γair (-)	Adiabatic index of air
γP (-)	Polytropic index
Np (-)	Number of pores
ξ (-)	Visibility of the volume filled with air
$ℛ\left(f\right)$	Frequency response of the loudspeaker when the chamber is empty
${ℛ}_S\left(f\right)$	Frequency response of the loudspeaker when an object is present inside the chamber
I0 (A)	Amplitude of applied sinusoidal current
f (Hz)	Frequency of applied sinusoidal current
f0 (Hz)	Transition frequency at which half of the pore volume is visible for the sensor
cP (J kg−1 K−1)	Specific heat capacity of air at constant pressure
T (K)	Temperature
ρ0 (kg m−3)	Density of air
ρp (kg m−3)	Density of air inside a pore
l1 (m)	Length of the wire in the coil of loudspeaker
l2 (m)	Length of the wire in the coil of microphone
rp (m)	Pore radius
Lp (m)	Pore length
S (m2)	Area of the loudspeaker membrane
V0 (m3)	Internal volume of the sensor chamber
∆V (m3)	Volumetric change caused by the movements of the loudspeaker membrane
VS (m3)	Object volume
VPt (m3)	Total volume of pores
C (m−3)	$=K_{ms}/\left({\gamma }_P{p}_a{S}^2\right)$ Fit parameter
vS (m s−1)	Speed of sound
F (N)	Lorenz force
Floss (N)	Force which concerns losses in the loudspeaker
$K_{ms}$ (N m−1)	Stiffness of the mechanical suspension of the loudspeaker
pa (Pa)	Atmospheric pressure
∆p (Pa)	Change in pressure caused by the excitation membrane
∆pmax (Pa)	Maximum change in pressure caused by the excitation membrane
µ (Pa s)	Air dynamic viscosity
t (s)	Time
B1 (T)	Magnetic flux density inside the coil of the loudspeaker
B2 (T)	Magnetic flux density inside the coil of the microphone
$\epsilon$ (V)	Electromotive force generated by the microphone
${\epsilon }_{rms}$(V)	Root mean square value of the electromotive force generated by the microphone when sensor chamber is empty
${\epsilon }_{rms}^{\left(s\right)}$ (V)	Root mean square value of the electromotive force generated by the microphone when an object is in the sensor chamber
${\epsilon }_{rel}$(-)	Relative value between the root mean square values of the electromotive forces generated by the microphone when the sensor chamber is empty and with an object inside
κ (W m−1 K−1)	Thermal conductivity of air