E.2Hearing aid near-field immunity measurement uncertainty

E.2Hearing aid near-field immunity measurement uncertainty

E.2.1Primary uncertainty contributors

RF reflections ± 0.8 dB Specification 4.2.1 (reflections < –20 dB)

Power meter (forward) ± 0.06 dB Specification Typical power meter data

Power meter (reverse) ± 0.06 dB Specification Typical power meter data

Directional coupler ± 1.0 dB Specification Typical acccuracy dir. coup. data

Cable loss ± 1.0 dB Uncertainty Calibration data

Hearing aid loading of antenna TBD Specification D.5 Antenna VSWR ≤ 1.9

Mismatch - directional coupler

Positioning variation ± 1.62 dB Specification E.2.3.1.3

Acoustic transmission line loss TBD

Microphone ± 1.0 dB Specification Calibration

2 cc coupler TBD

Pre-amplifier ± 1.0 dB Specification Calibration

Frequency analyzer ± 0.5 dB Specification Calibration

System repeatability ± 0.5 dB Std. dev. System repeatability is established by performing a series of measurements under equal conditions. For further guidance, consult UKAS M3003.

Repeatability of the hearing aid TBD

The following factors are assumed to be negligible if the conditions listed are met:

• 
  Ambient signals: Assumes an RF shielded environment.
  
• 
  Ambient environment: Assumes temperature, humidity and other environmental parameters are within normal laboratory tolerances.
  

E.2.2Sample estimation

Table E.15—Hearing aid immunity measurements

Hearing aid near-field immunity measurement uncertainty estimation
Contribution	Data dB	Data type	Prob. dist.	Weight	Uncertainty dB	Notes/comments
RF reflections	± 0.8	Spec	Rect	1/√3	± 0.46	Reflections < –20 dB
Power meter (forward)	± 0.06	Spec	Rect	1/√3	± 0.034	VSWR ≤ 1.08, Γ ≤ 0.04
Power meter (reverse)	± 0.06	Spec	Rect	1/√3	± 0.034	VSWR ≤ 1.08, Γ ≤ 0.04
Directional coupler	± 1.0	Spec.	Rect	1/√3	± 0.58	VSWR ≤ 1.15, Γ ≤ 0.07
Cable loss	± 1.0	Uncert’y	Norm.	1/2	± 0.5
Hearing aid loading of ant.	—	—	—	—	—	VSWR ≤ 1.9, Γ ≤ 0.31
Mismatch	± 0.19	Spec.	U-shaped	1/√2	± 0.13	20Log(1 ± Γ1Γ2)
Positioning accuracy	± 1.62	Spec.	Rect.	1/√3	± 0.94	E.2.3
Acoustic transmission line	—	—	—	—	—	TBD
Microphone	± 1.0	Spec.	Rect.	1/√3	± 0.58
2 cc coupler	—	—	—	—	—	TBD
Pre-amplifier	± 1.0	Spec.	Rect.	1/√3	± 0.58
Frequency analyzer	± 0.5	Spec.	Rect.	1/√3	± 0.29
System repeatability	± 0.5	Std. Dev.	Norm.	1	± 0.5
EUT repeatability	—			—	—	TBD
Combined standard uncertainty, uc(y)			Norm.	1	1.65
Expanded uncertainty, U			Norm.	2	3.29

E.2.3Positioning variability

E.2.3.1Resonant dipole field gradients

To measure the quantities reported in this subclause, a resonant dipole was used having the following characteristics with a 1 mW net input power. The quantities given are scaleable to adjust for the actual power used in an immunity test.

E.2.3.1.1At 1900 MHz and 10 mm separation distance

The maximum E-field is 33.3 V/m, which is located 33 mm from the center of the dipole. The H-field at this point is 878 μA/m. So the field impedance is 37.93 kΩ. The field varies by 10% 1 mm from center in the tangential direction and by 20% 2 mm from center.
The maximum H-field is 93.7 mA/m, which is located at the center of the dipole. The E-field at this location is 4.19 V/m. The field impedance is 44.74 Ω at this location. The field variation is the same as that given for the E-field.

E.2.3.1.2At 1900 MHz and 20 mm separation distance

The maximum E-field is 13.9 V/m, which is located 30 mm from the center of the dipole. The H-field at this point is 17 mA/m. The field impedance is 817.65 Ω at this point. The field varies by 10% 3 mm from center in the tangential direction and by 20% 6 mm from center.
The maximum H-field is 34 mA/m, which is located at the center of the dipole. The E-field at this location is 7.0 V/m. The field impedance is 205.88 Ω at this location. The field variation is the same as that given for the E-field.

E.2.3.1.3Uncertainty due to positioning variability

If the immunity test is performed at 10 mm from the dipole and the positioning system has a tolerance of
± 2 mm a variation of ± 17% can be expected. Converting ± 17% to decibels yields a ± 1.62 dB uncertainty due to positioning accuracy. For an uncertainty of ± 2.0 dB, a variation of ± 21% is required. This equates to a distance between readings of less than 2.5 mm.



Figure E.26—Example of axial field variation

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