# Tag Info

0

I don't think that holding the fob to the head does much good, but what does make a huge difference is holding it high up. The simplest flat plane multipath reflection model predicts that the received power is proportional to $$\left(\frac {h_1 h_2}{R^2}\right)^2$$ where $h_1$ and $h_2$ are the heights of the transmit and receive antennas and $R$ is the ...

0

Unfortunately I can't remember where I read this, but I recently read a theory/explanation that it's merely because the key is being held higher up.

-2

Are you sure holding it to your head really makes it better? Your experiment is very poorly designed because you have only sampled instances where the remote wasn't working when your head wasn't in the picture. This is blatant selection bias. No doubt, putting the remote near your head (or anything else conductive) will significantly alter the ...

5

Remote "key fob" designers intentionally limit size so they conveniently fit in your pocket. However, the convenience comes at a big price - the tiny loop antenna inside is extremely inefficient, transmitting less than 10% of the energy pumped into it, while the rest is simply converted into heat. When holding your remote to your head, your arm, shoulder ...

5

The way it works has nothing to do with your body. Remotes have their antenna as a more or less circular trace on the board (a loop antenna). The strongest signal is when the top or base of the remote is pointed at the receiver. The weakest signal is when the fob is pointed 90 degrees away, such as when pointing it like a TV remote. Guess which way most ...

48

This is a really interesting question. It turns out that your body is reasonably conductive (think salt water, more on that in the answer to this question), and that it can couple to RF sources capacitively. Referring to the Wikipedia article on keyless entry systems; they typically operate at an RF frequency of $315\text{ MHz}$, the wavelength of which is ...

0

Birefringence. Many substances such as cellophane or antistatic tape have two indices of refraction, a 'fast' axis, and a 'slow' axis, not necessarily at right angles to each other. Minute changes in the thickness of a birefringent material will appear to produce different colors between crossed linear polarizers because different thicknesses of ...

1

Like KsdLingen said a photon does not really have a length or size. You could ague that this is due to its wave-particle duality (a concept from quantum mechanics). The wavelength of a photon, $\lambda$, indicates what distance it will travel in vacuum while its electromagnetic field completes one period. The direction of these fields are always ...

2

The wavelength of light, and for any wave in general, is measured along the direction of propagation. It has every bit of the intuitive meaning that the wavelength of a water surface wave does. One of the most meaningful ways to visualize light is as an oscillation of the electric and magnetic fields over space and time: (Image source) The electric ...

1

The 'length' is indeed measured in the direction the wave is traveling. A lightwave is a transverse wave, consisting of an electric and a magnetic field. A photon can be imagined as a localized wave. Length and shape of a photon are meaningless concepts

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