Editing 2651: Air Gap

{{comic
| number    = 2651
| date      = July 27, 2022
| title     = Air Gap
| image     = air_gap.png
| titletext = You can still do powerline networking, but the bitrate does drop a little depending on the lightbulb warmup and cooldown delay.
}}

__NOTOC__

==Explanation==

This is another one of [[Randall|Randall's]] [[:Category:Tips|Tips]], this time an Energy Tip. The comic [[#Context for understanding the conflation joke|conflates the concepts]] of computer network security and home electrical power safety to comical effect, resulting in a deeply impractical and ineffective proposed solution. In {{w|computer security}}, {{w|Air_gap_(networking)|air-gapping}} is a measure used to secure sensitive computers or networks of computers by isolating them from the broader internet, since computers are often breached through the internet. 

[[Randall]] suggests increasing the security of your home power supply by air-gapping it, using the light from a powered lightbulb to power a solar panel which then supplies power to the home, such that there is no physical wired connection between your house and the public electricity network. This is a large and very inefficient version of an {{w|opto-isolator}}, but would protect equipment behind the solar panel from power surges such as lightning strikes (which in an improperly {{w|Ground (electricity)|grounded}} home could blow out the light bulb, but not so easily risk frying the equipment beyond the photovoltaic cell and its inverter). Due to its inefficiency, this approach would waste substantial amounts of energy. Optical power beaming is being investigated to recharge drones in flight.[https://www.youtube.com/watch?v=9MI2ph9jptM]

The title text mentions that a computer can still be connected to the internet via the power supply by using {{w|powerline networking}}, but that the bandwidth would be reduced by the lightbulb's warmup and cooldown delay, which would reduce the signalling rate the lightbulb could accomplish to no more than hundreds of bits per second, if that, for incandescent bulbs. However, as the light bulb cannot pick up any signals (possibly) emitted from the solar panel, the unidirectional link would be useless for traditional networking, because essential requests and acknowledgments would be unable to travel from behind the solar panel to the lightbulb. Early {{w|communication satellite}} systems for data networking used high-bandwidth unidirectional {{w|downlink}}s paired with low bandwidth ground telephone lines for outbound transmission, but such network configurations remain very uncommon.{{cn}}

Randall's solution is of course a joke. But in reality he could have used {{w|isolation transformer}}s, which serve to allow the transfer of power via changing {{w|electromagnetic field}}s without an electrically conductive path. Most transformers, including "wall wart" power adapters, provide this form of isolation and protect devices from noise, voltage transients, most surges, and shock hazard, using fuses and other circuitry. They also limit powerline networking bandwidth by filtering out high frequencies. One relatively obscure way this comic is funny involves the relationship of the two concepts being conflated. {{w|Power analysis}} in computer security is a form of {{w|side-channel attack}} where the attacker observes and/or manipulates the power use by a device for some reason — for example, to gain insight into an otherwise protected process, or to exfiltrate information without having to use a monitored network connection. Power analysis in fire safety means measuring the {{w|power factor}}, watts, resistance, inductance, capacitance, volts, and amps of electrical circuits.

The look and subject of this comic is reminiscent of the [[:Category:Cursed Connectors|Cursed Connectors]] series. But without the numbered cursed connector in the comic, this is not one of those connectors.

===Why this would be inefficient and impractical===
* Even energy-efficient LED lightbulbs are only about 35% efficient at turning electricity into light, with the rest emitted as heat.
* The air gap is inefficient at passing light from the bulb to the panel, causing some of the light from the lightbulb to be lost to places other than the solar panel, such as to the eye of the observer. A rough guess might be that in the configuration shown less than 60% of light produced will reach the panel, even assuming a perfect reflector.
* Solar panels are generally around 20% efficient at converting light into electricity, with claims at the world record from a single light source at around 40%.

All these efficiency-reducing factors, and others, multiply together. Therefore, only a small fraction of energy would be transmitted between the two ends of the air gap, making the circuit require much more electricity and be much less cost-efficient. For instance, the generous assumptions above lead to 96% of the power being lost. The solution as illustrated shows a single apparently-normal lightbulb, which typically draw no more than 250 watts, and usually much less power. Given the above efficiency issues, it would provide less than a tenth as much power.

===How this could have a theoretical benefit===
In electrical engineering, {{w|galvanic isolation}} is a measure to prevent an electric current flow between two circuits, instead, signals and energy are exchanged through indirect methods, e.g. magnetically, optically, or wirelessly. This is used to isolate a dangerous high-voltage circuit from the rest of the device, ensuring equipment and personal safety, it's also used to isolate sensitive measurement instruments from external noise, interference, and surges. Isolation transformers have several inherent limitations, and must be used together with other filtering and surge protection devices. The first problem is voltage rating, it's difficult to find a mains-voltage isolation transformer rated beyond a few kilovolts. Secondly, a transformer offers strong protection in steady-state DC and low-frequency 50/60 Hz AC faults, but only limited protection from differential-mode transients and surges. If an electrical surge has significant energy that happens to overlap with the transformer's working frequency (for a switched-mode power supply, this is around several kilohertz), the surge can partially bypass the transformer and enter supposedly-isolated sensitive equipment. Parasitic capacitance is another problem. A capacitor is formed whenever two conductors are separated by an insulator, and the insulated windings inside transformers are no exception. At 100 MHz, the impedance of even a tiny 20 pF capacitance is 79.5 jΩ. As a result, even though the DC impedance across a transformer is several megaohms, but it quickly deteriorates at high-frequency, allowing noise and interference to bypass the transformer and getting into sensitive measurement instruments. Worse, the primary and secondary sides of the transformer can radiate strong electromagnetic interference, since a dipole antenna is formed by two metal plates at different electric potentials. The radiation is suppressed by [https://www.analog.com/media/en/technical-documentation/application-notes/an-1109.pdf bridging the transformer with capacitors], forcing the electric potential to be the same at both sides at high frequency. The drawback is a further increase of capacitance, and a possible reduction of the isolation voltage rating, since [https://incompliancemag.com/article/designing-ethernet-cable-ports-to-withstand-lightning-surges/ capacitors are often the weakest part] of the barrier.

Thus, there are exotic situations where an electrical connection must be avoided at all costs regardless of its efficiency, when safety or electromagnetic interference problems are critical. [https://www.mdpi.com/2304-6732/8/8/335 Power over Fiber (PoF)] technology has been developed to address these needs. Using lasers, photovoltaic cells, and an optical fiber in between, the isolated load can be placed at a long distance away, allowing high voltage rating and extremely low parasitic capacitance. One example is high-voltage isolation at utility-grid scale, when the voltage can be 10 kV or higher. Electronic Design magazine [https://www.electronicdesign.com/technologies/power-electronics-systems/article/21189815/power-over-fiber-shines-at-voltage-isolation reported an early 2006 product], with the lasers in the transmitter consume about 48 watts or power, in order to deliver about 720 milliwatts at the receiver - an efficiency of 1.5%. More recently, [https://docs.broadcom.com/doc/AFBR-POCxxxL-DS Avago (now Broadcom) also commercialized] this technology, with receivers available for sale at $710. "With 1.5 W of laser light incident [...] up to 120 mA of current can be extracted at an operating voltage of 5.0 V and a total power delivery of 600 mW." Typical applications include "high voltage current sensors and transducers", "E-field and H-field probes", and "MRI/RF imaging coils and patient monitoring equipment".

Isolation transformers have several inherent limitations, and must be used together with other filtering and surge protection devices. The first problem is voltage rating, it's difficult to find a mains-voltage isolation transformer rated beyond a few kilovolts. Secondly, a transformer offers strong protection in steady-state DC and low-frequency 50/60 Hz AC faults, but only limited protection from differential-mode transients and surges. If an electrical surge has significant energy that happens to overlap with the transformer's working frequency (for a switched-mode power supply, this is around several kilohertz), the surge can partially bypass the transformer and enter supposedly-isolated sensitive equipment. Parasitic capacitance is another problem. A capacitor is formed whenever two conductors are separated by an insulator, and the insulated windings inside transformers are no exception. At 100 MHz, the impedance of even a tiny 20 pF capacitance is 79.5 jΩ. As a result, even though the DC impedance across a transformer is several megaohms, but it quickly deteriorates at high-frequency, allowing noise and interference to bypass the transformer and getting into sensitive measurement instruments. Worse, the primary and secondary sides of the transformer can radiate strong electromagnetic interference, since a dipole antenna is formed by two metal plates at different electric potentials. The radiation is suppressed by [https://www.analog.com/media/en/technical-documentation/application-notes/an-1109.pdf bridging the transformer with capacitors], forcing the electric potential to be the same at both sides at high frequency. The drawback is a further increase of capacitance, and a possible reduction of the isolation voltage rating, since [https://incompliancemag.com/article/designing-ethernet-cable-ports-to-withstand-lightning-surges/ capacitors are often the weakest part] of the barrier.

==Transcript==
:[A solar panel and a lamp are pictured together, with the lamp pointed at the solar panel, and electronic equipment connected to the solar panel. Lines point outward from the bulb, indicating that it is shining.]
:[Caption below the panel] 
:Energy tip: Increase the security of your home power supply by installing an air gap.

{{comic discussion}}

[[Category:Tips]]
[[Category:Computer security]]