Lobed PMUT Membrane with Active Damping for Echo Detection
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Solution Overview
Problem
Existing PMUT devices face challenges with low damping factors in low-density media like air, leading to undesired free oscillations and ringing signals that interfere with echo wave detection, especially at frequencies around 2 MHz.
Innovation Solution
The PMUT device incorporates a membrane element with a lobed shape and multiple piezoelectric elements, each corresponding to a membrane portion. A damper with a polymeric member and a damper cavity is used to reduce free oscillations, optimizing the viscosity and Young's modulus of the polymeric material for efficient damping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a passive damper is used to reduce free oscillations, then the damping effect is achieved, but strong power dissipation occurs
Solution Approach 1:
The patent replaces the mechanical passive damper with an active control system that uses sensors to detect membrane oscillations and actuators to apply counter-phase forces. This substitution eliminates the need for physical damping structures that dissipate energy, instead using electronic control to achieve the same stabilizing effect with minimal power consumption.
Solution Approach 2:
The system uses the membrane's own oscillation signals to generate the counter-phase excitation. The sensors detect the free oscillations, and the control system automatically generates the opposing signal without requiring external intervention or additional components, making the system self-regulating and energy-efficient.
2Measurement precision
If the Q-factor of the PMUT device is increased to improve sensitivity, then the resonance response is enhanced, but the duration of ringing signal increases
Solution Approach 1:
The system applies a counter-phase excitation signal immediately after the ultrasonic pulse to preemptively counteract the free oscillations. By detecting the onset of ringing and applying an opposing force before the ringing fully develops, the system suppresses the oscillations without affecting the initial echo detection sensitivity.
Solution Approach 2:
The active damper operates by applying periodic counter-phase excitations synchronized with the natural frequency of the membrane. This periodic action effectively cancels out the free oscillations over time, reducing the ringing duration while maintaining the high Q-factor needed for sensitive echo detection.
3Adaptability or versatility
If the bandwidth of the PMUT device is increased to improve echo detection, then the frequency range is expanded, but the damping of free oscillations becomes more difficult
Solution Approach 1:
The active damper system dynamically adjusts its control parameters based on the operating frequency and detected oscillation characteristics. By continuously adapting the counter-phase excitation frequency and amplitude to match the current operating conditions, the system maintains effective damping across the entire bandwidth, regardless of frequency changes.
Solution Approach 2:
The system changes the parameters of the counter-phase excitation (frequency, amplitude, phase) in real-time based on the detected membrane oscillations. This allows the damper to remain effective across a wide frequency range, maintaining damping performance as the operating parameters vary throughout the device's bandwidth.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design significantly increases the bandwidth of the PMUT device, effectively suppressing ringing signals and improving echo wave detection by ensuring efficient damping of free oscillations, even in low-density media.
Implementation Method 1
A PMUT device is a MUT device whose operation is based on the flexural motion of one or more thin membrane elements mechanically coupled with a thin piezoelectric element. When the PMUT device operates as a transmitter, the membrane element flexes and oscillates about an equilibrium position under the action of the piezoelectric element when an AC electric signal is applied to the latter.
Implementation Method 2
When the PMUT device operates as a receiver, ultrasonic waves hitting the membrane element cause the membrane to oscillate about its equilibrium position. The oscillations of the membrane element act on the piezoelectric element, which accordingly generates a corresponding AC electric signal.
Implementation Method 3
A damper with a polymeric member and a damper cavity is used to reduce free oscillations, optimizing the viscosity and Young's modulus of the polymeric material for efficient damping.
Data Source
AI summary
A PMUT device includes a membrane element extending perpendicularly to a first direction and configured to generate and receive ultrasonic waves by oscillating about an equilibrium position. At least two piezoelectric elements are included, with each one located over the membrane element along the first direction and configured to cause the membrane element to oscillate when electric signals are applied to the piezoelectric element, and generate electric signals in response to oscillations of the membrane element. The membrane element has a lobed shape along a plane perpendicular to the first direction, with the lobed shape including at least two lobes. The membrane element includes for each piezoelectric member a corresponding membrane portion including a corresponding lobe, with each piezoelectric member being located over its corresponding membrane portion.