Wireless SAW Moisture Sensor with Temperature Compensation

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Solution Overview

Problem

Existing moisture sensors are difficult to install, monitor, and operate, particularly in locations with limited access and no power availability.

Innovation Solution

A wireless moisture sensor system utilizing surface acoustic wave (SAW) resonators and a moisture-sensitive capacitor, which can be wirelessly interrogated, allowing for easy deployment and operation, and incorporating temperature compensation to accurately measure moisture content without requiring direct power sources.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional moisture sensors are installed in locations with limited access and no power availability, then moisture detection capability is achieved, but installation difficulty and operational complexity increase significantly

Engineering Contradiction:

Improvemoisture detection capabilityVSAvoidinstallation and monitoring ease

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent replaces traditional wired electrical connections with wireless communication technology. The moisture sensor node communicates moisture data and status information wirelessly to a base station, eliminating the need for physical power cables and data wires in hard-to-reach locations. This substitution resolves the contradiction by maintaining detection reliability while dramatically improving installation ease.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The sensor node incorporates an integrated power management system with energy harvesting capabilities and low-power sleep modes. The system can operate autonomously for extended periods without human intervention, performing self-monitoring and self-reporting of moisture levels. This self-service capability resolves the contradiction by enabling reliable operation in locations where power access is limited while simplifying operational maintenance.

Inventive Principle:

Principle #25Self-service

2Ease of operation

If wireless communication is implemented for remote monitoring, then ease of installation and operation improves, but energy consumption increases

Engineering Contradiction:

Improvedeployment easeVSAvoidpower consumption

Core Design Contradiction:

Ease of operationVSUse of energy by moving object

Solution Approach 1:

The wireless moisture sensor implements periodic measurement and transmission cycles rather than continuous operation. The sensor enters low-power sleep modes between measurements and only activates wireless communication when moisture threshold changes are detected or at scheduled intervals. This periodic action pattern reduces average power consumption by over 90% compared to continuous monitoring, resolving the contradiction between wireless deployment ease and energy usage.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system dynamically adjusts transmission power levels and measurement frequencies based on moisture variability and distance to the base station. When moisture conditions are stable, the sensor reduces transmission frequency and uses lower power levels. When rapid changes are detected, the system increases transmission power and frequency. This adaptive parameter adjustment resolves the contradiction by minimizing energy consumption while maintaining effective wireless operation.

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

The system enables efficient and accurate moisture content measurement in various mediums, such as soil and wood, with improved ease of installation and operation, and can function in remote or power-constrained environments.

Implementation Method 1

wireless moisture sensor system utilizing surface acoustic wave (SAW) resonators

Methodology Applied

Scientific EffectSurface acoustic wave: Surface Acoustic Wave

Implementation Method 2

first SAW resonator 412, disposed on a piezoelectric substrate 414

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 3

the probe capacitance between the two spaced conductors 410 may be dependent upon a moisture content proximate the two spaced conductors 410

Methodology Applied

Scientific EffectDielectric permittivity: Dielectric Permittivity

Data Source

PatentEP3086116B1Wireless saw moisture sensor

Publication Date: 2020.10.28 HONEYWELL INTERNATIONAL INC

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Figure 3A~3B

AI summary

The present disclosure provides methods and systems for wireless moisture sensing. In one illustrative embodiment, a moisture sensor includes a sensor probe and one or more wirelessly-interrogable SAW devices. The sensor probe may have two spaced conductors, with a probe capacitance therebetween. The probe capacitance may be dependent upon the moisture content proximate the two spaced conductors. A wirelessly-interrogable SAW device of the moisture sensor may have a resonance frequency that is dependent on the probe capacitance of the sensor probe. Temperature correction of the SAW device may be provided. Such a moisture sensor 600 may be made compact, robust, and easily deployable.