Table 2.

Principal technical performance characteristics of implantable sensors for hearing devices

Sensor type	ID	Bandwidth (kHz)	Sensitivity (dB ref. 1 mV/Pa)	SNR (dB ref. 1 mV/Pa)	EIN (dB SPL)	Power consumption (mW)
Subcutaneous mic.	A1	0.1–10	5	–	–	0.05–0.5a
Subcutaneous mic.	A2	0.2–6	− 10	–	–	0.05–0.5a
Subcutaneous mic.	A3	0.25–5	–	–	–	0.05–0.5a
Subcutaneous mic.	A4	0.1–8	35	–	–	0.05–0.5a
Electromagnetic sensor	B	0.25–3	− 30	37	57	$\approx$ 1
Optical sensor	C	0.5–10	− 46b	–	–	6.4
Piezoresistive MEMS accelerometer	D	0.9–7	6c	40	63	> 1
Capacitive MEMS displacement sensor	E1	0.5–5	20	55	60	$\approx$ 4.5
Capacitive MEMS displacement sensor	E2	0.8–8	30	70	34	$\approx$ 4.5
Capacitive MEMS accelerometer	F1	0.2–6	19	35	35	$\approx$ 4.5
Capacitive MEMS accelerometer	F2	0.5–6	− 9d	70	24	–
Capacitive microphone	G	0.1–10.0	28	18	29	$\approx$ 1
Piezoelectric force transducer	H1	0.5–10	45	–	–	–
Piezoelectric force transducer	H2	0.25–8	–	–	–	–
Piezoelectric force transducer	H3	0.4–4	− 15	60	20	–
Piezoelectric accelerometer	I	0.25–10	1	52	38	0.12e
Piezoelectric MEMS accelerometer	J1	0.5–2.5	62b	–	–	–
Piezoelectric MEMS accelerometer	J2	0.3–6	20	50	44	0.01

^aPower consumption of ECMs for hearing aids (diaphragm diameter 2.5–10 mm) [6, 46]

^bCalculated with 0.34 mm/s/Pa, from the umbo velocity transfer function at 1 kHz  [74]

^cSensitivity of 0.02 V/$g_0$ obtained from a similar piezoresistive sensor  [17]

^dTypical capacitive sensitivity is $1\times {10}^7\text{mV/m}$ [75]

^eData for preamplifier LMV1032, $60\mathrm{\mu }\text{A}$ current, 2 V voltage supply [76]