PMUT Sensor Package Decoupling Acoustic Resonance
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Solution Overview
Problem
PMUT sensors face inefficiencies due to energy being consumed by exciting the back cavity's acoustic resonance modes, which are within the operating frequency range of the sensor, leading to reduced sensitivity and accuracy in transmission and reception of acoustic signals.
Innovation Solution
The PMUT sensor design includes a MEMS die positioned within the back cavity such that the applied acoustic pressure corresponding to the acoustic resonance mode is balanced over the membrane, effectively decoupling the acoustic resonance modes from the operational modes of the PMUT sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PMUT sensor operates at frequencies that coincide with back cavity acoustic resonance modes, then the sensor can transmit and receive acoustic signals, but energy is consumed exciting the back cavity resonance modes, reducing sensitivity and accuracy
Solution Approach 1:
The patent extracts the harmful acoustic resonance modes from the back cavity by positioning the MEMS die at specific locations where the acoustic pressure from resonance modes is balanced (zero net pressure). This effectively removes the coupling between the resonance modes and the PMUT membrane, preventing energy loss to unwanted resonance while preserving the sensor's ability to detect acoustic signals.
Solution Approach 2:
The patent uses the acoustic pressure distribution pattern as an intermediary mechanism to decouple the resonance modes from the PMUT operation. By strategically positioning the MEMS die at pressure nodes or balanced pressure regions, the design creates a spatial intermediary that blocks the energy transfer path from resonance modes to the membrane, reducing energy consumption without affecting sensor functionality.
2Volume of stationary object
If the back cavity volume is large enough to support acoustic resonance modes within the operating frequency range, then the sensor package can be compact, but the resonance modes consume significant energy and interfere with transmission and reception
Solution Approach 1:
The patent applies local quality by creating specific localized regions within the back cavity where the acoustic pressure is balanced (pressure nodes). By positioning the MEMS die in these specific locations rather than uniformly distributing it, the design locally eliminates the harmful coupling at critical points while allowing the rest of the cavity to maintain its resonance characteristics. This enables compact cavity design without significant energy loss.
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 minimizes the energy used to excite the back cavity's acoustic resonance modes, thereby enhancing the efficiency of the PMUT sensor in transmitting and receiving acoustic signals, leading to improved sensitivity and accuracy.
Implementation Method 1
A PMUT sensor is implemented as microelectromechanical system (MEMS) device including a membrane that generates an acoustic output signal based on an electrical transmission signal applied across a piezoelectric material layer
Implementation Method 2
an acoustic signal received at the piezoelectric material layer of the membrane is converted by the piezoelectric material layer to an electrical reflection signal
Implementation Method 3
The back cavity volume may also be acoustically excited by the movement of the membrane, with a particularly large signal occurring when the membrane is excited at a frequency corresponding to an acoustic resonance mode of the back volume
Data Source
AI summary
A piezoelectric micromachined ultrasound transducer (PMUT) sensor is implemented with a microelectromechanical sensor (MEMS) die including a membrane of the PMUT sensor that transmits and receives acoustic signals. A back volume within the MEMS sensor package has an acoustic resonance mode that is within an operating frequency range of the MEMS sensor. The MEMS die is located within the MEMS sensor package such that an acoustic pressure that is applied to the membrane is balanced over the membrane, such that the back volume acoustic resonance mode is decoupled from the membrane operating mode.