Micromechanical Sensor Using Longitudinal Bulk Acoustic Waves

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Solution Overview

Problem

Current micromechanical sensors face challenges in analyzing liquid samples due to damping issues and limited sensitivity, as mechanical oscillations are heavily damped by the liquid's viscous properties and similar acoustic impedances, making it difficult to detect small mass changes effectively.

Innovation Solution

The use of longitudinal bulk acoustic waves in a micromechanical sensor array, with a wave guide portion separated from the substrate and equipped with an electro-mechanical transducer, allows for efficient energy coupling and reduced surface-normal displacement, enhancing sensitivity and reducing energy loss to the liquid.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If shear-horizontal SAW or TSM sensors are used for liquid phase analysis, then the sensor can operate in liquid environment, but the sensitivity is insufficient due to heavy damping from liquid viscosity and acoustic impedance matching

Engineering Contradiction:

Improveoperability in liquid environmentVSAvoidmass detection sensitivity

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent changes the acoustic wave parameters from shear-horizontal or thickness-shear modes to longitudinal bulk acoustic waves. This parameter change fundamentally alters the wave propagation characteristics, enabling the sensor to operate in liquid while maintaining high sensitivity by reducing energy loss to the liquid medium.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the traditional shear-horizontal SAW or TSM mechanical oscillation system with a longitudinal BAW system. This substitution changes the fundamental mechanical behavior of the resonator, allowing it to maintain higher Q-factors in liquid environments and improve mass detection sensitivity.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Speed

If the resonator thickness is reduced to improve frequency response, then the operational frequency can be tuned, but the energy storage capacity decreases leading to lower sensitivity

Engineering Contradiction:

Improveoperational frequencyVSAvoidenergy storage capacity

Core Design Contradiction:

SpeedVSUse of energy by moving object

Solution Approach 1:

The patent changes the wave mode from surface or thickness-shear waves to longitudinal bulk waves, which have different energy distribution characteristics. This allows the resonator to maintain sufficient energy storage even with reduced thickness, while still achieving the desired operational frequency through proper dimensional design.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If surface-normal displacement is increased to improve sensitivity, then mass detection capability improves, but energy radiation loss to liquid increases causing heavy damping

Engineering Contradiction:

Improvemass detection capabilityVSAvoidacoustic radiation loss

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

Instead of increasing surface-normal displacement to improve sensitivity (which causes energy loss), the patent inverts the approach by using longitudinal waves that primarily displace material parallel to the surface. This inversion of the displacement direction maintains sensitivity while minimizing energy radiation loss to the liquid.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the displacement direction parameter from surface-normal (vertical) to surface-parallel (longitudinal). This parameter change fundamentally resolves the contradiction by allowing the resonator to detect mass changes through longitudinal wave velocity changes without radiating significant energy into the liquid medium.

Inventive Principle:

Principle #35Parameter changes

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 approach enables sensitive detection of changes in liquid samples by minimizing acoustic radiation losses and maintaining sufficient energy storage, allowing for effective analysis of small amounts of liquid samples, including biological and chemical analyses.

Implementation Method 1

transmitting longitudinal bulk acoustic waves into the wave guide using an electro-mechanical coupling

Methodology Applied

Scientific EffectElectro-mechanical coupling: Piezoelectric Effect

Implementation Method 2

The longitudinal bulk acoustic waves are produced by at least one electro-mechanical transducer element located in the vicinity of the wave guide portion

Methodology Applied

Scientific EffectBulk Acoustic Waves: Sound

Implementation Method 3

the biochemical analysis can be made by using micromechanical resonators, whose resonant frequency is altered by changes on the surface mass of the sensor

Methodology Applied

Scientific EffectResonant frequency: Resonance

Data Source

PatentUS8136403B2Micromechanical sensor, sensor array and method

Publication Date: 2012.03.20 VALTION TEKNILLINEN TUTKIMUSKESKUS

AI summary

The present invention relates to a micromechanical sensor for analyzing liquid samples and an array of such sensors. The invention also concerns a method for sensing liquid samples and the use of longitudinal bulk acoustic waves for analyzing liquid phase samples micromechanically. The sensor comprises a body and a planar wave guide portion spaced from the body. At least one electro-mechanical transducer element are used for excitation of longitudinal bulk acoustic waves to the wave guide portion in response to electrical actuation and for converting acoustic waves into electrical signals. The wave guide portion is provided with a sample-receiving zone onto which the sample can be introduced. By means of the invention, the sensitivity of micromechanical liquid sensors can be improved.