Microphone Polar Plot Substitution Method Using Outline ET250-3D

This sequence measures the directional response of a microphone and graphs the result as a polar plot. A log sweep stimulus is played from 100 Hz to 10 kHz at each angular increment, and the acquired waveform is analyzed using the Time Selective Response algorithm. This method allows the test to be performed in a non-anechoic environment by placing a window around the direct signal, eliminating the influence of reflections. Commands are sent automatically to the Outline ET250-3D turntable via an ethernet connection, instructing it to move in 10 degree increments after each measurement. The sequence measures the response every 10 degrees from 0 to 180 and mirrors the polar image, which simulates a full 360 degree polar and saves test time. The response at each angular increment is compared against the on-axis response to create a normalized curve. This removes the influence of the device’s frequency response and sensitivity, such that the polar plot only shows the directional response. The final display also contains a graph of the directivity index in decibels versus frequency.


Linear Motor Test Sequence

Linear motors (also known as linear vibrators or linear resonant actuators) have become increasingly popular in handheld devices such as phones and tablets for providing haptic feedback to the device’s user. The typical linear motor design uses a fixed voice coil in conjunction with a moving magnetic mass. A spring is placed between the mass and the motor’s housing to provide compliance to the moving system.

The design goal of linear motor is to create a “High-Q” system so that the device has a very strong resonant frequency across a narrow frequency bandwidth. The motor is then operated at its resonant frequency to produce maximum output (vibration) while having minimal power demands on the portable device. The strength of the vibration is controlled by adjusting the magnitude of the AC signal input to the motor.