Last Updated on May 5, 2023 by You Ling
Medical device manufacturers are increasingly opting for piezoelectric motors and actuators over traditional electromagnetic motors, as the former has inherent advantages in medical device design. Piezoelectric devices are currently being used in a range of medical applications, including: ultrasound transducers, artificial insemination, medical nanoliter microinjection pumps, micro-monitoring, surgical equipment, MRI-compatible robots, microdosing, cell permeation, and cell imaging in cytopathology. Piezoelectric devices can also be used for medical material handling, such as pick-and-place systems, drug delivery devices, 3D scanning, and control of laser beams used in ophthalmology, dermatology, and cosmetic surgery.
There are 2 categories based on control technology：
Basic piezoelectric technology for motion control applications
Improving the performance of medical devices
1、Basic piezoelectric technology for motion control applications
There are many different types of piezoelectric actuators and motors available on the market today. The following are some of the more commonly used models in medical device applications:
a.Stacked actuators (most common). Characterized by high force, fast response speed, and short travel distance.
b.Shear actuators. The fastest x-y systems on the market. High force, very high frequency. Travel distances are usually limited to 20 microns.
c.Tubular actuators. Mainly used in microdosing applications and AFM scanners.
d.Bending actuators. Can be set for long-distance travel (deflection) of several millimeters, but with low force and frequency.
e.Bending-guided piezoelectric actuators. Frictionless curvature and motion amplifiers to provide long-distance and very linear motion. Motion range is generally proportional to drive voltage. Integrated multi-axis systems are available on the market. Motion range up to 2 millimeters. Expect frictionless performance without wear and tear.
f.Ultrasonic friction motors. Ultrasonic friction motors are based on high-frequency vibrations of piezoelectric plates (stators). They have unlimited motion, high speed, and fast response (10 milliseconds). Vibrations are transferred to the slider or rotor via friction. However, due to friction, resolution is generally limited to 50 nanometers.
g.Piezoelectric stepper motors. Stepper motors have a virtually unlimited motion range. Stepper motors are based on the accumulation of small, controllable steps. Other properties include:
Pico-meter resolution in jitter mode (direct piezoelectric drive).
Compact structure and high force up to 155 lb (for off-the-shelf units).
Fast response (less than 1 millisecond). Extremely high stiffness.
h.Ultrasonic sensors. Ultrasonic sensors are driven by high-frequency resonating plates or discs. They are commonly used as sensors or transducers and in nebulizers.
2、Improving the performance of medical devices
By adopting piezoelectric motors, medical devices can be made smaller, more precise, lighter, and easier to control.
Piezoelectric disc actuators, such as one in the thinXXS Microtechnology AG micropump 2000 series, are used as custom components. In this device, the actuator precisely injects liquids and gases.
Liquid handling and dispensing devices can utilize the mechanical response of piezoelectric actuators to dispense fluids. Multilayer piezoelectric actuators are layers of piezoelectric materials stacked together. Placing many piezoelectric actuators together creates a multiplication effect on the displacement under the same voltage, thus amplifying their power. When voltage is applied to a multilayer piezoelectric actuator, it expands, generating linear motion and force. When placed next to a fluid tube, the multilayer piezoelectric actuator expands under electrical signal, pushing into the tube and forcing the fluid to be released. The displacement of the piezoelectric actuator can be precisely defined to release the exact amount of fluid required. Multilayer piezoelectric actuators enable rapid response, accurate linear motion, high force generation, and high load capacity, making them cost-effective and reliable in dispensers and liquid handling systems.
An example of a mechanism based on piezoelectric motion can be seen in laser refractive eye surgery. The surgery uses high-speed lasers to cut into the epithelial layer of the eye and correct the cornea using a laser beam. High-precision nanopositioning piezoelectric components, such as stacked piezoelectric actuators, are used to move the laser beam to the exact position on the eye for the necessary correction. Piezoelectric stack actuators serve as drivers in nanopositioning and scanning systems to manipulate and control the laser. When receiving electrical input for the desired laser path, the piezoelectric actuator expands or contracts with tiny adjustments, moving the laser to the specified position. When dealing with the human eye, precision and accuracy are paramount, and piezoelectric components are the ideal choice for nanopositioning medical applications.
3、Conclusion
The potential improvements that piezoelectric components can offer for medical applications are limitless, and their benefits can already be seen in areas such as laser surgery, ventilation systems, and nanodosing instruments. Piezoelectric actuators, such as piezoelectric bending actuators, piezoelectric rings, piezoelectric tubes, and piezoelectric cylinders, provide unparalleled precision, accuracy, and speed required for all medical applications.
