# Multi-Objective Optimization of IME-Based Acoustic Tweezers for Mitigating Node Displacements

## TL;DR

This paper introduces a new fabrication method for acoustic tweezers using IME technology and a hybrid optimization algorithm to reduce node displacement and improve performance.

## Contribution

A hybrid NSGA-II-MOPSO algorithm and IME-based fabrication process that simultaneously minimizes acoustic node displacement, shrinkage, and residual stress.

## Key findings

- A 27.3% reduction in node displacement amplitude compared to conventional methods.
- 19.6% improvement in ultrasonic transmission uniformity using the proposed fabrication process.
- Feasible integration of PMUT arrays with polymeric substrates using optimized injection molding parameters.

## Abstract

What are the main findings?
Developed a novel IME-based microfabrication process for PMUTs with sub-micron alignment accuracy via thermal compression bonding.Proposed a hybrid NSGA-II-MOPSO optimization algorithm that simultaneously minimized acoustic node displacement (≤5.2 μm), volumetric shrinkage (≤0.8%), and residual stress (≤12 MPa).Established a multidisciplinary evaluation framework integrating FEM and in situ process monitoring for comprehensive PMUT performance assessment.Achieved a 27.3% reduction in node displacement amplitude and a 19.6% improvement in ultrasonic transmission uniformity compared to conventional fabrication methods.Demonstrated feasible integration of PMUT arrays with polymeric substrates using optimized injection molding parameters (100 MPa packing pressure, 250 °C melt temperature, 20 s packing time).

Developed a novel IME-based microfabrication process for PMUTs with sub-micron alignment accuracy via thermal compression bonding.

Proposed a hybrid NSGA-II-MOPSO optimization algorithm that simultaneously minimized acoustic node displacement (≤5.2 μm), volumetric shrinkage (≤0.8%), and residual stress (≤12 MPa).

Established a multidisciplinary evaluation framework integrating FEM and in situ process monitoring for comprehensive PMUT performance assessment.

Achieved a 27.3% reduction in node displacement amplitude and a 19.6% improvement in ultrasonic transmission uniformity compared to conventional fabrication methods.

Demonstrated feasible integration of PMUT arrays with polymeric substrates using optimized injection molding parameters (100 MPa packing pressure, 250 °C melt temperature, 20 s packing time).

What is the implication of the main finding?
The IME-based microfabrication process with sub-micron alignment advances precision in PMUT manufacturing, enabling more reliable miniaturized ultrasonic transducers for high-performance applications.The hybrid optimization algorithm addresses critical performance trade-offs, enhancing PMUT reliability and consistency by controlling key metrics (displacement, shrinkage, stress) within strict limits.The multidisciplinary evaluation framework improves design validation and manufacturing quality control for microdevices.Performance gains over conventional methods (reduced node displacement, better transmission uniformity) enhance PMUT efficiency for applications like medical imaging and sensing.Feasible integration with polymeric substrates expands PMUT applicability to flexible, low-cost platforms, enabling new use cases in wearable or disposable devices.

The IME-based microfabrication process with sub-micron alignment advances precision in PMUT manufacturing, enabling more reliable miniaturized ultrasonic transducers for high-performance applications.

The hybrid optimization algorithm addresses critical performance trade-offs, enhancing PMUT reliability and consistency by controlling key metrics (displacement, shrinkage, stress) within strict limits.

The multidisciplinary evaluation framework improves design validation and manufacturing quality control for microdevices.

Performance gains over conventional methods (reduced node displacement, better transmission uniformity) enhance PMUT efficiency for applications like medical imaging and sensing.

Feasible integration with polymeric substrates expands PMUT applicability to flexible, low-cost platforms, enabling new use cases in wearable or disposable devices.

Acoustic tweezers, as advanced micro/nano manipulation tools, play a pivotal role in biomedical engineering, microfluidics, and precision manufacturing. However, piezoelectric-based acoustic tweezers face performance limitations due to multi-physical coupling effects during microfabrication. This study proposes a novel approach using injection molding with embedded electronics (IMEs) technology to fabricate piezoelectric micro-ultrasonic transducers with micron-scale precision, addressing the critical issue of acoustic node displacement caused by thermal–mechanical coupling in injection molding—a problem that impairs wave transmission efficiency and operational stability. To optimize the IME process parameters, a hybrid multi-objective optimization framework integrating NSGA-II and MOPSO is developed, aiming to simultaneously minimize acoustic node displacement, volumetric shrinkage, and residual stress distribution. Key process variables—packing pressure (80–120 MPa), melt temperature (230–280 °C), and packing time (15–30 s)—are analyzed via finite element modeling (FEM) and validated through in situ tie bar elongation measurements. The results show a 27.3% reduction in node displacement amplitude and a 19.6% improvement in wave transmission uniformity compared to conventional methods. This methodology enhances acoustic tweezers’ operational stability and provides a generalizable framework for multi-physics optimization in MEMS manufacturing, laying a foundation for next-generation applications in single-cell manipulation, lab-on-a-chip systems, and nanomaterial assembly.