Energy Harvesting, For ADALM2000 [Analog Devices Wiki] (2024)

This version (03 Nov 2021 20:36) was approved by Doug Mercer.The Previously approved version (02 May 2017 12:27) is available.

Table of Contents

Energy harvesting (sometimes also called power harvesting or energy scavenging) is the process by which energy is gathered from an external source (for example kinetic or mechanical energy), converted, and stored for small low energy consumption devices, like those used in wearable electronics and wireless sensor networks.

Energy harvesters provide only a very small amount of power for low-energy electronics. While the energy source for grid-scale generation plants costs money (oil, coal, gas etc.), the energy source for energy harvesters is present in the ambient background and is thus free.

The piezoelectric transducer, LDT0 supplied in the ADALP2000 Analog Parts Kit is a flexible film device laminated to a polymer substrate. Two crimped contacts for mounting and electrical connections are provided. When the device is bent or displaced from its neutral position, a very high strain is generated in the piezo-polymer and a high voltage is generated. As a vibration sensor the LDT0 has a sensitivity of 50 mV/g. An electrical model of a typical piezoelectric device is shown in figure 1.

Figure 1 electrical model of piezoelectric sensor

A piezoelectric transducer has very high DC internal impedance, R_i and can be modeled as a proportional voltage source, V and filter network. The voltage produced is directly proportional to the applied force, pressure, or strain. The output signal is then related to this mechanical force as if it had passed through the equivalent circuit. For our purposes as an energy harvester where we will be converting the AC voltage generated by the movement or vibrations to a DC voltage, we can ignore the filtering effects.

ADALM2000 Active Learning Module
Solder-less Breadboard
2 - small signal diode (1N914 or similar)
2 - 1 uF electrolytic capacitors (or similar value)
1 - LDT0 Piezo Film Vibra Tab Mass

Build the energy harvesting circuit shown in figure 2 on your solder-less breadboard. Be sure to leave enough room around the LDT0 piezoelectric transducer so that it can be easily flicked back and forth with your finger.

Figure 2 energy harvesting circuit

Connect the ADALM2000 hardware as indicated by the green boxes. Set both scope channels to 1V/div. With the horizontal time base set to 200mS/Div and trigger set to none, rapidly flick the transducer back and forth with your finger. Observe the voltage waveform across the transducer on channel 1 and the rectified and filtered DC voltage on channel 2. What you observe should look much like the screen shot shown in figure 3. The channel 1 waveform in orange shows the vibrating waveform produced by the transducer as it is flicked back and forth. The channel 2 waveform in blue shows the DC voltage charging up from zero volts to higher voltages each time the transducer vibrates.

The large but still finite 1 megaohm input resistance of the scope channel will load down the peak voltage generated by the transducer. Remove the connection to scope channel 1 and again rapidly flick the transducer. The DC voltage seen at the output should be significantly higher now.

Figure 3 Scope Screen shot when flicking transducer rapidly

The energy stored in the capacitors is equal to:

Calculate the total amount of energy harvested based on the measured voltage and the capacitance value. Remember that the two capacitors are effectively in series and only half of the measured voltage appeared across each capacitor but there is energy stored in both capacitors.

http://en.wikipedia.org/wiki/Piezoelectric_sensor
http://en.wikipedia.org/wiki/Energy_harvesting

Device datasheet:

http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Sensors/ForceFlex/LDT_Series.pdf
http://www.parallax.com/Portals/0/Downloads/docs/prod/compshop/PiezoInfo.pdf

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