Principles, Characteristics, and Applications of Ultrasonic Sensors
Overview of Ultrasonic Sensors
Ultrasonic sensors are devices that convert ultrasonic signals into other forms of energy, typically electrical signals. Ultrasonic waves are mechanical waves with frequencies exceeding 20 kHz. These waves have important features. They have high frequency, short wavelength, and little diffraction. They also have great directivity, which helps them travel in a specific direction. Ultrasonic waves excel at penetrating liquids and solid materials, including those opaque to visible light. When these waves encounter impurities or material interfaces, they produce reflective echoes. Additionally, they generate a Doppler effect when reflected from moving objects. Thanks to these features, ultrasonic sensors find extensive application across industries, national defense, and biomedicine.
Classification of Ultrasonic Sensors
A sensor is a device that detects changes in the environment. It converts this information into usable signals, usually electrical, based on specific rules. Sensors usually have two parts: a sensitive element and a conversion element. They help gather and change measured information into signals. You can send, store, display, or use these signals in control systems. They serve as the foundational component for implementing automation in detection and control processes.
Although there is no universal standard for categorizing sensors, three common classification methods include:
1. **By Measurable Physical Quantity**
You can classify sensors by what they measure. This includes displacement, force, velocity, temperature, flow rate, and gas composition.
2. **By Working Principle**
This method includes resistance-based sensors, capacitive sensors, inductive sensors, voltage-based sensors, Hall effect sensors, photoelectric sensors, gratings, and thermocouples.
3. **By Output Nature**
– **Switch-Type Sensors** output binary states like “on/off” or “1/0.”
– **Analog Sensors** produce continuous signals.
– **Digital Sensors** output discrete pulse or coded signals.
Among these diverse sensor types, ultrasonic sensors are particularly notable for their wide usability in daily life. One of their most practical applications is in vehicle reversing radar systems.
Ultrasonic Sensors: Fundamental Concepts
Ultrasonic sensors leverage the unique properties of ultrasonic waves for detection purposes. Their operation involves creating and receiving ultrasonic waves. You use a device called an ultrasonic sensor to do this. People also refer to it as an ultrasonic transducer or probe.
Core Components of Ultrasonic Probes
The probe primarily consists of piezoelectric wafers capable of transmitting and receiving ultrasonic waves. The core element within the probe is a piezoelectric chip enclosed in a plastic or metal casing. Manufacturers can use various materials to create the wafer, including piezoelectric crystals that utilize electrostriction and nickel-iron-aluminum alloys based on magnetostriction. Notably, lead zirconate titanate (PZT) is a common choice for electrostrictive materials.
Sensors constructed with piezoelectric crystals are reversible in function. They can transform electric energy into mechanical oscillations to generate ultrasonic waves and also convert received ultrasonic waves back into electrical energy. As such, these sensors may act as transmitters, receivers, or both depending on design specifications.
Structure of Ultrasonic Sensors
An ultrasonic sensor system typically consists of several components:
1. **Transmitting Sensor (Wave Transmitter):**
Responsible for emitting the ultrasonic wave. This sensor generally features a ceramic vibrator transducer with a diameter of around 15 mm. The ceramic vibrator transforms electrical vibration energy into ultrasonic waves that radiate through the air.
2. **Receiving Sensor (Wave Receiver):** Comprised of a transducer connected to an amplifier circuit. This transducer takes in ultrasonic waves. It creates mechanical vibrations and changes them into electrical signals. These signals are the output for the receiving sensor.
3. **Control Unit:** Manages critical operations such as pulse chain frequency, duty cycles, sparse modulation, counting, and distance detection.
4. **Power Supply Unit:** Provides the necessary energy for system operation.
By combining these elements, ultrasonic sensors function seamlessly to detect objects or environmental changes in various applications.
Applications in Reversing Radar Systems
One popular everyday use of ultrasonic sensing technology is in vehicle reversing radars. These systems enhance driving safety by detecting nearby obstacles during parking or reversing maneuvers. The integration of ultrasonic sensors in such systems delivers highly accurate distance measurement and object detection capabilities, offering convenience and security in automotive applications.
Working Principle of an Ultrasonic Sensor
Ultrasonic sensors are devices that operate based on the unique properties of ultrasonic waves. Sound waves, in general, are mechanical vibrations transmitted through a medium. Ultrasonic waves, specifically, are sound waves with frequencies higher than 20,000 Hz, surpassing the upper hearing threshold of humans. Because people cannot hear them, we refer to such sound waves as ultrasonic.
Ultrasound represents a mechanical oscillation within an elastic medium and exists in two main forms: transverse oscillation (transverse waves) and longitudinal oscillation (longitudinal waves). Among these, industries predominantly utilize longitudinal oscillation in their applications. Ultrasonic waves can propagate through gases, liquids, and solids, although their propagation speed varies depending on the medium. Additionally, these waves exhibit phenomena such as refraction, reflection, and attenuation during transmission.
The basic principles of ultrasonic waves are like those of sound waves. These principles include reflection, refraction, diffraction, and scattering. However, ultrasonic waves possess distinct features compared to audible sound:
1. **Propagation Characteristics**: Ultrasonic waves do not bend well. They travel in a straight line through uniform materials. This effect becomes more pronounced as the wavelength shortens.
2. **Power Characteristics**: As sound propagates through air, it causes air particles to vibrate and perform work. For waves of equal intensity, higher frequencies deliver greater power. The high frequency of ultrasonic waves enables them to carry significantly more power than ordinary sound waves.
3. **Cavitation Phenomenon**: When ultrasonic waves pass through liquids, they induce rapid oscillations of liquid particles, creating small cavities. These cavities grow and shrink quickly. This causes strong collisions between particles. The pressures can reach thousands to tens of thousands of atmospheres. This interaction greatly increases the temperature of the liquid. This can make immiscible liquids, like water and oil, mix together. It also speeds up how fast solutes dissolve and makes chemical reactions happen faster. We refer to this entire process as ultrasonic cavitation.
Key Features of Ultrasound
1. Ultrasound exhibits strong directionality during propagation, allowing for focused energy concentrations.
2. It can move through various media and travel considerable distances.
3.The moderate interaction between ultrasound and the medium makes it a useful tool. It can analyze the medium’s state for diagnosis or actively influence it.
Role of Ultrasonic Sensing Technology
Throughout human history and industrial revolutions, sensing technology has consistently been an integral enabler across diverse domains. Sensors play a pivotal role in bridging technology with practical applications and appear almost everywhere one can imagine.
As sensor development continues, they are changing from basic judgment devices to ones that can learn and be creative. Looking ahead into the future, experts anticipate that ultrasonic sensors—recognized for their versatility and high utility—will experience considerable advancements. They will shift toward higher precision and enhanced positioning capabilities to meet the rapidly changing needs of society. In this transformation, sensors with innovative functionalities will play an increasingly prominent role in shaping future technologies.