Unveiling the Wonders of Piezoelectric Speaker Technology

Ⅰ. Definition of piezoelectric speakers

Speakers that work by utilizing the inverse piezoelectric effect of piezoelectric materials are called piezoelectric speakers. Initial mechanical motion is produced by applying a voltage to a piezoelectric material, and this motion is typically converted into audible sound using diaphragms and resonators.

Compared to other speaker designs, piezoelectric speakers are relatively easy to drive. For example, they can be connected directly to TTL outputs, although more sophisticated drivers can provide greater sound intensity. Typically, they operate well in the ultrasonic application range of 1-5kHz and up to 100kHz.

Piezoelectric effect:

When certain dielectrics are deformed by external forces in a certain direction, polarization will occur inside the dielectric, and at the same time, positive and negative charges will appear on its two opposite surfaces. When the external force is removed, it will return to its uncharged state. This phenomenon is called the positive piezoelectric effect.

When the direction of the force changes, the polarity of the charge also changes. Conversely, these dielectrics also deform when an electric field is applied in the direction of their polarization. When the electric field is removed, the deformation of the dielectric disappears. This phenomenon is called the inverse piezoelectric effect, or electrostrictive phenomenon.

Ⅱ. Piezoelectric schematic symbols

Shown below is a schematic diagram of a piezoelectric loudspeaker. Some piezoelectric speakers have built-in oscillation circuits that only require DC power (usually 9~12 V) when working. This type of device is called an internally driven piezoelectric device (or buzzer), while the one without a circuit is called an internally driven piezoelectric device (or buzzer). Externally driven piezoelectric devices (or piezoelectric devices).

Compared with internally driven piezoelectric ceramics, externally driven piezoelectric ceramics have no polarization phenomenon. Some have a third leg called a feedback pin. It can be used as an input to a driver circuit to drive a piezoelectric device at its resonant frequency.

Ⅲ. Classification of piezoelectric speakers

According to different structures and working principles, piezoelectric speakers can be divided into the following categories.

1. Piezoelectric Bluetooth Bone Conduction Headphones

The device does not need to be inserted into the ear, but uses bone conduction technology to transmit sound directly to the auditory nerve. It is suitable for outdoor sports and the hearing impaired.

2. Piezoelectric Ceramic Transducer

High-frequency sound or vibration can be generated by using piezoelectric ceramic material as an oscillator. Common applications include ultrasonic cleaners, ultrasonic humidifiers, and acoustic sensors, among others.

3. Ceramic Transducer

Loudspeakers made of piezoelectric ceramic materials have high power, wide frequency response range and good durability. Common applications include home audio, car audio, and public address systems, among others.

4. Piezoelectric Drive Speaker

It uses the piezoelectric effect to drive the speaker diaphragm to produce sound, and its working principle is similar to that of a conventional speaker. Piezoelectric-driven speakers have the characteristics of fast response, high efficiency, no magnetic field and low distortion, and are widely used in underwater communications, sonar systems, and ultrasonic medical imaging.

5. Piezoelectric Film Speaker

It uses a piezoelectric thin film or laminated structure as a vibration element, which has the advantages of ultra-thin, light and flexible. Common applications include handheld electronic devices such as cell phones and tablets, headphones and speaker arrays, among others.

Ⅳ. Piezoelectric speakers vs. ordinary speakers

1. Frequency response and sound reproduction

Piezoelectric speakers are good at reproducing high-frequency sounds with great clarity and accuracy because the radiating surface (cone) of the piezoelectric speaker is directly connected to the vibration source (piezoelectric element or substrate). Whereas the mechanical connection between the voice coil and the magnet (star wheel) of an electrodynamic loudspeaker is very compliant. Their ability to handle the high frequency range makes them suitable for applications requiring detailed audio reproduction, such as tweeters or high frequency drivers. On the other hand, normal speakers with electromagnetic drivers are usually good at reproducing mid and low frequency sounds.

2. Method of sound generation

Ordinary speakers use electromagnetism to move a diaphragm and produce sound. Piezoelectric speakers rely on the piezoelectric effect to directly generate vibrations in piezoelectric materials. This direct conversion of electrical energy into mechanical vibrations results in faster response times and increased efficiency.

Ⅴ. Piezoelectric speakers vs. electrodynamic speakers 

Piezoelectric speakers are similar to electrodynamic speakers in that they convert electrical potential differences into motion. But they have other properties that make them valuable in modern electronics.

1. Piezoelectric speakers are more environmentally friendly than electric speakers and can function in direct contact with substances other than air. For example, this feature is useful in underwater applications. Traditional electric speakers must be protected from the elements.

2. Compared with electric speakers, piezoelectric speakers require higher driving voltage. And their low impedance at higher frequencies means that high-frequency audio signals require large amounts of drive current.

3. Working principle: Piezoelectric speakers convert electrical signals into sound waves through the piezoelectric effect, while electric speakers use electromagnetic force to drive the vibrating membrane to produce sound.

4. Performance characteristics: Piezoelectric speakers have the advantages of good electroacoustic performance, solid structure, and low cost, but they have large distortion, narrow frequency band, and poor working stability. In contrast, electric speakers have the characteristics of soft sound, high power, and wide frequency response, but they require a magnetic circuit and an electrostatic speaker bias.

5. Structure: Piezoelectric speakers are mainly composed of piezoelectric sheets and horns, and their structures are relatively simple. The electric speaker consists of a vibration system (treble head) and a horn. The vibration system consists of a voice coil and a diaphragm.

Ⅵ. Advantages and disadvantages of piezoelectric speakers

1. Advantages

First of all, piezoelectric speakers are thin and light, only one-fifth the size of dynamic speakers. Therefore, it has greater advantages in application scenarios with limited volume, such as electric vehicles, drones, and small instruments.

Secondly, the power consumption of piezoelectric speakers is low, only one-tenth that of dynamic speakers. This greatly saves energy and is especially suitable for battery-powered scenarios.

Additionally, the piezoelectric speakers not only exceed expectations in reproducing high-frequency sounds, but also in delivering full-range audio output with superior transparency. As a result, these advanced piezoelectric speakers can replace individual woofers, midrange speakers, and tweeters, simplifying audio systems and enhancing overall performance.

Furthermore, the efficiency of piezoelectric speakers is as high as 90%, which is much higher than the 15% of dynamic speakers. It can convert electrical energy into sound energy more efficiently, enhancing the flexibility of its application.

Therefore, as a promising new speaker technology, piezoelectric speakers are particularly suitable for use in electric vehicles, drones, small instruments, players and other fields.

2. Disadvantages

Piezoelectric speakers have the following disadvantages.

First of all, piezo speakers have poor bass performance. The lowest F0 parameter is only 360Hz, which is difficult to meet scenes with high bass requirements.

Secondly, the sound pressure of piezoelectric speakers is not high enough, with a maximum of only 8dB. This may not provide sufficient volume in some noisy environments.

In addition, in order to achieve the ideal electric field effect, piezoelectric speakers generally require high voltage. In order to ensure the normal operation of the circuit, we also need to design the amplifier appropriately. However, under high pressure, the application of multi-layer piezoelectric technology will greatly reduce the thickness of the film, thereby improving the pressure resistance of the film. This solution can effectively solve the high voltage problem and improve the working efficiency of piezoelectric speakers.

Furthermore, piezoelectric speakers do not support Class D amplifiers, which may bring some limitations in some special applications.

Finally, piezoelectric speakers typically exhibit a narrower dispersion pattern than ordinary speakers, resulting in a more focused projection of sound in specific directions, known as a beam. This property is especially evident at high frequencies (>3 kHz). To overcome this problem, we usually arrange multiple piezoelectric speakers on the speaker. Additionally, using flat-panel piezoelectric speakers can help alleviate this problem by providing better directivity and wider dispersion.

When choosing and using a piezoelectric speaker, we must fully consider its potential shortcomings and make a reasonable choice and use plan according to actual application requirements.

Ⅶ. Misunderstandings about piezoelectric speakers

1. Power amplifier classification: The small power amplifiers used in digital products are actually only CLASS-AB and CLASS-D. Others such as K class, G class, and H class are based on the AB class and D class. Add a boost circuit, to achieve the purpose of increasing the output power of the power amplifier.

2. Rated power: The piezoelectric horn is a capacitive device, and the rated power is not considered. In application, the withstand voltage value is used as the basis for consideration. The piezoelectric audio amplifier also expresses the output size in terms of output voltage (Vp-p).

3. Insufficient bass: Piezoelectric ceramic speakers have excellent performance in the mid-to-high frequency range. It manifests itself in the sense of hearing that the high-frequency components will be prominent, while the low frequencies will be covered up, and there will be no bass in the sense of hearing. Without a sound cavity, the bass effect of dynamic speakers is not ideal. And when used to the extreme, dynamic speakers will be affected by the sound cavity, resulting in greater volume loss.

4. Piezoelectric horn cavity: The cavity plays a certain auxiliary role in any electroacoustic device. Piezoelectric speakers also require a cavity, but they are not as dependent on a cavity as dynamic speakers. The S.P.L of the piezoelectric horn will not be significantly reduced in a small cavity. Of course, with enough space, the volume and effect will be better.

Ⅷ. Common applications of piezoelectric speakers

In telephone and intercom systems, piezoelectric speakers are used to issue audible notifications and call alerts to ensure smooth and timely communication.

In home and office equipment, piezoelectric speakers or buzzers are used in devices such as printers, scanners, copiers, and vending machines. It issues audio prompts or feedback to enhance the user experience.

In medical equipment, piezoelectric speakers or buzzers are used as alarms, patient monitoring equipment, and audible indicators in medical instruments. It can promptly remind doctors and patients of important information.

In automotive applications, piezoelectric speakers are used for seat belt reminders, key ignition alarms and warning signals for low fuel indicators to ensure driving safety.

Alarm systems are another important application area for piezoelectric speakers or buzzers. It provides audible alarms in security, fire and industrial safety systems to protect people and property.

In addition, piezoelectric speakers or buzzers in consumer electronics are also widely used in clocks, watches, toys and household appliances to generate audible alarms to facilitate user operation and use.

Ⅸ. What are the new technologies for piezoelectric speakers?

A piezoelectric speaker is a device that uses piezoelectric materials to convert electrical signals into sound wave signals. In recent years, due to the increasing popularity of electronic products, people have higher and higher requirements for high-quality sound quality. Therefore, piezoelectric speaker technology has also undergone great development and innovation. Here are some new technologies for piezoelectric speakers.

1. Intelligent control technology

New piezoelectric speakers can be equipped with intelligent control systems. It automatically adjusts the sound output and gain of the speaker through real-time monitoring and processing of input signals and environmental noise, so that it can better adapt to different usage scenarios and environments.

2. Acoustic optimization technology

The quality and clarity of sound can be further improved by optimizing the design of the speaker's acoustic system. For example, by changing parameters such as the distance between the diaphragm and the air, the shape and material of the diaphragm, the size and layout of the sound holes, the acoustic performance of the speaker can be optimized to make the sound output by it more pure and natural.

3. Refined processing technology

The accuracy and reliability of piezoelectric speakers have a great influence on the quality and stability of sound. New fine processing technology can make the structure and shape of piezoelectric materials more uniform and stable, thereby improving the response speed and frequency response range of the speaker.

4. Adaptive diaphragm technology

Traditional piezoelectric speaker diaphragms are fixed and cannot adapt to different audio signals and sound frequencies. Adaptive diaphragm technology uses special structures and materials to adaptively adjust the shape and motion of the diaphragm according to the frequency and amplitude of the input signal, thereby achieving more accurate and clearer sound output.

With the continuous advancement of technology and the continuous discovery of new materials, piezoelectric speakers will have a broader space for the development of sound quality in the future. This technology is not only aimed at improving the sound quality of flat-screen TVs, but also provides a strong impetus for a new generation of portable devices. Piezoelectric speakers continue to inspire the creativity of hardware designers and music lovers, providing them with more diversified application scenarios and infinite possibilities. In the future, piezoelectric speakers will lead the trend and bring more excellent sound quality experience to the audio field.