Active Microvalves: Identifying the Correct Example
An active microvalve is driven by an actuator (e.g., electric or piezoelectric), so its opening/closing is actively controlled rather than relying purely on pressure direction or flow-induced mechanics. In contrast, many common microvalve configurations such as check valves and flap/ball designs are typically passive and respond to fluid forces.
To decide which option matches “active microvalve,” look for an option that explicitly implies external actuation/control.
Key idea: “piezoelectric” implies active actuation
A piezoelectric valve uses a piezoelectric element to move a membrane/actuator and control the flow path, which is characteristic of an active microvalve.
Therefore, the correct answer is (ii) Piezoelectric Valve.
(Options (i), (iii), and (iv) correspond to passive, flow-responsive valve behaviors rather than externally actuated microvalving.)
Microfluidic Valve Basics (Active vs Passive)
How to identify active vs passive quickly
If the option names an actuator material/driver (e.g., “piezoelectric,” “electrostatic,” “thermal,” “pneumatic”), it’s typically active. If it describes a mechanical flow-direction element (check/flap/ball), it’s typically passive.
Common confusion: geometry vs actuation
Some designs can exist in both forms, but exam questions usually classify by how the valve is controlled. “Piezoelectric” strongly signals external electrical actuation, i.e., active microvalving.
Answering the Multiple-Choice Question
- 1Step 1
Active means the valve state (open/close) is controlled by an external mechanism, not solely by fluid pressure/flow.
- 2Step 2
A piezoelectric valve uses applied voltage to generate motion—external control is inherent.
- 3Step 3
Check, flap, and ball valve behaviors are generally passive: they respond to flow direction or pressure rather than requiring actuation.
- 4Step 4
Choose (ii) Piezoelectric Valve.
Conceptual Control Pipeline
Input signal
1Applied voltage/current (for a piezoelectric actuator) to command opening/closing."
Actuation mechanism
2Piezoelectric element deforms, moving a microvalve membrane/closure."
Fluidic response
3Flow is allowed or blocked according to commanded valve state."
Result
4This is characteristic of an active microvalve."
Why the other options are typically not “active”
Knowledge Check
Which option is an example of an active microvalve?