Hello Fred,
You wrote: “To the best of my knowledge there never has been a demonstrated effect on the human body by magnetism.” I disagree. Human body hormones are directly affected by low frequency magnetism. You can increase or decrease a hormone by applying magnetic fields to certain organs in the human body. You wrote: “The skin effect (not to be confused with human skin) means that almost none of the energy penetrates the skull at 146 MHz. If it doesn't penetrate, how can it cause an effect?” You are right about skin effects, but you assumed that the human body is a good conductor. Using the Human Body Model For ESD testing, the body impedance at high frequency is in the range of 250 ohms to 1.5k ohms. I guess this would depend on the parts of the body and the electrolyte content of the body part. The head is enclosed by the skull, and the bones have lower electrolyte content, so I would assume the head impedance is at the upper end of the range, or near 1.5k ohms. The 146MHz will go right through the head with very little loss, so very little energy is dissipated in heating up your head. You are right. Your head feels no effects from the signal. At 2.4GHz (cell phone frequency), the skin depth is still very long and will penetrate the whole head. There will be a few dB loss to the signal. George Tang ________________________________ From: Fred Townsend [mailto:[email protected]] Sent: Friday, July 25, 2008 11:37 AM To: Tang, George Cc: Derek Walton; IEEE EMC Discussion Group Subject: Re: Another Cancer Scare? George, I'm no medical expert either but I think I understand a few laws of physics, Gauss's law, and Maxwell's equations in particular. If there is to be any effect on the human body, surely it must be directly from the magnetism or indirectly from the induced currents. To the best of my knowledge there never has been a demonstrated effect on the human body by magnetism. That leaves induced currents. Many ham and commercial handy talkies (HT) can put out 5 watts. When used, the rubber ducky runs right by the face or ears. From personal experiments I can say looking directly at the sun causes a noticeable heating effect while using my 5 watt HT @ 146MHz at night doesn't. The skin effect (not to be confused with human skin) means that almost none of the energy penetrates the skull at 146 MHz. If it doesn't penetrate, how can it cause an effect? As you point out modern cell phones put out much less power (<100 mW). Since the skin effect is much greater at cell phone frequencies, I don't think there is a snowball's chance of a cell phone causing damage to any part of the body with the possible exception of the eyes. There is anecdotal evidence that looking at a functional cell phone while driving can cause injury and even death to the whole body. Fred Townsend DC to Light Tang, George wrote: My personal opinion is that the research findings MAY have some valid points, however, the data they have is way out-dated. We know that in the late '80s, people use mobile phones that put out several watts of radiated power. In the early '90s when cell phones were just starting to appear on the market, most of them were still putting out more than 1 watt of radiated power. We have heard of technicians who worked on LAN equipment while talking on the cell phone, and the cell phone radiation induced data error in the Ethernet lines. Those were the days when the cell phone transmitted too much power. In the last few years, the goal of achieving longer talk time, thus lower power consumption, and the use of low voltage electronics due to the widely incorporation of sub-micron transistors have limited the cell phone transmitted power down to low mW range. The research is so far behind the improvements in technology tha t their findings are out-dated by the ne w products on the market today. Of course, I am not a medical expert in the cancer field, and I do not design or manufacture cell phones, so I certainly cannot speak for the experts in these areas. But I do know that these findings most likely are not applicable to the products out on the market today. George Tang From: [email protected] [mailto:[email protected]] On Behalf Of Fred Townsend Sent: Thursday, July 24, 2008 12:09 PM To: Derek Walton Cc: IEEE EMC Discussion Group Subject: Re: Another Cancer Scare? I heard the interview. The doctor appeared to dodge the question as to proof. He did say more research was needed (Ignoring this subject has already been extensively researched.). It appeared to be a blatant attempt to get research funding. Fred Townsend DC to Light Derek Walton wrote: Does anyone know more about the research spoken about in the BBC news artical? http://news.bbc.co.uk/2/hi/health/7523109.stm Is it really new unpublisged research or just rehashing the old? Sincerely, Derek Walton L F Research - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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