How Microwaves Could Revolutionize Healthy Buildings
In the hidden spaces within our walls, an unseen battle between human health and microbial life plays out, and the key to winning it may lie in the same technology that heats our leftovers.
When we think about the buildings we live and work in, we notice the architecture, the lighting, the temperature. But rarely do we consider the complex ecosystem of microorganisms that inhabits these spaces, or the hidden water that sustains it. With people spending over 90% of their time indoors, the indoor microbiome has profound implications for our health, from infectious diseases to allergies and immune development5 .
People spend the majority of their lives inside buildings, making indoor environmental quality crucial for health.
Moisture trapped in building materials creates ideal conditions for microbial growth that impacts health1 .
At the heart of this invisible world lies a simple element: water. Excess moisture, dampness, and hidden water in buildings create ideal conditions for microbial growth that negatively impacts occupant health1 . The problem is particularly insidious because this water is often hidden from view – trapped between concrete layers, collecting on metal surfaces, or permeating building materials where traditional detection methods cannot reach.
Recent advances suggest an unlikely solution: microwave technology. The same basic principle behind your kitchen microwave may hold the key to detecting and quantifying hidden water throughout buildings, potentially revolutionizing how we design, maintain, and remediate structures for health.
The relationship between building moisture and health is not merely theoretical. Visible signs of dampness and mold in buildings are epidemiologically associated with adverse health outcomes for occupants1 . The disparities in built environments, influenced by socioeconomic factors, have significant implications for the indoor microbiome and consequently human health5 .
Respiratory infections and building-related illness
Asthma exacerbations and allergy development
Metabolic and mental health challenges5
The COVID-19 pandemic particularly highlighted how the built environment can profoundly impact disease transmission, pushing researchers to better understand the various pathways – airborne, surface, waterborne – through which microorganisms move through our living spaces.
Understanding how microorganisms travel through buildings is crucial for preventing disease transmission.
Socioeconomic factors influence building quality, creating health inequities through indoor environmental conditions.
Microwave technology might seem like an unusual solution for building inspection, but it possesses unique properties that make it ideally suited for detecting hidden water. While common building materials like concrete are almost transparent to microwaves, water is strongly absorptive at microwave frequencies1 . This fundamental difference creates the perfect conditions for detection.
Water molecules absorb microwave energy, causing signal attenuation8
Microwaves bounce off material interfaces and metal surfaces8
Waves pass through non-metallic materials with minimal loss8
"Improving the detection of water in buildings could help design, maintenance, and remediation become more efficient and effective" – potentially even increasing the value of microbiome sequence data by providing crucial environmental context1 .
Microwave aquametry (water measurement) is already used to measure moisture during the preparation of building materials such as wood and concrete, as well as in various other materials including soils, seeds, cheese, and textiles1 .
Researchers conducted a simple but elegant experiment to demonstrate microwaves' ability to detect minute amounts of water in building materials1 . The setup was straightforward but revealing:
| Component | Function |
|---|---|
| Microwave horns | Send and receive microwave signals |
| Vector network analyzer | Measures reflection and transmission |
| Hollow concrete brick | Simulates hidden spaces within walls |
| Aluminium sheet | Represents metallic building components |
| Pipette | Precisely controls added water volume |
The findings were striking. Researchers successfully detected water volumes as small as 1 mL between two 7 cm thicknesses of concrete – a remarkable sensitivity that visual inspection or infrared imaging could never achieve1 .
Minimum detectable water volume
Concrete thickness penetrated
Detection on metal surfaces
Even more impressively, the reflection mode detected 1 mL of water on a metal surface, which would block traditional transmission methods1 . This is particularly valuable for real-world applications where water often collects on metallic pipes, beams, and other components.
| Scenario | Detection Capability | Primary Measurement Mode |
|---|---|---|
| Water between concrete layers | Detected as little as 1 mL | Transmission and reflection |
| Water on metal surfaces | Detected as little as 1 mL | Reflection only |
| Water in Pyrex container | Observed interference patterns | Both modes showing oscillations |
The research also revealed fascinating oscillations in transmitted and reflected microwave amplitude as a function of microwave wavelength and water layer thickness. These oscillations, attributed to thin-film interference effects, provide additional data points that could help characterize not just the presence but the nature and distribution of water deposits1 .
The physics underlying this detection method revolves around how microwaves interact with different materials. When microwaves encounter water, several phenomena occur:
Water molecules absorb microwave energy, causing the signal to weaken as it passes through – this forms the basis of transmission measurements8 .
Multiple transmission and reflection events at air-water and water-container boundaries produce waves that interfere with one another, creating observable patterns1 .
In more advanced implementations, the presence of water changes resonant frequencies in cavity-based sensors3 .
These interactions become particularly valuable when dealing with the challenge of hidden water – moisture that penetrates deep into building materials or collects in inaccessible spaces like wall cavities. Traditional methods like visual inspection or infrared imaging have significant limitations for detecting such water, especially when trying to quantify it or determine how deeply it has penetrated1 .
| Tool/Component | Function in Research |
|---|---|
| Microwave horns (A-info, LB-OH-159-15-C-SF) | Send and receive microwave signals in specific frequency ranges |
| Vector network analyzer (Agilent, PNA N5222A) | Measures complex S-parameters to quantify signal changes |
| Concrete test samples | Simulate real building materials for controlled experiments |
| Metal surface samples | Test detection on reflective surfaces that block transmission |
| Frequency range (4-8 GHz) | Provides appropriate wavelengths for building material penetration |
The implications of reliable hidden water detection extend far beyond simple leak finding. By accurately locating and quantifying moisture, we could fundamentally transform building design, maintenance, and remediation practices1 . This technology offers the potential for:
To detect water that appears only sporadically
Of moisture throughout structures
To guide remediation efforts and verify effectiveness
Perhaps most excitingly, improving water detection could help "perhaps increase the value of microbiome sequence data" by providing crucial environmental context for understanding microbial communities in built environments1 .
As one recent review noted, "The disparities in built environments, influenced by socioeconomic factors, have significant implications for the indoor microbiome and, consequently, human health"5 .
Future development will require unusual collaborations – among microwave physicists, architects, building engineers, epidemiologists, and microbiologists1 . But the potential payoff is enormous: buildings that actively promote health through better moisture management and, consequently, healthier microbial environments.
The marriage of microwave technology with building science represents more than just a technical innovation – it offers a new way of seeing our built environment. By revealing the hidden water that shapes the microbial worlds we inhabit daily, this approach could fundamentally change how we think about the relationship between buildings and health.
As research continues, we may eventually see buildings that continuously monitor their own moisture conditions, much like modern buildings monitor temperature and energy use today. Such advances would represent a significant step toward the vision of "healthy buildings" that not only shelter us but actively contribute to our wellbeing.
In the invisible interplay of microwaves and water molecules, we may have found an unexpected ally in the ancient quest to create healthier human habitats – proving once again that important solutions often come from where we least expect them.