The Power of the Sun

Developed by the start-up company, Skyrad, the dosimeter is a patch that can be worn on any apparel or inserted in multi-use tags and integrated into clothing labels, or sports or work equipment; the multi-use tags revert to the "normal" reading at the end of the day. Comprised of a photo-chrome material incorporated in a polymer, the patch changes color in the sunlight, as it measures the quantity of sun to which the wearer has been exposed.

Accumulated sun radiation triggers a gradual color change until the patch reaches the color that marks the maximum radiation dose recommended per day - signaling that it's time to seek shelter.

The advantages of the new dosimeter are numerous. First, the daily-dosage patch is not only small, light and disposable, it is also inexpensive - about 5 cents a patch. Second, the patch, which measures cumulative exposure, is more effective than existing monitoring devices that only measured the intensity of radiation. Finally, most previous patches were designed for a "standard skin" type. Skyrad's product is customized for five different types - from the darkest to the very lightest hair and skin color.

The creation of the dosimeter is in response to a growing need for protection from UV rays that not only age skin and are linked to cataracts, but can cause skin cancer. The medical community has found that for every 1% increase in UV levels, there is a 4% increase in incidence of skin cancer. It is expected that the ozone layer that filters out these UV rays will continue to decrease over the next 25 years. Although use of ozone-depleting CFC gases has been banned in industrialized countries, it takes 20-30 years until the gases already released by aerosols, refrigerators, etc. will actually reach the ozone layer about 25 kilometers above us in the stratosphere.

Dr. Ori Faran, general director of Skyrad, explained that the need to effectively monitor exposure to the sun is particularly acute in countries like New Zealand and Australia, where one out of three fair-skinned people is expected to develop skin cancer. The ozone layer at the South Pole is depleted by 50% in the spring, temporarily defusing the concentration in more ozone-rich areas north of Antarctica such as New Zealand and Australia.

Ironically, the same rays that can cause skin cancer may also actually be able to remove skin cancer - serving as an inexpensive and readily-available substitute for costly medical lasers.

In an article in Optical Engineering, Professor Jeffrey Gordon and Dr. Daniel Feuermann, of Ben-Gurion University of the Negev's Center for Environmental Energy and Physics, focus on the application of the attributes of a paraboloidal dish coupled with fiber optics.

Paraboloids are shaped like half of the "inside" of a hollow ball. Because of their cupped shape, they collect and concentrate sound or light waves. For example, acoustic mirrors can collect sound waves and allow two people to talk over a distance. Likewise, headlight reflectors are shaped to collimate a beam strong enough to pierce the darkness. A shiny parabolic-shaped dish is central in the design of solar ovens, first collecting and then concentrating the sun's rays with mirrors in one spot where a metal "oven" is positioned.

The solar oven's two-stage concentration technique should be equally applicable to medicine, in a system that the Feuermann-Gordon team call "solar surgery." Highly concentrated sunlight equals the power density used in many laser fiber optic surgical procedures, which typically use only a few watts of electricity. In their system, the parabolic solar dish can be miniaturized to a mere 20 cm. in diameter. Such a dish would collect the solar energy, magnify it with mirrors, and deliver it to a surgical fiber tip via a fiber optic cable. According to their calculations, the optic cable linking the dish with the operating theater could be as long as 100 meters.

Until now there has been no alternative to sophisticated laser systems because power densities from commercial high-brightness lamps are below the threshold needed for surgery. But by combining and modifying existing concepts for a unique application, this solar device would be an attractive alternative for developing countries that cannot afford the $120,000 price tag on laser surgery systems. Furthermore, the solar surgery system would be mobile, nearly maintenance free, and operate totally independent of any electric grid, making it highly suitable for outlying areas or field hospitals.

Such a "solar system" cannot perform all laser surgeries, but many operations do not require the 100 watts of energy per sq. mm. packed into laser systems. On a sunny day, the solar energy technique can produce 30-40 watts per sq. mm. "In many kinds of medical treatments involving minimally-invasive surgical procedures, only 10 watts of energy are needed," explained Feuermann.

Gordon added, "Solar energy should provide enough energy to open up clogged coronary arteries and destroy certain tumors - including various types of cancerous tumors - with great precision."

How could surgeons "schedule" solar surgery? Having examined the statistics, Feuermann and Gordon say solar radiation data indicates that in clear climates, solar surgery would be feasible on at least half of the days in a year, with operating windows of seven to ten hours a day.

While the team does not have a prototype of their own, they dream of finding the financial backing to develop the project into an "off-the-shelf" product. But publication of the paper puts the design into the public domain. "Since there is no patent on the idea, anyone can develop the instrument as a product, based on the application outlined in the paper," says Feuermann. They estimate that once the device is developed, the cost of such a "solar system" should not exceed a few thousand dollars.