose sparing despite using less modulation complexity. The dose of VMAT-HF was delivered with the same beam-on time with VMAT-FF but precise MLC leaf motions. The VMAT-HF potentially can play a valuable role in reducing OAR toxicities associated with WPRT.

Biohybrid generators based on living plants and artificial leaves: influence of leaf motion and real wind outdoor energy harvesting

Plants translate wind energy into leaf fluttering and branch motion by reversible tissue deformation. Simultaneously, the outermost structure of the plant, i.e. the dielectric cuticula, and the inner ion-conductive tissue can be used to convert mechanical vibration energy, such as that produced during fluttering in the wind, into electricity by surface contact electrification and electrostatic induction. Constraining a tailored artificial leaf to a plant leaf can enhance oscillations and transient mechanical contacts and thereby increase the electricity outcome. We have studied the effects of wind-induced mechanical interactions between the leaf of a plant (Rhododendron) and a flexible silicone elastomer-based artificial leaf fixed at the petiole on power output and whether performance can be further tuned by altering the vibrational behavior of the artificial leaf. The latter is achieved by modifying a concentrated mass at the tip of the artificial leaf and observing plant-generated current and voltage signals under air flow. In this configuration, the plant-hybrid wind-energy converters can directly power light-emitting diodes and a temperature sensor. Detailed output analysis has revealed that, under all conditions, an increase in wind speed leads to nearly linearly increased voltages and currents. Accordingly, the cumulative sum energy reaches its highest values at the highest wind speed and resulting oscillations of the plant-artificial leaf system. The mass at the tip can, in most cases, be used to increase the voltage amplitude and frequency. Nevertheless, this behavior was found to depend on the individual configuration of the system, such as the leaf morphology. Analysis of these factors under controlled conditions is crucial for optimizing systems meant to operate in unstructured outdoor scenarios. We have established, in a first approach, that the artificial leaf-plant hybrid generator is capable of autonomously generating electricity outdoors under real outdoor wind conditions, even at a low average wind speed of only 1.9 m s−1.

On the unsteady dynamics of synthetic leaves: Laboratory experiments using synchronized PIV and DIC

The unsteady 3D dynamics of various synthetic leaves and the induced turbulence are systematically studied experimentally for representative Cauchy numbers in a wind tunnel under nearly uniform incoming flows. Synchronized digital image correlation (DIC) and high-frame-rate particle image velocimetry (PIV) are employed to track the structure dynamics simultaneously and the surrounding flow field to uncover the fluid-solid interaction. A high-resolution six-axis load cell is also used to quantify the synthetic leaves' induced force and torque under various flows. The shapes of synthetic leaves inspected are representative of selected environments (e.g., calm to windy weather; tropical to temperate climate). The Cauchy number is set to resemble those observed in natural conditions. This presentation will discuss insights from synchronized PIV-DIC techniques on the synthetic leaves' distinct behavior and wake flow response. Particular emphasis is placed on characterizing flow instability and the leave shape's role in the motions and force. For this purpose, we inspected the instantaneous force and torque as well as their structure. We will also discuss the relationship between leave shapes with force and torque fluctuations linking them with the leaf motion obtained from DIC measurements. In particular, the results show that selected leaf shapes experience significantly larger and distinct force and torque fluctuations and larger pitch magnitude, as shown in Fig. 5. A shared monotonically decreasing trend of the nondimensional frequency (Strouhal number, St = fL/U) is evidenced for standard environmental conditions.

A biomechanical model of leaf inclination angle oscillations after raindrop impact

Raindrop impact exerts a force on the leaf resulting in a decaying oscillation of the leaf inclination angle. Nondestructive measurements of leaf oscillations is important for predicting changes in leaf angles in the field based on morphometric properties of leaves. The objectives of this study were to determine if a second order impulse response could describe experimentally observed changes in leaf inclination angle, to determine if field measurable, nondestructive leaf traits significantly correlate with model parameters, and to determine if the model parameters were species-specific. This study examined leaf oscillations for three common species in Colorado, USA (Acer saccharinum, Quercus gambelii, and Ulmus pumila) due to two different raindrop sizes. The drop impact was created by releasing a single drop of known size from a known height. The resulting leaf motion was recorded using a high-speed video camera. The images were then processed to measure the leaf inclination angle as a function of time, and a model was used to fit the data. The model was evaluated for quality of fit to the data. The experimental data closely fit the modeled data, indicating that the impulse response appropriately predicts leaf oscillations after raindrop impact. Strong linear relationships existed between leaf mass and maximum change in leaf inclination angle after drop impact for both the experimental and the modeled data. The model parameters were also found to be species-specific. The oscillations in leaf inclination angle are accurately described with a second order impulse response. The parameters of the impulse response correlate with field measurable leaf traits and the parameters are species-specific. The data and approach in this study provided a nondestructive tool for the prediction of changes in leaf inclination angle for many broad-leaved species with diverse leaf morphometric properties.