How to connect piezo in series

Piezoelectric devices, commonly referred to as piezos, are widely used in applications requiring the generation or detection of ultrasonic vibrations, such as medical imaging, ultrasonic cleaning, and distance measurement systems. Connecting piezoelectric elements in series is a practical technique to achieve higher voltage outputs or specific electrical and mechanical characteristics. This article will guide you step-by-step on how to connect piezoelectric elements in series accurately and effectively.

1. Understanding the Basics of Piezoelectric Elements

Before connecting piezoelectric elements in series, it is important to understand how they function. A piezoelectric element generates an electric charge when subjected to mechanical pressure or vibration. Conversely, applying an electric field causes the piezo material to deform, producing mechanical vibrations. This dual property makes piezos ideal for both sensing and actuation purposes.

When piezoelectric elements are connected in series, their electrical properties (specifically the voltage) add up. However, their capacitance reduces, which is an important factor to consider for designing an optimal circuit.

2. Benefits of Connecting Piezos in Series

Connecting piezoelectric elements in series can be advantageous in specific scenarios. Below are some key benefits:

• Higher Voltage Output: The combined voltage is the sum of the individual voltages generated by each piezo, making the configuration suitable for low-power signal generation or detection.
• Simplified Connections: For certain applications, connecting in series reduces the number of parallel paths to manage.
• Improved Efficiency in High-Impedance Loads: Series connection is more suited for high-impedance load applications since it reduces stray capacitance.

However, be aware that the total capacitance in a series connection decreases, potentially requiring adjustments in circuit design.

3. Step-by-Step Guide to Connecting Piezos in Series

Follow these steps to connect piezoelectric elements in series effectively:

Step 1: Gather Required Materials

Ensure you have the following items ready:

• Piezoelectric elements (such as those from Beijing Ultrasonic, known for their high-quality piezo components).
• Electrical wires.
• A soldering iron and soldering materials.
• Multimeter to test connections.

Step 2: Identify the Terminals

Each piezoelectric element has two terminals: the positive terminal (commonly marked with a "+" or a red wire) and the negative terminal (commonly marked with a "-" or a black wire). Identify these terminals clearly for each piezo.

Step 3: Connect the Terminals in Series

To connect the piezoelectric elements in series, follow these steps:

1. Join the negative terminal of the first piezo to the positive terminal of the second piezo.
2. Continue this pattern—connecting the negative terminal of one piezo to the positive terminal of the next—until all piezo elements are connected.

For example, if you have three piezoelectric elements:

• Connect Piezo 1’s negative terminal to Piezo 2’s positive terminal.
• Connect Piezo 2’s negative terminal to Piezo 3’s positive terminal.

Step 4: Connect External Leads

After establishing the series connections, you will have one free positive terminal (from the first piezo) and one free negative terminal (from the last piezo). These are your external connections for interfacing with other components in your circuit.

Step 5: Test the Connection

Use a multimeter to test the overall circuit. Check for continuity and measure the total voltage output by applying a mechanical force to the piezo elements. The measured voltage should be the sum of the individual piezo voltages.

4. Important Considerations When Connecting Piezos in Series

Electrical Characteristics

When piezos are connected in series, the voltage output adds up, but the total capacitance decreases. Use the formula for series capacitance:

1/C_total = 1/C1 + 1/C2 + 1/C3 + …

Where C_total is the total capacitance, and C1, C2, C3, … are the capacitances of individual piezo elements. Ensure that your circuit design accounts for this change in capacitance.

Mechanical Coupling

If the piezo elements are part of a single mechanical structure, ensure they are aligned properly to vibrate in phase. Misalignment can lead to destructive interference or reduced efficiency.

Matching Impedances

For ultrasonic applications, it is crucial to match the impedance of the piezo array with the driving circuit for optimal performance. Brands like Beijing Ultrasonic often provide detailed specifications to assist with impedance matching.

5. Practical Example: Connecting Three Piezos in Series

Below is an example of connecting three piezoelectric elements in series along with their electrical output characteristics. Assume each piezo generates 10V and has a capacitance of 100nF:

Parameter	Value
Individual Voltage Output	10V per piezo
Total Voltage (in Series)	10V + 10V + 10V = 30V
Individual Capacitance	100nF per piezo
Total Capacitance (in Series)	1/(1/100 + 1/100 + 1/100) ≈ 33.3nF

This configuration is suitable for applications requiring a high-voltage, low-capacitance signal.

6. Common Issues and Troubleshooting Tips

• Uneven Voltage Distribution: If the piezo elements are not identical, they may have differing capacitance and voltage output characteristics. Use matched piezo elements for consistent performance.
• Open Circuit: Ensure all connections are soldered properly and check for loose wires.
• Reduced Performance: If the output is lower than expected, verify alignment and ensure no external forces are dampening the piezo vibrations.

Connecting piezoelectric elements in series is a straightforward yet effective way to increase voltage output and optimize performance for specific applications. By carefully aligning the elements, matching their specifications, and considering electrical properties such as capacitance and impedance, you can achieve reliable and high-performance configurations. Whether using high-quality piezo components from Beijing Ultrasonic or other reputable brands, following these steps ensures a successful implementation suitable for ultrasonic and other advanced technologies.