Piezoelectric Actuators in Microfluidics: How Multilayer Ceramics Are Redefining Micro-valves and Micro-pumps

1.Why Precision Fluidics Is Getting Harder to Ignore
2.What Makes Multilayer Piezo Ceramics Different
3.Piezoelectric Micro-Valves: Getting Fluid Switching Right
4.Piezoelectric Micro Pumps: Mechanically Pumped Fluid with High Precision
5.Working with Bestarsensor
6.The Future of Piezo Fluidics

Why Precision Fluidics Is Getting Harder to Ignore
Over the last decade, the fluid-handling of small devices has undergone an incredible transformation. Chip Lab devices are no longer 1980s toys in university laboratories. They are engaged in shipping within POC devices, and wearable glucose check monitoring gadgets and hand-held remedy shipping devices. As of today, demand for fluid control at a nanoliter scale is no longer a niche requirement, it is the standard requirement. The standard requirement for an increasing number of product categories.
This is a true engineering challenge. When moving small amounts of liquid or gas needs volume accurate actuators that have fast response, consume very little power and are small. Tight tolerances at high speeds and with smaller leaks require traditional solenoid valves and rotary pumps. They are heavy, consume lots of electricity, and in closed/limited size situations, have a short service life due to mechanical wear.
Working on next generation, microfluidics require a different viewpoint. Multilayer piezoelectric ceramics fill that void. In this blog, the author will discuss how piezoelectric actuators can be used in micro valves and micro pumps and why multilayer ceramic stacks are the actuators of choice for engineering, from concept to production.

What Makes Multilayer Piezo Ceramics Different
A piezoelectric material provides a movement when given an electric voltage. A theory for the physics is accepted. The multilayer stack architecture is what has made microfluidics changes.
To achieve a useful displacement, the piezo disc needs to be thick and have high voltage applied to it in a single layer disc. This is not viable on portable equipment with a battery power. The problem is addressed by the multi-layer solution, many thin ceramic layers are physically in series, electrically in parallel. The contribution to displacements per layer is small. These small strokes all put together make a relatively useful stroke, and the assembly of all of them can be driven by the standard microcontroller drives.
Here is what that means in practical terms for a design engineer.
Response speed. Piezo actuators' actuation response is in the order of milliseconds. No coil to charge, no armature to pull and no fluid coupling to overcome. When you pulse a voltage, the ceramic will move. Such is the case with high frequency pulsed flow control; in such cases, a solenoid (which would seem to lag too far behind the flow control signal to be useful) would be not suitable.
Power consumption. Much of the current during transition (when it actually is moving) goes into drawing the piezo element. However it has a target position that it will also maintain with negligible direct power consumption. The ceramic is an electrical load that is capacitive. This attribute when combined with devices holding a valve in an open or a closed position, and for long durations, translates directly to long battery life. Solenoid valves use power all of the time they are supplied. A piezo valve doesn't.
Physical size. For example, small size footprint is possible for manufacturing of multilayer stack actuators. This is a useful actuator to fit in a few cubic mm for micro-valve applications. This provides integration opportunities, which were only possible with electromagnetic alternatives.
Bestarsensor's multilayer piezo ceramics are designed to have uniform polarization over the stack and an even thickness of the individual layers of the stack. This manufacturing information is important because if the property of the layers varies and ultimately is not consistent, there will be a non-linear displacement response in the system.

Piezoelectric Micro-valves: Getting Fluid Switching Right
A micro-valve is used for a specific purpose. Turns on or off a flow path. It sounds simple. But at the scale of a chip laboratory or a disposable drug delivery patch, the particulars become quite complex very fast.
1. The way the valve is operated by the actuator
A direct-drive piezo micro-valve uses an actuator to actuate a thin membrane. This membrane either seals on a valve seat or rises away, thus allowing a flow channel to open. The force is achieved with the piezo stack. It is passed through the membrane to the fluid path. No solenoid coil, no moving iron or lubricated seals.
In the end, it's a valve that performs millions of cycling without any mechanical wear on the actuator. The membrane is the wear part, and for the specific final fluid to be pumped, the selection of the appropriate membrane is a simple materials engineering problem.
2. Zero dead volume design
The fluid that flows around within a valve without being shifted during normal use is called "dead volume". It does not matter in most of the uses. It is very critical in microfluidics. The cost of reagents used in diagnostic cartridges is high. Drug delivery system implants deliver an exact dose of drugs. Fluid in still pots in the dead space of the valves is contributing to the reagent wastage and dosing error.
As the membrane can be pressed against the surface channel, it is possible to achieve a very low dead volume for piezo direct-drive valves. The distance between a membrane and a seat is very small. This geometry is possible with competitive actuator technologies, but will not be possible without sacrificing force output.
3. Compatibility with different media
The real product uses come to real valves with much more than potable water. Whole blood, buffered saline and reagent cocktails for diagnostic systems. Biological fluids are handled by drug delivery systems, as well as active pharmaceutical ingredients. Carrier gases used in gas flow control applications in analytical instruments come in contact with corrosive gases.
In a well-designed valve, the actual piezo piece does not come into contact with the fluid. The ceramic and the electrode structure are isolated from the flow path by the membrane and valve body. That's because there's a variety of options available at the membrane and body material level-silicones, PTFE, chemical-resistant polymers, stainless steel. Materials can be chosen to suit the required functionality without restriction of the actuator technology.

Piezoelectric Micro Pumps: Mechanically Pumped Fluid with High Precision
A micro-pump is more than a switch. It actively pumps fluid from one location to another, against some amount of back-pressure. The piezo method for pumping is based on the same simple mechanism: Every time the membrane is periodically mechanically displaced, fluid flows through the chamber.
1. How the pumping cycle works
A downward movement of the membrane by the movement of the actuator increases the volume of the pump chamber. Fluid is drawn in through the inlet. Then the actuator moves in the opposite direction and bends the membrane up and squashes the chamber. The fluid is then pressure forced through the exit. It is a one-way flow due to presence of check valves at inlet and outlet. This cycle goes on rapidly, and you get a flow stream that's continuous and metered.
The flow rate is given by cycle frequency multiplied by the volume of displacement per cycle. These are both controlled onboard via the drive electronics. This provides an easy method of changing the flow rate without requiring a hardware changeout.
2. Valved Pumps vs. Valveless Pumps
Not all micro pumps have check valves. There are times when you need to use a valved pump, and there are times to use a valveless pump which depending on your pumping operation and what the operation calls for.
Valved pumps have two physical check valves at the inlet and at the outlet, Such as flap valves, ball valves or disc valves. These may also provide excellent backflow prevention and enable the pump to function against higher outlet pressures. When there is a high resistance further down the stream, and when the system must maintain pressure between pump cycling, they are the correct pressure valve assembly. On the other hand, valves increase in complexity, and can become clogged if particulates are present that exceed a specific size.
Pumps that do not include moving mechanical parts use the geometry of the flow channel to direct flow to a preferred direction. Other than the pumping membrane, there are no moving parts. This ensures that they are strong against particulates and biological material that would impede a mechanical valve. This trade-off results in reduced back pressure performance and a certain amount of bi-directional leakage. Some applications, such as mixing or delivering the fluid without any resistance, or dealing with a more complex biological fluid, may be better in practice with a valveless type of fluid delivery system.
3. Things to consider before you select a micro-pump
The most important parameter for most of microfluidic applications is flow stability. Any reciprocating pumping system has this pulsation character and the amplitude has importance to downstream processes. Flow pulsation can impact uniformity, completeness of reaction, and sensor accuracy. Pay attention to the ripple specification of the pump and if needed design the flow circuit for an additional damping volume downstream of the pump.
Pressure capability refers to the ability of the pump to push the fluid in your particular channel geometry. Microfluidic channels, particularly those that are sub-millimeter, have high resistances. Calculate channel resistance before deciding on a pump design direction and compare it to the pressure output rating of the desired pump. 

Working with Bestarsensor
Bestarsensor is a manufacturer of multilayer piezoelectric ceramic actuator for microfluidic and precision industrial applications.  We will provide services much more than a product datasheet. In the concept phase, Bestarsensor is integrated into the design team in order to model the performance of the actuators in the actual application. Bestarsensor's process controls manage actuator-to-actuator consistency; a requirement more critical to the requirements in microfluidic dosing applications than in almost any other program.
Don't wait any longer to discuss your actuator options. Please contact Bestarsensor as soon as possible to get the right multilayer piezoelectric ceramic actuator.

The Future of Piezo Fluidics
Piezo actuator is not a new technology. The key feature of the new technology is manufacturing precision that allows the multilayer stack actuators the scale and cost point that is necessary in portable medical and analytical devices. The low sustained power consumption, fast response time and compact physical footprint combined with its long cycle life are a perfect fit for the demands of wearable medical devices and chip lab platforms.
Bestarsensor supplies the components for the actuator control, supports the application design and engineering and follows up from initial design to validated mass production.