What causes body loss?

The human body is a lossy dielectric with high water content (relative permittivity 40-60 at GHz frequencies). When a device is held against the body, the antenna's near field is loaded by body tissue, causing detuning, reduced radiation efficiency, and signal absorption. The head absorbs 3-5 dB during phone calls. The torso can block signals by 5-10 dB in shadowed directions.

Typical body loss values?

Head (phone call): 3-5 dB at 700-2600 MHz. Hand grip: 2-4 dB (covers part of antenna). Body-worn (belt clip): 5-10 dB at 900 MHz (torso shadow). Wrist (smartwatch): 3-7 dB depending on arm orientation. Higher frequencies generally suffer more body loss due to smaller skin depth and higher tissue conductivity.

How is body loss accounted for in link budgets?

3GPP specifies body loss margins in link budget calculations: 3 dB for data (hand/head), 1 dB for IoT (body-worn). Network planners add body loss to the total path loss to ensure coverage at cell edge. Some operators use 5-8 dB for indoor body-worn scenarios. Body loss is separate from building penetration loss and fading margin.

Propagation & Channels

Body Loss

Body Loss is the RF signal attenuation caused by the human body when a wireless device is held, worn, or implanted. The body's lossy dielectric properties (relative permittivity 40-60, conductivity 1-3 S/m at GHz frequencies) detune antennas, absorb radiated power, and create shadow regions. Typical values range from 3 dB (hand-held data mode) to 10 dB (body-worn, torso shadow at 900 MHz). 3GPP link budgets include body loss as a separate margin.

Category: Propagation & Channels

Typical: 3-10 dB

Understanding Body Loss

Body loss has three components: antenna detuning (impedance mismatch from body proximity), reduced radiation efficiency (power absorbed in near-field tissue), and body shadowing (blockage of far-field radiation in the direction opposite the body). The relative contribution depends on antenna-to-body distance, frequency, and body part.

For handsets, the hand grip alone reduces total radiated power (TRP) by 2-4 dB. Adding the head (phone call position) adds another 2-3 dB. The combined effect is measured as Total Isotropic Sensitivity (TIS) degradation in CTIA OTA testing.

Body Loss in Link Budget

MAPL = P_TX + G_TX − L_body − PL − M_fade − L_bldg

3GPP body loss values:
Voice (head+hand): 3 dB
Data (hand only): 1-3 dB
Body-worn IoT: 1-5 dB

Body Loss by Usage Scenario

Scenario	Loss (dB)	Frequency	Mechanism
Hand grip	2-4	700-2600 MHz	Detuning + absorption
Head (call)	3-5	700-2600 MHz	Absorption + shadow
Belt (torso)	5-10	900 MHz	Body shadow
Wrist (watch)	3-7	2400 MHz	Detuning + arm shadow

Common Questions

Frequently Asked Questions

What causes it?

Body is lossy dielectric (ε_r=40-60). Near-field absorption, antenna detuning, and far-field shadow. Head absorbs 3-5 dB during calls.

Typical values?

Hand: 2-4 dB. Head: 3-5 dB. Belt: 5-10 dB. Wrist: 3-7 dB. Higher freq = more loss generally.

Link budget?

3GPP adds body loss as separate margin: 3 dB voice, 1-3 dB data. Separate from building loss and fading margin.

Related Terms

← Body Area Network Body Phantom →

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