Microwave sound

Advanced Microwave Sounding Unit (AMSU) It is a 15-channel gauge to measure upper atmosphere temperature, radiation in the range 50 GHz to 60 GHz and at frequencies 23.8 GHz, 34.4 GHz, and 89 GHz, water vapor, and precipitation. Spatial resolution of 40 km-45 km. 

AIBS AIDS AIRS AMAP AMIP AMSR-E AMSU American Institute of Biological Sciences Acquired Immune Deficiency Syndrome Atmospheric InfraRed Sounder Arctic Monitoring and Assessment Program Atmospheric Model Intercomparison Project Advanced Microwave Scanning Radiometer for EOS Advanced Microwave Sounding Unit... 

The satellite-borne Microwave Sounding Unit (MSU) records lower stratospheric temperatures. Global mean increases of up to 1.4 K were apparent following both the Pinatubo and El Chichon eruptions due to the local heating of the volcanic aerosol (Parker et al., 1996). Interestingly, for the Pinatubo case, the temperature anomaly decreased as aerosol sedimented back into the troposphere, and, by early 1993, below average, lower stratospheric temperatures were observed. This could be due to cooling coincident with the destruction of stratospheric ozone (Section 3.04.6.2.2). 

The magnetostriction of nonconducting W paramagnets is specified by strong anisotropy, and at helium temperatures in relatively small magnetic fields (20-40 kOe) it may reach an enormous value, comparable to that in lanthanide metals. Since the relaxation times in VV paramagnets are small, these compounds hold promise for microwave sound oscillators. 

Waters J W 1993 Miorowave limb sounding Atmospheric Remote Sensing by Microwave Radiometry ed M A Janssen (New York Wiley) pp 383-496... 

Most, if not all, microwave biological effects and potential medical appHcations are beheved to be the result of heating, ie, thermal effects. The phenomenon of microwave hearing, ie, the hearing of clicking sounds when exposed to an intense radar-like pulse, is generally beheved to be a thermoelastic effect (161). Excellent reviews of the field of microwave bioeffects are available (162,163). 

Ultrasonic movement detectors utilize the principle of the Doppler effect on high-frequency sound waves. Ultrasonic movement detectors do not penetrate solid objects, but have smaller volume of coverage than microwave movement detectors. These units may also be affected by moving hot or cold air pockets in a room. 

The term sonochemistry is used to describe a subject which uses sound energy to affect chemical processes and the terminology is in keeping with that of the longer established methods such as electrochemistry (the use of electricity to achieve chemical activation). These older technologies require some special attribute of the system being activated in order to produce an effect e. g. the use of microwaves (dipolar species), electrochemistry (conducting medium) and photochemistry (the presence of a chromophore) whereas sonochemistry requires only the presence of a liquid to produce its effects. 

The retrieval of trace constituents in the troposphere is more difficult than in the stratosphere or mesosphere, because (i) pressure broadening and strong tropospheric absorptions makes the application of microwave, sub-millimetre and infrared techniques difficult if not impossible to invert (ii) for nadir sounding, multiple scattering in die... 

Waters, J.W., J.C. Hardy, R.F. Jamot and H.M. Pickett (1981) Chlorine monoxide radical, ozone and hydrogen peroxide by microwave limb sounding. Science 214 61-64. 

Absorption of microwave radiation to excite molecular rotation is allowed only if the molecule has a permanent dipole moment. This restriction is less severe than it may sound, however, because centrifugal distortion can disturb the molecular symmetry enough to allow weak absorption, especially in transitions between the higher rotational states which may appear in the far IR (c. 100cm-1). Microwave spectroscopy can provide a wealth of other molecular data, mostly of interest to physical chemists rather than inorganic chemists. Because of the ways in which molecular rotation is affected by vibration, it is possible to obtain vibrational frequencies from pure rotational spectra, often more accurately than is possible by direct vibrational spectroscopy. 

Human subjects exposed to pulse-modulated microwave energy can perceive a sound which seems to occur from within or near the subject s head. The sensation has been described as a click, buzz or chirp depending on the modulation characteristics of the impinging radiation. The effect was first described by Frey in 1961 ( . Although Frey published a series of papers over the... 

Human subjects, whose heads were irradiated with rectangular pulse modulated microwave energy with peak incident power density on the order of 300 mW/cm, perceived an audible sound. The frequencies of these microwaves ranged from 200 to 3000 MHz, while the pulsewidths varied from 1 to 150 js (1,6,9,10,11). The sensation appeared as a barely audible click, buzz or chirp depending on such factors as pulsewidth and repetition frequency of the incident radiation, and usually was perceived as originating from within or near the head. When earplugs were used to attenuate ambient noise, the subject would indicate an apparent increase in the level of microwave-induced sound. The sensation occurred instantaneously and was independent of the subject s orientation in the microwave field. 

There are three widely accepted routes by which bone-conducted sound stimulates the cochlea. These are the compres-sional, inertial and osseotympanic theories of bone conduction (12). Compressional bone conduction implies that the cochlear shell is compressed slightly in response of the pressure variation caused by a sound. Inertial bone conduction alludes to a relative motion between the ossicular chain and the temporal bone for low frequency vibrations. The osseotympanic theory denotes a mechanism by which relative movement of the skull, with respect to the mandible, sets up pressure variation in the air present in the auditory meatus. Since perception of microwave pulses are correlated with the capacity to hear high-frequency sound, it rules out inertial or osseotympanic bone conduction as potential mechanisms for microwave acoustic effect. 

A mathematical analysis of pressure waves created by thermoelastic expansion of brain matter showed that the sound pressure required for human subjects to barely perceive microwave pulses is about the same as the known minimum audible sound pressure for bone conduction (1 3,27). The frequency of sound provides another line of evidence. It was shown that the fundamental frequency of sound is given by... 

Thus, microwave-induced sound is a function of sound propagation speed (v), and the radius (a) or circumference (27Ta) of the head. Figure 5 illustrates measured cochlear microphonic frequency in cats and guinea pigs (8,1.5) and calculated fundamental sound... 

Figure 5. Microwave-induced sound frequency as a function of head radii or circumference (([J) constrained surface (O) stress-free)...

Figure 6. Variation of microwave-induced sound pressure and brainstem potential amplitudes as a function of pulse width (21)...

It should be mentioned that a recent publication (H ) showed that the pitch (frequency) of sound induced by microwave pulses of widths less than 50 ps persisted as the subject s head was lowered into saline water, while the loudness diminished roughly in proportion to the depth of immersion. Upon complete immersion, auditory sensation disappeared. For pulse widths longer than 50 ps, even partial immersion resulted in loss of perception. This was interpreted as being at odds with the thermoelastic theory. There is, however, an explanation that does seem to fit the data. 

Figure 8. Comparison oj measured loudness and calculated sound pressure as junctions of microwave pulse width for human subjects. (A) Relative loudness at 800 MHz (11) (B) calculated sound pressure for a 7-cm-radius head sphere at 918...

There are two alternate routes that might be taken by the microwave-induced thermoelastic pressure wave to reach the cochlea the well-known bone conduction route and a yet unspecified but perhaps a direct route from brain matter to the cochlea. While current information precludes elaboration of the latter, compressional bone-conduction appears to be the most likely candidate for the former, since the frequency of microwave-induced sound is very high and is inversely proportional to the radius or circumference of the head (15,26,27). 

The results presented demonstrate that auditory systems of animals and humans respond to pulsed microwaves. However, there is little likelihood of the microwave acoustic effect arising from direct interaction of microwave pulses with the cochlear nerve or neurons at higher structures along the auditory pathway. The pulsed microwave energy, instead, initiates a thermoelastic wave of pressure in the head that travels to the cochlea and activates the hair cells in the inner ear. This theory covers many experimental observations, but it may be incomplete and thus require further extension to account for certain additional experimental findings. Tyazhelov, et al. (1 1) found in their beat frequency experiment that matching of microwave pulses (10 ps, 8000 pps) to a phase-shifted 8 kHz sinusoidal sound input... 

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