Performance indicators specially required for receiving transducer
This is the most important indicator for the receiving transducer, and it is divided into voltage sensitivity and current sensitivity.
The so-called free-field voltage sensitivity of the receiving transducer refers to the output voltage of the receiving transducer and the
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The ratio of the free sound field sound pressure at the point before the transducer is introduced in the field
Mu (ω) = U (ω)
Pf (ω) (V/μPa)
In the formula, U (ω) represents the voltage (V) generated on the electrical load of the receiving transducer; Pf (ω) represents the receiving transducer
The sound pressure of the free sound field at the receiving surface (μPa), sometimes expressed in dB
Nu (ω) = 20lg
The reference sensitivity is taken as Mu0 (ω) = 1V/μPa. Nu (ω) is called the free-field voltage sensitivity level.
The so-called free field current sensitivity Mi (ω) (free field current response) of the receiving transducer refers to the receiving transducer
The ratio of the output current of the energy device to the sound pressure of the free sound field before the receiver is introduced into the sound field is recorded as
Mi (ω) = i (ω)
In the formula, the unit of i (ω) is A and the unit of Pf is μPa.
In practice, we generally use voltage sensitivity to discuss issues, and not often use current sensitivity.
1. 2. 3. 2. Equivalent noise pressure
When the transducer is used in the receiver, due to the electro-acoustic conversion device (such as piezoelectric ceramics) inside the receiver
Sheet) The thermal motion of internal molecules at a certain temperature will produce noise, which is called self-noise or inherent noise.
The magnitude of this self-noise determines the smallest possible value of the useful signal that the receiver can measure, and it contains many
For multi-frequency components, the root-mean-square voltage over the bandwidth of one Hz can be used to measure its magnitude.
There is a sinusoidal sound wave incident on the receiver (if the receiver size is not much smaller than the sound wave, it should be
Projected on the vibrating surface along the normal incidence direction), when the effective value of this voltage output is equal to the receiver’s self-noise
At the root mean square voltage value on the Hertz bandwidth, the effective value of the incident sound pressure is called the equivalent noise pressure. Receiver etc.
The effective noise pressure is numerically equal to the root mean square voltage value of the self-noise in a one-hertz bandwidth and the receiver sensitivity
Ratio. The equivalent noise pressure in decibels for the reference sound pressure of 1μbar is called the equivalent noise of the receiving transducer
Sound pressure level.
Above, we have only briefly introduced some of the most basic and important performance indicators of the transducer.
In the future, when researching various specific transducers, in-depth discussions are needed.