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F. Meder et al.
per square, Thorlabs Inc., USA) were coated with a thin layer of silicone rubber adhesive (Sil-Poxy TM , Smooth-On Inc., USA) applied on the ITO-layer by a doctor blade.
Immediately after, a layer of translucent silicone rubber was added (thickness 500 µm,
obtained from Modulor GmbH, Germany, previously washed with isopropyl alcohol and
dry wiped using dust-free tissue) and dried for a minimum of 24 h. The multilayer sheets
were cut into the desired shapes using a laser cutter (VersaLaser VLS3.60, Universal
Laser Systems Inc., USA). Self-adhesive Velcro® strips were glued onto the artificial
leaf as an attachment system to fix the artificial leaves to the plant leaf’s petioles. In addition, to connect the ITO electrode, the silicone film was carefully lifted from the ITO
electrode in one corner and a piece of copper tape with conductive glue was attached
to the ITO layer. Then the cable was soldered onto the copper tape and the silicone
layer was brought back and fixed using the silicone adhesive. All cutting edges were
sealed with silicone. The leaves were fixed at the petioles of the natural leaves to obtain
biohybrid plant energy harvesters.
2.3 Data Acquisition and Analysis
Voltages were measured with an oscilloscope using a 100 MOhm probe (MSO7014A,
Agilent Technologies, USA). Short circuit currents were measured using a high input
impedance electrometer (6517B, Keithley, USA). Experiments with different electrodes
(further described in the main text) have been conducted in a Faraday cage and, to generate charges in a controlled manner, an artificial leaf segment (25 mm 2 ) was mechanically
actuated to create contact with the leaf of F. microcarpa at a frequency of 5 Hz producing
an impact force of 0.5 N (the experimental setup was described in detail previously) [18].
Plant hybrid generators were exposed to wind of controllable speed in a specialized phytochamber (height: 2.13 m, depth: 2.75 m, width: 2.5 m) equipped with an active climate
control system and a wind source consisting of 96 individually adjustable nozzles that
were all oriented towards the plant which was placed in a distance of ~50 cm from the
nozzles. A ventilation system (MUB 042-500DV-A2, Systemair, Skinnskatteberg, Sweden, max speed: 1330 rpm) in combination with a frequency converter (VLT® HVAC
Drive FC 102, Danfoss, Nordborg, Denmark) allowed controlling the wind speed. Wind
speed at the leaf was measured at a distance of ~3 cm in front of the leaf using a hot
wire anemometer (405i, Testo SE & Co. KGaA, Germany). During all measurements,
illumination was kept constant and the temperature was kept at 22 ± 1 °C. The relative
humidity (RH) was typically 50 ± 3%. Videos of leaf oscillations have been recorded
with a GoPro Hero7 camera at 240 fps and they were analyzed by automatic and manual
positional tracking of plant and artificial leaf tips using the software Tracker, Version
5.1.3. Local derivatives of the vibrational profiles were obtained using Matlab, Version
R2019b. The thermometer powered by the plants was a DST-50 Digital Thermometer
(Elitech, UK) from which solar cell and battery have been removed before connecting
it to the described circuit. The green LEDs were NSPG500DS (Nichia Corp., Japan).
F. Meder et al.
per square, Thorlabs Inc., USA) were coated with a thin layer of silicone rubber adhesive (Sil-Poxy TM , Smooth-On Inc., USA) applied on the ITO-layer by a doctor blade.
Immediately after, a layer of translucent silicone rubber was added (thickness 500 µm,
obtained from Modulor GmbH, Germany, previously washed with isopropyl alcohol and
dry wiped using dust-free tissue) and dried for a minimum of 24 h. The multilayer sheets
were cut into the desired shapes using a laser cutter (VersaLaser VLS3.60, Universal
Laser Systems Inc., USA). Self-adhesive Velcro® strips were glued onto the artificial
leaf as an attachment system to fix the artificial leaves to the plant leaf’s petioles. In addition, to connect the ITO electrode, the silicone film was carefully lifted from the ITO
electrode in one corner and a piece of copper tape with conductive glue was attached
to the ITO layer. Then the cable was soldered onto the copper tape and the silicone
layer was brought back and fixed using the silicone adhesive. All cutting edges were
sealed with silicone. The leaves were fixed at the petioles of the natural leaves to obtain
biohybrid plant energy harvesters.
2.3 Data Acquisition and Analysis
Voltages were measured with an oscilloscope using a 100 MOhm probe (MSO7014A,
Agilent Technologies, USA). Short circuit currents were measured using a high input
impedance electrometer (6517B, Keithley, USA). Experiments with different electrodes
(further described in the main text) have been conducted in a Faraday cage and, to generate charges in a controlled manner, an artificial leaf segment (25 mm 2 ) was mechanically
actuated to create contact with the leaf of F. microcarpa at a frequency of 5 Hz producing
an impact force of 0.5 N (the experimental setup was described in detail previously) [18].
Plant hybrid generators were exposed to wind of controllable speed in a specialized phytochamber (height: 2.13 m, depth: 2.75 m, width: 2.5 m) equipped with an active climate
control system and a wind source consisting of 96 individually adjustable nozzles that
were all oriented towards the plant which was placed in a distance of ~50 cm from the
nozzles. A ventilation system (MUB 042-500DV-A2, Systemair, Skinnskatteberg, Sweden, max speed: 1330 rpm) in combination with a frequency converter (VLT® HVAC
Drive FC 102, Danfoss, Nordborg, Denmark) allowed controlling the wind speed. Wind
speed at the leaf was measured at a distance of ~3 cm in front of the leaf using a hot
wire anemometer (405i, Testo SE & Co. KGaA, Germany). During all measurements,
illumination was kept constant and the temperature was kept at 22 ± 1 °C. The relative
humidity (RH) was typically 50 ± 3%. Videos of leaf oscillations have been recorded
with a GoPro Hero7 camera at 240 fps and they were analyzed by automatic and manual
positional tracking of plant and artificial leaf tips using the software Tracker, Version
5.1.3. Local derivatives of the vibrational profiles were obtained using Matlab, Version
R2019b. The thermometer powered by the plants was a DST-50 Digital Thermometer
(Elitech, UK) from which solar cell and battery have been removed before connecting
it to the described circuit. The green LEDs were NSPG500DS (Nichia Corp., Japan).