Maternity Radiation-protective Clothing Testing

Maternity radiation protection clothing inspection mainly conducts scientific testing and analysis on shielding effectiveness testing, fabric composition and metal fibre content analysis, electrical property testing, fabric structure and uniformity evaluation, washing durability testing, and safety and environmental protection item testing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Shielding effectiveness testing: This is the core indicator for measuring the performance of the radiation protection clothing. It mainly refers to the attenuation ability of the electromagnetic waves in the specific frequency bands, usually expressed in decibels (dB). In the testing, the common non-ionizing radiation sources such as the mobile communication base stations and Wi-Fi routers are simulated, and the attenuation effect of the garment fabric on the electromagnetic wave power density is tested. Generally, it is required to have a stable shielding value within the working frequency band (such as 800 MHz-2.4 GHz).

Fabric composition and metal fibre content analysis: The radiation protection fabrics are usually blended with the metal fibres (such as silver fibres and stainless steel fibres) and cotton, polyester and other fibres. For this item, the type, diameter and content percentage of the metal fibres in the fabric are qualitatively and quantitatively analysed through the methods such as the spectral analysis and chemical dissolution, which is the material basis determining its conductivity and shielding effect.

Electrical property testing: Mainly tests the surface resistivity or volume resistivity of the fabric. Since the electromagnetic shielding depends on the formation of the conductive network, a lower resistivity means a better conductivity and shielding potential. Equipment such as a four-point probe tester is used to measure under the standard temperature and humidity conditions, evaluating the electrical basis of the fabric to form the effective electromagnetic shielding.

Fabric structure and uniformity evaluation: Checks the distribution uniformity of the metal fibres in the fabric, the weave density, and whether there are defects such as break points and holes. A high-power microscope or electron microscope is used for the observation. The uniform structure is the key to ensuring the shielding effectiveness without dead corners, and the local defects will lead to the electromagnetic leakage.

Washing durability testing: Simulates the actual use situation of the garment in its life cycle. In accordance with the relevant standards (such as GB/T 8629), the sample is washed for multiple times (such as 10 and 20 times), and then its shielding effectiveness and electrical properties are retested, evaluating the durability and reliability of its performance, preventing the functional failure caused by the daily care.

Safety and environmental protection item testing: Including the pH value, formaldehyde content, decomposable carcinogenic aromatic amine dyes and heavy metal contents (such as lead and cadmium). It is ensured that the safety of the garment fabric when in direct contact with the skin meets the requirements of the national general safety technical code for textile products (GB 18401), avoiding the chemical hazards to the pregnant women and the fetus.

Testing Scope

Working frequency range: The maternity radiation protection clothing mainly targets the non-ionizing radiation in the daily environment. The testing frequency covers the typical life and working frequency bands, usually including the FM broadcasting band (87-108 MHz), mobile communication bands (such as 800 MHz, 900 MHz, 1.8 GHz and 2.1 GHz), Bluetooth/Wi-Fi band (2.4 GHz-2.5 GHz) and the low-frequency electromagnetic fields generated by some household appliances.

Garment covering parts: The testing needs to cover the key protective areas of the radiation protection clothing. For the belly patches and vests, the front abdominal core area is key-tested; for the styles such as the vests, dresses and camisoles, the wrapping areas of the abdomen, waist and sides need to be tested, ensuring that the main protective surfaces have no performance shortcomings.

Different fabric types: The testing scope covers the mainstream fabric types on the market, including the metal fibre blended fabrics, silver fibre fabrics, multi-ion fabrics and the fabrics using the coating technology. For the fabrics of different principles, the testing methods and evaluation emphasis may be adjusted.

New products and used products: The testing is not only for the new products leaving the factory, but also covers the products after a certain period of use by the consumers. Through the comparative testing, the performance attenuation of the product after the actual wearing, washing and friction is evaluated, providing a basis for the life cycle evaluation of the product quality.

Influence evaluation of the auxiliary accessories: The testing scope needs to consider the accessories such as the zippers, buttons and sewing threads. The metal accessories may affect the electromagnetic field distribution, and the non-conductive sewing threads may cause shielding gaps. The integrity of the overall garment needs to be evaluated, including the shielding effectiveness at the seams.

Multi-scenario simulation: The testing needs to simulate the electromagnetic environment in the real use scenarios, such as the frontal incidence of a single radiation source, the multi-radiation-source environment, and the influence of the fabric stretching and folding caused by the posture changes when worn on the human body on the shielding effectiveness.

Testing Methods

Shielding effectiveness testing — flange coaxial method (ASTM D4935): This is the internationally common standard test method for the shielding effectiveness of the planar materials. The circular fabric sample is placed in the coaxial transmission line, and the transmission loss of the microwave signal before and after the insertion of the sample is measured with a vector network analyser, precisely calculating its shielding effectiveness within the 30 MHz to 1.5 GHz frequency band. The result is accurate and highly repeatable.

Shielding effectiveness testing — anechoic chamber method/antenna method: In an electromagnetic shielding anechoic chamber, a system is built with a signal source, transmitting antenna, receiving antenna and power meter (or spectrum analyser). The radiation protection clothing is worn on a model simulating the human torso, and the field strength or power density difference at the receiving antenna with/without the clothing is measured. This method is closer to the actual wearing state, and can evaluate the overall and local protective effects.

Surface resistivity testing — four-point probe method: A four-point probe resistivity tester is used. The four metal probes equally spaced are arranged in a line and pressed on the surface of the measured fabric. A constant current is passed through the outer two probes, and the voltage drop between the inner two probes is measured, calculating the surface resistivity through the formula. This method has good contact and can effectively evaluate the conductive uniformity of the fabric.

Fibre composition analysis — chemical dissolution method (GB/T 2910): A representative fabric sample is selected, and a specific chemical solvent is used to selectively dissolve one of the fibre components (such as using sulfuric acid to dissolve the cellulose fibres, leaving the metal fibres). By weighing the mass difference of the sample before and after dissolution, the dry weight percentage content of each component fibre is calculated.

Durability testing — standard washing method (GB/T 8629): The sample is placed in a standard washing machine, washed with the specified detergent, water level, mechanical action and time, and then dehydrated, air-dried or oven-dried. This is one washing cycle. After repeating for the specified number of times, the shielding effectiveness and physical properties of the sample are tested again, evaluating its durability.

Safety testing — chemical analysis method: In accordance with the standards such as GB 18401, a liquid chromatograph is used to detect the formaldehyde content; a gas chromatography-mass spectrometer (GC-MS) is used to detect the decomposable carcinogenic aromatic amine dyes; and an atomic absorption spectrometer (AAS) or an inductively coupled plasma mass spectrometer (ICP-MS) is used to detect the heavy metal contents.

Testing Standards

Domestic Standards:

1. GB 18401-2010, National general safety technical code for textile products

2. GB/T 23463, Protective clothing — Protective clothing against microwave radiation

3. GB/T 8629, Textiles — Domestic washing and drying procedures for textile testing

4. GB/T 2910, Textiles — Quantitative chemical analysis

International Standards:

1. ASTM D4935, Standard Test Method for Measuring the Electromagnetic Shielding Effectiveness of Planar Materials

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Vector network analyser: The core equipment for the flange coaxial method testing. It can transmit the swept frequency signals and precisely measure the scattering parameters (S parameters) of the measured fabric sample to the signals, especially the transmission coefficient S21, and the shielding effectiveness is obtained through the calculation. It has a wide frequency coverage and high measurement accuracy, and is the key instrument for the laboratory standard testing.

Electromagnetic shielding anechoic chamber: A closed space with the inner walls covered with the wave-absorbing materials, used to create a pure electromagnetic testing environment and isolate the external interference. The antenna method testing is carried out in the anechoic chamber, which can accurately simulate the free-space conditions and evaluate the overall protective performance of the radiation protection clothing in the actual radiation field.

Spectrum analyser and standard antenna: In the anechoic chamber method or open field testing, the signal source generates the electromagnetic waves of the specific frequency bands through a standard-gain transmitting antenna; at the receiving end, a receiving antenna is connected to the spectrum analyser to measure the field strength or power spectral density at a certain point in the space. The antennas need to be calibrated to ensure the accuracy of the measurement results.

Four-point probe resistance tester: An instrument specially used to measure the surface resistivity of the semiconductor materials, films or conductive fabrics. The four-point probe design avoids the influence of the contact resistance on the measurement, and can directly read the resistance value or obtain the resistivity through the calculation. It is the common equipment for evaluating the conductive performance of the radiation protection fabrics.

Scanning electron microscope (SEM): Used for the micro-morphology observation. It can view the distribution state of the metal fibres in the fabric, the fibre surface morphology, the integrity of the coating layer and the interweaving situation of the warp and weft yarns of the fabric at high resolution, providing intuitive evidence for the study of the relationship between the shielding effectiveness and the structure.

Standard washing and drying equipment: Including the program-controllable rotary drum standard washing machine, dryer or air-drying device. These equipment need to meet the provisions of the standards such as GB/T 8629, and can precisely control the parameters such as the water temperature, rotating speed and washing time, to ensure the uniformity and comparability of the durability testing conditions.

Chemical analysis instrument set: Mainly including the UV-visible spectrophotometer or liquid chromatograph for detecting the formaldehyde; the GC-MS instrument for detecting the prohibited dyes; and the atomic absorption spectrometer or ICP-MS for detecting the heavy metals. These equipment are the technical guarantee for ensuring that the product meets the safety and environmental protection standards.