A recent paper, Testing the Effectiveness of Small Radiation Shields for Mobile Phones," authored by Oliver, Chou and Balzano, has been published in the January 2003 journal Bioelectromagnetics. The study concludes, that small shields are ineffective in reducing the exposure of the head to RF energy emitted by a mobile phone.
The study, conducted at the Motorola Florida Research Laboratories, tested nine small radiation shields at the 914 and 1880 MHz range. Scientists tested five oval patches that were advertised as being 99% effective in blocking radio frequency (RF) energy. These oval patches were constructed of a mesh material designed to cover the speaker port of the wireless phone. Also, the scientists tested four products advertised to emit oscillating waves that would counteract against RF energy from the wireless phone. These shields attach to the case of the phone and can take the shape of a small container. All nine of the shields were tested using a single wireless phone and measurements were taken to compare the exposure to the head with and without the shield device; the same method to test and determine SAR phone compliance was used. The study concluded that there was no change to the SAR distribution or the peak value of the phone with any of the shields tested.
The study reinforces the claims these shields do not block or reduce the amount of RF energy emitted from the antenna or case of the phone.
Contact: Katie Tourtillotte
On May 10, 2002 the UK's Department of Trade and Industry (DTI) released its report on phone radiation shields and their ability to reduce RF exposure. DTI commissioned an independent lab to conduct the research utilizing four different phone shields found on the market.
The DTI report concluded that many of the shield devices can reduce the maximum SAR from the handset in large amounts, however this reduction is due to the device limiting the useful, radiated transmit power. Dr. Michael Manning, one of the principle researchers for the project said, The main finding of this report is that you can buy shielding devices which do reduce the dose of radiation but many of them reduce the effectiveness of the phone. If the user is looking to reduce the exposure from a mobile phone, they would do well to consider the option of a hands-free kit, rather than using shield devices.
Four different types of RF shields -- shielded cases, earpiece pads and shields, antenna clips and caps, and absorbing buttons -- were tested using the standard SAR test method for wireless phones. The identity of the phone shields was held confidential.
The report found the following for each phone shield tested:
The report notes that it is a user's choice whether to take a precautionary approach to limiting their personal exposure to RF radiation and various approaches can be considered. If the user is concerned about RF exposure it is recommended, personal hands-free kits remain one of the best approaches for SAR reduction. Shields have disadvantages because they can reduce the power of the phone, thus shortening the battery life and quality of service is compromised.
A full copy of the report can be found on the DTI website.
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