Subcutaneous Transmitter (A3049)

Contents

Description

[11-JUN-25] The Subcutaneous Transmitter (A3049) is an implantable telemetry sensor for small animals. It provides amplification and filtering for two independent biopotentials. When equipped with a CR1220 coin cell, its mass is only 2.0 g, making it suitable for implantation 20-g mice. When equipped with a CR2477 coin cell, its mass is 14 g, making it suitable for implantation in large rats. All versions of the A3049 operate within our Telemetry System. All versions turn on and off with a magnet.

Figure: Subcutaneous Transmitters (A3049). Left: A3049E single-channel transmitter for rats. Right: A3049J two-channel EEG/ECG transmitter for mice.

The A3049 amplifiers can be configured to provide gain of anywhere from ×10 to ×100. Their low-pass filters can be configured for a corner frequency of 20, 40, 80, 160, 320, or 640 Hz. Their high-pass filters can be configured to provide a corner frequency of 0.2 Hz or 2 Hz, or can be removed entirely to provide gain all the way down to 0.0 Hz (DC). The A3049 logic can be programmed to sample at 64, 128, 256, 512, 1024, or 2048 SPS, so as to suite the corner frequency of the low-pass filter. All versions of the A3049 are equipped with flexible leads and a loop antenna. The length of the leads, the size of the battery, the operating life, the termination of the leads, the sample rate, the gain of the amplifier, and the passband of the amplifier vary from one version to the next.

The A3049 can be configured to provide either one or two inputs. The two inputs can share a common reference potential or they can each have their own reference potential. A one-input sensor will transmit one signal on one telemetry channel. As a two-input sensor will transmit on two telemetry channels. The first channel number will always be an odd-numbered. The color and number of leads loaded on the transmitter depend upon its "input configuration", as shown below.

Each transmitter has a label under its silicone coating. This label specifies the batch number, B, and the first channel number, N. A one-input transmitter uses channel N only. A two-channel transmitter uses channel N for the X input and N+1 for the Y input. In a two-channel transmitter, N is always odd.

All versions of the A3049 are covered by a one-year warranty against corrosion and manufacturing defect.

Ordering

[06-JUN-25] There are many possible configurations of the A3049 SCT. Each configuration becomes an established "version" when we manufacture it for a customer. We list the available A3049 versions in the section below. You will find our latest prices in our Price List. To determine which SCT is best for your application, feel free to consult the OSI Chatbot. To obtain a quotation for manufacture and delivery, or to ask us questions directly, please email us at info@opensouresintruments.com.

Versions

[27-MAY-25] The Subcutaneous Transmitter (A3049) can be equipped with a dozen different sizes of battery and leads up to 280 mm long. It can be configured with one or two inputs, a dozen different lead terminations, several types of antenna, and a range of passbands, dynamic ranges, and sample rates. You specify which transmitter you want with a full SCT part number. The part number begins with A2049 and is followed by the primary version letter. This letter spceifies the battery and the input configuration. Following the primary version letter, we have the sample rate code number. We use code numbers 1-5 for 128, 256, 512, 1014, and 2048 SPS respectively. We add the letter "Z" to indicate that the passband extends down to 0.0 Hz, making a "DC transmitter". We add an "S" to indicate that the battery should be mounted on the side of the circuit, making a "slim transmitter". Now comes a dash followed by letters indicating the terminations of the leads. After another dash comes a letter and a number specifying the type and length of the leads. After a final dash we have a letter specifying the antenna.

Figure: A2049 Part Numbering Scheme. Click on the large boxes to jump to tables listing letter codes and options.

See our Electrode Catalog for a list of available lead terminations, and also for a presentation of the various depth electrodes to which these terminations can be attached. See our Leads Table for a description of our several types of insulated, helical steel leads. See our Antennas table for a description of the various types of antenna we can deploy on our implants. The following versions are defined already, but we are happy to define new ones to suit your needs. The operating life is the minimum time for which a newly-made transmitter will operate continuously. The shelf life is the time the transmitter can remain turned off in storage and still retain 90% of its operating life.

For each analog input we specify the bandwidth, sample rate, dynamic range, and channel number offset. In terms of ADC counts, the dynamic range is always 0-65535, as produced by a sixteen-bit ADC. The zero-value of an input is the sample we obtain when we short the two inputs together. The zero-value depends upon the battery voltage, VB, according to zero-value = 1.8 V × 65535 ÷ VB. The dynamic range is the battery voltage divided by the gain of the amplifier. When we specify dynamic range, we assume VB = 3.0 V, which is true for almost the entire life of the lithium batteries we use with the A3049 SCTs. When the amplifier gain is 100, the dynamic range is 30 mV and spans −18 mV to +12 mV.

Figure: Subcutaneous Transmitter A3048Q. The Q-versions are two-channel rat transmitters equipped with a CR2450 battery. Their mass is 8.7 g. Their battery capacity is 25,000 μA·d (microamp-days).

See the Battery Life chapter of our telemetry manual for an explanation of how operating life varies with SCT mass and sample rate. In almost all cases, we set the sample rate of an input equal to 3.2×B, where B is the bandwidth in Hz. This sample rate makes it possible for the low-pass filter to provide 20 dB attenuation at one half the sample rate, which is 1.6×B. Frequencies above one half the sample rate will be distorted by sampling, but the 20-dB attenuition ensures that such signals do not corrupt the signal we record from the SCT's passband.

Analog Inputs

[07-FEB-25] The A3049 provides up to four signal inputs: X+, X−, Y+, and Y−. Each of these inputs has a reserved color for its leads: red, blue, yellow, and green respectively. These four leads are present or absent in accordance with each transmitter's input configuration. Whenever the X+ (red) lead is present, it uses the X− (blue) lead as its reference potential. When the Y+ (yellow) lead is present without the Y− (green) lead, the Y+ lead uses the X− lead as its reference potential. When the Y− lead is present, the Y+ uses the Y− lead as its reference potential. When equipped with three leads, the A3049 is a two-channel sensor with a shared reference potential. When equipped with four leads, it is a two-channel sensor with separate reference potentials.

The figure below shows the frequency response of a batch of five A3049DZ3 transmitters recorded during Quality Control Two (QC2). You will find a database of such plots here. We send one such plot along with each batch of transmitters we ship. What is the frequency response of an A3049 SCT?

Figure: Frequency Response of a Batch of A3049DZ3s to 10-MΩ Sweep. These are two-input "DC transmitters" with shared reference potential, passband 0.0-160 Hz, and sample rate 512 SPS. We apply a sinusoid through a 10-MΩ resistor.

In the response shown above, we see the low-pass corner frequency marked by a bump in the gain just below the corner. If we define "corner frequency" as the frequency at which the gain drops to 70% of the gain in the passband, the corner frequency for this batch of transmitters is 180 Hz, which is slightly higher than the nominal 160 Hz we specify for the A3049D3Z. The most important function of the low-pass filter is to reduce the amplifier voltage gain by at least a factor of ten at a frequency that is one half the sample rate. We see that this is indeed the case for our batch of A3049D3Zs. They sample at 512 SPS and their gain at 256 Hz is less than 10% of their gain at 20 Hz.

We specify for each analog input its absolute dynamic range, which is the difference between the high and low potentials at which the amplifier will saturate. The table above gives these high and low potentials for each standard A3049 input dynamic range.

Figure: Frequency Response of a Batch of A3049B3 to 10-MΩ Sweep. Here we see the high-pass filter dropping the gain below 1 Hz. These are "AC transmitters".

The impedance of X input, as seen at the tips of its electrode leads, is 10 MΩ. When the Y input uses X− as its reference, the Y input impedance is 10 MΩ. When the Y input uses Y− as its reference, the Y input impedance is 20 MΩ. Most transmitters provide a high-pass filter by placing a capacitor in series with the input. The corner frequency of this high-pass filter is 0.2 Hz. When the input impedance is 10 MΩ, the high-pass filter presents a 100-nF capacitor in series with the input, and when the input impedance is 20 MΩ, the series capacitance is 50 nF. When we modify the transmitter to remove the high-pass filter, these capacitors will not be present at the input.

Figure: Output vs Frequency for 20-mV Input. Shown for various high and low-frequency cut-offs.

The X signal is supposed to be a measure only of difference between X+ and X−. The average voltage of X+ and X− is the common mode voltage on X, and the difference between X+ and X− is the differential mode voltage. Suppose we apply the same sinusoidal voltage to both X+ and X−. The common mode voltage is the sinusoidal voltage and the differential mode voltage is zero. Under these circumstances, we would like X to be zero, but instead we will see a trace of the common-mode voltage appearing in the X signal. The ratio of the common-mode voltage amplitude and the X signal amplitude is the common mode rejection ratio, or CMRR. The plot below shows how the CMRR of X and Y vary with frequency.

Figure: Common Mode Rejection Ratio (dB) of X and Y for the A3049A3. We apply a 15-mVpp 100-kΩ common-mode sweep to each input while measuring the recorded signal amplitude.

The X-input provides CMRR of 40 dB for frequencies below 160 Hz. The signal we see on X will be 1% the amplitude of the common-mode signal we apply to X. The CMRR of the Y-input is >40 dB for frequencies below 10 Hz, but drops for higher frequencies.

The distortion of a signal by an SCT is the extent to which the SCT changes the shape of the signal's sinusoidal components. We apply a 10 mVpp sinusoid to the X and Y inputs of an A3049A3, which provides passband 0.2-160 Hz and dynamic range 30 mV. We increase the frequency from 0.25 Hz to 200 Hz. For each frequency, we obtain the spectrum of the signal and measure the power outside the sinusoidal frequency as a fraction of the sinusoidal power using this script. We express the result in parts per million.

Figure: Distortion of 10-mVpp Sinusoid by A3049A3 SCT versus Sinusoidal Frequency. Non-sinusoidal power as a fraction of sinusoidal power in parts per million. Sine wave generated by BK Precision 4053B, specified total harmonic distortion <1 ppm.

The distortion of the X is dominated by random electronic noise. There are no significant peaks in the spectrum outside the fundamental frequency of the sinusoidal input.

Figure: Spectrum with 50-Hz, 10-mVpp Sinusoid. Horizonal: 10 Hz/div. Vertical: 0.4 μV/div. The peak is 4000 μV.

We note that the distortion generated by the A3049 is hundreds of time less powerful than that of its predecessor, the A3028. The A3049 samples the signal uniformly, thus eliminating the scatter noise present in the A3028 signal.

Battery Voltage

[08-JUN-25] We refer you to the Battery Voltage chapter of our Telemetry Manual for a discussion of how we can measure an A3049-family SCT's battery voltage during operation.

Battery Life

[07-JUN-25] All A3049 SCTs are equipped with non-rechargeable lithium coin cells. Their operating life is how long they can amplify and detect their single input voltage when their battery is fresh. Their shelf life is how long they can wait on the shelf in their sleep state before they have used 10% of their battery capacity. We list operating and shelf life in the A3049 Version Table. We provide a detailed discussion of SCT operating life in the Battery Life chapter of our Telemetry Manual. Here we will present some tables and measurements specific to the A3049 family.

The above table of operating life shows how sample rate and battery capacity dictate operating life. The table gives the minimum operating life of a newly-made transmitter. The average operating life is roughly 10% higher.

Figure: Measured Current Consumption versus Total Sample Rate for A3049AV1. The green line is the linear fit 20 μA + 0.095 μA/SPS.

The current consumption of A3049 SCTs increases linearly with sample rate, but starts at around 20 μA for sample rate zero.

Implantation

[11-JUN-25] We refer you to the Implantation chapter of our Telemetry Manual for a discussion of implantation procedures. To record two EEG signals, we use a transmitter with input configuration III, in which the two signals share a common reference potential. We recommend connecting the blue lead to the cerabellum. The other two leads detect the potential somewhere else in the brain. To record EEG and EMG, we need each signal to be recorded with its own reference potential. Input configuration IV is the one with four leads: red and blue for one signal, yellow and green for the other. We implant the SCT and secure the red and blue leads to the skull to record EEG. We secure the yellow and green leads to a muscle in the neck to record EMG.

Synchronization

[19-APR-23] When we want to mark in our SCT recordings the time at which some event took place, such as the start of a video recording, the moment that a light was flashed, or when an noise commenced, we can use an auxiliary SCT to record a synchronizing signal along with the signals received from implanted SCTs. See the Synchronization section of the A3028 manual for details.

Encapsulation

[29-NOV-23] All versions of the A3049 are encapsulated in black epoxy and coated with silicone. The silicone is "unrestricted medical grade" MED-6607, meaning it is approved for implants of unlimited duration in any animal, humans included. The A3049's leads and antenna are encapsulated with dyed silicone, then coated with the same unrestricted medical grade silicone. The only materials the transmitter and its leads present to the subject animal's body are either unrestricted medical grade silicone or stainless steel. When we solder screws or pins to the ends of the leads, there is also solder. Solder reacts slowly with saline, so solder joints must be protected from body fluids by an insulating layer of cement during implantation.

Design and Development

[09-JUN-25] For design files and development logbook, see the A3049 design and development page at D3049.