Modulated Pulsed Acoustic Field for Sub-Micronic Particle Focusing
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Solution Overview
Problem
Existing methods for manipulating objects in microfluidic channels using ultrasonic standing waves face challenges with acoustic streaming, which complicates the focusing and manipulation of sub-micronic objects due to strong fluid displacements, making it difficult to control and reduce its impact while maintaining sufficient acoustic forces.
Innovation Solution
A modulated pulsed acoustic field is applied, varying in amplitude and/or frequency, to control acoustic streaming, increase acoustic forces, and improve focusing of objects, particularly for colloidal and micron-sized objects, by using a series of acoustic wave pulse groups with specific durations and separations, allowing for reduced heating and enhanced manipulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a continuous ultrasonic standing wave is applied to manipulate objects, then acoustic forces are maintained to keep objects focused, but acoustic streaming generates strong fluid displacements that drag sub-micronic particles away from focal positions
Solution Approach 1:
The patent applies periodic pulsed ultrasonic waves instead of continuous waves. The acoustic field is activated in pulses with specific duty cycles (e.g., 10-90% duty cycle where active time exceeds inactive time), creating periodic acoustic radiation forces that manipulate objects while allowing fluid displacement to dissipate during inactive periods, thereby reducing acoustic streaming effects
Solution Approach 2:
The patent dynamically adjusts the duty cycle of the pulsed acoustic field to optimize the balance between acoustic forcing and streaming reduction. By varying the proportion of active versus inactive time, the system adapts the acoustic force application to achieve effective particle manipulation while minimizing fluid displacement artifacts
2Manufacturing precision
If the acoustic field strength is increased to improve focusing of sub-micronic objects, then acoustic forces become stronger, but acoustic streaming becomes more pronounced and heating increases
Solution Approach 1:
The patent uses pulsed acoustic fields with optimized duty cycles to deliver strong acoustic forces during active periods while allowing cooling and streaming dissipation during inactive periods. This periodic action enables high peak forces for precise focusing without the continuous heating and streaming problems of constant high-power operation
Solution Approach 2:
The system dynamically controls the duty cycle parameter to adjust the balance between force strength and streaming suppression. By optimizing the active-to-inactive time ratio, the patent achieves strong focusing precision when needed while reducing thermal and streaming effects during inactive intervals
3Ease of operation
If ultrasonic standing waves are used to manipulate and focus objects, then objects can be levitated and positioned, but inhomogeneity in energy distribution causes particles to agglutinate at nodal planes
Solution Approach 1:
The patent applies periodic pulsed acoustic fields that create time-varying force distributions. The pulsing action prevents continuous exposure to the same nodal plane energy maxima, reducing the tendency for particles to aggregate at fixed locations while maintaining effective manipulation during active periods
Data Source
AI summary
Systems, methods, and devices are provided for manipulating objects in a liquid using a pulsed acoustic field that is modulated in amplitude. The amplitude modulated pulsed acoustic field may form the objects into a layer or layers. The objects may be colloidal objects having an average size of about 50 nm to about 5 μm, or a mixture of colloidal and non-colloidal objects.