These are more efficient than photovoltaic solar cells. Michael is a longtime contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies.

Michael Anissimov. Concave mirror concentrates all the rays to its focus. So a concave mirror is used in a solar furnace to produce high temperatures.

Concave mirrors are used in solar cookers. Concave mirrors absorb all the incident light and reflect it to a single focal point. This reflected light is very powerful because it carries a lot of thermal energy. The cooking pot is placed on the focal point where the light is concentrated. Plane mirrors and convex mirrors only produce virtual images. Like spherical convex mirrors, spherical concave mirrors have a focus. Concave mirrors, on the other hand, can have real images.

If the object is further away from the mirror than the focal point, the image will be upside-down and real—meaning that the image appears on the same side of the mirror as the object.

Well actually the image is formed on your retina inside the eyes and you are able to see the refracted rays after they intersect in air. Thus you see the real image without a screen. I was delighted to see that all nine cipher rotors turned and the machine printed a few characters on the paper tape.

But the printout was intermittently blank and distorted. I replaced the corroded nickel-cadmium battery and rewired the power transformer, then gradually applied AC power.

To my amazement, the motor, rotors, and the printer worked for a few keystrokes. But suddenly there was a crash of gnashing gears, and broken plastic bits flew out of the machine. Printing stopped altogether, and my heartbeat nearly did too. I decided to disassemble the HX into modules: The rotor bank lifted off, then the printer. The base contains the keyboard, power supply, and controls.

These snubbers had disintegrated. Also, the foam disks that ink the alphabet wheels were decomposing, and gooey bits were clogging the alphabet wheels. I made some happy, serendipitous finds. To rebuild the broken printer parts, I needed a dense rubber tube. I discovered that a widely available neoprene vacuum hose worked perfectly. Using a drill press and a steel rod as a mandrel, I cut the hose into precise, millimeter sections.

But the space deep within the printer, where the plastic snubbers are supposed to be, was blocked by many shafts and levers, which seemed too risky to remove and replace. So I used right-angle long-nosed pliers and dental tools to maneuver the new snubbers under the mechanism.

After hours of deft surgery, I managed to install the snubbers. The HX has nine rotors and also uses a technique called reinjection. Each rotor has a set of conductors that connect each and every electrical contact on one side of the rotor with a different contact on the other side. For every rotor the pattern of these connections is unique. When the operator strikes a key on the keyboard, representing one of 26 letters, current travels through the set of nine rotors twice, once in each direction, and then through a separate set of 15 rotor contacts at least two times.

This reinjection technique greatly increases the complexity of the cipher. The ink wheels were made of an unusual porous foam. I tested many replacement materials, settling finally on a dense blue foam cylinder.

Alas, it had a smooth, closed-cell surface that would not absorb ink, so I abraded the surface with rough sandpaper. After a few more such fixes, I faced just one more snafu: a bad paper-tape jam. I had loaded a new roll of paper tape, but I did not realize that this roll had a slightly smaller core.

The tape seized, tore, and jammed under the alphabet wheels, deeply buried and inaccessible. I was stymied—but then made a wonderful discovery. The HX came with thin stainless-steel strips with serrated edges designed specifically to extract jammed paper tape. I finally cleared the jam, and the restoration was complete. One of the reasons why the HX was so fiendishly secure was a technique called reinjection, which increased its security exponentially.

Rotors typically have a position for each letter of the alphabet they're designed to encrypt. So a typical rotor for English would have 26 positions. But the HX's rotors have 41 positions. That's because reinjection also called reentry uses extra circuit paths beyond those for the letters of the alphabet.

In the HX, there are 15 additional paths. Here's how reinjection worked in the HX In encryption mode, current travels in one direction through all the rotors, each introducing a unique permutation. After exiting the last rotor, the current loops back through that same rotor to travel back through all the rotors in the opposite direction.

However, as the current travels back through the rotors, it follows a different route, through the 15 additional circuit paths set aside for this purpose. The exact path depends not only on the wiring of the rotors but also on the positions of the 41 modificators. So the total number of possible circuit configurations is 26! And each of the nine rotors' internal connections can be rewired in 26!

In addition, the incrementing of the rotors is controlled by a series of 41 mechanical pins. Put it all together and the total number of different key combinations is around 10 Such a complex cipher was not only unbreakable in the s, it would be extremely difficult to crack even today.

Small, at the U. Army's Signal Intelligence Service. It was the subject of a secret patent that Small filed in and that was finally granted in No. Meanwhile, in , Hagelin applied for a U. Perhaps surprisingly, given that the technique was already the subject of a patent application by Small, Hagelin was granted his patent in No.

Friedman, for his part, had been alarmed all along by Hagelin's use of reinjection, because the technique had been used in a whole series of vitally important U. Friedman Collection. After a career as an electrical engineer and inventor, author Jon D.

Paul now researches, writes, and lectures on the history of digital technology, especially encryption. In the s he began collecting vintage electronic instruments, such as the Tektronix oscilloscopes and Hewlett-Packard spectrum analyzers seen here. In order to increase overall efficiency of the heat transfer process, the area around the pressure vessel is preferably evacuated.

In use, this vacuum may be provided by forming said substantially convex-shaped top, pressure vessel and removable sides as a sealed unit. Additional provisions to evacuate air may be provided via an air evacuation valve and vacuum pumping system.

Preferably, in use, said heat transfer medium is injected under pressure into said pressure vessel by means of a solar powered pump and a plurality of fine spray nozzles that are mounted at the inlet of said pressure vessel.

The heat transfer medium is preferably pre-heated using solar energy directed onto a pre-heater tank which is located underneath and in direct contact with said reflector portion. In order to optimise that overall efficiency of the heat transfer process, a plurality of attemperators are strategically positioned within said pressure vessel. The plurality of attemperators serve to prevent the heat transfer medium becoming too dry, as this would then cause a loss of pressure energy kinetic energy.

In use, said plurality of attemperators are provided by a plurality of spray nozzles that automatically spray a fine mist of cooler heat transfer medium into said pressure vessel. Said cooler heat transfer medium may be supplied from either a bypass chamber located in the unit or said pre-heater tank. Once the treated heat transfer medium exits the pressure vessel at said outlet, it is put to work.

In use, said treated heat transfer medium can be used to drive a turbine to generate electricity. Furthermore, the treated heat transfer medium can be put to further work, such as, for example, air conditioning, pasteurisation or desalination.

The heat transfer medium eventually returns to an integral condenser unit situated above a main reservoir to start the cycle again. Preferably, in use, the unit requires no external power other than light and solar energy. The solar powered pump can be provided with an auxiliary battery, if required for low-light conditions. Further according to the present invention there is provided a solar furnace for raising the temperature of a heat transfer medium, comprising; a lens array for admitting incident thermal and solar energy onto a reflector portion and a pressure vessel, said reflector portion being generally shaped so as to concentrate said solar energy onto said pressure vessel, said pressure vessel having an inlet through which said heat transfer medium is injected and a series of inner chambers having pressure sensitive one-way valves that allow said heat transfer medium to gather temperature and pressure energy and exit said pressure vessel at an outlet.

Also according to the present invention there is provided a method of utilising incident solar energy to raise the temperature of a heat transfer medium, comprising;. It is believed that a solar furnace in accordance with the present invention at least addresses the problems outlined above.

In particular, the advantages of the present invention are that in use the heat transfer medium at the outlet of the solar furnace can be used to generate electricity or be put to other work, such as, for example, air conditioning, pasteurisation or desalination.

The heat transfer medium is then advantageously returned through a condenser to start the cycle again. The present invention can be used in isolation, or a number of such units can be coupled together to provide an environmentally-friendly, tangible energy source or as a mobile unit to be used to supply emergency electrical power at humanitarian sites or situations.

It will be obvious to those skilled in the art that variations of the present invention are possible and it is intended that the present invention may be used other than as specifically described herein. A specific non-limiting embodiment of the invention will be described by way of example and with reference to the accompanying drawings in which:. Referring now to the drawings, the implementation of the present invention is shown in FIGS. In use, the solar furnace according to the present invention is provided as a sealed unit comprising a main frame which is constructed of galvanised mild steel, with aluminium bulkheads and removable ABS or tubular sides 27 , which can be secured using side panel fasteners The unit is supported on shock mounts 8 , which are situated at each corner of the main frame, and leveled before use.

The bulkhead at each end of the main frame supports a pressure vessel 2 through which a heat transfer medium is injected by means of solar powered pump 4. The pressure vessel 2 is fabricated of copper, although other materials having suitable thermal and mechanical properties could be utilised. In use, distilled water is used as the heat transfer medium, although further additives may be included to enhance heat transfer and prevent corrosion.

The internal structure of the pressure vessel 2 comprises a central core 13 having a substantially helical cross-section which defines a continuous heat transfer path for the heat transfer medium to contact the internal surface of the pressure vessel 2. In use, the surface of the pressure vessel 2 is extremely hot due to its constant bombardment with solar energy. The continuous heat transfer path enables the heat transfer medium to obtain optimum temperature and pressure energy kinetic energy over the full length of the pressure vessel 2.

Situated around the pressure vessel 2 is a reflector portion 24 that serves to direct incident solar energy onto the pressure vessel 2.

The reflector portion 24 ensures that pressure vessel 2 is bombarded with greatly enhanced solar energy and light, and is substantially parabolic-shaped so as to direct as much of the incident solar energy onto the surface of the pressure vessel 2. Situated on top of the main frame is a convex top 1 which incorporates a series of light filters to stop light of unwanted frequency being admitted, and a lens array to enhance the wanted light values and solar energy.

This gives a purer and more productive light that passes through the lens array being amplified many times before it bombards the pressure vessel 2. Those whose path has been so designed to bypass the pressure vessel 2 fall on the surface of the pre-heater tank This surface has the ability to reflect back onto the pressure vessel 2 a percentage of the energy yet absorb the required quantity of heat and solar thermal energy to increase the heat transfer medium within the slab tank 12 to reach and maintain the required temperature.

The convex top 1 also acts as a protective cover that automatically closes down in low-light conditions or during hours of darkness, thus protecting the unit from adverse weather.

Furthermore, in order to increase the overall efficiency of the heat transfer process, the area around the pressure vessel 2 denoted as numeral 6 in FIG. In use, this vacuum could be provided by forming the convex top 1 , pressure vessel 2 and side plates 27 as a substantially sealed unit, with additional provisions to evacuate air, if required, via air evacuation valve 15 and a vacuum pumping system not shown.

Each side 27 of the unit, which is insulated, contains a reserve slab tank if required than can maintain the heat transfer medium at an even temperature throughout the hours of darkness.