Symbol	Definition and unit
$\lambda$	Free-space wavelength (m)
${\rho }_{\mathrm{p}\mathrm{o}\mathrm{l}}$	Forward-link polarization-coupling factor (dimensionless, 0–1)
${\mathit{P}}_{\mathbf{E}\mathbf{I}\mathbf{R}\mathbf{P}}$	Reader EIRP (W)
$G_{\mathrm{t}\mathrm{a}\mathrm{g}}$	Directional tag gain in the reader direction (linear, dimensionless)
${\mathit{P}}_{\mathbf{t}\mathbf{h}}$	IC activation threshold (W)
$\tau$	Antenna–chip power-transfer coefficient (dimensionless, 0–1)
${\mathit{d}}_{\mathbf{t}\mathbf{a}\mathbf{g}}$	Ideal forward-link chip-activation distance (m)
$d_{\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{d}\mathrm{e}\mathrm{r}}$	Ideal reader-limited backscatter-detection distance (m)
${\mathit{d}}_{\mathbf{s}\mathbf{y}\mathbf{s}\mathbf{t}\mathbf{e}\mathbf{m}}$	Usable system range (m)
$G_{\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{d}\mathrm{e}\mathrm{r}}$	Reader receive gain (linear, dimensionless)
${\mathit{\sigma }}_{\mathit{d}}$	Differential radar cross section of the detected modulation component (m2)
$S_r$	Reader detection threshold for the modulation component (W)
${\mathit{Z}}_{\mathbf{a}\mathbf{n}\mathbf{t}}$	Antenna input impedance (Ω)
$Z_{\mathrm{c}\mathrm{h}\mathrm{i}\mathrm{p}}$	Chip input impedance (Ω)
${\mathit{R}}_{\mathbf{a}\mathbf{n}\mathbf{t}}$	Resistive component of antenna impedance (Ω)
$R_{\mathrm{c}\mathrm{h}\mathrm{i}\mathrm{p}}$	Resistive component of chip impedance (Ω)
${\mathit{X}}_{\mathbf{a}\mathbf{n}\mathbf{t}}$	Reactive component of antenna impedance (Ω)
$X_{\mathrm{c}\mathrm{h}\mathrm{i}\mathrm{p}}$	Reactive component of chip impedance (Ω)
$\mathit{j}$	Imaginary unit, $\sqrt{-1}$
$R_{\mathrm{r}\mathrm{a}\mathrm{d}}$	Radiation resistance (Ω)
${\mathit{R}}_{\mathbf{l}\mathbf{o}\mathbf{s}\mathbf{s}}$	Dissipative resistance due to conductor and dielectric losses (Ω)
$L_{\mathrm{e}\mathrm{f}\mathrm{f}}$	Effective circuit inductance (H)
${\mathit{C}}_{\mathbf{e}\mathbf{f}\mathbf{f}}$	Effective circuit capacitance (F)
$\omega$	Angular frequency, $2\pi f$ (rad/s)
$\mathit{f}$	Frequency (Hz)
$R_{\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{e},\mathrm{D}\mathrm{C}}$	Direct-current trace resistance (Ω)
${\mathit{R}}_{\mathit{s}}$	Sheet resistance (Ω/sq)
$\mathcal{l}$	Trace/current-path length (m)
$\mathit{w}$	Trace width (m)
$g$	Gap between adjacent traces (m)
$\mathit{\sigma }$	Electrical conductivity (S/m)
$h$	Conductor thickness (m)
${\mathit{\eta }}_{\mathbf{r}\mathbf{a}\mathbf{d}}$	Radiation efficiency (dimensionless)
$\delta$	Skin depth (m)
$\mathit{\mu }$	Magnetic permeability (H/m)
$Q$	Antenna quality factor (dimensionless)
$\mathit{k}$	Wavenumber (rad/m)
$R$	Radius of the smallest enclosing sphere (m)
${\mathit{Z}}_{\mathit{j}}$	Inverse Ohnesorge number (dimensionless)
$\rho$	Ink density (kg/m3)
$\mathit{\gamma }$	Surface tension (N/m)
$d_n$	Nozzle characteristic diameter (m)
$\mathit{\eta }$	Dynamic viscosity (Pa·s)
${\epsilon }_r$	Relative permittivity (dimensionless)
$\mathbf{tan}\mathit{\delta }$	Dielectric loss tangent (dimensionless)
$R_a$	Arithmetic mean surface roughness (length)
${\mathit{R}}_{\mathit{p}}$	Maximum profile peak height/peak roughness parameter (length)
$S_{11}$	Input-port reflection coefficient (dimensionless; commonly reported in dB)
${\mathit{E}}_{\mathbf{i}\mathbf{n}\mathbf{c}}$	Incident electric field (V/m)
$H_{\mathrm{i}\mathrm{n}\mathrm{c}}$	Incident magnetic field (A/m)
${\mathit{E}}_{\mathbf{t}\mathbf{a}\mathbf{g}}$	Electric field associated with the tag response (V/m)
$H_{\mathrm{t}\mathrm{a}\mathrm{g}}$	Magnetic field associated with the tag response (A/m)
${\mathit{E}}_{\mathbf{s}\mathbf{c}\mathbf{a}\mathbf{t}}$	Scattered electric field from the tag (V/m)
$H_{\mathrm{s}\mathrm{c}\mathrm{a}\mathrm{t}}$	Scattered magnetic field from the tag (A/m)
${\mathit{Z}}_{\mathit{A}}$	Chip/load impedance in modulation state A (Ω)
$Z_B$	Chip/load impedance in modulation state B (Ω)
${\mathit{R}}_{\mathit{c}\mathit{o}\mathit{n}\mathit{d}}$	Equivalent conductor-loss resistance (Ω)
${\mathit{R}}_{\mathit{d}\mathit{i}\mathit{e}\mathit{l}}$	Equivalent dielectric-loss resistance (Ω)
Abbreviation	Definition
3D	Three-dimensional
ABS	Acrylonitrile butadiene styrene
ACA	Anisotropic conductive adhesive
ACNF	Acetylated cellulose nanofiber
AgNP	Silver nanoparticle
AI	Artificial intelligence
AJP	Aerosol jet printing
AMC	Artificial magnetic conductor
bio-PE	Bio-based polyethylene
CO2-eq	Carbon dioxide equivalent
DC	Direct current
UV	Ultraviolet
EIRP	Equivalent isotropically radiated power
ERP	Effective radiated power
ETSI	European Telecommunications Standards Institute
GO	Graphene oxide
GWP	Global warming potential
HEC	Hydroxyethyl cellulose
HF	High frequency
IC	Integrated circuit
ILCD	International Reference Life Cycle Data System
INGEDE	International Association of the Deinking Industry
IoT	Internet of Things
LCA	Life-cycle assessment
MXene	Family of two-dimensional transition-metal carbides, nitrides, and carbonitrides
NFC	Near-field communication
NR	Not reported
PEN	Polyethylene naphthalate
PET	Polyethylene terephthalate
PETG	Glycol-modified polyethylene terephthalate
PI	Polyimide
PLA	Polylactic acid
PR	Photoresist
PSO	Particle swarm optimization
PVOH	Polyvinyl alcohol
QR	Quick response
R2R	Roll-to-roll
RCS	Radar cross section
RF	Radio frequency
RFID	Radio-frequency identification
RSSI	Received signal strength indicator
SD	Standard deviation
SEM	Scanning electron microscopy
SIW	Substrate-integrated waveguide
UHF	Ultra-high frequency
USB	Universal Serial Bus