Microwave scanning-a new technology for detecting water seepage in buildings

Microwave (Microwave) refers to the part of the electromagnetic spectrum with a wavelength from one millimeter to ten centimeters, which is between light and radio waves (Figure 1). Like other electromagnetic waves, microwaves are composed of electric and magnetic fields that are perpendicular to each other. They travel at the speed of light in space (in vacuum, the speed of light "c" is about 300 million meters or 300,000 kilometers per second). In addition to the well-known microwave ovens, microwaves can also be used in long-distance communications, such as radar, wireless computer networks, television broadcasting, and mobile phones.

Microwave cooking uses microwaves to excite water molecules in food, so food materials (such as oil) that do not contain water cannot usually be cooked in microwaves. Water molecules are polarized molecular structures with negative charges on one end and positive charges on the other end. Microwaves generated by microwave ovens generally have a frequency of 2.5 GHz (1 GHz = 1 billion Hz), which means that the electric field generated by the magnetron will vibrate at 2.5 billion times per second (1 billion = 1,000,000,000). Because water molecules are polarized, water molecules in food are also pulled at 2.5 billion times per second. This rapid movement between water molecules creates friction and thus generates heat.

Microwave Tomography (MT) (Figure 2) is an advanced technology that uses specific frequencies in a broad microwave spectrum for structural leak detection. The principle of microwave scanning is to generate a slight electric field through the magnetron and penetrate and penetrate the detected structure. Since the water molecules are polarized, the water molecules in the structure also start to vibrate following the frequency of the electric field, and a dielectric effect is generated. Because the water molecule has a strong and obvious dielectric effect under the microwave electric field, its dielectric value is about 80. However, most of the structural materials have only a slight dielectric effect under the microwave electric field, and the dielectric value is mainly between 3 and 6. Due to the great difference between the dielectric values ​​of water molecules and structural materials, even a small amount of water molecules can be detected in the structural materials. Through rapid detection at different positions and depths of the structure, and using computer technology to combine the data into a planar or three-dimensional microwave scanning image, the internal leakage of the structure is displayed (Figure 3). The operation process is similar to that of X-ray CT in the hospital.

Microwave scanning does not pose any danger to the human body. Like visible light (Visible Light), microwave does not refer to a specific frequency, but refers to a wide frequency band (Frequency Band) between hundreds of megahertz (MHz) to millions of megahertz. The microwave frequency from the microwave oven is about 2450 MHz, which is just equal to the natural frequency of water molecules. Therefore, the water molecules in the food can effectively absorb the energy of this microwave, and then violently shake up, the food can be heated in a short time. In fact, the microwave frequencies used in microwave scanning and microwave ovens are not the same. It cannot transmit energy to water molecules as efficiently as microwave ovens.

Technically, microwave scanning is more reliable and accurate than the currently available Moisture Meter and Infrared Scan. The hygrometer can only measure the surface conductivity by measuring the surface electrical conductivity (Electrical Conductivity). The hygrometer is affected by the salinity. Infrared scanning only measures a slight surface temperature difference (Surface Temperature Difference) and indirectly evaluates the surface humidity (Surface Moisture). In fact, infrared not only cannot penetrate the structure; moreover, the common smooth and shiny building materials, such as tiles, paints, rubber bricks, wax, teak and stone surface, are completely erroneous due to light reflection. According to the BD's information, the common causes of leakage are mainly related to leaks in hidden drains and water supply pipes, damage to the waterproof layer in the floor slabs, and sewage or rainwater seepage into the interior of rooftops and external walls. Therefore, effective structural leak detection must target and reflect the internal leakage of the structure, otherwise simply using a hygrometer or infrared to evaluate the surface humidity will often cause serious errors. Microwave scanning has greatly improved the current water seepage detection technology in Hong Kong. The Director of Buildings of Hong Kong and several assistant directors have personally learned about the operation and application of microwave scanning.

The German (HF SENSOR) microwave scanning is the first instrument in Hong Kong to use the microwave scanning structure to leak (Figure 4). It uses Germany's advanced microwave scanning (Microwave Tomography) technology to quickly and deeply determine, display and record the potential location, area, depth and severity of the leak, and analyze the cause of the leak. It can be widely used in civil and civil structures, buildings and houses to seep and leak water. Its detection time is about 1 second, and the penetration depth can reach 300 mm. Microwave scanning does not need to excavate, drill holes and destroy any structure, and the instrument is lightweight, one-person operation, simple and easy to use. The instrument can be connected to computer software to establish plane analysis images and reports. Jianke Testing Instruments (China) Co., Ltd. is the sole distributor of microwave scanning in Hong Kong, Macau and China of Germany (HF SENSOR).

Microwave Tomography (MT)

New Technology for Water Seepage Investigation in Buildings

Microwave is a part of electromagnetic wave spectrum with the wavelength from 1mm to 10cm, which is between light wave and radio wave (picture 1). Microwave, same as other electromagnetic wave, is a combination of vertical electrical wave and magnetic field. Its transmission speed is same as the light (the speed of light “c” is about three hundreds millions meters or three hundreds thousands kilometers per second). Besides the microwave oven, microwave is also used for signal transmission in long distance, such as radar, radio computer network, television broadcast and mobile phones.

Microwave cooking uses the microwave to stimulate the water molecule in food, therefore any food material without water content, such as oil is generally unable to be cooked by microwave. Water molecule is a highly polarized molecule structure, one side is negative and another side is positive. The frequency of the microwave generated by the microwave oven is 2.5G Hertz (Hz) (1G Hz is about 1 billion Hz). It means that the vibration frequency of electric fields generated is 2.5 billion times per second (1 billion is equal to 1,000,000,000). Since the water molecule is highly polarized, the water molecule in food is also pulled at the vibration frequency of 2.5 billions times per second. The acceleration movement of the water molecule causes fiction and therefore heat up.

Microwave Tomography (MT) (picture 2) is an advanced technology for water seepage investigation with specific frequency in the wide range of microwave spectrum. The principle is the slight electrical field generated penetrates the structure under test. Since the water molecule is highly polarized, the water molecule in the structure vibrates at the same frequency and the dielectric effect is also generated. Since the water molecule has very strong dielectric effect under the microwave field, its dielectric constant is about 80. However, most building material has very small dielectric effect under the field, its dielectric constant is from 3 to 6. Since there is a great difference of dielectric constant value between water and building materials, a very small amount of water molecule in the structure can be easily detected. With the internal moisture detection in various location and depth in the structure, a two-dimension or three dimension microwave tomographic image can be produced with a computer. It shows the conditions of water seepage or leakage inside the structure (Picture 3). Its working process is similar to the X-ray Computerized Tomography (X-ray CT) used in hospitals.

Microwave Tomography (MT) does not cause any danger to human. Same as visual light, microwave is not a specific frequency. In fact, it is a wide frequency band with frequency from several hundreds Megahertz (MHz) to several million MHz. The microwave frequency generated by microwave oven is about 2450 MHz, which is exactly the same as the natural frequency of water molecule. Therefore the water molecule of food can effectively absorb the microwave energy and is strongly stimulated. The food can then be heated up shortly. In fact, the frequency of microwave tomography and microwave oven are different. Microwave Tomography does not heat up the material same as microwave oven.

Technically, microwave tomography is more reliable and accurate than the moisture meter and infrared scan currently used in the market for water seepage investigation. The moisture meter just measures the surface electrical conductivity so as to measure the surface moisture. Its reading is also affected by salt content in the material. The infrared scan only measures minor surface temperature difference so as to estimate the surface moisture content indirectly. In fact, infrared scan is unable to penetrate the building structure. For any common building material with smooth and shine surface, such as ceramic tiles, painting, plastic tiles, wax material, wood and marble stones, the test result is not reliable due to the reflection of infrared energy. According to the information from Buildings Department, the common causes of water seepage are always come from the internal conditions of structure, such as the leakage in the hidden drainage pipes and water supply pipes, deteriorated wate rproofing of floor slabs and seepage of waste water or rain water through roof and external wall. Therefore, the most effective water seepage detection should focus on and reflect the conditions of the internal structure but not the surface moisture. Otherwise, the detection of surface temperature or moisture easily causes serious mistakes. Microwave tomography greatly enhances the current technique of water seepage investigation. The Director and Assistant Directors of Buildings Department of HKSAR Government also studied its operation and applications in person.

HF SENSOR Microwave Tomography is the first instrument using microwave technology for water seepage investigation in Hong Kong (Picture 4). It adopts the advanced Microwave Technology from Germany. It can rapidly and non-destructively detect, display and record the potential locations, areas, depth and seriousness of internal moisture for water seepage investigation. It can be widely used for civil engineering, building and construction water seepage and leakage. It takes one second only for one measurement and its depth of penetration is up to 300mm. It does not require any drilling, coring or any damage to structure. It is very portable, easy to use and operated by one person only. The computer software is available for image analysis and report. Build & Test Instrument (China) Limited is the sole and exclusive agent of HF Sensor Microwave Tomography in Hong Kong, Macau and China.