There is more than one meaning of “pulse.”
A mechanical pulse moves a parcel of air and carries directed momentum. An acoustic field creates oscillating pressure and velocity; it can also produce mean flow. A thermal or optical pulse first deposits energy according to its absorption mechanism. Sharing a repetition rate does not make these the same intervention.
Weatherhill is exploring these mechanisms as research directions. The public explanation here describes physical questions and comparisons. It does not specify a demonstrated product architecture, an airport operating envelope or a field efficacy.
What sound might change.
Droplets of different sizes respond differently to oscillating air. Their relative motion can alter encounters. Depending on the apparatus, acoustic forces, streaming and heat or mass transfer can also change where droplets concentrate or how quickly they evaporate. Chamber and resonator studies demonstrate why several explanations must be considered. Sources S6–S7 →
| Possible observation | What must be resolved |
|---|---|
| Fewer counted droplets | Did they coalesce, evaporate, leave the sample or fall outside the sizing instrument’s range? |
| A local clear region | Did liquid leave the useful volume or move into a neighboring region? |
| More collected water | Did sound improve delivery beyond the same collector and matched airflow without sound? |
| Higher transmission | Did the effect persist downstream and remain after temperature, humidity and window effects were considered? |
A frequency cannot be selected independently of geometry, fog population, exposure time and sound level. Chamber results are not a universal “fog frequency.” Larger drops still need a removal route, and an intense disturbance can introduce other effects. Acoustic containment, measured noise and operational compatibility are engineering requirements.
Pulsed mixing needs favorable air.
A jet entrains surrounding air. If a reachable air reservoir has sufficient heat and capacity to accept water vapor, bringing it into fog can help droplets evaporate. But mixing is not automatically drying: cooling and moisture redistribution can leave a mixture saturated or produce fog. Temperature, dew point and the final mixed state are therefore central measurements. Source S10 →
Synthetic-jet experiments show how vortex formation and breakdown influence entrainment. Those studies support investigating placement and geometry; they do not establish an electrical-energy advantage for fog clearing. A meaningful Weatherhill comparison would keep total input energy explicit and compare pulsed with steady flow. Sources S8–S9 →
A clear opening has to survive refill.
Outdoor fog keeps moving. Even if an intervention temporarily lowers droplet concentration, the incoming flow can replace the treated air. A screening model can illustrate that time dependence without pretending to predict a runway.
τ = V / QThis ideal well-mixed replacement model begins with concentration fraction c₀, then applies untreated inflow Q to a fixed volume V after treatment stops. It assumes no ongoing sink, condensation, settling or spatial gradients. The interactive example starts at c₀ = 0.30 by assumption.
The model shows why a momentary optical change is not the same as sustained useful clearance. Real open flow can be strongly nonuniform. Measurements at multiple paths, heights and times are needed, with untreated reference observations and a record of incoming fog.
Heating still needs an energy account.
Paverage = Epulse × repetition rateThe first equation accounts for phase-change energy; surrounding air can supply some heat. The second relates pulse energy to average power. Neither by itself predicts fog clearance, heat-transfer efficiency or an operating cost.
Evaporation shifts liquid water into vapor; it does not remove water from the air. The resulting air must retain sufficient thermal and vapor-capacity margin or export moisture to avoid re-fogging. Claims about low duty cycle, selective absorption or strong momentary effects still need a whole-system comparison.