Findings, Analysis and Challenges
This section discusses the key observations, analysis and issues faced during the implementation of this POC.
Observation 1: When the entire circuit is connected in parallel, the output voltage is higher than when connected in series. The average voltage generated in parallel is around 3.5 - 5 volts depending on the pressure and duration of the tapping on the piezoelectric sensors.
Observation 2: When the entire circuit is connected to a 12 V LED Strip, the LED strip does not light up.
Observation 3: When the last line of the Piezoelectric sensor is disconnected from the rest of the piezoelectric circuit, the LED Strip (which is connected to the last line) lights up.
Observation 4: Some of the piezoelectric sensors have a higher voltage and some of the piezoelectric sensors have 0 Voltage
Observation 5: When using a board covering and hitting the piezoelectric sensors, the LED strip lights have brighter with a higher voltage. The board covering is used to mimic an upper layer of a typical piezoelectric tile.
Observation 6: When lesser piezoelectric sensors are connected to the LED strip, the LED strip lights up brighter with a higher voltage.
Analysis and Challenges
The higher voltage being generated when the circuit is connected in parallel is an observation that coincides with and proves several research on piezoelectric material such as this research by Fang et al. in 2017, published by IEEE.
As per the key observations of this proof of concept, it seems that the energy produced (which is directly proportional to the potential difference/voltage) is being dissipated/leaked in the circuit.
In other words, the piezoelectric sensors are utilising their own produced energy, leaving behind minimal or negligible voltage for the LED strip to light up. Thus, when the last line is disconnected from the rest of the circuit and connected directly to the LED strip, the LED Strip lights up. This is because in this case, only 5 piezoelectric transducers are connected to a LED strip.
Interesting observation: In the case of piezoelectric transducers, more is always not better. Eventhough 98 Piezoelectric sensors were connected in parrallel, a simple 12 V LED Strip did not light up.
Formula-based Analysis
The relationship between the voltage generated by a piezoelectric material and the applied force or deformation can be described by the piezoelectric equation:
where V is the voltage generated, d is the piezoelectric coefficient, and F is the applied force or deformation.
The piezoelectric coefficient is a material property that quantifies the magnitude of the piezoelectric effect in a given material. The values of piezoelectric coefficients vary depending on the specific material and crystal structure. In this proof of concept, the value of d is assumed to be constant as all the piezoelectric sensors were identical in nature.
When multiple piezoelectric sensors are connected in parallel, the average total voltage generated can be calculated using the following formula:
where V1, V2, ..., Vn are the voltages generated by each piezoelectric sensor and n is the number of sensors connected in parallel.
However, in a real circuit, the voltage generated by the piezoelectric sensors may be dissipated or leaked due to internal resistance in the circuit or other factors as mentioned earlier in this analysis. This can be modelled using the equivalent circuit of a piezoelectric sensor, which includes a capacitance C and a resistance R in parallel with the piezoelectric material. The voltage across the capacitance can be expressed as:
where V0 is the initial voltage, t is the time, R is the resistance, and C is the capacitance.
This equation shows that the voltage across the capacitance decreases over time due to the internal resistance in the circuit. Therefore, since the piezoelectric sensors are using their own produced energy, the voltage available for the LED strip will decrease over time, making it difficult for the LED strip to light up.
A proposed solution to this issue is provided in the Recommendations section.
Last updated