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Sensors Without Batteries

Continued from page 1

By Kate Greene

Monday, May 15, 2006

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Just like RFID tags, the battery-free sensors turn on only when they encounter a reader. As long as the RFID reader is within range of the device, Smith says, it can collect data and send it to the reader.

Battery-free sensors could be useful in many areas, including medicine, says Zeke Mejia, chief technology officer of St. Paul-based Digital Angel, an RFID tag maker. They could "check the status and certain conditions in the body" at any moment, Mejia says, from glucose levels in people with diabetes to the pH of blood and other body fluids.

In their current form, Intel's sensors need to be within about a meter of a reader to be activated. That's closer than would be ideal for some applications, such as measuring the temperature of foods packed in large crates or vibrations in thick walls. The problem is that while the microcontroller needs only a milliwatt of power to run, it needs three volts of electricity to turn on, and the sensor has to be within a meter of an industry-standard RFID reader to generate that much energy. But with minor changes to the way the microcontroller processes data, Smith says, the group could reduce the voltage requirement to 1.8 volts, thus extending the range to about five meters.

The team's latest prototype incorporates a light sensor, temperature sensor, and even a tilt sensor into one battery-free device. The researchers are working on ways to integrate the microcontroller and antenna into a single chip that would be easier to install in the field. In the meantime, they have developed a visual demonstration of just how much energy an RFID antenna can garner from a reader: they've used it to power the second hand on a wristwatch.

"It's surprising to people that this invisible form of energy –- radio waves -– can actually make a watch hand move," Smith says. And a single tick of a second hand, Smith says, takes about as much energy as sending one bit of data from his sensor.

Comments

  • Invisible Sensors
    So is throwing out the batteries used for making the sensors "invisible"? If such radio energy can be used to place batteries in other fields, won't that be good?
    Rate this comment: 12345
    Guest (Brad Wang)
    05/15/2006
    Posts:1
  • [no subject]
    Why do you make so difficult to print out articles? I'm sure there is a simpler way.
    Rate this comment: 12345
    Guest (Karl G. Schick)
    05/15/2006
    Posts:1
    • x
      there's a print link on the right-hand nav. looks like it works quite well, though it create an extra page, with the article on the second page (in my case).
      Rate this comment: 12345
      Guest (x)
      05/15/2006
      Posts:1
  • energy, power, voltage
    Voltage has nothing to do with energy. Power is energy per unit time. So the phrase "that much energy" makes no sense.
    Rate this comment: 12345
    Guest (ms)
    05/15/2006
    Posts:1
    • Voltage
      Isn't voltage 'energy' per unit of electrical charge ?
      Rate this comment: 12345
      Guest (Joe)
      05/16/2006
      Posts:1
      • Voltage
        Voltage is not energy. Proximity to the reader's restricted e-m field will increase the voltage realized at the RFID device. A minimum voltage is req'd to operate the components in the device. 1.8V can be realized at a greater distance than 3.0V.
        Rate this comment: 12345
        Guest (Hayes)
        05/16/2006
        Posts:1
        • Voltage
          Voltage is basically the force of the electron flow - Think pressure. This is half of the story when looking at energy/work. voltage x amperage (a measure of the amount of electrons, think volume) = energy/work
          Rate this comment: 12345
          Guest (Klc)
          07/30/2006
          Posts:1
  • How soon will NSA adopt this technology
    They're already monitoring all our calls and emails, so obviously this it the next step - implanting them in everybody when they go through customs.
    Rate this comment: 12345
    Guest (Paranoid)
    05/15/2006
    Posts:1
    • NSA
      Why customs? They'd fit easily into a Twinky or Oreo. Bon apetite.
      Rate this comment: 12345
      Guest (Powernoid)
      05/16/2006
      Posts:1
  • Josh Smith is all wet!
    Mr. Smith clearly doesn't understand how passive RFID tags are "powered." They are powered by the electromagnetic energy generated by the RFID reader, not from solar, vibration, motion, or thermal sources. The reader's EMF field generates enough power that is picked up by the antenna on the RFID tag which then modulates the reader's query with the ID information on the tag. If there is no reader in the near-field, there is no power and the tag cannot do anything. This is NOT a solution for wireless sensor network that need power for their sensor over a longer time period than the field of a reader.
    Rate this comment: 12345
    Guest (Dick Caro)
    05/15/2006
    Posts:1
    • dick caro is all wet
      Mr. Caro clearly doesnt understand how to read.
      "One way to achieve this sort of ubiquitous computing is to disperse tiny sensors that measure, for instance, light, temperature, or motion."
      doesnt say that the rfid tags are "powered" by solar, vibration, motion, or thermal sources....nope not at all....its saying that sensors to monitor these things could and most probably will become common....and the rest of the article that just as as an "RFID tag which then modulates the reader's query with the ID information on the tag"....a microprocessor could simularly modulate the data...stealing power from the readers induced current.
      Rate this comment: 12345
      Guest (Dick Caro is all wet)
      05/15/2006
      Posts:1
  • Sensors without batteries
    Josh does not distinguish between inductive coupling (near field technology) and capacitive coupling (far field technology).  These two modes of coupling energy into an RFID tag or a sensing device operate at different distances.  Inductive coupling is more efficient, and one would think that this would be the mode to use to power up "power hungry" microcontrollers.
    Rate this comment: 12345
    Guest (Marc)
    05/17/2006
    Posts:1
    • Inductive vs. Capacitive coupling
      Unfortunately, you want RANGE for these applications. This implies capacitive coupling. It makes no sense if you have to be very close to a reader. You might as well have a wire and plug into a wall in that case.
      Rate this comment: 12345
      Guest (James)
      05/19/2006
      Posts:1
      • Power me up Scotty
        You guys are great!  I'm not an electro wiz like most of you, but the reality of Inductive and Capacitive coupling is something that will be very handy in the near future.

        Sensing remote information will greatly advance our knowledge of what is going on with the planet and then maybe, given an influx of greater range of thinking ability, we just might save ourselves from... ourselves.

        Please think on this, design some new products and lets get on this wonderful opportunity of life and invention!

        Thanks!
        Rate this comment: 12345
        Guest (Cullen)
        06/22/2006
        Posts:1

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