The adult head as an electromagnetic cavity resonator at around 400 MHz 

Also, the head as an acoustical resonator.

The head modelled as a ~10 cm sphere is an electromagnetic cavity resonator with a resonant frequency at around 400 MHz

A cavity acting as an electromagnetic cavity resonator will "trap" waves of the resonance frequency via standing-wave generation. 

If a signal for reading or influencing brain activity uses a carrier wave of the above frequency range, it will demonstrate maximal interaction with the brain and will therefore exhibit enhanced delivery and EEG enactment. 

The above frequencies instead of just transversing the head, set up standing waves inside the head, are confined or "trapped" within it and deposit electromagnetic energy.

If we wish to transfer electromagnetic waves, for instance from their production source to their utilization location, as in the case of the microwave oven, where we transfer EM waves from the magnetron to the heating chamber, or in the case of RADAR, we may use a metal pipe which, in this case, is called a waveguide (given that it guides waves towards a location). In general, electromagnetic waves can be found in pipes or closed cavities, as in the case of the microwave heating chamber. A closed cavity has certain resonance frequencies depending on its dimensions. This means that if electromagnetic waves of a frequency that is equal to a resonance frequency of the cavity are applied or sent to a cavity, then as the waves move back and forth, the opposing-moving waves will interfere and will form standing waves inside the cavity. As a result, electromagnetic energy will be stored in it. The ability of the cavity to sustain the oscillations, without dissipation, is measured by the "quality factor" or Q factor.

The lowest resonant frequency of a cavity is termed the fundamental frequency. This corresponds to the frequency for which the half-wavelength (λ/2) is equal to the width of the cavity. It is interesting to mention that a microwave oven uses a wavelength that can fit inside it and accomplishes resonance and generation of standing waves. Consumer ovens use a frequency of 2.45 gigahertz (GHz) corresponding to a wavelength of 12.2 centimetres (4.80 inches). Different experimental settings can be used to visualize the standing wave pattern, such as for instance, using moist paper inside the microwave oven.

Using modelling approaches, where the human head is represented by a sphere of a radius of approximately 10 cm, it has been determined that its resonant frequency is a function of its size, ranging from around 700 MHz in the infant to 400 MHz in adults (Gandhi et al., 1977).

Below is an excerpt from the ARRL Handbook for Radio Amateurs found at the URL http://www.arrl.org/rf-radiation-and-electromagnetic-field-safety under the section entitled "Thermal Effects of RF Energy"(the section is expandable as indicated by the “+” sign):

"At frequencies near the body's natural resonant frequency, RF energy is absorbed more efficiently, and maximum heating occurs. In adults, this frequency usually is about 35 MHz if the person is grounded, and about 70 MHz if the person's body is insulated from the ground. Also, body parts may be resonant; the adult head, for example is resonant around 400 MHz, while a baby's smaller head resonates near 700 MHz. Body size thus determines the frequency at which most RF energy is absorbed. As the frequency is increased above resonance, less RF heating generally occurs. However, additional longitudinal resonances occur at about 1 GHz near the body surface."

The ARRL is the U.S. national association for Amateur Radio. It was founded in 1914 as "The American Radio Relay League". It is noted that the excerpt in bold has been cited by McLean C. (2019).

If we take into account the detailed shape of the cavity of the head, including the shape of the brain, as well as its structural characteristics in addition to its dimensions, a finer determination can be provided. Similar studies use techniques such as Finite-Difference Time-Domain (FDTD) modelling.

Based on the above, the frequencies of the mentioned range instead of just transversing the head, will form standing waves inside the head and will be confined or "trapped" within it, resulting in electromagnetic energy being deposited in the head.

It could be argued that if a signal for reading or influencing brain activity uses a carrier wave of the above frequency range, it will benefit from maximal interaction with the brain and will therefore demonstrate enhanced delivery and EEG enactment.

It has been alleged that remote neural monitoring is based on neural monitoring techniques related to functional magnetic resonance (cf. MR current density imaging), including EPR/ESR and Proton Electron Double Resonance imaging (Overhauser Magnetic Resonance Imaging or OMRI). It is interesting to note a section from Wikipedia referring to  microwave resonator cavities on the Electron Paramagnetic Resonance (ERP) Wikipedia page:

"The microwave resonator is designed to enhance the microwave magnetic field at the sample in order to induce EPR transitions. It is a metal box with a rectangular or cylindrical shape that resonates with microwaves (like an organ pipe with sound waves). At the resonance frequency of the cavity microwaves remain inside the cavity and are not reflected back. Resonance means the cavity stores microwave energy, its ability to do this is given by the quality fact (Q) defined by the following equation: (...)".

Please note that it has also been alleged, independently of the above testimony, that Finite-Difference Time-Domain (FDTD) modelling is used to determine the resonance frequency of the head cavity of an individual (cf. shape/dimensions and structural features of head and brain) with the purpose of electromagnetic harassment.

For more details on FDTD please refer to section "Vacuum Electronic Devices - Cavity Resonators".

Former senior DARPA scientist reports transmissions of frequencies in the range of head resonance with the purpose of targeting citizens

Paul Batcho Ph.D. (Princeton University), former senior DARPA scientist and staff member at Los Alamos National Laboratory warns of unlawful use of cell phone and microwave towers in Florida

Letter to U.S. Federal Agencies:

"Please investigate the transmission of the various frequency signals in the 450 MHz range. The band from 437 MHz to 478 MHz with peaks at roughly 6 MHz intervals appear to have sizable spectral energy components."

"There is unlawful use of the various lethal aspects of the technology. The technology is active and civilians are being targeted with harmful health effects."

References

https://www.naturalnews.com/053684_rf_radiation_cell_phone_towers_darpa_scientist.html

https://thecommonsenseshow.com/conspiracy/senior-darpa-scientist-warns-widespread-lethal-attacks-upon-public-coming-microwave

(alternative link: https://www.rlighthouse.com/dr-paul-batcho-phd.html)

Physics Professor reports his experience of the remote auditory effect following acquisition by perpetrator of his personal biofrequency using device

Dr. Goychuk is Senior Researcher at the Institute for Physics and Astronomy, University of Potsdam and Privatdozent (adjunct position) at the Institute of Physics, University of Augsburg.

In the following excerpt from Dr. Goychuk's blog, the professor shares his experience and discusses the hypothesis of the head as an acoustical resonator.

"March 2001, Airport Seattle, awaiting a flight to Washington DC (short visit to National Institutes of Health, Bethesda). I was an invited speaker at the March Meeting of the American Physical Society. My very first personal encounter with V2K, I suppose, a very bizarre experience, some voices suddenly emerge directly in the center of your head, and chatter about you. Scary. I turned back, they were a Chinese looking girl keeping a flat device in her hands directed at me and a man who said: We have his frequency". 

"Indeed, for realizing V2K via a thermoelastic acoustic mechanism one has to find first the main acoustic frequency of the resonator made by your head. For a resonator of a very complicated form such as your head this can be done only empirically. The amplitude of acoustic wave excited at this resonant frequency (in the range from 7 to 10 kHz for a human head) is maximal and it can easily exceed the human hearing threshold already for small microwave intensities. Then, one can realize an amplitude modulation of this main acoustic frequency via modulation of the microwave pulse duration, read here and pay attention to Eq. (1), which perfectly works empirically even for very complex resonators. How to transmit intelligible sound via this mechanism is explained here (https://patents.google.com/patent/US6470214)".

EM harassment frequency detection using an RTL-SDR dongle and a specialized program

Please refer to this webpage: https://www.havana-syndrome-infosite.com/community-research/sdr-spectrum-analyzer

The most inexpensive Software-Defined Radio dongle is based on a chip (controller) by Realtek, termed RTL2832U which is matched to tuner chip R820T2 receiving radiofrequencies from 25 MHz to 1700 MHz. Therefore, the 400 to 700 MHz frequency range mentioned above is within the range that can be detected by the dongle.

A specialized program has been created by Clint McLean that compares the intensity of signals of two measuring sessions. It is hypothesized that if a person is targeted with a frequency corresponding to the electromagnetic cavity resonator frequency of their head, this frequency signal will be increased in their vicinity, as it will be resonating with their head and will be scattered by it. By comparing two sessions, one during the presence of the person near the antenna and one during their absence, it is possible to determine the frequency used.