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GEMS
User Manual
39 pgs1.23 Mb0

Aliph GEMS User Manual

GENERAL ELECTROMAGNETIC MOVEMENT SENSOR
[GEMS]
USER’S MANUAL________
Revision B Version 2
1 TABLE OF CONTENTS
2.1 GENERAL DESCRIPTION .......................................................................................5
2.2 SENSOR UNIT.......................................................................................................5
2.3 CHARGER.............................................................................................................8
2.4 ANTENNAE...........................................................................................................9
2.5 PARTS LIST ........................................................................................................10
2.6 GETTING STARTED.............................................................................................11
4.1 TEST SETUP........................................................................................................13
4.2 PERFORMANCE TESTS .......................................................................................13
4.2.1 Highpass Filter Distortion Compensation................................................15
4.2.2 Measurement sheet ...................................................................................16
4.3 CALCULATING THE SNR AND THE MINIMUM DETECTABLE AMPLITUDE...........17
5.1 NATIONAL INSTRUMENTS’ LABVIEW VIS ..........................................................19
5.1.1 Installation of the software..............................................................................19
5.1.2 Main and configuration screens ......................................................................20
5.1.3 Real time data display .....................................................................................22
5.1.4 4 channel recording.........................................................................................23
5.2 RECORDING DATA FROM THE GLOTTAL AREA ..................................................24
5.3 RECORDING DATA FROM THE CHEEK AREA ........................................................26
5.4 OTHER LOCATIONS ............................................................................................28
9.1 GEMS SIGNAL..................................................................................................35
9.2 LABVIEW PROGRAMS.........................................................................................36
9.3 TECHNICAL SUPPORT .........................................................................................36
2 INTRODUCTION
Thank you for choosing an Aliph sensor. We hope this sensor will serve you well for many years and become the basis for many discoveries.
The General Electromagnetic Movement Sensor (GEMS) was developed at Aliph for the purpose of detecting vibratory motion of human tissue. The present sensor is the third iteration of a design first constructed in 1999. It was designed to be mass-producible and easily constructed using standard parts.
The sensor is an extremely sensitive phase-modulated quadrature motion detector that accurately determines the motion vs. time of one or more moving objects in its field of view. If several moving objects are present and detectable, the GEMS signal will represent a combination of their motions. Thus the output of the GEMS is a one­dimensional voltage that represents a combination of three-dimensional velocities. Therefore, care must be taken when interpreting the GEMS signal as it is not always clear what object is responsible for the observed signal.
This manual is intended to inform a scientifically minded user how to use the GEMS to record vibratory signals associated with human speech. It is not necessary for the user to have a background in electromagnetics (EM) or radiofrequency (RF) to use the sensor effectively. Although the sensor can be used to detect any type of motion anywhere on the body, we will restrict ourselves to motion caused by voiced speech in the sub-glottal and cheek/jaw areas. As we will see, the subglottal region can yield information on the excitation function of human speech and the cheek/jaw area may contain phonetic information about the produced speech. The user is encouraged to capture signals from other parts of the body, but we will restrict this manual to the two above as they return the most reliable and repeatable signals.
Any comments on the sensor or this manual are welcome and contact information is included in chapter 10. Additional information on the sensor and its interaction with the
human body can be found in Gregory C. Burnett’s doctoral thesis, available at UMI (http://www.umi.com/hp/Products/Dissertations.html), thesis # 9925723, or online at
www.aliph.com/Burnett_thesis.
2.1 General Description
The GEMS consists of three major subsections – the sensor, the antenna, and the battery and its charger. The sensor body is installed in an empty battery charger shell, and the rechargeable battery simply slides into a receptacle at the bottom of the sensor body. On the opposite side is a belt clip that can be used to attach the sensor to a belt or similar object. The antenna plugs into the top of the sensor body with the supplied reverse polarity SMA cable. Due to FCC regulations, only the antennae supplied by Aliph can be used with the sensor. If you wish to use other types of antennas, you should contact Aliph. Aliph is not responsible for any liabilities relating to user safety or FCC compliance that may arise from connecting antennas or other components not supplied and/or certified by Aliph.
2.2 Sensor Unit
The sensor body is shown in Figures 2.1, 2.2, and 2.3 and the charger in Figure 2.4. On the bottom front of the sensor body, the power switch is flanked by two indicator lights. The red power indicator is lit when power is applied, while the battery condition light varies:
Indicator light: Steady Green Blinking Green Steady Orange
Battery state: Battery Good Battery Charging Battery Low
Underneath the lights and power switch are the filter selector switches, illustrated in Figure 2.2. The switches can be manipulated to select both the highpass 3-dB point (20 or 100 Hz) and the lowpass 3-dB point (500, 2000, or 8000 Hz). The use of the filters
Filter
Power LED
Power
Output
Switch
Gain Potentiometer
Battery Bay
Selection
Battery LED
DC Power Connector
Figure 2.1. Isometric view of the bottom of the sensor body
can introduce phase distortion (see Chapter 6), so it is recommended that if low distortion is desired to use a highpass frequency of 20 Hz and a lowpass of 8000 Hz.
On the sides near the power switch there is a 3.5 mm power connector that connects to the charger, and a potentiometer that varies the gain by approximately 20 dB. The power connector is used in concert with the charger to charge the battery on the sensor, which can be used while the battery is charging. The charger itself can be used to charge an extra battery. HOWEVER, UNDER NO CIRCUMSTANCES SHOULD A
BATTERY BE USED ON THE CHARGER AND THE SENSOR AT THE SAME TIME WHEN BOTH UNITS ARE CONNECTED. IN ADDITION, THERE MUST BE A BATTERY ON THE CHARGER OR ON THE SENSOR WHEN THE
SENSOR IS OPERATING. Failure to follow these guidelines can damage the sensor,
SMA
Belt Clip
the charging components, and the battery.
The gain potentiometer should be used to control the signal size so that the size of the signal corresponds well to the A/D recording device. For example, if the A/D is set to acquire signals from +- 1 Volt, the gain should be set during normal voiced speech to approximately +- 0.5 V. This allows for larger transients to be captured while using most
Auxiliary Connector
of the resolution of the A/D. Setting the gain to be too large can result in clipping of the
(not used)
signal, where the level of the signal no longer corresponds to the amplitude of motion. This distorts the signal and should always be avoided by choosing a lower gain.
On the bottom of the sensor are the antenna connectors and the stereo output connector.
Stereo Audio Output
The stereo output contains the demodulated in-phase (I) and quadrature (90 degrees out of phase, or Q) signals. These signals represent the motion of the target and it is recommended that the largest energy signal of the two be used, as it is normally the best (least distorted) representation of the motion. The smaller the signal, the more distortion can be present. In any situation, however, one of the modulations will always be nearly distortion -free due to the use of quadrature modulation.
Antenna
(under)
Figure 2.2. Isometric view of the top of the sensor body.
The sensor has two antenna connectors to allow a future bi-static (different transmit and receive antennae) mode. However, this is disabled in the current version and only a single antenna connection is used (mono-static configuration). Due to FCC requirements, it is not possible to use antennae not supplied or approved by Aliph. Only the supplied antennae are to be used with the supplied reverse-polarity cables. If there is a specific antenna that you wish to use with the Aliph sensor, please contact us.
Charging State LED
Battery Bay
Power LED
To Sensor
To AC Power
Figure 2.3. Isometric view of the battery charger. Make sure that at all times there is only one battery on
either the charger or the sensor. The use of no or two batteries may damage the sensor electronics.
2.3 Charger
The charger will charge a battery in its battery bay OR a battery in the sensor’s battery bay, but not both at the same time. TRYING TO CHARGE TWO BATTERIES
WITH THE SAME CHARGER WILL RESULT IN DAMAGE TO THE GEMS ELECTRONICS. The sensor can also be used while its battery is being charged but
should not be used with an AC power supply if the battery is not connected – this will introduce noise into the output signals and may damage GEMS components. The charger has two LEDs – one red LED to indicate that the AC power is connected, and red/green LED to indicate charging state. The changing state is indicated as follows:
LED: Steady Red Red with slow
Red with rapid flash Steady Green
f lash
Charging
state:
Normal
charging
Minor fault,
slow charging
Major fault, follow
reactivation procedure
Recharging
complete
“Slow flash” means 1 flash every 5 to 10 seconds, “rapid flash” is 1 flash every second. A fault may be introduced in the battery if it is deeply discharged. To reactivate a battery with a major fault (deeply discharged or shorted) follow this procedure:
Place the battery in the charger and power up the charger. Allow the battery to remain in the charger for at least 10 minutes with the Charge Mode LED flashing quickly. After more than 10 minutes, remove the battery and disconnect the charger from AC power. Re-insert the battery into the charger and power the charger unit. If this procedure does not reactivate the battery (i.e.. the charging state LED is still flashing quickly) the battery has been destroyed and a new battery must be procured.
2.4 Antennae
The antennae supplied with the sensor are specially designed to work well next to human tissue. Normally, antennae are designed to function efficiently in air, which has a relative dielectric constant near unity and very low conductivity. However, at 2.4 GHz, the body has a relatively high dielectric constant (ranges from ~30-50) and significant conductivity (~2 S/m). Operation of the antenna near the body therefore affects the efficiency and resonant frequencies of the antenna and this must be taken into account during the design and testing phase.
The net effect of the operation of the antenna near the body is an overall lowering of the resonant frequencies of the antenna. For example, for one type of antenna the resonant frequency was observed to drop from 4.2 GHz (in air) to 2.7 GHz (near the body). The amount of drop is determined by several factors, including the radiating pattern of the antenna, the substrate of the antenna, and any materials present between the antenna and the body. It has been observed that even very thin materials can shift the resonance frequency 50 MHz or more, depending on the material and thickness.
Therefore the antennae can be “tuned” to operate more efficiently by placing ordinary cellophane (“Scotch”) tape on the surface of the antennae. This works best with the rectangular micropatch antennae, and will be discussed further in Chapter 5.
There are three rectangular patch antennae and one spiral patch antenna supplied with the sensor. The rectangular antennae are recommended for the neck region, and the spiral for the cheek, although they will work in both places. Insight into the selection and tuning of the antennae will also be covered in Chapter 5.
2.5 Parts List
The parts that were included with your Aliph GEMS kit should include the following:
Quantity Description
1 General Electromagnetic Movement Sensor (GEMS) Unit 4 Micropatch antennae (3 rectangular, 1 spiral) 2 SMA cables (30cm and 90cm) 1 3.5 mm Stereo to RCA Cable 2 RCA to BNC connectors 1 Battery charger with AC power cable, sensor power cable 1 Li -Ion rechargeable battery 1 CD with Data Acquisition software and support materials 1 User’s manual 1 GEMS/accelerometer measurement sheet
Please take a moment to check the contents of your kit and contact us if there are any discrepancies.
Additional batteries and chargers are available and can be ordered directly from Aliph. Only the antennae supplied by Aliph have been approved with by the FCC as legal to use with this device. If you would like to use an antenna of your own design with the GEMS, contact Aliph and we will make arrangements for the necessary manufacturing and testing procedures.
2.6 Getting Started
Step 1: Slide the battery provided into the battery bay on the sensor body Step 2: Attach the power cable between the charger and sensor Step 3: Plug in the charger’s AC power supply Step 4: Firmly attach one SMA cable to the operating antenna port Step 5: Firmly attach 1 antenna (e.g. 9p6+7_80) to the SMA cable Step 6: Make sure the bandpass filter switches are in the desired positions Step 7: Insert the stereo 3.5 mm cable between the sensor and a DAQ device Step 8: Switch on the sensor unit Step 9: Apply the antenna to your trachea (and speak) to observe signals Step 10: Adjust the audio output gain using the sensor gain adjustment knob
Note: Please read instructions on proper battery charging routines, antenna uses, and DAQ guidelines.
3 SPECIFICATIONS
The GEMS sensor is a continuous wave phase modulated radiofrequency device that operates at a frequency of precisely 2.4 GHz. It uses a monostatic antenna configuration that uses reverse polarity SMA connectors. The maximum theoretical RF power output is 1 milliwatt while the effective power will depend on the efficiency of the antenna. It returns a voltage signal limited to +- 2.5 V that indicates the amplitude of motion of a periodic or quasi-periodic motion of a target in its field of view. It is capable of measuring very small (micron order) vibrations from 20 Hz to 8 kHz both inside and outside the body. It operates on a rechargeable 7.4 V Li-Ion battery and draws approximately 170 mA of power.
GEMS Maximum RF Power Output (Antenna Port) 0 dBm (1 mW) Audio Signal Output ~5.0 V max peak -to-peak Output Signal Operating Bandwidth 20 Hz - 8000 Hz Maximum Sensitivity In Air (at 10dB SNR) ~5 µm AC Power Supply 110V - 120V AC Input Voltage 6V - 9V DC (Regulated) Operating Temperature (recommended) 0° to 35° C Dimensions (approx) 115 x 60 x 32 mm Weight 200 g
Battery Battery Capacity 1180 mAh Battery Maximum Output Voltage DC 8.4 V Low Voltage Threshold 6 V Operating Temperature 0° to 40° C Dimensions (approx) 38 x 20 x 56 mm Weight 76 g
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